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The geology and geography of Northern Ni
THE GEOLOGY AND GEOGRAPHY
OF NORTHERN NIGERIA
MACMILLAN AND CO., LIMITED
LONDON BOMBAY CALCUTTA
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THE MACMILLAN COMPANY
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TORONTO
PLATE XVII

 

 

INSELBERGE LANDSCAPE AROUND ABUJA.

 

 

INSELBERGE LANDSCAPE IN NORTHERN YOLA.

[Frontisptece.
THE

GEOLOGY AND GEOGRAPHY

OF

NORTHERN NIGERIA

BY

J. D. FALCONER, M.A.. D.Sc.

BG.S., FP. BSE, FoReas,

With Notes by the late
ARTHUR LONGBOTT: OM, B.A, F.G.S
and an Appendix on the Paleontology of the C-rtsctous Depocite, by

HENRY WOODS, M.A. F.G.5.
University Lecturer in Patamoblosy. 4 Candvialer

WITH FIVE MAPS AND TWENTY-FOUR PLATES

MACMILLAN AND CO, LIMITED
ST. MARTIN’S STREET, LONDON
Igit
THE
GEOLOGY AND GEOGRAPHY

OF

NORTHERN NIGERIA

BY

J. D. FALCONER, M.A., D.Sc.

F.G.S., F.R.S.E., F.R.G.S.

With Notes by the late
ARTHUR LONGBOTTOM, B.A., F.G.S.,
and an Appendix on the Paleontology of the Cretaceous Deposits, by

HENRY WOODS, M.A., F.G.S.
Oniversity Lecturer in Paleozoology, Cambridge

WITH FIVE MAPS AND TWENTY-FOUR PLATES

MACMILLAN AND CO., LIMITED
ST. MARTIN’S STREET, LONDON
IQII
vi
eee ee
Ricuarp Cray anp Sons, LIMITED
BREAD STREET HILL, E.C., AND
BUNGAY, SUFFOLK.
TO

MY OLD TEACHER AND FRIEND

PROFESSOR JAMES GEIKIE
PREFACE

Tue observations upon which these outlines of the
Geology and Geography of Northern Nigeria are
based, were made in the course of the operations of
the Mineral Survey of the Protectorate of which I had
the honour to be the principal officer. The Survey
was instituted by the Colonial Office in 1904 upon the
recommendation of Professor Wyndham R. Dunstan,
under whose general direction the work of investi-
gation was carried out both in Nigeria and in the
laboratories of the Imperial Institute. From 1904
to 1909 five expeditions in all were made to Northern
Nigeria, in the course of which every province of the
Protectorate was visited in turn. On the first two
expeditions I was accompanied by Mr. Douglas R.
Home, F.R.G.S., and on the remaining three by Mr.
Arthur Longbottom, B.A., F.G.S. On an average
seven months of each year were devoted to the actual
field work, but the great extent of territory to be
investigated, coupled with the difficulties of transport,
rendered it impossible to do more in the time available
than make a series of cross traverses through the
warious provinces with the object of ascertaining in a

vil
viii PREFACE

general way their geological structure and mineral
resources. |

In the following pages I have attempted to correlate
the various observations which were made in the
course of our travels and to weave a more or less
consecutive story out of the disconnected contents of
our notebooks. I am myself, however, only too
conscious that many of my deductions may have
been drawn from insufficient data and that further
knowledge may overturn many of my hypotheses.
In a new land someone must do the pioneering, and
I shall be amply satisfied if my work affords some
foundation, however insecure, for the investigations of
future workers.

It is with the deepest regret that I have to record
the death of my friend and former colleague, Mr.
Arthur Longbottom, since this work went to press.
He died of dysentery, after much suffering, in
November, 1910, at Naraguta, on the Bauchi plateau
in Northern Nigeria, whither he had returned on a
tour of inspection on behalf of a private syndicate.
We had hoped that he would be able to continue the
work which we had begun together and that he would
return to England with a fresh store of observations
which would increase our scanty knowledge of the
geology and geography of the Protectorate. His
extensive experience in various parts of Northern
Nigeria would have rendered those observations of
the greatest value, but his untimely death has put an
end not only to a most promising career but to all
hope of any further immediate advance in our
PREFACE ix

knowledge of the structure of this outlying portion
of the Empire.

Before he left England Mr. Longbottom contributed
all the paragraphs and sections throughout the book
marked with his initials (A. L.). He also supplied
the photographs from which have been prepared
Plates I, II, VI, VII, VIII, Fig. 1, and XVI. For
Plate VIII, Fig. 2, I am indebted to the Public
Works Department of Northern Nigeria. Mr. Woods
has kindly contributed the Appendix on the Cre-
taceous Mollusca and the note upon the Eocene
fossils on p. 165.

I gratefully acknowledge a Grant towards the cost
of publication of this work from the Carnegie Trust
for the Universities of Scotland. I am especially
indebted to Sir Archibald Geikie for help and
encouragement in the matter of publication. My
acknowledgments are due also to various friends for
assistance and advice, and more particularly to
Professor James Geikie, Professor Wyndham R.
Dunstan, Professor Knight, Dr. Horne, and Dr.
Flett.

J. D. Fatconer.
JANUARY, I9QII.
CONTENTS

CHAPTER I

PHYSICAL GEOGRAPHY . : f : . 4 . .

Introduction

Hydrographical Systems .

The Niger .

The Benue .

The Niger Basmaes Tene “Teen, Boi iKontegom,
Nupe : i . .

The Benue Provinces =n Keene, Muri, Yola ‘

The Central Provinces :—Zaria, Bauchi

The Northern Provinces :—Bornu, Kano, Sokoto

CHAPTER II

CRYSTALLINE ROCKS
Typical Traverses ; ;
Borgu and the Niger Valley hetweeh jebba. and Valve
Kabba and Ilorin -
The Central Crystalline Area .
Southern Muri and Yola .

CHAPTER III

PETROGRAPHY OF THE GNEISSES AND SCHISTS AND ASSOCI-
ATED IGNEOUS INTRUSIONS
The Gneisses and Schists
The Intrusive Rocks
a. The Older Granites
6. The Younger Intrusions . . . ,
1. Granites and Pegmatites
2. Syenites and Diorites .
3. Porphyries, Porphyrites, Diabases and Bacais

xi

16
25
35
50

63
64
69
75
86
103

108
108
123
123
129
129
135
137
xii CONTENTS

CHAPTER IV

CRETACEOUS ROCKS :
The Cretaceous Rocks of Muri Beoviiiee
The Cretaceous Rocks of Yola Province
The Cretaceous Rocks of Bauchiand Bornu. St

CHAPTER V
EOCENE ROCKS F
The Sokoto and Lokoja Seties
The Duguri, Gombe, and Kerri-Kerri Saiiddatties
The Upper Benue Sandstones
CHAPTER VI

SUPERFICIAL ACCUMULATIONS
In Hausaland and Borgu .
In Bornu and Katagum
In the Middle Gongola Valley
In the Benue Valley

CHAPTER VII
TERTIARY CRUSTAL MOVEMENTS AND DRAINAGE CHANGES

CHAPTER VIII

TERTIARY VOLCANIC ACTION

APPENDIX I—Mineral Resources
APPENDIX II—Palzontology of the Cretaceous Deposits .
INDEX OF AUTHORS

GENERAL INDEX

PAGE

144
147
154
157

164
165

175
184

194
196
215
222
223

227

253
265
273
287

289
PLATE

PLATE
PLATE

PLATE

PLATE

PLATE

PLATE

PLATE

PLATE

PLATE

PLATE

PLATE

PLATE

LIST OF ILLUSTRATIONS

To face
I.—Fic. 1. On the Niger above Igbo . oa
Fic. 2. Lokoja and Mt. Patti 12
II].—The Confluence of the Niger and the Bante, 20
III.—Fic. 1. Abuja Rock . 28
Fic. 2. Abuja Rock from the Walls of Abuja 28
IV.—Fic. 1. A Granite Mount near Abuja 48

Fic. 2. The Margin of the Nassarawa Tableland
from Jaginde 3 48
V.—FIG. 1. Worn Volcanic Cones near Awe 60
Fic. 2. The Wase Rock . ‘ 60
VIL—FIic. 1. Yendam Hill, Yola Province 76
Fic. 2. Craters at Mboi ‘ 76
VII.—Fic. 1. Craters in the Mboi Hills go
Fic. 2. A Crater in the Mboi Hills go
VIII.—Fic. 1. Exfoliation in the Kilba Hills . 104
Fic. 2. The Gorge of the Kaduna at Zungeru 104

IX.—FIic. 1. On the Summit of the Bauchi Plateau ;
the Parade Ground at Bukuru 120

Fic. 2. On the Plateau looking Westward. from
Bukuru i 120

X.—Fic. 1. A Worn Volcanic Hill on thie Bauch
Plateau near Zamagan . » 134
Fic. 2. The Twin Cones of Kereng from Panyam 134

XI.—Fic. 1. Hillocks of Drift on the Bauchi Plateau
: near Vom 152
Fic. 2. Hillocks of Drift to the West of Nara 152
XII.—-Fic. 1. A Granite Mount near Bauchi . 170
FIG. 2. ” ” 170
XIII.—Fic. 1. The Sandstone Hills of Ture 190
Fic. 2. Ture or Tangale Peak 190

xiti
xiv LIST OF ILLUSTRATIONS
To face
page
PLATE XIV.—Fic.1. Dozi Hill, Kerri-Kerri y 210
Fic. 2. A Trench-like Valley near Lele in Kerri-
Kerri . 210
PLATE XV.—FIG.1. Cretaceous Sandstones ‘aga cuales sane 224
Fic. 2. A Flat-topped Hillock of Drift above
Naraguta . » 224
PLATE XVI.—UpperBenue Sandstones and eee ates upon
a Hummocky Granitic Floor 245
PuaTE XVII.—Fic. 1. Inselberge Landscape around
Abbie Frontispiece.
Fic. 2. Inselberge Easdacoah in North-
ern Yola
PLATE XVIII.—Fic. 1. The Salt Fields of eee ; wine
Hills in the Background 260
Fic. 2. Akiri Saltings 260
PLATE XIX.—Cretaceous Mollusca . 286
PLATE XX.— a 33 286
PLATE XXI.— 9 $5 286
PLATE XXII.— ” ” 286
PLATE XXIII.— ” ” 286
PLATE XXIV.— ” ” 286
MAPS—
To pace
bage
I.—PRIMARY WATERSHEDS AND RIVER SYSTEMS 4
II.—THE BAUCHI PLATEAU AND THE NASSARAWA TABLE-
LAND : 40
III.—AXEs OF ELEVATION 236
IV.—MINERAL RESOURCES 266

V.—COLOURED GEOLOGICAL AND Trobeciuenicnd: Map

AND SECTIONS

At end of Volume
THE GEOLOGY AND GEOGRAPHY
OF NORTHERN NIGERIA
NORTHERN NIGERIA

CHAPTER I

PHYSICAL GEOGRAPHY

Introduction. Hydrographical systems; primary watersheds. The
Niger: Lokoja and Mount Patti; Jebba and the Juju Rock; the
rapids of the Niger. The Benue: the great plain of Muri; sand-
banks. The Niger Provinces: the tableland of central Kabba ;
domes and inselberge ; the plain of Ilorin; Borgu; Kontagora ;
typical scenery of crystalline and sedimentary regions ; the plains of
Nupe ; the sandstone plateaux of the Niger. The Benue Provinces :
Bassa and Nassarawa ; the river belt of sandstones ; the Karshi hills
and the Abuja Rock ; the central plain; the northern tableland ;
the plains of Muri; volcanic hills of the middle Benue ; the Wase
Rock ; the Murchison hills ; the plateau of southern Yola ; the lower
Gongola ; volcanic craters and granite inselberge. The Central
Provinces : Zungeru and the gorge of the Kaduna; the plains and
hills of Zaria; the Bauchi plateau; the Ningi hills; Angass and
Kanna; the eastern plains; the Gongola valley; the cliffs of
Tongolan ; the Kudu valley ; the Gateri hills; Tangale and Waja ;
The Peak. The Northern Provinces : southern Bornu; the Bima
hills; the Barbur volcanic plateau; the Tagum hills; eastern
Bornu ; firki land and blown sand ; Lake Chad; the central plains
of Bornu ; the Kerri Kerri plateau ; intersecting trench-like valleys ;
the plains of Katagum; Kano; Mounts Dala and Kogon Dutsi ;
Kazaure; Katsina; Sokoto; the Gulbin Kebbi; dallols and
dissected sandstone plateaux.

Tue Protectorate of Northern Nigeria comprises an

area of about 255,700 square miles, of which the

greater part is enclosed within the obtuse angle formed

by the Niger with its great tributary the Benue. The
B
2 NORTHERN NIGERIA CHAP.

north-eastern corner is occupied by Lake Chad, whence
irregular lines forming the northern and eastern
boundaries between the Protectorate, the French
Sudan and the Kameruns run west and south
respectively to the Niger and the Benue. Within the
oblique figure thus formed lie the provinces of Sokoto,
Kano, Bornu, Bauchi, Zaria, Kontagora, Nupe, Nas-
sarawa and portions of Muri and Yola. West of the
Niger lie Borgu, Ilorin and Kabba, which adjoin
Dahomey and Southern Nigeria, while south of the
Benue lie Bassa and parts of Muri and Yola, march-
ing with Southern Nigeria and the Kameruns. The
administrative headquarters of the Protectorate are at
present fixed at Zungeru on the Kaduna in western
Zaria, while the subordinate headquarters of the four-
teen provinces enumerated above are located respect-
ively at Sokoto, Kano, Maidugari, Bauchi, Zaria,
Kontagora, Bida, Keff, Ibi, Yola, Kiama, Ilorin,
Lokoja, and Dekina. Lokoja also, in addition to
being the headquarters of Kabba province, is from its
situation at the confluence of the Niger and the Benue
the natural emporium of European commerce.

Many of the more striking physical features of the
Protectorate are now comparatively well known. The
Niger with its flat-topped sandstone hills, the Benue
and the plains of Muri, the peaks of the Murchison
Hills, Lake Chad, and the sands and swamps of Bornu,
have become familiar from the writings of both early
and recent explorers.!. Equally striking, however, are

1 Mungo Park ; Denham and Clapperton ; R. and J. Lander; Laird
and Oldfield ; Allen and Thomson ; Baikie ; Crowther ; Barth; Vogel ;
Passarge ; Lenfant ; Lugard ; Wallace ; Boyd-Alexander.
1 PHYSICAL GEOGRAPHY 3

the broad, flat-bottomed valleys of the north-west, in
which diminutive streams now represent the mighty
rivers of old; the rolling sandy plains of Hausaland’
with their sluggish rivers, their isolated granite domes
and groups’ of rounded hills; and the mysterious
Bauchi plateau, the home of innumerable pagan tribes,
whose precipitous walls on the south and west long
marked the limit between the known and the unknown.

Hydrographical Systems. (Map. p. 4).

The Bauchi plateau, which rises to a height of 4,000
to 4,500 feet above the sea, is the hydrographical
centre of the Protectorate. From it the rivers radiate
north, south, east, and west ; but while at first they flow in
such diverse directions, they become ultimately included
within one or other of the two great hydrographical
systems, the Niger-Benue system and the Chad or
Inland system. All the rivers leaving the plateau, with
the exception of those flowing directly north, belong to
the Niger-Benue system. The “ primary watershed,” or
dividing line between the two great hydrographical
systems, runs from the neighbourhood of Daura on the
northern frontier of the Protectorate south-westward
between Katsina and Kano to the twelfth parallel.
Thence it runs south-eastward to the latitude of Zaria,
and then southward to the neighbourhood of Bukuru, on
the summit of the plateau. From Bukuru it strikes
approximately north-eastward to Kerri Kerri, and

1“ Fausaland,” in the general sense of the term, may be taken to
include the provinces of Sokoto, Kano, Kontagora, Zaria and Bauchi.

B 2
4 NORTHERN NIGERIA CHAP.

thence south-eastward to the Yola border in the neigh-
bourhood of Mubi. Within the Chad system the
only important river is the Yo, of which the rivers
Hadeija, Katagum, Delimi, and Shidya form the head-
waters. The Yedseram, the only other large river of
Bornu, forms for some distance the boundary line
between Nigeria and the northern territories of the
Kameruns. In the west the primary watershed of
the Niger system coincides approximately with the
boundary of the Protectorate from the eleventh parallel
to the neighbourhood of Aiedi on the eighth parallel,
whence it runs eastward to Kabba, and thence south-
ward through the Egbira and Kukuruku hills into
Southern Nigeria. South of the Benue, the primary
watershed runs through Southern Nigeria and the
Kameruns entirely beyond the southern limit of the
Protectorate.

The Niger.

The Niger enters the Protectorate at Ilo in the
north-west, and flows within the Protectorate for a
distance of four hundred and fifty miles to Idah on the
Southern Nigerian frontier. Its breadth varies in
places from a few hundred yards in the dry season to
several miles during the rains. The annual variation
in depth may reach at Lokoja as much as thirty-five
feet, and when in flood the river is navigable for small
ocean-going steamers as far as Baro, the terminus ot
the Baro-Kano railway, and for light stern-wheelers as
far as Bajibo, twenty miles north of Jebba. Its largest
tributaries within the Protectorate join the Niger on
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I PHYSICAL GEOGRAPHY 5

the left, those on the right being comparatively short
and unimportant. On the left are the Kebbi, Malenda,
Kontagora, Kaduna, Bako, Gurara, and Benue; on
the right the Wessa, Oli, Teshi, Awo, Oshin, Oyi,
Oro, Kampi, Mimi, and Meadowbank. Of these the
Gurara is navigable in flood for small stern-wheelers
for a distance of thirty miles from the Niger, the
Kaduna as far as Wushishi at the foot of the rapids,
and the Kebbi as far as the confluence of the Jega
river.

The alternation of narrow gorge and open plain is
a striking feature of the Niger valley within the
Protectorate. Where the channel is narrow and
bounded by steep cliffs on either side the seasonal
variation in level gives rise to comparatively little
change in the aspect of the river. The blackened
rocks in the river bed and the sandy stretches on either
shore may be lost to view, but the flood is still confined
within its walls of rock. It is where a plain tract
intervenes in the course of :the river that the contrast
between the Niger in flood and the Niger at low water
becomes particularly striking. The sandy bars and
shallows which in the dry season present such obstacles
to navigation, as well as the grassy banks and islands
of alluvium with their terraced slopes of sand and clay,
are buried during the rains under a flood, which may
spread for miles over the plain on either side of the
river.

At Idah the Niger narrows and flows swiftly
between low cliffs of white sandstone which pass
northward into stretches of wooded rising ground on
6 NORTHERN NIGERIA CHAP.

either bank. Ten miles above Idah a group of flat-
topped hills approach the right bank of the river, only
to turn off abruptly inland in a line of buttresses six
to seven hundred feet in height. Farther on, the low,
flattened ridges on the left bank run out in a line of
rounded hills: and beyond, the river broadens and
a broken plain stretches inland to distant groups of
lofty hills. Nearing Itobe Mount Purdy stands out,
a solitary cone, in advance of the level-crested plateau
beyond. From Itobe to Igbo the Niger flows through
the most picturesque portion of its lower course. The
hills rapidly close in, the channel becomes narrow and
rocky, lofty granite domes and rounded hills separated
by narrow gloomy valleys rise up on either bank, and
on the left the level crest of the plateau looms behind
on the sky-line (Plate I, Fig. 1). Below Lokoja the
river opens out, the hills die down on either side, a n
from the left bank a broken hummocky plain stretches
inland to the base of the Bassa hills, while at Lokoja
itself flat-topped Patti (Plate I, Fig. 2), with its
projecting buttresses and the red roofs of the canton-
ment at its base, stands sentinel over the confluence
of the Niger and the Benue (Plate II).

An extensive alluvial plain annually flooded during
the rains stretches away to the Benue from the left
bank of the Niger for long miles above Lokoja.
The right bank is occupied more or less continuously
by the worn escarpment of the plateau of which

Mount Patti forms the southernmost extremity. Above

' Of Laird and Oldfield, Expedition to Africa, 1837, p. 136. The hills
between Itobe and Igbo are here erroneously described as the eastward
prolongation of the Kong Mountains,
I PHYSICAL GEOGRAPHY ¥

Koton Karifi the hills reappear on the left bank, and
for more than twenty miles the Niger flows between
the broken walls of what has once been a magnificent
river gorge. In places for considerable distances the
flat-topped hills still rise up with precipitous slopes
on either side in all their ancient grandeur. More
frequently, however, the escarpments are rounded off
and much eroded by lateral valleys, while at times they
recede to a distance, and leave between themselves
and the river a more or less extensive swampy plain,
with here and there a flat-topped remnant of the once
continuous plateau. Before Baro is reached, however,
the plateau has disappeared on the right bank, and on
the left is represented only by more or less isolated
flat-topped fragments. The bend of the Niger at
Egga and Kacha marks the eastward limit of an
extensive alluvial flood plain, which includes the lower
courses of the Kampi and the Bako, and stretches
westward on the north bank as far as the Kaduna.
On the south bank the pinnacle peaks of Egbom’ tower
high above the river, while a flattened ridge extends
westward as far as Pategi. Beyond the Kaduna
the Niger flows through a broad and shallow valley
with extensive swampy plains on either hand, and only
at Shonga on the right bank and at Rabba on the left
does the river approach the rising ground which
elsewhere bounds the valley in the distance.

At Jebba the hills close in on either side, and the
Niger issues by a double channel from a picturesque
gorge which extends northward as a deeply cut and

1 Cf Vandeleur, Geographical Journal, X, 1897, p. 349.
8 NORTHERN NIGERIA CHAP.

rocky valley as far as Bussa, a distance of seventy-five
miles. For eight hundred yards above Jebba the
gorge is narrow and bounded by vertical walls of
quartzite. The Juju Rock’ and the other islands
which interrupt the channel mount steeply from the
river, the rapid current pours over sunken rocks which
rise abruptly from the river bed, and mighty whirlpools
bear witness to the depth of the water. Beyond Jebba
the quartzite gives place to granite, the vertical walls
become rounded, wooded slopes, the river broadens
its rocky bed and flows in a narrow valley between
two belts of broken hilly ground which lead up to the
plains of Kontagora and Borgu, five hundred feet
above the level of the river. In spite of the
obstructions in the channel the river is navigable with
caution for small stern-wheelers as far as Bajibo.
Above Bajibo, however, navigation becomes precarious
and dangerous even for native canoes. The current
becomes more violent ; rocks, cascades, and whirlpools
more numerous, and small rapids more and more
frequent, until above Leaba the Niger flows in a rocky
gorge which leads to the base of the Great Rapid
of Wuru.? Here the river is formed of two branches
with a rocky island between. The fall of forty feet
between the summit and foot of the rapid is distributed
over some thirteen hundred yards of river, giving
a slope of at least 1 in 100 and a current of from
fifteen to eighteen miles an hour. In the rains the
granite boulders are completely submerged under

1 Vide Lenfant, Le Niger, 1905, illus., pp. 72, 73.
2 Lenfant, of. cit, p. 78 et seg.
I PHYSICAL GEOGRAPHY 9

a seething flood, and even in the dry season the water
is thrown up by the projecting rocks in sheets of foam,
and the roar of the rapid is heard for long distances
on either side.

A stretch of two and a half miles of comparatively
smooth water, broken only by some small rapids and
cascades, separates the Great Rapid of Wuru from the
rapid of Patassi, which is composed of two sets of
cascades, each twelve to fifteen feet in height and
separated by a straight reach of some two hundred
and eighty yards. Twenty miles farther on, the third
important set of rapids is reached, the rapids of
Garafiri, whose cascades and whirlpools occupy a
stretch of about three miles between the villages
of Garafiri and Malali. At Bussa, the scene of Park’s
disaster, the channel is still much obstructed by
projecting rocks and islands, and the small cascades
and the rapid current still render navigation both
difficult and dangerous. The right bank of the river
is here formed of low, wooded rising ground, while on
the left ranges of low hills rise in series one behind
the other. Soon, however, the hills die down and the
rocks disappear from the river bed, and at Warra the
river is broad and smooth with an extensive flood
plain on either side. From Warra to Ineku the Niger
is formed of two branches, of which the more westerly
preserves the calm aspect of the river at Warra, while
the more easterly becomes again obstructed by rocks
and rapids. Between Ineku and Yelwa the river is
bounded by low, rounded hills covered with scanty
forest, innumerable islands rise from the river bed
10 NORTHERN NIGERIA CHAP.

supporting an abundant vegetation, while several sets
of lesser rapids obstruct the channel. At Yelwa the
banks become low and swampy, the hills begin to
recede from the river, and five miles farther on, near
the village of Sakassi, the last set of minor rapids
occurs in the channel. Beyond Sakassi the whole
aspect of the river changes, the channel becomes
broad and sandy and obstructed by nothing more
serious than sand bars. On the north bank a broad,
swampy flood plain, with low rising ground in the
distance, bounds the river as far as the mouth of the
Kebbi, and from the Kebbi to the swamps of Ilo
an open sandy plain stretches northward between
the river and the base of the plateau. On the south
bank the gently undulating plain which bounds the
river stretches westward to the Dahomey border,

broken only by some scattered groups of flat-topped
hills.

The Benue.

The Benue enters the Protectorate to the east
of Yola, and after a course of nearly five hundred
miles joins the Niger at Lokoja. Its principal
tributaries are on the right bank the Gongola, Kudu,
Wase, Simanka, Ankwe, Modu and Okwa; on the
left bank the Faro, Ini, Mainarawa, Tarabba, Donga
and Katsena. The Benue is navigable when in flood
throughout its whole course for steamers of light
draught. The Katsena is navigable as far as Katsena
I PHYSICAL GEOGRAPHY II

Allah, the Gongola as far as Nafada, and the
Donga and Tarabba for considerable distances up
stream.

In the matter of scenery the Benue presents a
striking contrast to the Niger. There is on the Benue
no picturesque alternation of narrow gorge and open
plain; no rapids trouble its surface from Lokoja to
the flat-topped hills of Yola, and even in the dry
season it is only at long intervals that rocks are
exposed in its sandy bed or in its steep banks of
alluvium. The precipitous front of Mt. Patti and the
level crest of the plateau on the right bank of the
Niger are visible from the Benue for twenty miles
above Lokoja, across the great alluvial plain which
marks the confluence of the two mighty rivers.
Above Mozum a range of flat-topped hills with
occasional peaks follows the right bank for some
distance, but soon turns inland and leaves a broken
plain between the river and the base of the hills. A
similar range, also separated from the river by a
broken plain, runs parallel with the left bank a few
miles inland. The escarpments of these ranges on
either side of the river represent the walls of a broad
flat-bottomed valley which is comparable in origin with
the steep-sided gorge of the Niger above Lokoja.
Here on the Benue, however, erosion has been more
intense, and the hills have been cut farther back on
either hand.

Above Umaisha a tract of broken country stretches
eastward on the north bank and gives place in the
neighbourhood of Loko to alluvial swamps in the
12 NORTHERN NIGERIA CHAP.

foreground, with undulating sandy plains beyond. On
the left bank, meanwhile, the hills approach the river at
Amara and pass eastward into a hummocky plain,
which is bounded to the south by a distant range of
flat-topped hills. Above Loko the Doma Hills touch
the river at Udeni on the right bank, but turn off
abruptly inland with their low, buttressed slopes over-
looking an extensive swampy plain which stretches
eastward as far as Akwaneja. Beyond Akwaneja the
right bank assumes a similar aspect to that of the left.
The river is bounded by low, well-wooded banks, with
here and there a projecting mass of sandstone, while a
hummocky plain stretches inland on either side to
distant rising ground. The volcanic tract above
Abinsi introduces an agreeable change into the
monotony of the scenery. The worn and weathered
cones and banks of lava stand out picturesquely from
the wooded plains, and on the river-side the black
basalt and the yellow sand offer a pleasing contrast to
the eye. Soon, however, the low banks resume their
familiar aspect and a featureless plain spreads out on
either hand. Nearing Ibi the right bank becomes low
and swampy, and the great plain of Muri opens out
beyond. From Ibi to Lau the channel is broad and
sandy, and the river winds about amongst ever-
changing sand-bars and banks of alluvium. In the
rains broad stretches are flooded on either side, and for
long distances on the right bank the plain beyond
becomes an almost impassable swamp, while on the
left long tongues of marshland run up the tributary
valleys. Far to the north the peaks of the Murchison
Prare I

 

 

 

 

 

 

ON THE NIGER ABOVE IGRo.

 

 

 

 

LokolA AND Mount PArri.
I PHYSICAL GEOGRAPHY 13

Hills! tower high above the plain, while to the south
the rock of Bantaji guards the swamps of the
Donga.

Farther east, and especially between Numan and
Yola, the river plain is traversed by a large number of
anastomosing channels, which in many cases are only
connected with the main stream during the rains, and
in the dry season are cut off by sand-bars into strings
of shallow pools and marshes. Alluvial mud covers
the rocks for some miles inland, and while in the rains
travel on foot is impossible and the villages are isolated
one from another, in the dry season the ground shrinks
and is broken everywhere by wide cracks. This
alluvial plain is perfectly level, so that the small
volcanic mounds, dotted here and there, which in a
more varied country would be overlooked, form
conspicuous landmarks. The most striking of these
hillocks is Jeme Hill, below Numan, which stands on
the river bank and can be seen for twenty miles
around. (A. L.)

The Benue plain, which is so extensive in Muri
province, contracts near Lau, and thence eastward it is
limited on both sides by plateau areas which rise
suddenly and steeply at distances of fifteen miles from
the river. These masses of hills with their varying
outlines introduce a pleasing change into the hitherto
monotonous river journey, and contrast sharply with
the river plain. Here the plain of the Benue is like a
broad and shallow trench, bounded by sharply rising
walls, whose height is small compared with the

1 Boyd-Alexander, From the Niger to the Nile, 1908, p. 47.
14 NORTHERN NIGERIA CHAP.

distance between. At the same time the height is
considerable in itself, for the rise to the plateau is well
over a thousand feet. (A. L.)

These hills running eastward parallel to the river
are breached by the Gongola plain, about ten miles
wide, entering from the north, and by the plain of
the Ma-Ini and Maio Belwa entering from the south.
Farther on the hills come in again. To the north
they are rather scattered and detached, with long
tabular outlines, or, as in the Bagele Hills, with
terraced sides and abrupt scarps. On the other side,
though flat-topped hills do occur, the outlines are
usually more varied, while south of Yola rises the
typical plateau of the Vere Hills—a solid mass fronting
boldly outwards upon the surrounding plains with
continuous rocky faces indented by a few deeply-cut
and narrow valleys. Meanwhile the plain of the
Benue with its flat and marshy character continues
eastward beyond Yola and the Faro river into the
German Kameruns. (A. L.)

Along the whole course of the Benue from Lokoja
to Yola exposures of the underlying rocks are very
infrequent, and this remark applies equally to the
lower courses of the tributaries. The main trunks of
the Benue system have long passed the stage at which
they effected any appreciable erosion, and now serve
only as the channels along which detrital material
brought down by the head-waters is transported to
the Niger. The finer portion of the material is
carried in suspension, and is responsible for the
covering of alluvial mud found over those parts of the
I PHYSICAL GEOGRAPHY 15

river plain which are inundated during the annual
rise. The coarser portion is rolled along the bottom
and gives rise to the sandbanks. These are covered
in flood, but for the other part of the year they are a
constant feature of the river scenery. The stream,
much lessened in volume, swings first to one side and
then to the other of the wide river bed, with the broad
sandbanks occupying the bends. (A. L.)

The sand is rather coarse, principally of clean
grains of quartz and felspar, but at times with pebbles
of vein quartz or occasionally of polished limonite.
Typically, a spread of sand, many acres in extent and
with its level surface only a few feet above the water,
ends on the down-stream side in a slope which plunges
into deep water at perhaps 4o°. While the river is
falling, the formation of these sandbanks can be well
studied. The water, covering the sandbank by only
a few inches, is seen to sweep grains of sand or
occasional pebbles along over the level surface till
they reach the end of the bank and roll down into
deep water, thus helping to form the next lamina. In
this way the sandbank is built up of successive laminz
inclined down stream at a steep angle to the horizontal,
and wherever a bank is cut into by a change in the
direction of the current the inclined lamination is
beautifully displayed. The lamination is of course
only a particular instance of the “current bedding”
produced whenever detritus in process of deposition
is subjected to currents of air or water, but it is
important to understand that the oblique lamination
of the sandbanks is brought about by the river
16 NORTHERN NIGERIA CHAP.

currents, and not by the wind as has been supposed.
Any slight rearrangement of the. surface layers by
wind is obliterated by the next rise of the river.

(A. L.)

The Niger Provinces——Kabba, Llorin, Borgu,
Kontagora, Nufpe.

The orographical structure of Kabba and Ilorin is
somewhat complex. The primary watershed of the
Niger basin which runs from Kabba to Aiedi and
thence westward a few miles south of the Ilorin
frontier, is not defined by any range of hills or
mountains, but by the crest line of a lofty plain which,
like a low, extended arch, slopes gently northward
towards the Niger and southward towards the sea.
In central Kabba the high plain assumes, to some
extent, the character of a tableland, which is bounded
to the north-east by the Lukke hills and the broken
ground beyond the Mimi valley. To the east and
south-east the tableland is abruptly limited by the
worn escarpments of the Shokko Shokko, Agwede
and Egbira hills, at whose base, 500 feet below,
are spread out the broad, well-watered and well-
wooded plains which stretch away eastward to the
Niger, and of which passing glimpses are caught
from the river below Itobe. To the south these
undulating plains slope gently upward and inward
from the Niger and lose themselves in the narrow
valleys of the Kukuruku Hills.

Although such in brief is the orographical character
1 PHYSICAL GEOGRAPHY 17

of the major portion of Kabba and Ilorin, the actual
conditions of the surface and the peculiar character
of the scenery to some extent obscure the issue. In
central Kabba the undulating surface of the tableland
is in places densely wooded, in places covered with
thin bush, in places open, grassy, and park-like with
cultivation near the towns and villages, while above
the plain at frequent intervals rise isolated rounded
hills or groups of hills, or even short rocky ranges,
which form secondary watersheds between the minor
streams. Similarly, on the lower plains adjoining the
Niger, the attention is arrested by the dome-shaped
island mountains and picturesque clusters of rounded
hills which rise abruptly into view. The full signifi-
cance of this peculiar type of scenery can only be
grasped when gazing from the summit of one of the
isolated hills themselves, or from some favourable spot
on the crest of the escarpment which separates the
higher from the lower plains. Then all the minor
irregularities disappear, and the level, wooded surface
of the plain can be seen stretching up to and around
and between the bases of the hills which rise like
rocky islands from a verdant sea. The hills may be
covered to the summit with angular déérzs and scanty
forest, or the lower slopes may be littered with ex-
foliation fragments, amongst which a few trees find a
precarious footing, while the summit may be smooth
and bare, with a few large boulders perched pictur-
esquely in apparently impossible positions. The
contours of the bare and treeless summits are
frequently particularly graceful with beautiful domes
c
18 NORTHERN NIGERIA CHAP.

and cupolas rising from gently-rounded slopes of
granite or gneiss. In many cases a precipitous path
leads to the village which caps the summit, while for
long acres round the base the plain is cleared and
cultivated. (Plate XVII.)?

The northern part of Kabba is more rugged, the
population is more scanty and forest more abundant.
The rocky valley of the Mimi is bounded to the
north by the broken, hilly ground between Jakura and
Akpara, which passes to the east and north under the
flat-topped sandstone hills which fringe the Niger.
The Jakpara Hills with their conical peaks upon
rounded bases are landmarks for miles around. The
white quartzite hills in the neighbourhood of Lukke
alternate with belts of soft schists which support a
luxuriant forest growth. Farther west by Moppa,
Sanlu and Takete detached groups of granite hills
rise upon an undulating plain. The thicker vegetation,
however, obstructs the view, and it is only when the
landscape is surveyed from the summit of one of the
higher hills that the structure is seen to be very similar
to that of southern Kabba. To the west, Ogga and
Eri are set within a cluster of rocky hills, while to the
north there is a comparatively rapid fall to the plains
of the Kampi. Between the Kampi and the Niger a
steep-sided range of sandstone hills capped by the
pinnacle peaks of Egbom (p. 7) runs out westward in
a succession of rounded ridges two hundred feet above

1 An excellent illustration of this peculiar type of scenery (Inselberg-
landschaft) is given by Bornhardt, Deuétsch-Ost-Afrika—Géologie, Ba.
VII, 1900, Taf. 3, p. 30.
I PHYSICAL GEOGRAPHY 19

the level of the river, and not until near Share is the
river belt of sandstones again bounded by a low
escarpment. The Shappa and Orissa Hills form the
only prominent range in central Ilorin. The Shappa
Hills are of granite, and many of the peaks are
gracefully rounded and most picturesque, while the
quartzites and gneisses of the Orissa hills give more
rugged and irregular contours. West of the Orissa
hills lies the great plain of Ilorin, thickly populated
and well cultivated, in broad undulations trending
generally north and south, with scattered inselberge
and many kopjes of granite boulders, but with no
conspicuous ranges or groups of hills. The Jebba
hills, which extend southward for some distance
towards Ilorin, pass westward into an extensive tract
of hilly country, high lying, little known and largely
uninhabited, which forms a natural boundary between
Horin and Borgu.

The primary watershed of the Niger basin follows
the frontier of the Protectorate more or less closely
from the eighth parallel to the south of [orin as far
as Okuta in the west of Borgu, whence it runs north-
ward to the latitude of Nikki before turning off west-
ward into Dahomey. With the watershed the high
plains, along whose crest it runs, also swing round to
the west of Borgu and fall off gently towards the Niger
on the right, while along the river itself from Bussa to
Jebba a narrow belt of broken country marks the tran-
sition from the high plains of Borgu to the gorge-like
valley of the Niger.

Southern Borgu is one of the least inviting districts

c 2
20 NORTHERN NIGERIA CHAP.

in the Protectorate. The rocks are concealed almost
everywhere by recent alluvium or by surface ironstone,"
which in places forms extensive platforms entirely bare
of vegetation. Where rocks do emerge from the
superficial accumulations they seldom form hills. The
granite hills around Kiama are an exception to this
rule, and along the western frontier a number of
granite domes rise from two to three hundred feet
high. These domes, however, are separated by wide
stretches of country over which all geological processes
seem to have come to a standstill. The drainage
system is very poorly defined, and for the most part
the water is carried off, not by stream courses with
sand and boulders, but along shallow, soil-covered
depressions in the plain. Such streams as there are
dry up soon after the end of the rains, and the natives
then resort largely to wells dug in the surface soil.
The crests of the gentle undulations follow one another
on the sky-line in endless succession, and the journey
becomes monotonous in the extreme. The northern
part of the province is diversified by a number or
sandstone hills, and some swift, clear streams, fed from
springs at the base of the hills, afford a welcome
change to the jaded traveller. (A. L.)

In the provinces which lie to the east of the Niger
the intimate relation which exists between the character
of the scenery and the nature of the rocks becomes
increasingly evident. In Kabba, Ilorin, and Borgu,
where crystalline rocks of a granitic or gneissic
character cover by far the larger part of the surface,

' Erroneously designated lava by the earlier explorers.
“HONUQ GWHL ANY UAOIN] GH tO WONANTINOD) WAY

 

 

 

 
I PHYSICAL GEOGRAPHY 21

the prevailing and most characteristic type of scenery
is that of rolling sandy plains with isolated hills or
groups of hills rising abruptly above the general level.
On the other hand, where sedimentary rocks, such
as sandstones and ironstones, cover the surface, as in
the river belt of sandstones in Kabba and Ilorin, the
characteristic type of scenery is that of steep-sided and
flat-topped ranges and plateaux, with detached tabular
and conical hills rising from the lower plains. Over
the greater part of Kontagora province, to the north
of the parallel of Kontagora itself, granites and
gneisses form the surface rock. In the west, near
N’gashki, a group of granite hills rises abruptly from
the plain which stretches away to the east, with its
surface diversified in typical fashion by occasional
inselberge. A belt of slaty rocks much pierced by
quartz veins runs along the left bank of the Niger
from N’gashki to Yelwa, and gives rise to a stretch of
broken country adjoining the river. The granites and
quartzites in the lower valley of the Malenda river
also give rise to much rough and stony country, which
culminates in the quartzite hills of Maibirro. Beyond
Jindani and Yelwa the plain reappears in a more
typical character, and stretches northward as a gently
undulating surface covered with deep, sandy drift, from
which emerge at long intervals low, rounded, or rocky
hummocks of granite or gneiss.

It is in the east of the province, however, between
Banaga and Kotonkoro, that the landscape assumes
the typical aspect of the high plains of Hausaland. In
front, behind, and for long miles on either hand, the
22 NORTHERN NIGERIA CHAP.

open, sandy plain stretches away to the horizon, with
here and there a low turtleback or heap of granite
boulders, and at long intervals a loftier dome or a
group of rounded granite hills. The rivers flow in
almost imperceptible valleys in broad, sandy channels,
or over smooth and bare surfaces of rock, level with
the plain, while the low watersheds between the rivers
are crossed almost unconsciously by the traveller.

The country around Kotonkoro and to the south-
west is extremely picturesque. Numerous domes of
bare rock rise from a grassy park-like country. The
plain around one of these domes passes imperceptibly
into a gentle slope of sandy wash, which leads the eye
up to the spring of the dome. As the path winds
along, first one and then another of these domes
engages the attention. On approaching Mahorro two
of the highest hills have flattened summits and are
found to be capped by about twenty feet of stratified
ironstone. To the north-east of Kontagora these
outliers are more numerous, though seldom of a
sufficient size to mark on the map. The country is in
consequence very rough and broken and the track
becomes difficult and stony. The poor agricultural
prospects, however, are compensated for by good iron
ore, and the crude native furnaces soon come to be a
familiar sight. When these outliers are finally left
behind at Libo, a belt of very rough broken country
has to be crossed before descending to the Kara
river. (A. L.)

The town of Kontagora is set in an open undulating
sandy plain, deeply covered with surface drift, which
I PHYSICAL GEOGRAPHY 23

stretches eastward to Moriga and the Kara river, with
its surface diversified by a few isolated sandstone hills
near Kontagora and a group of granite hills at Beri.
To the south of Kontagora begins the sedimentary
series which stretches southward into Nupe province
and westward to within a few miles of the Niger.
The change in the nature of the surface rock is
accompanied by corresponding changes in the char-
acter of the scenery. Here at first are the same
rolling sandy plains, if possible more deeply covered
with drift than before ; but here are no turtlebacks or
lofty domes of granite forming conspicuous features in
the landscape, no rivers flowing over smooth surfaces
of rock in valleys so shallow that they are almost
indistinguishable from the plain. In place of these are
low, flat-topped sandstone hills rising singly or in
groups above the general level, and deep and narrow
canyon-like valleys cut down, it may be, fifty or a
hundred feet below the surface of the plain. A
typical group of hills with their level summits of hard
ferruginous grit and their slopes covered with rounded
boulders of the same occurs at Madara, a few miles
south of Kontagora, while at Kagara, Kaboji, and
Sonko the streams run in typical canyon valleys,
whose presence is unsuspected upon the plain until
the chasm opens abruptly at one’s feet. The larger
rivers flow in broad, trench-like valleys, with their
steep and wooded slopes covered with rounded
pebbles and boulders of ironstone and grit. To the
west the plains pass into the belt of hilly ground
which leads to the Niger valley, and which in its
24 NORTHERN NIGERIA CHAP.

eastern portion shows the characteristic tabular out-
lines of the sedimentary series, and in the west,
adjoining the river, the rugged irregular contours of
broken crystalline hills.

The province of Nupe is somewhat unequally divided
into two parts by the Kaduna river. With the
exception of the quartzite and granite hills of Jebba
and Kailema and the crystalline rocks of the eastern
corner of the province between Badegi and the Gurara
river, the entire surface is covered by sandstones,
which are continuous with the sedimentary series of
southern Kontagora. West of the Kaduna, however,
the high plains become much dissected and broken up
into extended tabular ridges and irregular plateau-like
masses, with the tracks leading over a succession of
low, well-wooded hills and shallow, flat-bottomed valleys
bounded by rough and stony slopes. On either side
of the Kaduna rise isolated tabular hills and short
ranges separated by long stretches of open plain, while
to the east of Bida there open out the great rolling
sandy plains of Nupe, which extend from the Bako
river to Badegi and southward to the bend of the
Niger. Beyond Kacha the character of the landscape
again changes: scattered hills and short ranges
diversify the surface and coalesce southward into the
extended flat-topped ranges and plateaux, whose wooded
slopes dip steeply down to the narrow ledge of crystal-
line rock which fringes the Niger. In the north-eastern
angle of the province beyond Badegi the sandstones
give place imperceptibly to granites and gneiss. The
sandy plains of Nupe are continued eastward, but their
I PHYSICAL GEOGRAPHY 25

drift-covered surface presents now the characteristic
features of a crystalline floor. Knobs and hummocks
and low ridges of gneiss project here and there above
the general level, while lofty groups of rounded granite
hills, like those of Gaung, rise abruptly and pictur-
esquely from the plain.

The sandstone plateaux which bound the Niger to
the north of the Gurara river are continued southward as
far as Koton Karifi, and pass eastward into Nassarawa
as a dissected system of flat-topped and conical hills.
To the south of the confluence of the Niger and the
Benue, the scenery on the left bank of the Niger in
Bassa province, as already described (p. 6) is that of a
hummocky plain with groups of rounded hills in the
foreground, backed and capped by lofty plateaux
and conical hills. Such a type of scenery is readily
explicable as that of a dissected sedimentary series
resting upon an irregular crystalline floor of granite
and gneiss.

The Benue Provinces. Bassa, Nassarawa, Muri, and
Yola.

With the exception of the narrow strip of crystalline
rocks exposed along the Niger, the province of Bassa,
so far as known, is entirely covered by the sedimentary
series whose western and northern escarpments are
visible respectively from the Niger and the Benue.
These escarpments, however, which from a distance
appear continuous, are found on nearer view to be
much incised by river valleys which have been cut
26 NORTHERN NIGERIA CHAP.

back for long distances into the high ground behind.
A system of lofty, flat-topped and conical hills, extended
ranges and plateau-like masses, separated by narrow,
steep-sided valleys, has thus been dissected in the north
and west out of the once continuous tableland. In the
interior the relief lessens, and the surface of the table-
land becomes broken up into a succession of tabular
ranges and rounded ridges, separated by shallow
valleys well cleared for cultivation. The hills are
usually thickly wooded and the paths frequently rough
and stony and covered with pebbles and broken frag-
ments of ironstone. In the south the Akpoto country
becomes in places particularly hilly and difficult, while
the little known Munchi country in the east is said to
open out into undulating park-like plains beyond the
belt of forest which fringes the river.

For purposes of description the province of
Nassarawa may be conveniently divided into three
portions, the river belt of sandstones, the central
crystalline plains and hills, and the northern tableland.
The Gurara river forms the greater part of the western
and northern boundary and drains all but the eastern
portion of the elevated plains in the north. The river
belt of sandstones between the Gurara and the Okwa
in the west presents the characteristic and familiar
scenery of a dissected sandstone tableland. Beyond
the Okwa river the flat-topped hills and ranges die
down into undulating sandy plains which stretch east-
ward as far as the Modu river, while the detached
group of hills, which strikes inland from Udeni, is the
last prominent tabular range on the lower Benue.
1 PHYSICAL GEOGRAPHY 27

Farther east, the low-lying plains stretch into the
unexplored land of the Munchis, while to the north
the trade route from Loko to Ibi leads over well
wooded undulating plains deeply covered with sandy
drift. The solid rock is frequently exposed in the
beds of the larger rivers and streams which have cut
their channels through the superficial accumulations ;
and here and there, as at Doma and Lafia, groups of
low rounded sandstone hills and projecting hummocks
of grit diversify the surface of the plain.

Central Nassarawa is, in the west, particularly broken
and rugged. Around Gwombe and Gwagwada and
as far east as Buga a mass of low rounded hills has
been carved out of a series of soft micaceous schists.
The rocks are much decomposed on the surface into
red gritty earth which supports an abundant vegetation
and in which the rivers and streams have cut deep and
narrow channels. To the north these rounded hills
pass into a tract of exceedingly difficult and broken
country where precipitous hills of granite and gneiss,
separated by narrow rocky valleys, rise to a height of
two thousand feet above the sea. This mountainous
tract, of which the Karshi hills are the northern pro-
longation, forms the secondary watershed between the
river systems of the Gurara and the Okwa. Beyond
the Karshi hills a lofty and rapidly undulating plain,
in places rough and stony, and much diversified by
inselberge (Plate IV, Fig. 1) and short ranges of
granite hills, stretches north-westward towards Abuja.
The Abuja Rock, atypical granite mount, streaked and
channelled by the summer rains, is a far-famed local
28 NORTHERN NIGERIA CHAP.

landmark and an object of superstitious veneration to
the inhabitants of the surrounding country. (Plate ITI,
Figs. 1 and 2.)

Eastward from Buga to Nassarawa extends a
broken plain with hummocks of gneiss and detached
groups of granite hills. At Kurudu, the Okwa river
flows through a narrow picturesque gorge between two
rounded granite hills, with the bare rock in the river
bed honeycombed with potholes. Nassarawa itself
is set in the midst of gently undulating park-like plains,
well wooded and well cultivated, which extend north-
ward as far as Keffi and are continuous southward
with the sandy plains of the river belt. To the east
they are limited by the rocky mass of the Anagoda
hills and the broken hilly ground between Keffi and
the Modu river. To the north of Keffi there opens
out the great central plain of Nassarawa which extends
from the neighbourhood of Abuja in the west to the
Mada country in the east, and is limited northward by
the worn escarpment of the northern tableland.
Turtlebacks and kopjes of granite and broken
hummocks of gneiss rise at intervals from the undula-
ting surface of the plain, while the minor irregularities
are obscured, as usual, by deep sandy drift. The
larger rivers flow in broad sandy beds with long
stretches of swampland on either hand, or, where the
drift is thinner, in narrow rocky channels with belts of
broken plain on either side from which the surface
drift has been in large part removed.

Viewed from the central plain, the margin of the
northern tableland is in places particularly picturesque.
PLATE III

 

 

ABUJA ROCK.

 

 

ABUJA ROCK FROM THE WALLS OF ABUJA.
I PHYSICAL GEOGRAPHY 29

A well-marked, though much worn and rounded escarp-
ment (Plate IV, Fig. 2), extends continuously from the
neighbourhood of Kari in the west by way of Kukwi,
Tatara, and Jaginde, to Darroro and Assab in the east,
and the skyline is variously ornamented by domes,
cupolas, conical peaks and perched blocks, with here
and there, as beyond Darroro, a jagged wall of granite
rising perpendicularly from the plain. The escarp-
ment is steeper in the east than in the west, and
beyond Kari it is lost in the broken hilly ground
around Abuja, which falls in a succession of rocky
steps to the plains of the Gurara. The tableland
itself slopes gently towards the Gurara, and in the
west, in the picturesque Gwari country, the numerous
domes and turtlebacks of granite afford ideal sites for
pagan villages. Parallel with the escarpment runs a
narrow belt of broken country which represents the
worn edge of the tableland, while to the north the
undulating park-like plains, diversified by inselberge
and groups of rounded hills, wrapped closely round
with sandy drift, recall in every detail of scenery the
central plain of Nassarawa below. A belt of broken
rising ground, stretching northward from Jaginde,
separates the Gurara system from the Kogin Kogom
which drains the grassy plains of Morrua and issues
behind Jaginde from a narrow rocky valley cut back-
ward for a considerable distance into the plateau.
The flat-topped granite massif of the Kagoro hills,
whose precipitous wall forms the continuation of the
escarpment from Darroro to Assab, projects also on
the north above the plateau and overlooks the lofty
30 NORTHERN NIGERIA CHAP.

undulating plains of Morrua and Akul which stretch
away northward towards the Kaduna. Far away to
the south of Darroro, the peaks of the Mada hills
can be seen across a broken wooded plain: but this
eastern portion of the province is as yet unknown
and unexplored.

The great plain, which forms the major part of Muri
province, extends from the base of the Murchison
hills on the north to the frontier of the Protectorate on
the south, and from the Ankwe river in the west to
the Wurkum and Shebshi hills in the east. With the
exception of the narrow margin of crystalline rock in
the north-west which runs parallel with the Murchison
hills, and the broader belt in the south between Takum
and Bakundi, the plain possesses throughout a floor of
sedimentary rock. The flat-topped hills, which are
such a conspicuous feature of the scenery of the lower
Benue and the Niger, are here, however, entirely
wanting. The surface of the plain slopes gently
towards the Benue from either side, and into it the
tributary rivers have cut a succession of shallow
swampy valleys separated by tracts of gentle rising
ground, which run approximately at right angles to
the Benue. The undulating plain thus produced is
deeply covered with surface drift and relieved only by
an occasional hummock of sandstone or grit. The
thin forest, which usually covers the rising ground,
gives place in the neighbourhood of the rivers to
extensive stretches of open grass land, which, in the
rains, become almost impassable swamps.

West of the Ankwe river the surface of the plain is
I PHYSICAL GEOGRAPHY 31

more frequently broken by ridges of rock, and around
Awe and on either side of the Benue to the south a
number of worn volcanic cones are scattered over the
plain. (Plate V, Fig. 1.) Similar volcanic hills project
above the surface on the northern margin of the
plain between Yelua and Wase. The Wase Rock’
itself, a pillar of trachyte, is a landmark for miles
around. (Plate V, Fig. 2.) At Namu, also, in the
north-west of the province, and at Bantaji on the
Donga to the south of the Benue, solitary hills of
similar origin form striking features in the landscape.
Turtlebacks and kopjes of granite boulders are found
only on the margins of the plain where the floor is
crystalline. In the north-west the narrow belt of
hummocky crystalline ground, with its inselberge and
groups of granite hills, is limited by the domes and
pinnacles of the little known Murchison hills,? while in
the south the undulating plains which stretch along
the frontier of the Protectorate from the Katsena river
to the Tarabba present all the characteristic features
of a crystalline floor. In the north-east of the
province, between Bashar and Jeb-jeb, the plains stretch
northward up the Kudu valley but are limited to the
east by the Ligri, Wurkum, and Jenoe hills, whose
steep and rocky sandstone slopes become in places
quite rugged and picturesque. The Kwana and
Mumuye hills, which bound the plain to the south of
the Benue, are largely granitic and present the usual
rounded contours, while the foothills of the Shebshi

1 Cf. Boyd-Alexander, From the Niger to the Nile, 1908, p. 86.
2 Cf. Boyd-Alexander, of. cit., p. 46.
32 NORTHERN NIGERIA CHAP.

range are of quartzite and gneiss and give rise to more
rugged and irregular outlines.

The Mumuye and Shebshi hills are portions of an
extensive tract of hilly country which stretches into
German territory and which occupies the southern part
of Yola province." The western boundary of this
tract runs almost northward, past Jalingu and Kwana,
as if to approach the Benue at Lau, but instead turns
sharply at right angles. Running eastward from near
Kwana there is a practically continuous wall of rock,
and at Bamga a steep and almost precipitous climb
brings the traveller from Lau to Yola on to the rim of
the plateau area. From this position he looks out over
the Benue plain several hundred feet below. The
river is far away to the north, while beyond that again,
just discernible on a clear day, is the further wall of
hills stretching continuously from the Wurkum country
to the Gongola. Turning south, he sees the tumbled
Shebshi hills as a faint silhouette in the distance, while
in the foreground, slightly below him, stretch sandy
uplands with a gentle eastward slope. The track
drops down upon the uplands and then proceeds just
within the rim of the plateau towards Yola. For the
first day this rim is made up of a chain of rounded
hills. Then a number of sandstone outliers arrests the
attention. (Plate VI, Fig 1.) The sandstone is massive
and breaks down along vertical faces. The fallen
blocks, in assuming their position of rest, smooth off
the irregularities of the granite base, and from the

1 Cf. Whitlock, “The Yola-Cross River Boundary Commission,” G. /.,
XXXVI, 1910, p. 426.
I PHYSICAL GEOGRAPHY 33

truncated cones thus produced, the cliff-sided outliers
rise and dominate the landscape, like great fortresses.
From this point the plateau descends gently to the
plain of the Maio Belwa and Ma-ini rivers. (A. L.)

Opposite Lau the hilly ground to the north has
similar outlines to those of the crystalline plateau to
the south. Farther east, behind Wuduku, its appear-
ance changes and the hills are composed of sandstone.
Here the ridge seems to be a bold escarpment limiting
the unknown Yam-yam country in precipitous cliffs,
but with a dip slope to the south which plunges down
below the marshy levels of the Benue. Further east-
ward again there is another change and the outlines of
the hills become regular and flat. Where the plain of
the Gongola enters the Benue valley, they turn at right
angles and run northward parallel to the river. At the
angle which separates the two plains the mass is seen
from a distance to be made up of horizontal beds, with
seven or eight terraces onits sides. These hills, which
run up to the west of Kombo, are still, however,
unentered and unexplored. (A. L.)

The plain of the lower Gongola is a repetition of
the Benue plain on a somewhat smaller scale. The
floor of the trench is about ten miles wide and the
height of the walls perhaps a thousand feet. On
travelling up the Gongola, Kwaba hill is conspicuous
two or three days before it is actually reached. Itisa
massive hill of granite with numerous satellites, of
which some are of granite while others are outliers of
horizontal sandstones, bounded by vertical cliffs. The
successive beds are exposed in their sides like string-

D
34 NORTHERN NIGERIA CHAP.

courses of masonry, the Gongola outliers differing in
this respect from those of southern Yola, which have
been carved out of unbedded sandstones. (A. L.)

The plateau of the Vere hills has been already
mentioned (p. 14). It is completely separated from
the Karin mountains, Alantika mountains, and other
hilly ground to the south by broad and level plains.
The essential feature of the scenery is the contrast
between the plain and the plateau masses. They rise
up from one to two thousand feet higher than the plain,
with no transitional foothills or slopes. The base is
concealed by sandy wash, and at intervals streams,
issuing from the plateau by narrow ravines, trench down
through the compacted wash to form steep-sided
nullahs. (A. L.)

Opposite to the Vere hills and across the Benue
stand the Bagele hills. A little further north is the
Hossere Furo. Both groups are of sandstone, rising
up from the smooth grassy plain. The rise, however, is
not immediate, as it is in the Vere hills, but through
basal slopes and foothills toward the higher summits.
North-eastern Yola consists of a high-level plain,
elevated considerably above the plain of the Benue,
but passing into it more gradually than do the plateaux
to thesouth. There is, however, one step of about 200
feet running eastward from Song to the frontier, while
the belt of country twenty miles broad to the north of
it forms rather a curious contrast to the remainder of
north-eastern Yola. Possibly there has been a slight
local uplift. Granite is seen over almost the whole
surface breaking down into coarse sand and giving rise
I PHYSICAL GEOGRAPHY 35

to a hummocky country difficult to travel. The
variations in level are only small, and taken as a whole
it is still a plain, but the breaking down of the granite
is going on actively over the whole surface. Parallel
to this country and almost in alignment with it, is an
interesting string of craters and flows of basalt. (Plate
VI, Fig. 2, VII, Figs. 1, 2.) The eastern extremity of
this line appears to be at Song, but westward it extends
across the Mboi hills into the Yungeru country, to
what distance is not yet known. The remainder of
north-eastern Yola, with its rocky islets set in ex-
tensive thinly wooded plains, is similar in character
to that of so many other parts of the Protectorate.
Some of the inselberge, especially in the Kilba hills
(Plate VIII, Fig. 1.), afford excellent examples of
exfoliation. (A. L.)

The Central Provinces.—Zaria and Bauchi.

The province of Zaria lies almost entirely within the
drainage basin of the Kaduna river, only a narrow
belt of country in the south and south-west being
drained by the rivers Gurara and Bako. With the
exception of the uppermost springs of the Kaduna and
the lower navigable portion of its valley below
Wushishi, the whole course of the river is included
within the province. At Wushishi the river narrows
and its channel becomes much obstructed by rocks
and rapids, as it winds through the belt of hills which
separate the rocky plains of western Zaria from the
lower plains of Nupe. At Zungeru the Kaduna flows in

D2
36 NORTHERN NIGERIA CHAP.

the dry season in a narrow picturesque gorge between
white walls of quartzite, which in the rains are buried
under a rushing foaming torrent. (Plate VIII, Fig. 2.)
From the bend of the river above Girku in the east of
the province, the Kaduna flows south-westward over
stretches of drift-covered plain and through scattered
groups of hills with its channel marked by frequent
rocks and rapids, while beyond Girku the river
meanders peacefully over the lofty plains which stretch
eastward to the boundary of the province. The
larger tributaries of the Kaduna on the north bank,
the Kara, Koriga, Tubo, and Shika, take their rise
upon the high plains of Hausaland, along whose crest
runs the primary watershed between the systems of
the Niger and Lake Chad, and, like the Kaduna itself,
they flow in their middle and lower courses over broken
plains and between groups of hills which separate the
minor streams. The Leri river in the east rises on
the high plains of the Bauchi border, while the Dunia
and Serakin Pawa, the principal tributaries on the left
bank, as well as the headwaters of the Gurara, take
their rise amidst the scattered hills upon the lofty
plains of the south-east. The Bako river rises in the
hilly ground around Fuka and, with the Gurara, drains
the extreme southern portion of the province.

The hills in Zaria province are of two types; (1)
ranges or belts of low rounded and somewhat broken
hills, composed largely of the more resistant schists, or
of a mixture of granite and schist; (2) kopjes, insel-
berge and small detached groups of rounded granite
hills, with here and there an extensive elongated mass
1 PHYSICAL GEOGRAPHY 37

of granite with a more or less flattened tabular summit
and steep though worn and rounded slopes rising
abruptly from the plains which encircle its base. To
the first type belong the tract of hilly country in the
west of the province which stretches from Mikonkeli to
the south of the Kaduna as far as Kagara to the north,
the belt of hills between Gwari and Koriga in the
north of the province, the broken stony country around
Fuka in the south, and the line of hills in the centre
of the province from Dorka to Kaserimi. To the
second type belong the solitary turtlebacks and
detached masses of granite hills which so abundantly
diversify the plains, while the Kudaru, Ruruma, and
Kerko hills are somewhat worn examples of the
steep-sided granite massifs, whose flattened though
hummocky summits form the retreat of numerous
pagan tribes.

Over the greater part of the province the configura-
tion of the surface presents a very close resemblance to
the characteristic scenery of the plains of Kabba
(p. 17). Between and around the island mountains
and groups of hills and tracts of hilly country, spread
undulating thinly-wooded drift-covered plains. The
towns and villages are set picturesquely on the slopes
and summits of the hills or in patches of thick forest in
the midst of the plain. For long distances round the
bases of the hills the plains are cleared and cultivated,
and from the summit of any of the isolated mounts the
peculiar character of the landscape impresses itself, as
before, upon the observer. Here and there the solitary
hills raise their rounded crests in lonely grandeur, while
38 NORTHERN NIGERIA CHAP.

around and between them the rivers pick their
sluggish course over the monotonous plain. The lofty
drift-covered levels of the south-east are largely un-
inhabited and cultivated only by the pagans who daily
descend from their rocky strongholds in the Ruruma
Hills or on the margin of the Bauchi plateau. Only in
the north-east between Girku, Leri, and Zaria do the
plains assume the typical aspect of Hausaland (p. 21).
The gently undulating surface is deeply buried in
sandy drift, and in places floored with surface iron-
stone : extensive stretches of the grassy plains become
swampland in the rains: the landscape is diversified
only at long intervals by occasional turtlebacks and
groups of granite hills, while well-walled towns and
villages are set here and there upon the open plains or
built round the bases of the solitary hills themselves,
which serve as watch-towers in times of danger.

The major part of the province of Zaria may be
conceived as a shallow, elongated basin, draining west-
ward, and shut in on the north and north-east by the
high plains of Hausaland and on the south-east by the
Amo, Piti, and Chawai hills, the lofty plains of Katab,
and the tableland of Nassarawa. The greater part of
Bauchi province, on the other hand, may be looked
upon as an undulating plain sloping gently towards
the north-east. The south-western portion of the
province is occupied by the great plateau of Bauchi,
which is limited on the north and south by well-
defined walls of rock. (Map p. 40). The plateau,
however, is not a true tableland in the sense of an
elevated plain marked off on all sides by precipitous
t PHYSICAL GEOGRAPHY 39

walls from the lower plains around. Like the table-
lands of Kabba, Nassarawa, and Southern Yola,
which are at most inclined plains bounded by escarp-
ments on one side only, the Bauchi plateau from its
summit at Bukuru slopes gently eastward and merges
gradually into the plains of the Gongola, while on the
west between the northern and southern escarpments
it is continuous for a short distance between Kwoll
and Assab with the highest portion of the tableland
of Nassarawa. The intimate relation which exists
between the Bauchi plateau and the tableland of
Nassarawa is further demonstrated by the continua-
tion of the escarpment of the tableland beyond Assab
to form the southern wall of the plateau. From Assab
the escarpment, here 1,500 to 2,000 feet in height,
runs south-eastward to the neighbourhood of the ninth
parallel before swinging round to the north-east and
losing itself amongst the rocks of Angass, where the
single escarpment appears to be replaced by a suc-
cession of rocky steps leading down to the tract of
broken country between Angass and Kanna, which is
drained by the headwaters of the Wase river.

The northern margin of the plateau is more irregular
than the southern and marked by projecting spurs
which have now assumed the character of mountain
ranges. In the west the escarpment begins in the
neighbourhood of Kwoll and Miango and stretches
westward as a somewhat worn and rounded cliff, 1,000
feet in height, separating the lofty plains of Rukuba
from the lower plains of Zaria. Beyond Chawai and
Piti the escarpment is continued as the western slope
40 NORTHERN NIGERIA CHAP.

of the Amo, Jengre, and Gura hills, which run out
upon the broken plains to the north, while the eastern
slope of the hills again assumes the character of an
escarpment and bounds the valley of the Delimi as
far as the gorge of the river below Naraguta. To
the east of the Delimi, however, the single escarp-
ment is replaced by at least two steps which inter-
pose the broken plains of Toro and the summits of
the Kwandokaya hills between the plateau and the
northern plains, while to the south-east of Polchi the
escarpments run out upon the plains of the upper
Gongola in groups of picturesquely rounded hills.
There is some reason also to believe that the plateau
is stepped or broken in the neighbourhood of Basak
in the Rukuba country, but this point must await
further investigation.

The surface of the plateau reaches its highest eleva-
tion of about 4,100 feet in the neighbourhood of Ngell
and Bukuru, whence the headwaters of the Delimi,
Sungo, Gongola, and Kaduna radiate approximately
north, south, east, and west. Of these rivers the
Delimi ultimately joins the Yo and falls into Lake
Chad, the Gongola and Sungo join the Benue, and
the Kaduna the Niger. Thus the few square miles
in the neighbourhood of Ngell and Bukuru may
rightly be claimed as the hydrographical centre of the
Protectorate (p. 3), and even the most casual observer
cannot fail to be impressed here with that peculiar.
character of the primary watershed which has already
been remarked in the case of the western tributaries
of the Niger and the northern tributaries of the
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I PHYSICAL GEOGRAPHY 41

Kaduna. There is no group of rocky mountains, no
rugged peak at the hydrographical centre of the
Protectorate, no lofty ranges forming the watersheds
between the radiating rivers: only an undulating,
swampy, alluvial plain, diversified by a few short,
broken ridges and low kopjes of granite boulders.
Into these plains, however, the rivers which flow
north, west, and south are rapidly carving narrow
rocky valleys, and their descent to the lower plains is
marked in every case by picturesque waterfalls and
narrow gorges cut back for considerable distances into
the plateau itself. The wooded gorge of the Delimi
below Naraguta, the steep waterfalls of the Kaduna
between Kwoll and Miango, and the deep rocky
channel of the Kogin Rim above Assab afford striking
evidence of the activity of the rivers. Only in the
east where the plateau inclines gently towards the
Gongola do the streams flow in sandy beds between
deep banks of alluvium, with broad stretches of swamp
on either bank wherever the slope is insufficient to
drain the summer floods.

The Bauchi plateau, in the more restricted sense,
may be taken to include all those portions of the
elevated plains which rise above 3,500 feet. Upon
this definition the plateau is bounded on the south
by the continuous escarpment which stretches from
Sura to Assab, and on the west by a line drawn
northward from Assab to Kwoll and Miango. Beyond
Miango the plateau is again limited by an escarpment
as far as the Jengre Hills, whence the boundary runs
southward to Naraguta and thence eastward along the
42 NORTHERN NIGERIA CHAP,

higher escarpment behind Toro. The eastern boundary
of the plateau is formed bya line drawn approximately
from south to north from Kereng to Toro. The most
striking feature of the greater part of the plateau
as thus defined, with the exception of the Rukuba
country to the north, is the bare and treeless aspect of
the surface, which assumes the character of undulating
grassy downs extensively cultivated in the neighbour-
hood of the towns and villages (Plate IX, Figs. 1, 2).
Only amidst the clusters of rocky hills which diversify
the surface do a few wind-worn trees bear witness
to the former extent of the forest, while round the
bases of the hills and among the boulders on their
slopes are set the rectangular compounds of the pagan
villages, whose dark green hedges of prickly cactus add
a pleasing touch of colour to the mellow landscape.
The low hills which rise from the plateau have alsoa
peculiarity all their own, which is to be directly
correlated with the greater diurnal variation in
temperature. The turtlebacks and domes and rounded
hills of the lower plains are here conspicuously absent,
and in their place appear heaps of boulders and jagged
ridges of granite, with picturesque peaks and pinnacles
and perched blocks adorning their crests. Here and
there, also, in the Rukuba and Kibyen country in the
west and in Sura in the south-east, more or less worn
and rounded volcanic cones rise above the general level
of the plateau (Plate X, Fig. 1). The craters of Kereng
(Plate X, Fig. 2) in the south-east, however, are remark-
ably well preserved. The surface of the plateau itself
is, moreover, deeply covered with drifted alluvium and
I PHYSICAL GEOGRAPHY 43

provided in places with a crust of surface ironstone
through which the rivers and streams have in many
cases cut to the rock below. Above Assab the drift
has been largely removed from the surface, and between
Rim and Woran numerous grassy, flat-topped hills
of red, gritty earth, capped by a hard ferruginous crust,
rise in places to a height of at least 300 feet above the
level of the plateau margin. These hillocks recall in
appearance the tabular sandstone hills of the Niger
valley, and bear striking witness to the former extent
and thickness of the superficial accumulations (Plate XI,
Fig. 1). The broken, rocky character of the marginal
belt of plateau on the north in the neighbourhood of
Zammagan, Basak and Naraguta is probably also
largely due to the removal of the covering of drift
which formerly obscured many of the irregularities
of the surface. Isolated hillocks of drift indeed are
common throughout Rukuba to the west of Jos and
Naraguta (Plate XI, Fig. 2), while at Basak they may
be seen capping the very summit of the cliffs.

Beyond the limits of the plateau proper, a thinly
wooded drift-covered plain, in places somewhat broken
and hummocky and diversified in the usual manner by
inselberge and scattered groups of granite hills and
drained by the headwaters of the Gongola, stretches
eastward to the meridian of Bauchi. Similarly, beyond
the worn and rounded escarpments and projecting
spurs which form the northern margin of the plateau,
an undulating wooded plain, drained by the Delimi and
its tributaries, extends north-eastward towards the
Kano border. The western watershed of the Delimi
44 NORTHERN NIGERIA CHAP.

valley runs along the hummocky drift-covered plain
which stretches northward between the Gura hills and
the detached mass of the Liruei-Kano hills, and thence
through the rocky hilly country round Tirkunya into
the Ningi hills, which form the most striking feature
of the north-western portion of the province. This
elongated mass of hills, which stretches from Bura in
the west to Ari in the east, is a typical instance of those
steep-sided and more or less tabular granite massifs, of
which examples have already been noted in the
Ruruma hills of Zaria, the Kagoro hills of Nassarawa
and the Vere hills of Yola. The Ningi massif reaches
a higher elevation in the west than in the east, its
slopes are much rounded and incised by narrow valleys,
its summit is broken and hummocky with a scanty soil
of disintegrated granite, while wooded drift-covered
plains stretch outward from its base towards Zaria on
the west, towards Kano and Katagum on the north,
and towards the Delimi valley on the east and south.
The surface of these wooded plains rises gently in the
north to form the low watershed between the valleys
of the Delimi and the Shidya. The headwaters of the
Shidya rise in the tract of broken hilly country which
lies to the north and north-east of Bauchi, and forms in
part the northern watershed of the Gongola basin.
Around Bauchi itself domes and turtlebacks and groups
of rounded hills, rising from the stony and drift-covered
plains, are particularly numerous and often remarkably
picturesque in their outlines, the lion couchant being

one of the commonest forms which the bare granite
hills assume. (Plate XII, Figs. 1 and 2.) South of the
I PHYSICAL GEOGRAPHY 45

Gongola the plains slope gently upward to the base of
the Jarawa and Kanna hills, becoming more and more
broken and stony as they approach the watershed of
the Wase river. The granite massif of the Wadai
hills between Angass and Sura is only known
along the northern margin, while Angass® itself is a
particularly broken and rugged district separated from
the Murchison Range by aseries of rocky valleys still
largely unexplored. Between Angass and Kanna the
high drift-covered plains of Bauchi pass into a tract of
broken country which is drained by the headwaters of
the Wase river and falls rapidly to the plains of Yergum.
The line of fracture to the west which forms the margin
of the plateau appears to be replaced here by a simple
flexure or perhaps by a succession of worn and broken
steps. Farther east rise the Kanna and Kantana
hills, with their projecting spur towards Kwankyam,
whose steep though worn escarpments interpose an
ascent of 700 to 1,000 feet between the lower and
higher plains. The western hills, which are prolonged
northward into the Jarawa country, are composed of
crystalline rocks, and the more prominent peaks
possess the usual rounded outlines of granite hills.
The Kantana hills to the east, however, are sedi-
mentary in origin, and froma distance show the familiar
tabular outlines of horizontal sandstone hills, the
narrow plateau on top being, however, much eroded
and incised. Eastward the escarpment appears to be
much stepped, and in the neighbourhood of Tukkur
wheels northward to form the eastern slope of the

1 Cf. Boyd-Alexander, of. czz., p. 98. 2 Tbid., p. 94.
40 NORTHERN NIGERIA CHAP.

Jarawa hills which run out upon the plain of the
Gongola.

The eastern portion of the province is almost
entirely covered with sedimentary rocks. In the
centre, a little to the south of the parallel of Bauchi,
broad plains stretch eastward from Goram and
Lafiangale to Deba Habe and the Gongola, bounded
on the north by the broken sandstone plateaux which
are enclosed within the bend of the Gongola, and on
the south by the slopes of the Kudu valley, the
rounded hills of Gateri and the picturesque peaks of
Tangale. In the west the plains are deeply covered
with sandy drift, through which the headwaters of
the Kudu have cut narrow canyon valleys into the
sandstones below. Farther east the summer rains
render the plains for long distances almost impassable
swamps which drain imperceptibly east or west, and
leave in the dry season a gently undulating surface
of black, gritty clay, baked and fissured by the summer
sun. To the north of the central plain and within the
bend of the Gongola lies a region of detached tabular
masses of elongated or irregular outline, together with
groups of worn and rounded sandstone hills, separated
by stretches of sandy plain, presenting all the familiar
scenic features of the dissected sandstone plateaux of
the Niger. The narrow valley of the Gongola,
between Deu and Gombe, bounded by flat-topped
ranges on either side, presents a marked contrast in
scenery to the upper course of the river above Baddera,
where it threads its way over the high plains of
Bauchi between turtlebacks and domes of granite.
I PHYSICAL GEOGRAPHY 47

Below Gombe, however, the valley opens out and the
river flows as far as Nafada through an open sandy
plain, diversified by occasional flat-topped sandstone
hills. Between Nafada and Ashaka the channel
winds between detached hills and short tabular
ranges which rise from an undulating, thinly-wooded
plain, while below Ashaka the river enters the deeply
drift-covered plain which stretches from the base
of the Tilde and Dukul hills on the west to the
foot of the escarpment of the Barbur plateau in Bornu
on the east. As far as Jurara and Deba Filani the
plain is thickly populated, well-cleared and cultivated ;
southward, however, within the Habe country, the
scattered villages are separated by longer stretches of
bush, while the plain is diversified by hummocks of
sandstone and worn hillocks of basalt with the inter-
vening irregularities of the surface deeply buried in
drift. Beyond Deba Habe, the plain of the Gongola
forms the eastward continuation of the central plain of
Bauchi, whose sandy and swampy surface stretches
southward to the base of the Tangale hills.

The south-eastern portion of the province is
occupied in part by the upper valley of the Kudu
river and in part by the extensive mass of hills which,
with the exception of the outer margin around Gateri,
Tangale, and Waja, is still largely unentered and
unexplored. A series of narrow valleys, terminated
by canyon-like gorges, have been cut by the
headwaters of the Kudu into the elevated plains of
Pali and Lafiangale. The difference in level between
the upper plains and the river bed is greatest in
48 NORTHERN NIGERIA CHAP.

Dugari in the west, where the streams flow in narrow
flat-bottomed valleys, bounded by perpendicular walls
of white sandstone three to five hundred feet in height.
From the cliffs above Tongolan the scenery recalls in
miniature the chasms, amphitheatres, and canyons of
Colorado, with their promontories and projecting
buttresses, steep slopes and vertical ledges, while
south-eastward towards Yuli the remnants of a lower
plateau mark a former pause in the activity of the
river. Farther east, by Panguru and Putu, the relative
height of the upper plains decreases, the sandstones
become broken and inclined, and the tributary valleys
are bounded, not by cliffs, but by rounded, drift-covered
slopes leading upward to the higher undulating plains.
The folded sandstones of Gateri and Ligri give rise to
a group of rounded hills deeply incised by narrow
valleys and backed by the ridges and peaks of the
unexplored Wurkum and Pero hills, which stretch
north-eastward towards the Gongola. From Gateri
northward to Putu the track leads over somewhat
broken country, while eastward from Putu to Tangalto
stretch open, undulating, swampy plains, diversified
only by occasional conical stumps of basalt.

The tract of country which lies between Tangale
and the Gongola is one of the most picturesque within
the Protectorate. The hills rise in detached groups
from an irregular hummocky plain, and form the
advanced guard of the belt of lofty highlands which
intervene between the northern plains and the Benue.
While the whole district may be spoken of generally
as Tangale, the Tangale tribe itself occupies a very
Prare TV

 

 

ti) i i
Cara

Fa
4
e

 

 

 

A GRANITE Mount NEAR ABUJA.

 

 

 

THE MARGIN OF THE NASSARAWA TABLELAND FROM JAGINDE.
I PHYSICAL GEOGRAPHY 49

restricted area and is lodged within only the western-
most group of hills, the successive groups to the east
and south being inhabited by the kindred but mutually
hostile tribes of Chongwom, Ture, Awok, Tula, and
Waja. Tangalto and Tall, the strongholds of the
Tangale tribe, are set on the slopes of rounded granite
hills, picturesquely pierced by worn pillars of trachyte
and basalt, and separated by a narrow undulating
plain from the neighbouring group of granite hills
inhabited by the pagans of Chongwom and Kaltungo.
Beyond Chongwom the character of the scenery
entirely changes. In place of the rounded crystalline
hills there rise precipitous and more or less tabular
masses of well-bedded sedimentary rock, forming
natural fortresses in the midst of an undulating park-
like plain, diversified by knobs and hummocks and
standing rocks of sandstone (Plate XIII, Fig. 1). At
times the summit ridges are gently curved and the
hills are bounded on one side by a steep escarpment
and on the other by a dip slope sinking gradually to
the plains below, while the whole landscape is domi-
nated by the Ture or Tangale Peak, a picturesque
pillar of trachyte rising from a worn and flattened basal
cone of sandstone (Plate XIII, Fig. 2). Eastward,
around Jelengu and Reme, somewhat similar pillars of
volcanic rock project here and there above the sand-
stone hills, while the worn escarpments of Waja
appear to be continuous with those which form the
the western boundary of the lower Gongola valley.
The country which lies to the south of Tangale and

Waja is quite unknown. From the upper slopes of
E
50 NORTHERN NIGERIA CHAP.

the Ture Peak, a second distant range of hills can be
seen running parallel with the jagged ridge in the
foreground, and it is probable that, instead of a mass
of hills or a continuous plateau, there is within this
unexplored land a succession of broken valleys and
rocky ridges, forming one of the last strongholds of
paganism within the Protectorate.

The Northern Provinces—Bornu, Kano, and Sokoto.

The southern portion of Bornu, which lies imme-
diately east of the Gongola, presents, so far as the
character of its physical features is concerned, a
greater affinity with the central provinces of Bauchi
and Zaria than with the northern Hausa States or with
the northern portion of Bornu itself. The valley of
the Gongola to the east of the river is more broken
and hummocky than it is to the west. The sandstones
are much faulted and variously inclined and form belts
of rocky plain between the swampy valleys of the
tributary streams. Here and there, as at Wuyo and
Gulani, a circle of jagged ridges forms a natural battle-
ment round a pagan town, or, as at Balbea, a flattened
sandstone hill forms a natural stronghold in the midst
of the plain. More striking, however, are the level
crests, the dip slopes and the steep escarpments of the
Bima and Wadi hills, which form the landmarks of the
Gongola plain from Ashaka to Wuyo. From Gulani
north-westward to Ashaka stretches an extensive undu-
lating plain, broken only by an occasional ridge of
sandstone, with black swamp earth covering all the
I PHYSICAL GEOGRAPHY 51

minor irregularities of the surface and creeping up the
slopes of the sandstone. hills themselves. Eastward
the broken plain of the Gongola is bounded by the
worn escarpment of the Barbur volcanic plateau which
becomes higher towards the north, and between
Bilaraba and Dukshi is fringed with a series of flat-
topped and conical outliers of basalt. To the east of
Gulani and Balbea the ascent to the plateau is over
basal sandstones capped by black volcanic rock.
Farther north, however, in the neighbourhood of
Dukshi, the escarpment is entirely composed of basalt
and rises from an irregular crystalline floor. The
summit of the plateau is broken and rocky in the west,
deeply trenched by the tributary streams of the
Gongola, and diversified by numerous worn and
rounded cones of ash and lava. Eastward towards
Buratai the plateau descends by a series of low rocky
steps separated by drift-covered levels to the plains of
Hong and Ajigin, whose deep covering of dark gritty
clay, hard and fissured in the dry season, forms an
almost impassable swamp in the rains. In the south-
east, towards Biu and the little-known Burra country,
the volcanic cones become higher and more con-
spicuous, while the surface of the plateau, according to
native information, becomes much dissected and
broken up into narrow plains and rocky valleys.

Two tracts of hilly country, separated by the swamps
of Hong and Ajigin, lie respectively to the north-west
and north-east of the volcanic plateau. The worn and
flattened hills of sandstone and ironstone, which stretch
westward from Buni and Ligdar towards Gabai, pass

£2
52 NORTHERN NIGERIA CHAP.

northward into the high, drift-covered plains of Mutwe
and Gujba, which form the watershed between the
Gongola and Lake Chad. In the east the Tagum and
other groups of flat-topped hills around Lua, Ndufa,
and Korode represent the remains of a sandstone
plateau once continuous with the hills of Buni and
Ligdar across the swamps of Ajigin. To the north and
north-east of the Tagum hills stretch the great wooded
plains of Bornu, with their gently undulating surface
sloping imperceptibly towards Lake Chad, and with not
a single hill nor even a hummock of boulders to relieve
the monotony of the scenery. To the south-east of
the Tagum hills the sandstones run out upon a
crystalline floor which stretches southward into Yola
province, with its surface diversified only at long
intervals by island mountains and groups of granite
hills.

The plains of Bornu, which stretch northward from
the rocks of Chibuk and the Tagum hills to Lake
Chad and the river Yo, are in the east so imperfectly
drained that extensive tracts of their surface become
marshy and swampy during the rainy season. The
swamps reach their greatest development in the valley
of the Yedseram and in the immediate neighbourhood
of Chad, where the whole country is flooded after the
rains. Barth* has described in a sufficiently vivid
manner the featureless and cheerless aspect of the
swampy plains to the south and south-east of Chad.
Along the caravan road from Maidugari to Kukawa
transverse stretches of swamp land (firki) alternate with

1 Barth, Central Africa, 1857, Il, p. 355.
I PHYSICAL GEOGRAPHY 53

belts of slightly higher ground, hard and smooth on the
surface, or thinly coated with loose yellow sand or dark
grey loam. The character of the vegetation reflects
immediately the changes in the nature of the surface
soil. In the dry season, after the grass is burnt, the
cracked and fissured surface of the firki land is
absolutely bare and treeless, the hard and smooth sur-
faces of sandy clay are covered with thin mimosa bush,
while the stretches of loose sandy loam support a more
abundant growth of trees and scrub. The ancient
dunes and the undulating sandy plains which bound the
northern basin of Chad support an open forest growth,
while recent accumulations of blown sand are now
found only within the towns themselves, or in places
which have been cleared of forest for purposes of
cultivation.

The Maidugari river, which rises on the Yola border
and loses itself in swamp a few miles to the north of
Maidugari, has cut deeply into the superficial sandy
drift in the neighbourhood of Maidugari and Maifoni
and formed a comparatively narrow valley with steeply-
rounded slopes. From Maifoni a gently rolling plain
stretches westward to Gujba, with occasional thick-
stemmed kukas rising prominently above the low
growth of scrubby trees and prickly mimosa which
covers the surface, and with here and there a dry
“tubka” or shallow swampy hollow forming an open
space within the forest. At Murguba, and again at
Gujba, the plain is broken by shallow water-courses,
bounded by low and ill-defined ridges of rising ground.
These extended swampy hollows are flooded during the
54 NORTHERN NIGERIA CHAP.

rains, and in the dry season marked by a line of wells
and occasional pools separated by sandy bars. Beyond
Gujba the rolling plains become again marked by a
rapid alternation of sandy rising ground and clayey
shallows draining southward in the rains. Between
Chumga and Abakri, however, rock begins to appear
in places on the surface of the drift-covered undulations
which separate the swampy valleys, while a few isolated
flat-topped or rounded hills are scattered over the
plains. From Abakri can be seen to the west the long
flattened and rounded ridges and tabular hills, half
buried in sandy drift, which introduce the Kerri Kerri
plateau. Daura and Durua are set within this broken
country, each at the base of a low flat-topped range of
ironstone hills, while the track leads over a suc-
cession of stony ridges and shallow cultivated valleys
to the continuous plateau surface which is reached
about half-way between Durua and Momdo. The
plateau itself is no higher than the summits of the
marginal hills, which with their drift-filled valleys
represent merely the dissected eastern front of the
tableland. The surface of the plateau, at first thinly
wooded and in places somewhat stony, passes west-
ward into the open sandy undulating plains around
Potiskum, which fall away gently to the north and
west into the valley of the Kogin Shidya. Here
and there a low hill or a rounded ridge of sandstone or
ironstone rises above the general level, with the sandy
drift which obscures all the minor irregularities of the
surface deeply banked against its slopes.

The Kerri Kerri plateau, like the tableland of
I PHYSICAL GEOGRAPHY 55

Nassarawa and the elevated plains of Bauchi, is not
a true plateau in the strict sense of the term, but
rather an inclined plane, bounded by more or less
worn escarpments on the south and passing gradually
northward into the plains of Ngizem. The escarp-
ments which stretch from the neighbourhood of
Daura south-westward to the provincial boundary
reach their greatest elevation behind Dozi, Lewe,
and Gamari to the north-west of Nafada, where pre-
cipitous cliffs of white sandstone 500 to 600 feet high
rise abruptly from the sandy plains which stretch
southward to the Gongola. The escarpment, however,
is in no sense a continuous one, for, as already noted
in the neighbourhood of Daura, the margin of the
plateau has been much cut up and dissected, especially
in the east, into a system of more or less detached
flat-topped ranges and tabular masses separated by
narrow valleys or by short stretches of open plain.
Westward where the escarpment is higher, as in
the neighbourhood of Dozi and Kadi, the cliffs are
furnished with the characteristic buttresses and in-
dentations of horizontal sandstone rocks, while the
margin of the plateau is fringed with a series of
detached tabular and conical outliers of varying size
and elevation (Plate XIV, Fig. 1), the larger of which
form natural strongholds for pagan villages.’ The
most remarkable feature, however, about the margin
of the plateau is that, behind the fringing belt of
detached ranges and outlying groups of hills, the
main mass of the plateau has been grooved or incised

1 Cf. Boyd-Alexander, From the Niger to the Nile, pp. 112, 164.
56 NORTHERN NIGERIA CHAP.

by a series of narrow flat-bottomed trench-like valleys,
bounded by perpendicular walls of white sandstone and
notched and indented by lateral gullies (Plate XIV,
Fig. 2). For long distances the narrow valleys preserve
a very constant breadth, while frequently they turn
abruptly at right angles or are joined by lateral valleys
of similar character which unite the whole series into
an interlacing system through which it is possible to
travel from Daura to Zai without once ascending to
the level of the plateau above. At their upper ends
the valleys rapidly contract and run out upon the
plateau as steep and rocky gullies. Their floors, like
the surface of the plateau above, are well cleared for
cultivation and studded with scattered trees, while the
villages are set aloft on the margin of the cliffs over-
looking the wells in the valley below.

Beyond the western boundary of Bornu the escarp-
ments die down, and the drift-covered surface of the
plateau falls gently to the swampy valley of the Kogin
Shidya. The last trace of the sandstones of Kerri
Kerri is found in the low hills of conglomerate and
grit around Hardawa, while twenty miles to the north
according to native information the sandstones dis-
appear in the neighbourhood of Lise under the sands
and swamps of Katagum. Beyond Hardawa begin
the undulating plains of Hausaland (pp. 21, 38),
which stretch westward, to the north of the Ningi
massif, through the heart of Kano and the north-
eastern portion of Zaria into Kontagora and Sokoto.
Here and there a heap of granite boulders or an
isolated group of rounded hills, as at Shira, Fagam and
I PHYSICAL GEOGRAPHY 57

Kila, rise out of the red sandy drift which is deeply
banked against their slopes, and which elsewhere
effectually buries the irregularities of the crystalline
floor. Occasionally a smooth and rounded surface of
gneiss or granite outcrops level with the plain, while
the rivers which flow in broad, shallow and ill-defined
valleys, indistinguishable at a distance from the rest of
the plain, have here and there succeeded in cutting
their channels through the sandy drift to the solid rock
below. Where uncultivated the plains are covered
with prickly mimosa bush, or with trees well spaced or
in bushy clumps with open grass around. The farm-
land, however, is well cleared and comparatively bare
with a few large trees scattered here and there amongst
the furrows, while the fallow is thickly covered with
tall aromatic grass and low scrubby trees of a few
seasons’ growth.

From Jemaari north-eastward to Katagum, and
thence westward to the immediate neighbourhood of
Kano, not a single rock is anywhere exposed, and not a
single block or boulder or even a pebble of quartz is to
be found in the sandy loam which covers the surface.
North of Jemaari the track leads through gently un-
dulating country presenting the usual alternations of
farm-land and thinly wooded plain. Between Itas and
Murmur the surface becomes in places quite hummocky
with ancient dunes in the form of low rounded ridges
of loose sandy drift, extended approximately east and
west, rising in succession upon the level plain and
bearing witness to the former prevalence of desert con-
ditions. Around Katagum the drainage is so imperfect
58 NORTHERN NIGERIA CHAP.

that long stretches of the plain are under water in the
rains, while westward beyond Kwotolu the surface
resumes its undulating aspect with its alternation of
sandy rising ground and clayey shallows. Here and
there, as at Koya, a rounded ridge of loose sand, now
covered with grass and scattered trees, affords evidence
of the former activity of the wind, while in places in
the hollows are small sheets of fresh water forming
lakes which are more or less permanent throughout the
year.

Around Kano and north-westward towards Katsina
the open undulating plain presents all the characteristic
features of a crystalline floor. For long distances
round the towns the red sandy loam which covers the
surface has been cleared of all but the larger trees and
subjected for generations to intense cultivation. Here
and there around Kano smooth surfaces of rock appear
level with the plain, or rise into low rounded turtlebacks
or heaps of granite boulders. The two prominent
tabular hills of weathered diorite, Dala and Kogon
Dutsi,’ within the walls of Kano, have a peculiar
interest of their own which will be related in the sequel
(p. 201). Northward between Kano and Kazaure the
undulating sandy plain is diversified only by the low
flat-topped hillocks of earthy grit and conglomerate in
the neighbourhood of Sai and Ingogo and by the
broken ridges of amethystine quartz which rise from
the plain immediately south of Kunchi. Kazaure is
set in the midst of rocky ridges of blue quartzite with
red sandy drift filling up the valleys and banked

1 Cf Barth, Central Africa, 1857, p. 96.
I PHYSICAL GEOGRAPHY 59

against the slopes of the hills. Around Rauni rise low
extended flattened ridges, which appear to be composed
throughout of dark red vesicular ironstone. At
Tummas, half way to Ingawa, low granite knobs and
heaps of boulders project above the surface, but from
Ingawa north-westward to Katsina the undulating
plains are featureless, with no prominent granite hills
or kopjes to break the monotony of the landscape.
Smooth surfaces of rock are here and there exposed
level with the plain or in the channels of the streams,
but otherwise the deep sandy drift which covers the
surface effectually obscures all the minor irregularities.

Around Katsina both sandstones and granites are
exposed upon the surface of the plain, but it is not until
the neighbourhood of Kurefi is reached that a decided
change takes place in the character of the scenery.
From Kurefi to Runka the track leads through rocky
granite country which assumes its wildest aspect in the
neighbourhood of Tummo, where the landscape, as far
as one can see, is made up of an assemblage of low
rounded hills, domes, tors, heaps of boulders, perched
blocks and smooth surfaces of granite, with no
particularly high or prominent peaks. On the margin
of the mass near Kurefi and Runka the aspect of the
country is smoother; the turtlebacks and rounded
hills are separated by narrow stretches of plain, and
often half-buried under the sandy drift which is banked
up against their slopes. From Runka south-westward
to Kotorkoshi, and thence north-westward to Karakai,
the landscape assumes its familiar aspect of a gently
undulating thinly-wooded surface, diversified by isolated
60 NORTHERN NIGERIA CHAP.

groups of granite hills which, at Duru and Kotorkoshi,
rise abruptly and picturesquely from the drift-covered
plain. A belt of broken hilly country stretches N.N.E.
and S.S.W. between Karakai and Maradu, parallel
with the strike of the quartzites, phyllites, and gneisses
out of which the hills are carved. Immediately be-
yond Maradu knobs and hummocks of volcanic
agglomerate project from the surface of the plain,
while northward the track leaves the hummocky
crystalline floor in the neighbourhood of Gora and
follows the level swampy plain of the Gulbin Gandi as
far as Dankaiwa. At Dankaiwa, in the cliff which
faces the river, is the first exposure of the red earthy
sandstones of Sokoto, while at Dampo, a little farther
on, the first flat-topped sandstone hill rises above the
sandy plain. From Dampo the track again runs along
the swampy valley of the river as far as Rara, whence
it leads across undulating park-like plains to the broken
sandstone hills of Sokoto.

The northern and western portions of Sokoto pro-
vince, which consist of a dissected plateau of horizontal
sandstones, possess in general all the familiar scenic
features of such a formation as already described from
other parts of the Protectorate. The apparent differ-
ences are differences more in degree than in kind.
Like the Niger above Lokoja, the Benue in its lower
and upper course and the Gongola above Gombe, the
Gulbin Kebbi or Sokoto river flows in a broad flat-
bottomed trench-like valley between two steep and
worn escarpments, which lead up to the plateau on
either side. The breadth of the valley of the Gulbin
PLATE V

 

 

 

 

 

WorN VOLCANIC CONES NEAR AWE.

 

 

 

 

THE WasE Kock.
 
I PHYSICAL GEOGRAPHY 61

Kebbi is, however, out of all proportion both to the
height of the bounding walls and to the volume of the
river itself. The floor of the valley is usually several
miles in breadth, while the cliffs on either side rarely
reach 200 feet in height. Inthe rainy season a sluggish
flood covers the bottom of the valley, but in the dry
season the river is represented by one or more
diminutive streams, which disappear from time to time
in stretches of swamp. The continuity of the flat-
topped escarpments is much broken by lateral valleys,
and here and there the vertical walls are replaced for
long distances by steeply-rounded rising ground. The
tributaries of the Gulbin Kebbi, where they flow
through sandstone country, are likewise bounded by
worn and broken escarpments. Similar broad flat-
bottomed valleys with diminutive streams are common
also within the French Sudan to the north of Sokoto,
and are there generally known as “‘dallols.” Of them
all, however, the Gulbin Kebbi possesses the greatest
volume of water, which is contributed practically
entirely by its numerous southern affluents which rise
on the high and well-watered plains on the borders of
Kano, Zaria, Kontagora and Sokoto.

The plateau areas between the larger valleys are
themselves much dissected, especially in the east and
north, by the smaller tributary streams. In the west
there are some fairly extensive stretches of continuous
tableland, whose gently undulating and thinly-wooded
surface is diversified by occasional flat-topped and
conical hills, the relics of a former plain which has
now been almost entirely removed in the course of
62 NORTHERN NIGERIA CH. I

denudation. To the north and north-east of Sokoto
the irregularities of the dissected plateau are softened
in contour by accumulations of blown sand which
covers the floors of the smaller valleys and creeps
up their lateral slopes, rounding off the steeper cliffs
of the flattened ridges on either side.
CHAPTER If

CRYSTALLINE ROCKS

Distribution of the crystalline rocks. Typical traverses. The harder and
softer gneisses. The Jebba quartzites: the phyllites and slaty
schists of the Niger valley ; the sheared trachytes of Bussa ; the
Ngashki phyllites ; replacement of the softer gneisses by the harder
banded types. The gneisses and schists of Ilorin ; the quartzites of
the Orissa hills ; the stanniferous pegmatites of Eri. The muscovite
schists of Northern Kabba ; the quartzites of Lukke; the crystal-
line limestone between Jakura and Wa ; the mica schists of Sequarre ;
the magnetite and hzmatite schists of Eastern Kabba; the Igbo
limestone. The phyllites and schists of Sokoto province; the
volcanic agglomerate of Maradu; the blue quartzite of Kazaure ;
the diorites of Kano; Mounts Dala and Kogon Dutsi ; the gneisses
and schists of north-eastern Kontagora; the Zungeru belt of
phyllites and schists ; auriferous quartz reefs ; the quartzites and
schists of Eastern Zaria ; the gneisses and granites of Abuja; the
tourmaline rocks of Darroro; the mica schists of Gwombe; the
banded gneisses of Bauchi province ; the granites of the Murchison
Hills ; the later intrusions. The inliers of Arofu ; the granites and
gneisses of southern Muri; the Vere Hills ; exfoliation in the Kilba
Hills ; the crystalline rocks of Bornu.

Wuite crystalline rocks undoubtedly everywhere
form the foundation of the Protectorate, there are
extensive tracts over which the later sedimentary
rocks obscure the underlying granites, gneisses, and
schists. The largest area over which these crystalline
rocks are exposed is that which occupies the centre of

the Protectorate and extends from the Niger in the
63
64 NORTHERN NIGERIA CHAP.

west to beyond Bauchi in the east, and from Nassarawa
in the south to the neighbourhood of Katsina in the
north. The major portion of the provinces of Kabba,
Torin and Borgu to the west of the Niger also possess
a crystalline floor, while similar rocks cover a narrow
strip on the southern border of Muri and Yola, as well
as a considerable tract of country to the east of the
Gongola, lying partly in Yola and partly in Bornu.

Typual Traverses.

The following typical traverses show the character
of the exposures along the tracks.

I. Filelin (near Lokoja) to Ohoto :

9.20 A.M.—Left Filelin.

9.34 4, Blocks of ferruginous sandstone and grit.

9.38 ,, Masses of biotite pegmatite ; large felspars often graphic.

9.40 ,,  Fine-grained, non-foliated reddish biotite granite with streaks
and veins of graphic biotite pegmatite. The granite at
places on the margin follows the foliation of the adjoining
biotite gneisses, in places crosses the foliation, or is in
part injected into the gneiss. The biotite gneiss is often
folded and distorted ; in places there is an alternation of
dark bands of biotite gneiss with lighter coloured felspathic
layers. The foliation is much disturbed, but in a general
way E.N.E. and vertical. The gneiss is cut by granite
and pegmatite veins and dykes.

9.45. 4 Reddish granite continued. In places the granite shows
distinct banding and alternation of coarse and fine layers ;
sometimes banded with pegmatites.

9.50 ,, Same pink granite; but here an irregular mixture of coarse
and fine material with in places knots of coarse granite in
a fine grained matrix.

10.0 4, Small granite knobs on right.

10.3 4,  Sandstones.

10.10 ,,  Biotite gneiss, strike N.E.—S.W., foliation dip 40° N., cut
by coarse pegmatites as before ; in places interfoliated
bands of segregation pegmatite.
Il

CRYSTALLINE ROCKS 65

10.15 A.M.—Soft biotite gneisses.

10.30
10.40

10.50
II.0
11.30

11.35
11.40

12.30
12.40

12.45

12.50
1.15

”

”

Large blocks of pink granite and pegmatite.

Granite piercing hard white biotite gneiss with knots of
amphibolite. Strike of gneisses N. 35° E., foliation dip
N.W. There is a sharp junction between the granite and
gneiss, but no chilled margin.

Granite.

No exposures.

Extensive mass of coarse-grained biotite gneiss, crossed by
pegmatite veins and dykes of coarse red granite with
large felspars.

Biotite augen-gneiss with felspars sometimes two inches

long ; crossed by veins of fine red granite or aplite.
No exposures.

P.M.—Bare surface of augen-gneiss level with the plain.

Dyke or sheet of fine grained reddish granite showing distinct
foliation.

Fine grained and finely banded biotite gneisses crossed and
injected by granite veins.

Sandstones.

Ohoto.

I]. Jakura to Wa (north side of Mimi Valley).

6.30 A.M.—Left Jakura hill; on brow of hill quartz schist, strike N.

6.55
6.58

7.12

7.20
7-35

7.40
8.15
8.30
8.35

8.45

10° W., foliation vertical ; at foot of hill fine grained pink
granite with pegmatite, passing into friable pink granite
with large crystals of graphic quartz and felspar in a finer
matrix.

Soft biotite gneisses, strike N.N.E., dip W.N.W.
Band of amphibolite, dip unascertainable, followed by soft
biotite gneisses. Pebbles of hornblende epidote schist.
Bare exposure of red pegmatite dyke cutting fine grained
felspathic gneiss, with in places a sharp junction and in
others not.

Quartz schist.

Magnetite hornblende schist, strike N. 10° W., foliation dip
practically horizontal.

Quartz hematite schist, dip unascertainable.

Massive and granular quartzite and quartz schist.

Biotite gneiss.

Quartz-muscovite schist, strike N.N.E., dip low to W.N.W.

Pebbly muscovite schist, strike N.—S., foliation vertical or
highly inclined.

Pegmatites.
66

NORTHERN NIGERIA CHAP.

8.50 A.M.—White marble forming rounded knobby hills cut by pegma-

9.5
9.8
9.15
9-35
9.50

10.10

10.25

10.35

10.45

”

tite veins and enclosing streaks and veins of quartz.
epidote-calcite-idocrase rock on right hand ; on left the
marble is foliated, with folia of pyrites and knots of
quartz ; strike of foliation N. 10° E., dip 10° W.

Marble ends.

No exposures,; grass land.

Quartzites.

Soft biotite gneiss; foliation generally vertical; strike
N.N.E., dip vertical or high towards W.

Garnetiferous biotite gneiss with quartz segregations ; folia
crumpled and contorted ; strike generally N.—S.

Garnetiferous biotite gneiss as before ; folia practically
horizontal.

Soft micaceous schists pierced by granite; strike N. 35° E.,
dip S.E.

Pink granite in places foliated ; graphic pegmatites on slope
of Wa hill.

Wa. On top of hill white mica schists with magnetite
knots, strike N.—S., dip 20° W. ; cut by quartz-muscovite-
magnetite pegmatites.

III. Olle to Sura (Central Kabba).

6.20 A.M.—Left Olle.

6.25
6.27

6.35
6.40

75

7-25
7.30
8.10

8.35
8.40

9.0
9.5
9.20

”

Quartz schists and quartz-muscovite schists, strike N. 40°E.,
dip 55° W.

Soft fine-grained quartz-muscovite schists, strike N. 10° E.,
dip 70° W.

Muscovite schists, strike N. 30° W., foliation vertical.

Thick dyke of graphic quartz and felspar, with crystals of
tourmaline.

Fine grained white granite.

Coarse white granite in river bed.

No exposures.

Micaceous gneiss, strike N. 35° E.; much folded and con-
torted with streaks and knots of pegmatite, probably
proceeding from a thick intrusive mass of quartz-felspar
pegmatite which adjoins the gneiss.

Muscovite schists, strike N.—S., foliation vertical.

Track leads along valley between hills of white quartzite ;
loose blocks of compact and granular quartzite.

Summit of pass ; blocks of white quartzite.

Muscovite schists, strike N.—S., foliation vertical.

Lukke.
I

CRYSTALLINE ROCKS 67

g.30 A.M.—Soft muscovite schists and quartzites.

9.40
9.50

10.10
10.15

10,20

10.40
11.0
11.5

11.30

11.40

”

”

”

Muscovite schists, strike N. 10° W., foliation vertical.

Broken fragments of quartzite, quartz-muscovite pegmatite,
and quartz-tourmaline pegmatite on road; intrusive
masses of graphic felspar and quartz with crystals of
muscovite, associated with exposures of coarse muscovite
granite.

Biotite gneisses much crumpled and folded, exposed in bed
of stream, strike N.W.

Quartzites and muscovite pegmatites.

Intrusive mass of muscovite granite with large crystals of
graphic quartz and felspar in a fine grained granitic
matrix ; banded in places with coarse and fine layers.

Exposures of quartz-muscovite pegmatite.

Soft micaceous schist, strike N. 10° W., foliation vertical.

In bed of river and for 500 yards beyond, garnetiferous
mica schists with quartz lenticles, strike N. 10° W., dip
15° W.

Schistose biotite granite, with schistose pegmatite veins
forming Sura hill. °

Sura.

IV. Agwede to Kabba.

6.30 A.M.—Left Agwede hill. On top, white granite usually showing

6.40

7.0
7.20

8.20

9.5

9-30
10.30
11.30

11.45
12.0

faint foliation and frequently enclosing portions of dark
mica schist ; on slope, whitish ribboned gneisses, often
folded and contorted, strike N.E. to E., foliation vertical.

Dyke of graphic pegmatite in gneiss; sharp junction.
Frequent bands of schistose pegmatite in the pale
coloured banded gneisses ; in places the gneisses are
hornblendic with knots of fine-grained hornblende gneiss
or schist.

Ascent to plateau over contorted gneisses.

Same contorted gneisses passing into and invaded by white
schistose granite ; wooded plain, few exposures.

Occasional exposures of similar contorted and granitised
gneiss ; strike E. 10° N. to E. 10° S.

Faintly banded and indistinctly foliated biotite gneiss.

Odouape.

Level surface of composite gneiss.

Much crumpled and folded biotite gneiss; strike N.—S.
Followed by garnetiferous biotite gneiss.

Composite gneiss ; foliation vertical ; strike N. 10° W.

Kabba.

FE 2
68

NORTHERN NIGERIA CHAP.

V. Izon to Abuja (Nassarawa province).

6.25 A.M.—Left Izon. Open grassy or thinly-wooded plains for two

8.20

9.0

9.30

9.42
10.0
10.30
10.35

10.45

11.0

IL.I5

be

”

hours ; no exposures.

Hills ; ascent of 300 feet ; biotite and hornblende gneiss and
amphibolite ; epidote-hornblende gneisses; in places
twisted and contorted and extensively invaded and in-
jected by masses of biotite granite ; strike varies between
N. 10° E. and N. 10° W.; foliation mostly vertical.

Open plain ; thick granite wash.

Hills ; granite invading hornblende epidote gneisses.

Abuchi. Amphibolite veined with granite.

Narrow plain ; thick drift.

Hills ; soft micaceous gneisses, strike N. 10° W., foliation
vertical or high to E.

Hard biotite gneisses, strike N.—S., foliation linear and
vertical.

Ribboned and banded biotite gneisses with quartz veins
parallel to or crossing the foliation ; strike N.—S.;
foliation vertical.

Abuja granite with foliated margin ; vertical crush lines in
granite striking N.—S.

Abuja Residency.

VI. Boi to Ronn (Southern Bauchi).

6.30 A.M.—Left Boi ; hornblende epidote gneisses broken and invaded

6.40
7.20

7-45
8.40
8.45
9.3

9.20
9-35
10.15
10.45

11.10

by granite ; in places much folded and crumpled.

Felspathic gneiss, strike E. —W., dip high to S.

Complex of quartz epidote rock, amphibolite, epidote-
hornblende schist, and gneiss, in places much granitised ;
general strike E. 10° N.

Hummocks of banded gneiss ; open country ; few exposures.

Hornblende epidote gneisses.

Goshin Duchi. Hills of biotite granite behind town.

Quartz schists, fine grained gneisses, epidote hornblende
and quartz hornblende rocks, much granitised in places
veins and dykes of pegmatite and basalt.

Blocks of basalt and porphyry.

Hills of fine grained biotite granite.

Granite rocks, in places schistose.

Rocky, hilly country; banded and contorted gneisses
micaceous and hornblendic; general strike E. 10° S.

Ronn.
1 CRYSTALLINE ROCKS 69

It is unnecessary, however, to quote the details of
particular traverses at greater length, especially as
such descriptions serve only to show the character of
the phenomena to be correlated. It is sufficiently
evident that there are within the Protectorate two
fairly well-defined series of crystalline rocks, a less meta-
morphosed series of quartzites, schists and gneisses
representing an original sedimentary succession, and a
more highly metamorphosed series of banded and
contorted gneisses, whose relation to the less meta-
morphosed group will be discussed in the sequel.
The less metamorphosed gneisses present in the field
somewhat granular and incoherent outcrops and may
be conveniently termed the “softer” gneisses, while
the “harder” or more highly metamorphosed gneisses
are readily distinguishable by the smooth and compact
character of their exposed surfaces. The softer
gneisses appear to disintegrate readily into a gritty
sand under present conditions, while the harder
gneisses exfoliate and pass into angular débris. Both
series are extensively invaded by granitic and other
igneous intrusions.

Borgu and the Niger Valley between Jebba and Yelwa.

In the province of Borgu the superficial accumula-
tions are so extensive and the exposures so few and
so widely scattered that the general character of the
underlying rocks is somewhat difficult to ascertain.
It is probable, however, that, like the neighbouring
region of Nikki,’ there is a floor of well foliated and

1 Hubert, Miss. Sc. au Dahomey, 1908, p. 325.
70 NORTHERN NIGERIA CHAP.

granitoid gneisses of varied origin, much pierced and
invaded by veins of granite, pegmatite, quartz por-
phyry and quartz. Tremolite schists are known from
Mori, and sheared porphyries from Kanikoko. The
occasional inselberge are composed invariably of grey
porphyritic granite. At Jebba the gorge of the Niger
is carved out of a series of sheared quartzites and
pebbly grits with the shear planes at times well
spaced and the deformed pebbles still distinctly visible.
Secondary mica has been sparingly formed along the
planes of movement, together with knots and streaks
of tourmaline and tourmaline quartz. The predominant
strike is N.—S., and the prevailing dip of the folia-
tion 65° W. The well-jointed Juju Rock is composed
of a laminated quartzite schist, which splits readily
into thin curving slabs, whose surfaces are coated
continuously with white mica and show a well-defined
strain-slip corrugation. Westward the Jebba quartz-
ites pass into highly sheared quartz schists, quartz
mica schists and granulitic gneisses, which are followed
by crumpled and contorted muscovite biotite schists
and gneisses and by granite at the river Awo. The
quartzites and granulitic gneisses are produced along
the strike to form the range of low wooded hills
which stretches southward from Jebba towards Ilorin.
To the east of Jebba the quartzites are abruptly
limited by hard banded and composite gneisses pierced
by masses of porphyritic biotite granite.

To the north of Jebba the Kailema granite, over
which the track leads from Jebba to Bajibo, is a massive
hornblende granite, porphyritic with white and pink
u CRYSTALLINE ROCKS 71

felspars and somewhat finer-grained on the margin.
The granite has evidently pierced a series of horn-
blende, epidote and talc schists and micaceous gneisses
which outcrop imperfectly to the east. Still farther north,
at Wuru, the channel of the Niger is occupied by a
hard and coarsely foliated epidote hornblende gneiss,
much pierced by irregular veins of schistose granite
and pegmatite. The foliation planes of the gneiss are
vertical and strike approximately N. 20° E. On the
left bank the gneiss is succeeded by thinly bedded
quartzites and quartz schists with scattered knots,
lenticles and veins of quartz and finely fibrous tour-
maline. Intercalations of much corrugated and
wrinkled mica schist bear witness to differential move-
ments along certain lines. The whole series, which
strikes N.—S. and dips vertically or at high angles to
the east or west, has apparently suffered a rapid and
repeated folding. These rocks are followed by a series
of fine-grained green and yellow quartzites and well-
cleaved slaty schists with numerous quartz reefs, which
pass eastward into a complex of hornblende gneisses,
epidote hornblende gneisses, amphibolites and fine
grained schistose granites which disappear at Kumboji
under the sandstones of southern Kontagora.

At Bussa on the right bank of the Niger, near the
Residency, there are exposures of much decomposed
shaly phyllites, vertical or highly inclined to the east
and striking N. 10° E. These are followed on the left
bank by a thick series of little altered grey and greenish
granular quartzites, which in places become pebbly and
conglomeratic. and enclose bands of greenish trachyte,
72 NORTHERN NIGERIA CHAP,

also showing little or no sign of shearing. Further
exposures of black and coarsely-sheared trachytes are
found in the swamps between Bussa and Libata.
Eastward the quartzites are much invaded by masses
of dark green diorite and by thick veins of tourmaline
quartz, the latter showing every variation between a
banded tourmaline quartz rock and a felted mass of
finely fibrous tourmaline. Nearer Auna these rocks
are succeeded by well-foliated augen gneisses which are
overlaid by the sandstones of southern Kontagora.

To the north of Bussa phyllites are again exposed in
the low rounded hills to the north-west of Ngashki,
where they strike N-S., and possess a high dip of 65°
to the east. Locally, however, the strike may be
directed as much as 35° to the east of north, indicating
that the rocks do not pursue a constantly rectilineal
direction from south to north, but rather possess a
zig-zag character with short and sharp deflections to-
wards the east. The phyllites, which are mostly grey
in colour, but in places mottled with large irregular
whitish spots on a grey ground, pass eastward into soft
grey sericitic schists with crystals of magnetite and
pyrites. The whole series is pierced by quartz tour-
maline veins, in which all proportions are to be found,
from almost pure quartz through banded quartz tour-
maline rocks to masses of pure tourmaline of the finely
fibrous variety. Sills of much decomposed vesicular
dolerite are common also amongst the phyllites. Farther
east intercalations of micaceous gneiss become abundant
within the schists, and a red fine-grained granulitic
gneiss intervenes between them and the massive biotite
ra CRYSTALLINE ROCKS 73

granite of Abara, with its large crystals of felspar.
To the north of Ngashki, phyllites and green slaty
schists with lenticular streaks and veins of quartz and
tourmaline quartz occur near Lokofe. A good ex-
posure in the river Malenda shows pebbly lustrous
schists striking N.-S., and dipping steeply towards
the east. At Yelwa a narrow strip of phyllites and
slaty schists on the left bank of the Niger, passes
westward into knotted mica schists and biotite gneisses
in the river bed and eastward into the granitic gneiss
of Bin Yauri. In the country which lies to the east
of Lokofe and Yelwa, and especially in the neighbour-
hood of Tabachi and Maibirro, green slaty schists of
varying hardness are frequently exposed, usually
associated with harder gritty bands and much invaded
by veins of quartz and tourmaline quartz, and irregular
intrusions of granite. In places also there may be
found intercalations of hard, gritty, carbonaceous and
little-metamorphosed slaty beds. At Chuggu, more-
over, between Tabachi and Maibirro, there is a parallel
belt of biotite gneisses, hornblende gneisses, and
epidote hornblende gneisses, while at Maibirro the
slaty schists, here associated with thinly-bedded
quartzites, quartz schists and quartz muscovite schists,
striking N. 35° E., with a dip to the north-west of
65°, are succeeded in the river Malenda by well-banded
biotite gneisses much veined with felspathic and
granitic material. The actual junction of the banded
gneisses with the quartz schists is, however, not
exposed.

The rocks of the Niger valley, between Jebba and
Th NORTHERN NIGERIA CHAP.

Yelwa, are thus of many and varied types. The
quartzites and phyllites, the slaty schists and micaceous
gneisses, and the green hornblendic and epidotic beds
represent the sandstones, shales, grits and arkoses of
the sedimentary series, while the sheared trachytes and
porphyries, the schistose granites and the coarse-
grained amphibolites represent the original igneous
intrusions within the sedimentary succession. Thewhole
series strikes fairly constantly N.—S., and forms a
practically continuous belt between Jebba and Yelwa.
In. most places there are indications that the rocks have
suffered a repeated folding into fairly sharp anticlines
and synclines with vertical axial planes, the folding
being apparently more rapid in the phyllites and schists
than in the quartzites and “gneisses. There has un-
fortunately been no opportunity of tracing the belt in
detail along the strike, and little is known of the lateral
variation or repetition of the individual members or of
the original sequence of the sedimentary succession.
There is no reason to believe that there has been any
increase or decrease in the intensity of the metamor-
phism throughout the belt from south to north, and no
indication has been found of the occurrence of any
thermal metamorphism in the neighbourhood of the
later granitic intrusions.

The most remarkable feature, however, about this
belt of schistose rock within the Niger valley is the
manner in which the less metamorphosed series of
quartzites, phyllites and schists is bounded abruptly
and locally replaced by a more highly metamorphosed
and much granitised series of well-foliated and often.
ul CRYSTALLINE ROCKS 75

banded gneisses. At Maibirro, for example, the schists
are abruptly succeeded by banded gneisses of a type
which is nowhere found between Maibirro and the
Niger. Similarly at Wuru and Jebba, the quartzites
give place unexpectedly to composite granitised
gneisses, which must have originated under very
different conditions from those which brought about
the metamorphism of the phyllites and schists. This
is a peculiarity of the fundamental architecture which
is repeated in many other parts of the Protectorate.

Kabba and Tlorin.

Over the greater part of the province of Ilorin the
surface accumulations are so extensive that the nature
of the underlying rocks can be judged only from small
and scattered exposures. So far as known there are
no belts of phyllites and quartzites upon the western or
central plains comparable with that of the Niger valley
above Jebba. The predominant rock in central Ilorin
is a fairly coarse-grained, granular and felspathic
muscovite biotite gneiss, sometimes an augen-gneiss
with large eyes of felspar, which disintegrates readily
into a felspathic sand. With it are associated in places
thin bands of quartzite, quartz schist, quartz muscovite
schist, mica schistand gneiss, often garnetiferous, amphi-
bolite and schistose granite, which, however, are neither
sufficiently extensive nor sufficiently resistant to give
rise to any prominent feature upon the surface. The
whole series which strikes approximately N.—S. is
76 NORTHERN NIGERIA CHAP.

much veined by muscovite and tourmaline pegmatites
and invaded by masses of granite usually of a more or
less foliated character. The larger masses rise into
turtlebacks or heaps of boulders, and in their neigh-
bourhood the gneisses have often been so intimately
veined and traversed by the granite as to produce a
composite or banded rock. At Share hard biotite
gneisses with linear foliation are extensively developed
and associated with hornblendic gneisses and amphi-
bolites and cut by tourmaline pegmatites.

In the Orissa hills, which lie to the east of the great
plain of Ilorin, the softer gneisses enclose for the first
time a prominent series of quartzites, quartz schists,
quartz mica schists and granulitic gneisses which, with
their general meridional strike and high dip to the
west, are very similar to those which form the low hilly
ground to the south and west of Jebba. The Shappa
hills which succeed the Orissa hills to the south are
composed in great part of biotite and hornblende
granites, coarse-grained, fine-grained and porphyritic,
which appear to be intrusive into a series of hard
biotite and hornblende gneisses, in places well-banded
and much veined with pegmatites, which occupies the
south-eastern corner of the province. Around Eri
the softer gneisses are again well developed and
extensively exposed, the series here consisting of thin
quartzites, felspathic gneisses and much contorted and
occasionally garnetiferous micaceous gneisses and
schists, with interbedded hornblende schists and
irregular masses of coarse-grained amphibolite, prob-
ably of intrusive origin. The whole series is much
PLATE VI

 

 

 

 

YENDAM HILL, YOLA PROVINCE.

 

 

CRATERS AT MBOt.
I CRYSTALLINE ROCKS 77

pierced by veins of quartz, tourmaline quartz and
muscovite pegmatite, the latter in places carrying
tinstone.

The softer gneisses and schists are found everywhere
in northern Kabba between Eri and the Ilorin border
and the. sandstone plateaux which fringe the Niger.
The usual succession of thinly bedded micaceous and
felspathic gneisses and hornblende schists is varied by
the intercalation of several belts of platy muscovite
schists and quartz muscovite schists, whose deeply
decomposed surface usually supports a luxuriant forest
growth. Within the area mentioned there are at least
four of these belts, more or less well-defined and
continuous along their strike from north to south.
The first runs southward from the neighbourhood of
Idofin by way of Kponyon, Onore, Ote, and Omwo
into southern Kabba: the second strikes southward
from Okoro and Iye, skirting Sanlu to the east and
Moppa ‘to the west: the third runs from Shale and
Oferre by way of Lukke, Olle, and Appe to the neigh-
bourhood of Odouape, and the fourth is exposed along
the track leading from Wa to Jakura on the north side
of the Mimi valley, While the fissile quartz muscovite
schist may be taken as the index rock of the various
belts, each belt is in itself a complex of muscovite
schists, quartz muscovite schists, quartz schists, quartz-
ites, biotitic and hornblendic schists and other rocks
and the proportions of these rocks vary not only in the
successive belts but at different points within the same
belt. In the third belt for example there is along
with the muscovite schist a great development of
78 NORTHERN NIGERIA CHAP.

quartzites and quartz schists around Lukke, where they
form prominent rocky hills (v. Traverse No. III.
p. 66). Farther north several bands of chlorite and
talc schist are found in the same belt in the neighbour-
hood of Iye, while in the fourth belt between Wa and
Jakura there are intercalations of such other rocks as
quartz magnetite schist, magnetite hornblende schist,
and crystalline limestone (v. Traverse No. II. p. 65).
The limestone is a white coarse-grained saccharoid
marble which may be traced for at least 1,000 feet
across the strike without affording any indication of
repetition by folding. On the margin the marble is
distinctly schistose with the foliation planes striking
N. 10° E. and dipping at a low angle towards the west.
The rocks in the neighbourhood are somewhat
irregularly folded with the foliation planes as a rule
parallel with the bedding. Their junction with the
marble is not exposed, but if the marginal foliation of
the latter be also parallel with the bedding, the actual
thickness of the original limestone must have been
very much less than 1000 feet. The marble is very
pure, consisting almost entirely of calcite with
occasional streaks and segregation bands of quartz-
epidote-calcite-idocrase rock representing the original
impurities within the limestone. Minute spots of
graphite are abundant throughout and on the margin
streaks and knots of quartz and pyrites are common
along the foliation planes. In places the marble is
irregularly crossed by later pegmatite veins.

The tracts which intervene between the various
belts are occupied by a variety of soft micaceous and
u CRYSTALLINE ROCKS 79

hornblendic schists and differ from the belts already
described only in the comparative rarity of muscovite
schists and quartzites. The absence of sufficiently
detailed investigation, however, makes it impossible to
say to what extent the various belts described above
represent repetitions of one and the same belt, or to
what extent they represent the original sequence of the
sedimentary succession. While the average strike of
the whole series is meridional, its undulating or zigzag
character is evident from the occurrence of indivi-
dual exposures showing every angle between north
and east. The different members of the series, while
frequently vertical, may dip at various angles to the
east or west or even in places approach the horizontal.
Individual bands are frequently puckered and contorted
and the whole series is invaded in places by extensive
masses of biotite granite which rise into turtlebacks
and groups of rounded hills. The granites are usually
foliated on the margin and sometimes throughout and
frequently show at their junction with the gneisses and
schists a narrow zone of injected rock. Small de-
tached exposures of the harder banded gneisses, elon-
gated upon a parallel strike, are distributed irregularly
throughout the softer series. The gneisses and schists
are abundantly pierced by muscovite and tourmaline
pegmatites and veins of quartz and tourmaline quartz,
the latter in the neighbourhood of Iye being minutely
banded as in the case of some of the tourmaline quartz
veins at Bussa and Ngashki. With the pegmatites
appear to be connected some small intrusive masses
of non-foliated granite which become more numerous
80 NORTHERN NIGERIA CHAP.

in the eastern portion of the area under consideration
(v. Traverse No. I. p. 64).

The striking feature of the architecture of the high
plains of central Kabba is the manner in which the
softer gneisses of the north with their intercalated
bands of schists and quartzes are invaded, and in part
replaced, by masses of granite and of hard banded
and composite gneisses. The first belt of schists can
be traced southward with intervals from Omwo to the
neighbourhood of Arigidi and Sequarre, where the
soft micaceous schists carry much staurolite. Harder
gneisses however appear to bound this softer belt
irregularly to the west and east. The prolongation
of the second belt of schists in northern Kabba is
probably represented by two narrow strips of quartzite
enclosed in the harder gneisses between Kabba and
Lupa. The third belt appears to be somewhat abruptly
replaced in the neighbourhood of Odouape by a com-
plex mass of granites and hard composite and banded
gneisses which extends westward across the high plains
of Kabba from Agwede and Shokko Shokko to Ikinre
and Omwo (v. Traverse No. IV., p. 67), and is
apparently prolonged southward into the Egbira hills.
The fourth belt appears to suffer much lateral varia-
tion, and is represented on the main road between
Lokoja and Kabba only by some thin bands of mus-
covite schist enclosed within a series of micaceous and
felspathic gneisses.

In southern Kabba the few facts at our disposal
seem to indicate the almost complete absence of
quartzites and muscovite schists and a repeated alterna-
I CRYSTALLINE ROCKS 81

tion of the softer and harder gneisses, the whole series
being pierced by pegmatite veins and intrusive masses
of granite. Quartzites and quartz schists reappear,
however, in the Kukuruku hills on the borders of
Northern and Southern Nigeria.’

The lower plains which stretch eastward to the Niger
from the escarpments of the Egbira and Agwede hills
are occupied very largely by gneisses of the softer
series. Quartzites, quartz schists and quartz-mus-
covite schists occur within the series, but their dis-
tribution over the plains is so irregular, and their
prolongation along the strike so inconstant, that they
cannot in any way be correlated with the quartzites
and schists of either the third or fourth belts in
northern Kabba. It would seem, indeed, that instead
of the regular alternation to be found in the north,
there is over these eastern plains a greater mixing
of types and a greater variation in character of the
individual members when traced along the strike.
Quartz-magnetite and quartz-hematite schists are
fairly common, typical occurrences being found in
the neighbourhood of Bangede and around Okuruku
and Anamu near Okeli, and on the plains to the west
of the Againyi hills, as well as at the foot of their
western slope. Amongst the granites and granitoid
gneisses which form the escarpment of the Egbira
hills, bands of felspathic gneiss and micaceous schist
are frequently enclosed, and on the plains the gneisses
and schists are crossed in the usual manner by peg-
matite veins and pierced by masses of more or less

! Parkinson, Q. J. G. S. (63), 1907, p. 317-
G
82 NORTHERN NIGERIA CHAP.

foliated granite, which form the prominent isolated
hills which diversify the surface of the plain. Here
and there also may be found a small exposure of
composite or banded gneiss, but it is only in the im-
mediate neighbourhood of the Niger that the harder
gneisses attain any extensive development. There
they form a narrow belt, marked by prominent in-
trusions of granite, which stretches southward from
Lokoja along the right bank of the river, and adds
picturesqueness to the Niger valley between Igbo and
Itobe (p. 6). At Lokoja the harder gneisses are
exposed in the river bed, and the softer gneisses and
schists at the foot of Mt. Patti. The average strike is
N.E. to S.W., and the whole series is much pierced
by veins of granite and graphic pegmatite, the latter
containing frequent knots of magnetite.

To the east of the Niger the softer gneisses
reappear in the narrow strip of crystalline rocks in
Bassa province which fringes the left bank of the
river. Typical exposures are found in the neighbour-
hood of Igbo and Itobe, where the gneisses are
associated as usual with early foliated or partially
foliated granites and with later intrusions of muscovite
and tourmaline granites and pegmatites, the tourmaline
occurring as a rule in large and well-formed crystals.
At Igbo the micaceous gneisses enclose a number of
narrow bands of fine-grained, crystalline limestone,
each 3 to 4 feet in thickness. The limestone
varies much in colour and hardness, the purest
varieties being blue, while weathering and impurities
produce grey and brown tints. Much of the lime-
0 CRYSTALLINE ROCKS 83

stone is gritty, but the commonest accessory is a pale-
coloured tremolite in rosettes and felted veins of
fibrous crystals and in scattered well-formed prisms.
The crystalline rocks of Kabba and Ilorin thus
present considerable resemblances in individual types
to those of the Niger valley above Jebba. The most
striking differences are the occurrence of such new
types as crystalline limestone and magnetite and
hematite schist in eastern Kabba and Bassa, and the
apparent absence in the southern provinces of the
characteristic phyllites and slaty schists of the Niger
valley to the north. The place of the phyllites,
however, is probably taken by the muscovite and
quartz-muscovite schists, which form such prominent
members of the metamorphic series in northern
Kabba. If so, there would seem to have been a slight
increase in the intensity of the regional metamorphism
in these southern provinces as compared with the
Niger valley above Jebba. Of thermal metamorphism,
on the other hand, there is little trace. The schists
and gneisses in the neighbourhood of Sequarre in
western Kabba and in several localities in northern
Kabba and Ilorin contain a considerable quantity of
staurolite and other metamorphic minerals. Their
distribution, however, appears to possess a linear
character which is somewhat inconsistent with a
contact origin, while sufficiently extensive igneous
intrusions, to whose influence their local development
might be ascribed, have nowhere been definitely
recognised in the vicinity. The numerous intrusive
masses of both foliated and unfoliated granite through-
G2
84 NORTHERN NIGERIA CHAP.

out these provinces appear to have induced little or no
contact metamorphism in the surrounding gneisses and
schists. An exception to this rule may perhaps be
made in the case of the tourmaline granite behind
Igbo on the Niger, to whose influence may possibly
be ascribed the extensive development of tremolite in
the neighbouring crystalline limestones. At the same
time it should be remembered that the occurrence of
tremolite in metamorphic limestones cannot be taken
as an invariable indication of contact action.

The irregular association of a less metamorphosed
series of quartzites, schists, and gneisses with a more
highly metamorphosed series of well-foliated, banded
and contorted gneisses, exhibited by the crystalline
rocks of the Niger valley above Jebba, forms likewise
a striking feature of the crystalline rocks of Kabba
and Ilorin. The banded gneisses may be either
biotitic or hornblendic and the lighter and darker
bands may alternate so regularly and rapidly as to give
rise to a striped or ribboned appearance even in the
hand specimen. They are for the most part of a
medium and even grain and never _ porphyritic,
although sometimes they enclose lenticular masses of
finer grained biotite gneiss or of amphibolite. As a
rule they are much invaded by granite and frequently
rendered composite by thin granitic intrusions. The
foliation, which may be parallel or oblique to the
striation, is their least conspicuous feature. Pegmatite
veins are usually abundant and frequently foliated.
As already described (p. 74) these hard banded and
contorted gneisses are found irregularly replacing
Ir CRYSTALLINE ROCKS 85

the softer gneisses both along and across the
strike.

So far as known there are no schistose rocks in
Kabba and Ilorin comparable to the sheared trachytes
of the Niger valley and the sheared porphyries of
Borgu. Rare occurrences of thin basaltic veins have
been observed, but as a rule the later intrusions in
Kabba and Ilorin take the form of small masses of red
or white aplitic granite or of dykes and veins of mus-
covite and tourmaline pegmatite or of graphic granite.
These later granites have usually a peculiar granular
and incoherent character and never possess chilled
margins. Frequent occurrences have been noted of
the granular granite acting as a kind of ground mass
to large scattered porphyritic masses of graphic quartz
and felspar (v. Traverses Nos. I, II, III, pp. 64-66).
Frequently also the granites show an_ ill-defined
banding caused by an alternation of coarser and finer
grained layers. It is possible that the muscovite and
tourmaline pegmatites, the veins of graphic granite, the
quartz reefs, the banded tourmaline quartz rocks, and
the small intrusive masses of acid granite may all
possess a certain genetic connection. Only at Igbo,
however, does there occur an extensive mass of reddish
muscovite tourmaline granite which to some extent
unites the characters of all the dyke rocks and re-
presents in a general way the original magma from
which the various dykes and veins and intrusive
masses have been differentiated. The abundance of
tourmaline throughout Kabba and Ilorin led to the
hope that tinstone would in places be associated with
86 NORTHERN NIGERIA CHAP.

it, but only at Eri in eastern Ilorin have the pegmatites
proved stanniferous. The quartz reefs also have no-
where been found to yield more than the minutest trace
of gold.

4. The Central Crystalline Area.

The peculiarities of structure which have been
remarked in the western provinces are continued
throughout the larger crystalline area in the centre of
the Protectorate. To the east as to the west of the
Niger there has been an irregular and local replace-
ment of a series of softer gneisses, quartzites, and schists
by a complex of harder composite and often well-
banded gneisses. There is also in the western part of
the central area within the softer gneissic series a well-
defined grouping of the quartzites and phyllites or
micaceous schists into regular and definite belts which
preserve their identity for considerable distances along
the strike. In the east, however, this regular grouping
appears to be absent, the quartzites and mica schists
being distributed irregularly and in short and narrow
bands amongst the felspathic and micaceous gneisses.

In the east of Sokoto province there are at least
two broad and well-defined belts of phyllites and
indications of a third. The first is found between
Bukwium and Anka near the Kontagora border, and is
well exposed in the Anka river. The strike of the
phyllites varies from N.—S. to N. 20° E. Surface
creep here and there makes the dips uncertain, but
the inclination is usually high, and is sometimes to the
II CRYSTALLINE ROCKS 87

west, sometimes to the east. This fact probably
accounts for the great width of the belt. It is not
known whether the phyllites extend to the east of
Anka, but after crossing them at right angles to the
strike for thirty miles to Bukwium they are still in full
force, and the western limit is unknown. There are
numerous quartzite bands, especially about Anka and
to the south of it. The phyllites are soft, fine-grained
and dark-coloured, and are traversed by abundant
quartz veins, some of which carry pyrites. It is
interesting to note that the phyllites are only exposed
in the neighbourhood of the river. Away from the
river, on the level plain, there is no indication of them,
and this fact is of significance when considering the
possible extension of the phyllite belts. There is a
numerous and interesting series of igneous rocks
within the phyllite area, including such types as horn-
blende granite and syenite, pegmatite and quartz
porphyry. These rocks, as a rule, show no sign of
crushing, and are probably later intrusions. Some of
the porphyries, however, show an imperfect foliation,
and appear to have been exposed to some of the later
crustal movements. Bands of amphibolite and veins
of tourmaline quartz also occur within the phyllitic
series. (A.L.)

The second group of phyllites and quartzites forms
a belt of low hilly country striking N.N.E.—S.S.W.
across the Sokoto-Kano caravan route between the
villages of Maradu and Karakai, and continues north-
ward at least as far as Bazai. The series attains
across the strike a breadth of about thirteen miles,
88 NORTHERN NIGERIA CHAP.

and consists of a succession of slaty schists and
knotted phyllites and quartzites, much pierced by
quartz veins and thin bands of schistose granite, and
dipping fairly constantly in the west at 70° E.S.E.,
but gradually heeling over in the east to the W.N.W.
Towards Karakai the quartzites predominate and
contain much tourmaline, and many samples may be
found showing quartz and tourmaline or quartz, slate
and tourmaline in alternating ribbon-like bands. The
third belt is very imperfectly exposed on the borders
of the province between Woneka and Duru, and is
represented only by some scattered outcrops of slaty
phyllite and mica schist.

Between Maradu and the margin of the Sokoto
sandstones to the west, the softer gneisses are exposed
upon the sandy plains in a very fragmentary manner,
and appear to consist of micaceous and hornblendic
gneisses and schists, and of hornblende epidote
gneisses and amphibolites with numerous small
granitic intrusions. The rocky knobs and kopjes two
miles west of Maradu are formed of a coarsely banded
volcanic agglomerate, dipping eastward at angles of
30°—40°... The agglomerate may be traced to within
a mile of the village, where it gives place to a thinly
bedded series of red ashy sandstones and ash beds.
East of the rest camp, these beds strike N.N.E. and
dip at 4o° E.S.E. while west of the camp they strike
E.N.E. and dip at 30° S.S.E. The ash is exposed in,
and to the west of, the village, but to the east its place
is taken by a much broken and shattered granitic rock.
The actual junction, however, was not observed,
pet CRYSTALLINE ROCKS 89

Such evidence as there is points to the former
existence of a volcanic neck or vent in this locality.
Between Karakai and Woneka the surface accumula-
tions obscure the rock for long distances, especially to
the west and east of the granite hills of Kotorkoshi.
Around Bungudu, however, there are numerous
exposures of a coarse-grained composite gneiss which
probably extends eastward to the boundary of the
province. Beyond Duru a grey biotite granite with a
distinctly foliated margin forms the broken hilly
country between Runka and Kurefi, but between
Kurefi and Sani the granite gives place to a group
of dark-coloured biotite gneisses before the crystalline
rocks disappear under the sandstones of Katsina.
Knobs and hummocks of granite, however, protrude
through the sedimentary rocks round the walls of the
town, and Barth’ has reported the occurrence of
similar mounds and ridges immediately to the north.
To the south-east of Katsina the surface rock appears
to be everywhere a reddish granite as far as Duru,
but beyond Duru the superficial accumulations so
effectually cover up all but the occasional kopjes and
boulders of granite that the character of the underlying
rocks is difficult to ascertain. From the scattered
fragments of quartzite, gneiss and amphibolite, and
occasional granite boulders in the surface drift, it is
probable, however, that for a considerable distance to
the west of Kazaure the floor is formed of the
sedimentary gneisses with the usual granitic intrusions.
The hills around Kazaure are composed of hard blue

1 Barth, Central Africa, 1857, Vol. II, pp. 41, 42.
go NORTHERN NIGERIA CHAP,

quartzite much pierced by later veins of white quartz,
and striking N.N.E.—S.S.W. with a dip of 30° to the
west. This belt can be traced southward to the
neighbourhood of Kasuan Kuka, where the quartzites
become more micaceous and where some rocky
exposures of granular amethystine quartz probably
represent the intrusive quartz veins of Kazaure.
From Kasuan Kuka to Kano, granites and an
occasional quartz vein are the only rocks exposed,
while the deep drift effectually prevents the discovery
of the relationship between the surrounding rocks and
the decomposed diorites of the two flat-topped hills
within the walls of Kano. A few miles east of Kano
the crystalline rocks disappear under the sands and
clays of Katagum and Bornu. There is every reason,
however, to believe that they are continuous to the
north-east with the granites, gneisses and quartzites
of Machina, Zinder and Mounio.

The two detached hills, Dala and Kogon Dutsi, the
landmarks of Kano, with their precipitous slopes and
tabular summits, 150 feet above the level of the plain,
present from a distance a decidedly sedimentary
appearance. Clapperton,’ indeed, described them as
consisting of ‘‘argillaceous ironstone mixed with
pebbles and a rather soft kind of marl,” while Dala,
the eastern mount, ‘is of clay-ironstone and con-
glomerate lying upon a bed of soft light clay apparently
mixed with vegetable remains.” Closer investigation
has shown, however, that both hills are of crystalline
origin, Dala being composed entirely of earthy de-

1 Denham and Clapperton’s Marrative, 1826, pp. 5°, 57.
PLATE VII

  
   
   
 

GRANITE

GRANITE

GRANITE
Pate WE

 

 

CRATERS IN THE Mor HItts.

 

 

 

A CRATER IN THE Mpo1 HILts.
u CRYSTALLINE ROCKS gl

composition products with a gritty ferruginous cap,
while Kogon Dutsi still retains cores or kernels of
undecomposed diorite in the midst of the friable earthy
material which forms the greater part of the hill. The
felspar and hornblende of the original diorite have
decomposed in the lower part of Dala into a whitish
clay streaked and spotted with dark green chloritic
material. In the upper part the colouration is more
uniformly white or yellow, the bulk of the iron having
been leached out to form the red ferruginous cap.
That the latter is itself composite, however, is evident
from the occurrence of gritty grains, subangular frag-
ments of quartz and rolled pebbles of ironstone in the
vacuolar and concretionary crust. Kogon Dutsi
presents a similar composition, with the exception that
the material becomes coarser and more granular in the
neighbourhood of the kernels of undecomposed rock.
The extensive decomposition of the crystalline rocks
to which the earthy hills of Dala and Kogon Dutsi
bear witness will be found in the sequel (p. 201) to be
an important factor in the evolution of the character-
istic scenery of the high plains of Hausaland.

Around Kontagora and beyond the northern limit
of the sandstones which occupy the southern portion of
the province of the same name, there are found hard
biotite gneisses in places well striated with pink
felspathic and dark biotitic bands and crossed by
numerous pegmatite veins. To the east the crystalline
floor is deeply covered with drift, and outcrops are
comparatively rare. In the Beri river, however, there
is a good exposure of soft felspathic biotite gneisses,
92 NORTHERN NIGERIA CHAP.

with knots and bands of pegmatite, while at Beri a
pink granite forms a compact group of rocky hills.
The granite possesses a distinctly foliated margin, and
is followed to the east by hard hornblende and biotite
gneisses much pierced by granite veins, which may be
traced to within six miles of Bobi before they are
replaced by the softer micaceous series. On account
of the extent of the superficial accumulations, however,
these softer gneisses are well exposed for the first time
only in the rocky bed of the Kara river which forms
the boundary between the provinces of Kontagora and
Zaria.

Though the structure of the north-eastern part of
Kontagora province is complicated in detail, it may be
described in general terms as a succession of gneiss
and quartzite bands alternating with one another.
They strike a few degrees east of north, and probably
pass to the east of the Bukwium-Anka phyllites. The
quartzites are frequently tourmaline-bearing, and one
band west of Kotonkoro carries scales of graphite.
This fact is interesting in connection with the
graphitic schists reported from a neighbouring part of
Zaria! The gneisses are usually biotite gneisses,
sometimes markedly banded, at other times indis-
tinctly so. Schistose rocks are seen in places, quartz
schists being prominent to the south of Mahorro, where
talc schists are also seen. The gneiss and quartzite
country is traversed by pegmatite and quartz veins,
but intrusions of unfoliated granite are rather un-
common. Most of the turtle-backs are foliated through-

1 Dunstan, Colonial Reports—Miscellaneous, No. 26, p. 15.
n CRYSTALLINE ROCKS 93

out, differing in this respect from those of many other
parts of the Protectorate. Where the Sokoto road
leaves the province, the boundary is marked by a high
sharp ridge of amphibolite. (A. L.)

A tract of broken hilly country, almost entirely
carved out of the softer gneissic series, occupies the
south-western corner of Zaria province, and a diagonal
traverse across the hills from Moriga on the Kara
river by way of Garun Gabbas and Zungeru to Kato
and Mikonkeli presents a particularly instructive
section. The hills which begin about ten miles south-
east of Moriga consist between Inga and Garun
Gabbas of a succession of quartz schists, quartz mus-
covite schists, micaceous and hornblendic schists,
felspathic gneisses and amphibolites, pierced by numer-
ous quartz reefs and veins and by a few dykes of
basalt and porphyry, the whole series possessing an
average strike of N. 10 E. Between Garun Gabbas
and the Kaduna river ridges of quartz and quartzite
rise conspicuously at intervals out of the pebbly drift
which covers the surface. In the railway cutting on
the right bank of the Kaduna near Zungeru, quartzites
and quartz schists are associated with bandsof a hard and
minutely foliated granulitic gneiss containing knots
and lenticles of quartzo-felspathic and chloritic material.
In the river bed below the railway bridge the most
conspicuous rock is a well-bedded white quartzite
striking N. 30° E. and dipping at an angle of 64° to the
south-east (Plate VIII, Fig. 2). The quartzite varies
much from a massive variety with knots of pyrites and
scattered flakes of white mica through a streaky
94 NORTHERN NIGERIA CHAP.

lustrous micaceous quartzite with linear foliation planes,
into a well-foliated quartz muscovite biotite schist.
The different varieties are often arranged in alternating
parallel bands and the whole series is pierced by
occasional narrow veins of quartz. The trench which
at the Kaduna bridge forms the low water channel of
the river has been carved out of a band of hornblende
schist intercalated along the strike of the quartzites.
The schist, which in places is composed almost entirely
of hornblende, but in others interfoliated and streaked
with felspar, has been more easily worn away than the
quartzite, and grooved and pot-holed by the action of
the river. The quartzites and quartz schists, with
intercalated sills of hornblende schist, continue east-
ward to the adjoining channel of the Dago, where they
are replaced by finely striated biotite gneisses. At
Zungeru micaceous and felspathic gneisses are mingled
with soft, thinly bedded and repeatedly folded horn-
blende mica epidote gneisses or schists. The whole
series is pierced in the usual manner by veins of quartz,
pegmatite and granite and strikes in a general way
N. 10° E. with a dip of 60° to the east. Immediately
east of the railway station, however, these rocks give
place to well-foliated granulitic gneisses with knots of
felspar, striking N. 20° E. and dipping at 45° E.
These gneisses, which probably represent more com-
pletely altered portions of the sedimentary series, are
in places well striated, with the bands wavy and con-
torted and crossed irregularly by veins of quartz.
They are followed in the vicinity of Kwarra-town by
coarsely schistose grits which are among the least
an CRYSTALLINE ROCKS 95

altered rocks within the Protectorate. Between
Zungeru and Gidan Motu there are numerous ex-
posures of green hornblendic beds similar to those at
Zungeru. They become, however, more fissile and
contorted towards the east. The strike oscillates
between N.N.E. and N.N.W., and the dip varies
between vertical and high angles to the east or west,
while at Gidan Motu there is an intercalated belt of
platy biotite gneisses which strike N. 60° W. and dip at
60° S.S.W. Between Gidan Motu and Kato green
slaty schists and phyllites are extensively developed
and steeply folded at Kato into sharp anticlines and
synclines which possess an average strike of N. 20° W.
The phyllites enclose much quartz in lenticles and
veins and contain abundant knots and spots of pyrites.
Beyond Kato the phyllites are succeeded by soft mica
schists, which in turn give place to micaceous and
felspathic gneisses. The latter around Mikonkeli,
Minna and Paiko are replaced by hard composite and
in places banded rocks and invaded by extensive
masses of granite which usually show a distinct mar-
ginal foliation.

Southward the Zungeru belt of quartzites and
phyllites disappears under the sandstones of Nupe, but
any correlation with the quartzites and schists of
Kabba cannot yet be attempted. Northward the belt
has been followed as far as Birnin Gwari and from its
pronounced development in the neighbourhood of that
place, it is probable that it extends considerably
farther north again. For twenty or thirty miles north
of Tegina there are a number of granite hills strung
96 NORTHERN NIGERIA CHAP

together on a roughly north and south line, the granite
having apparently been intruded along the strike of
the schistose rocks. The granites become foliated
locally. Between Bugai and Koriga there is a twenty
mile belt of phyllites and subordinate mica schists
which runs northward to Birnin Gwari, where the
phyllites form a number of sharp north and south
ridges and are excellently exposed, both in the sides
of the ridges and in the intervening streams. The
phyllites are traversed by many quartz veins and gold
is widely disseminated in the streams. At Koriga
there is an extensive development of hornblende
gneiss. To the east are mica schists, and graphitic
schists are reported from the neighbourhood.’ The
rocks which rise above the plain in the vicinity of
Zaria are all of granite. (A.L.)

So far as known, the Zungeru belt is the last
prominent group of phyllites which can be traced
within the Protectorate. To the east their place is
taken by muscovite and biotite schists, which are to be
regarded as more completely reconstructed represent-
atives of the original shales, the metamorphic action
having apparently been somewhat more intense in
eastern and southern Zaria and Nassarawa. Several
belts of quartzites and schists are enclosed in the
usual manner within a complex of softer and harder
gneisses to the east of Minna and Mikonkeli. At
Kuta, for example, there is a belt of quartz muscovite
schist passing on the one hand into knotted micaceous
schists and on the other into quartzites and carrying

* Dunstan, Colonial Reports—Miscellaneous, No. 26, p. 15.
ba CRYSTALLINE ROCKS 97

much sillimanite and magnetite and large lenticles and
knots of quartz and tourmaline quartz. The whole
series strikes approximately N. 30° E. and dips at
45° N.W. Again between Chiri and Guni there is
much soft micaceous schist rising into low rounded
and well-wooded hills, striking generally N.—S., well
frilled in places, with a high content in ilmenite and
numerous knots and veins of tourmaline quartz.
Farther east the hills which run from the neighbour-
hood of Dorka to Kaderri and Kaserimi are composed
very largely of quartzites, quartz schists, quartz
muscovite schists and micaceous gneisses, striking
N. 1o° W., dipping at an angle of 60° W., and pierced
by quartz veins, muscovite pegmatites and granites.
Between these more prominent belts occur numerous
smaller exposures of schists and quartzites and of both
the softer and the harder gneisses. To the east of
Kaserimi and Duchi and in the valley of the Kaduna
the surface is so deeply and extensively covered with
drift that little rock beyond the marginally foliated
biotite granites of the isolated hills is available for
investigation. There are, however, indications from
occasional fragments in the drift and rare exposures in
the stream courses that a considerable extent of the
buried surface is composed of a softer gneissic
series. To the east of the Kaduna, the Ruruma and
Kerko hills which rise so prominently from the south-
eastern plains are composed throughout of a coarse-
grained biotite granite, locally carrying hornblende in
addition and in places distinctly foliated on the margin.
The junction with the gneisses is only rarely seen on
H
98 NORTHERN NIGERIA CHAP.

account of the thick masses of drift which envelop the
base of the hills. At Guri on the eastern slope of the
Ruruma hills there are exposures of finely laminated
hornblende epidote gneisses, while the granites and
the marginal rocks are pierced by numerous dykes
of basalt, dolerite and quartz porphyry.

The high plains of south-eastern Zaria are occupied
by mica schists and gneisses, with granite hills in one
or two localities. Along the eastern border of the
province the Rukuba plateau ends in a ragged edge of
biotite granite which veins the gneisses at its foot.
The country around Jengre and Limoro is interesting
on account of the occurrence of masses of soda granite
and especially on account of numerous intrusions of
dyke rocks, felsites often with flow structure, por-
phyries and quartz porphyries. Tinstone is frequently
met with in the streams of the district. Similar dyke
rocks are exposed around the base of the Kudaru hills:
to the north-west of Leri and there, in addition, dykes
and veinlets of basalt penetrate the granite. These
hills are made up of hornblende granites with syenitic
modifications, and locally, towards the boundary, the
granite takes on a distinctly foliated structure, with
rounding of the porphyritic felspars as in augen-gneiss.
(A. L.)

In Nupe, between the Gurara river and the sand-
stones of the Niger valley, the crystalline series is
introduced by muscovite biotite gneisses, quartzites,
hornblende and talc schists and amphibolites, pierced
by extensive masses of granite around Gaung, Lefu
and Paiko, In the bed of the Gurara, between Gaung
ra CRYSTALLINE ROCKS 99

and Izon, soft gneisses and hornblende epidote rocks
alternate with hard and well-foliated gneisses striking
a little west of north, and varying in dip from vertical
to 40° or 50° E. Five miles beyond Izon, the Abuja
road ascends over a crumpled and contorted series of
biotite, hornblende, and epidote hornblende gneisses
much injected by masses of biotite granite. Beyond
Abuchi a second ascent over soft micaceous gneisses,
striking N. 10° W and vertically foliated, leads up to
the striated, ribboned and banded gneisses which have
been invaded by the biotite granite of Abuja. The
banded gneisses strike N.—S., and are much granitised
in the immediate neighbourhood of the intrusive rock,
while the granite itself is marginally foliated and crossed
by crush lines at the Izon gate (v. Traverse No. V,
p. 68). Partially foliated granites and banded and
composite gneisses continue to within five miles of
Kao, whence a belt of soft micaceous gneisses and
quartz muscovite schists, striking N. 20° E., stretches
eastward to the neighbourhood of Kari. At Kari
the escarpment of the northern tableland is formed
of soft biotite gneisses, much pierced by veins of
quartz and tourmaline quartz. Eastward by way
of Kukwi, Anta, Tatara and Jaginde the escarp-
ment shows much granite, associated both with
banded gneisses and with softer micaceous and horn-
blendic rocks. The gneisses and granites are exten-
sively invaded by muscovite and tourmaline pegma-
tites, and by irregular intrusions of basalt and dolerite.
Between Jaginde and Darroro quartzites, quartz
schists and mica schists outcrop along the escarpment,
H 2
100 NORTHERN NIGERIA CHAP.

and at Darroro a similar series of thin quartzites and
gneisses, striking generally:N.—S., is pierced by exten-
sive masses of quartz~-muscovite-tourmaline pegmatite,
and capped by the basalts of the Morrua plateau. The
pegmatite is rudely banded parallel with the strike of
the gneisses, the various bands being distinguished by
their richness in tourmaline. All proportions may be
found between quartz muscovite and quartz tourmaline
rock, the tourmaline in the latter being either in large
well-formed prisms, or in thin alternating bands of
felted fibrous crystals. North-east of Darroro the
vertical granite cliffs of the Kagoro massif form the
margin of the Bauchi plateau, while in the neighbour-
hood of Assab the later basalts much obscure the
crystalline rocks of the lower plains. At Assab the
escarpment is largely composed of biotite granite, in
places porphyritic, and apparently intrusive into a series
of micaceous gneisses which strike N. 10° E. and dip
at an angle of 40° to the west.

The northern tableland and the central plains of
Nassarawa are composed very largely of the softer
gneisses with scattered outcrops of harder composite
rocks. Quartz muscovite schists occur in a broad belt
on the tableland in the vicinity of Aribi, and calc-
silicate rocks between Kwai and Jaginde. The com-
posite and banded gneisses reach their greatest develop-
ment in the Karshi hills between Abuja and Keff.
The Mada hills and the greater part of eastern
Nassarawa are still unexplored. In southern Nassarawa
a broad belt of quartz muscovite schists, mica schists,
hornblende schists and chlorite schists extends between
"I CRYSTALLINE ROCKS IOI

Gwombe and Buga, the mica schists in the neighbour-
hood of Zagabutu being particularly rich in staurolite,
garnet and imperfectly crystallised knots of andalusite,
presumably of contact origin. The whole series has
been steeply folded on a meridional axis and then
coarsely corrugated transversely, the result being that
individual exposures may strike at any angle between
E.—W. and N.—S. The average strike is inclined
around Gwombe to the north-west, and around
Buga to the north-east. To the east of Buga the
schists give place to the usual varied succession of
softer gneisses, pierced in the usual manner by veins of
quartz and tourmaline quartz, and associated from time
to time with banded and composite rocks and detached
masses of granite. Numerous dykes of basalt and
quartz porphyry appear to be associated with the
granites of the Kurudu and Anagoda hills, which lie
respectively west and south-east of the town of
Nassarawa.

The crystalline rocks of Bauchi province present
similar characters to those of other parts of the
Protectorate. The broad belts of schists and quartz-
ites found in other provinces are here, however,
conspicuously absent, such types being represented
only by thin bands intercalated within the softer
gneisses. Banded and composite rocks, on the other
hand, appear to be present in somewhat greater pro- |
portion than elsewhere, while domes and turtlebacks
of foliated or partially foliated granite (Plate XII,
Figs. 1, 2) are in places particularly abundant. The
softer and harder rocks are, however, so intimately
102 NORTHERN NIGERIA CHAP.

mingled that a detailed description of the succession is
impossible. Excellent exposures of the harder series
are to be found in the Kogin Delimi below Naraguta
in the west of the province, and of the softer gneisses
in the Jarawa hills to the south of Bauchi, and of both
in the broken rocky country between Kanna and
Angass in the southern portion of the province
(v. Traverse No. VI, p. 68). The strike of the
gneisses, while very variable, appears to have a
greater tendency to assume an E.—W. direction in
Bauchi than in other provinces, a tendency which is
probably due to the greater intensity of the trans-
verse forces which have elsewhere corrugated the
prevailing meridional strike of the gneisses and schists.
This feature is particularly marked in the neighbour-
hood of the Ningi massif, which is elongated approxi-
mately along the strike of the surrounding softer and
harder gneisses.

Another notable feature of the province of Bauchi
is the number and variety of the later igneous intru-
sions. Pegmatites, quartz reefs and veins of tourmaline
quartz are as abundant in Bauchi as elsewhere, but
the attention is somewhat diverted from these
commoner intrusive types by the presence of an
abundant series of dyke rocks, and of extensive
masses of non-foliated granite and syenite. The
pegmatites are in places particularly rich in ilmenite,
rutile and chalcedonic quartz; the dyke rocks present
almost every variety between basalt and quartz
porphyry; and many of the granites are especially
rich in soda, and in places show chilled margins at
re CRYSTALLINE ROCKS 103

their junction with the gneisses. The summit of the
plateau around Bukuru is occupied by one of these
extensive granitic intrusions, which is of peculiar
interest from the fact that in places it is veined and
impregnated with tinstone and other minerals. A
similar granite, also carrying tinstone, forms the
greater part of the Kwandokaya hills to the north of
Toro. Many intrusions of syenite are found around
and to the east of the town of Bauchi. The Ningi
massif is largely composed of a soda granite, with a
well-chilled margin, accompanied by numerous dykes
of granite and porphyry, and in places carrying tin-
stone. Similar granites are found at Kila and Fagam
on the borders of Bauchi and Kano, at Shira in
Katagum to the north, and at Gurkawa on the Muri
border to the south. The Murchison Hills are
believed to be largely granitic, but they and the
southern margin of the plateau are still practically
unexplored. A small detached area of granite and
gneiss, pierced by numerous pipes of basalt and
trachyte, is found around Tangalto and Chongwom in
the south-east of Bauchi province.

Southern Muri and Yola. (A.L.)

The strip of crystalline rocks which runs along the
southern boundary of Muri and Yola has an average
width of forty miles and is separated from the central
area by the sedimentary rocks of the Benue plain.
The crystalline floor appears at the surface, however,
in a number of small inliers around Arofu in western
104 NORTHERN NIGERIA CHAP.

Muri, and thus quite near to the river. Five miles
east of Arofu a small area of fresh biotite-granite
about fifty yards in diameter peeps from beneath the
limestone. Immediately north of the town itself there
is a knoll of granitoid gneisses striking north and
south. On proceeding southward along this line of
strike limestone is passed over for three miles, but
then the gneiss appears at the surface again, and this
time forms a ridge running southward for at least
some miles. It may well be that other inliers of
crystalline rocks occur in the unexplored Munchi
country.

Farther south the transition from sedimentary to
crystalline rocks is not accompanied by any feature in
the drift-covered plain. Though the exposures are
not good, it appears that biotite-gneisses and schists
with the customary northerly strike are penetrated by
granite veins. The rocky masses which lie south and
south-west of Takum are probably largely or entirely
of granite. The bulk of the material which forms the
scattered hills around and to the north of Takum is
also granite, but here it is inextricably mixed up with
gneiss which is met with in patchy fashion from top to
bottom of the hills. The foothills of Shebshi are
schistose grits and gneisses invaded by granites in the
usual manner.’

Only the northern part of the Mumuye-Manna
plateau has been traversed. The rock there is almost
always biotite-granite, but it is by no means always of

1 See also Downes, Yola and Cross River Boundary Delimitation,
1910, p. 35.
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EXFOLIATION IN THE Ki_sBa HIILts.

 

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THE GORGE OF THE KADUNA AT ZUNGERU.
0 CRYSTALLINE ROCKS 105

the same variety. Occasional quartz veins are seen on
the plateau and also on the lower ground between
Numnai and Panteti, where the quartz carries pyrites.
Intrusions of quartz-porphyry are often seen cutting
through the granites, e.g., east of Numnai, around
Shega Mundi hill, around Panti Baturi and at Yendam
Hl. The granites only occasionally carry included
blocks and fragments of gneiss, but on descending to
the plain biotite-gneiss is met with striking N. 10° E.,
and the plain from Chukol eastward to the Vere Hills
is occupied by biotite-gneiss, with some intrusions of
granite. The Vere Hills themselves are made up
almost entirely of granite, though to a small extent of
gneiss also. Biotite-gneiss is frequently seen round
the base of the plateau, generally much penetrated by
granite or quartz-porphyry. Thus, speaking generally,
the plains of southern Yola are mainly of gneiss and
the plateau areas mainly of granite.

To the north of the Benue plain again, the country
around Song, Goila and Korubi is a biotite-granite
area with some conspicuous dykes of quartz-porphyry
running for miles across the country. Near Zummu
porphyry rises just above the soil of the plain and
exhibits flow-structure, while between Zummu and
Holma a felsite dyke is seen cutting through the
granite. The hills around Holma are built of a well-
jointed biotite-granite, and the sides of the hills are
concealed by the loose blocks split off along the
joints. The granite of the Kilba Hills, near Pella,
is a very fresh, coarsely-crystalline biotite-granite, and
locally, where the Kilba Hills rise out of the plain to
106 NORTHERN NIGERIA CHAP.

the west, the granite takes on an augenstructure.
In consequence of exfoliation (Plate VIII, Fig. 1)
most of these hills rise up as smooth bare rocks, but
some are made up of heaps of blocks, and it is not
possible to explain the contrast as due to a difference
in material. Between the hills around Holma and those
around Pella there is a plain of gneiss about fifteen
miles broad. The gneiss has been formed by the
injection of a micaceous gneiss or schist with
innumerable strings and veins of granite. The
exposures are excellent throughout, but the gneiss
never forms hills.

The country north of Pella is comparatively
uninteresting. It consists of an extensive plain with
isolated hills and rocks of biotite-granite. The nature
of the rocks underlying the plain is practically
unknown. The small area of the Kwaba Hills is
composed of biotite-granite with some quartz-
porphyry. (A. L.)

Crystalline rocks, largely of a gneissic character, are
exposed also in southern Bornu around Kwoia to the
east of the Gongola and along the base of the escarp-
ment on the north-western margin of the Burra volcanic
plateau. In eastern Bornu the granite rocks of Chibuk
and Kobshi are the first prominent outcrops of
crystalline rocks to the south of Maidugari. Barth,’
however, mentions an isolated granitic cone, Mt. Dela-
deba, to the N.N.E. of Isge, while Courtet,’ Gentil and
Freydenberg® note the occurrence of knobs of crystal-

1 Barth, Central Africa, 1857, Vol. I, p. 369.
2 Courtet, C. Rd. Ac. Sc., 140, p. 160.
3 Gentil and Freydenberg, Bud/. Soc. Geol. Fr. (4), VIII, 1908, p. 44.
I CRYSTALLINE ROCKS 107

line rock between Lake Chad and Lake Fittri. It is
highly probable indeed that the thick alluvial accumu-
lations to the east and south-east of Chad and in the
lower Shari valley rest for the most part upon a crys-

talline floor, provided with scattered relics of Tertiary
sandstone. (J. D. F.)
CHAPTER III

PETROGRAPHY OF THE GNEISSES AND SCHISTS AND
ASSOCIATED IGNEOUS INTRUSIONS.

Subdivision of the gneisses and schists ; predominant meridional strike.
Gneisses and schists of sedimentary origin ; variation in degree of
metamorphism ; phyllites and slaty schists ; green schists ; quartz-
ites ; quartz schists and granulitic gneisses ; crystalline limestones ;
micaceous and felspathic gneisses; calc silicate rocks; epidote
hornblende rocks ; magnetite and hzematite schists ; sheared trach-
ytes of Bussa ; altered dolerites of Ngashki ; amphibolites and talc
schists ; granulites. Petrography of the banded Archzan gneisses :
relationship of the two groups of gneisses. The gneisses and schists
of the Sahara and of West Africa. Age of the sedimentary gneisses.
Intrusive rocks : the older granites ; variation in degree of recon-
struction ; brecciation and injection structures ; the younger granites ;
aplitic and tourmaline-bearing granites and pegmatites ; tourmaline
quartz veins ; stanniferous pegmatites ; schorl rocks ; soda granites ;
biotite and riebeckite granites ; tinstone associated with soda granites ;
biotite and augite syenites ; augite diorites ; riebeckite quartz por-
phyries; zgirine granophyre; augite syenite iporphyries; alkali
syenite porphyries ; diorite porphyrites ; mica porphyrites ; horn-
blende porphyrites ; diabases and basalts. Granites and dyke rocks
of the Sahara. Age of the soda granites; successive periods of
intrusion.

THe GNEISSES AND SCHISTS.

For descriptive purposes it has been found convenient
to separate the crystalline rocks of the Protectorate into
two groups, (1) a group of quartzites, phyllites, schists,
and soft felspathic and micaceous gneisses, and (2) a
group of hard well-foliated, much granitised and fre-

108
CH. II THE GNEISSES AND SCHISTS 109

quently banded and contorted micaceous and _horn-
blendic gneisses. The first group occupies by far the
greater area within the Protectorate, and presents in
the west a well-marked alternation of belts in which
quartzites, phyllites and schists predominate, with belts
of which the prevailing members are felspathic and
micaceous gneisses. The second group has no definite
distribution within the Protectorate, but appears to
replace locally and irregularly the members of the
first group throughout the whole crystalline area. The
members of both groups appear to be irregularly folded
along axial planes, which are usually vertical or highly
inclined, but it is probable that detailed investigation
would reveal a regular system of major folds, ac-
companied by much local and minor crumpling. The
folding, which is typically meridional, has been affected
by equatorial stresses in such a way as to produce a
transverse twisting or corrugation of the predominant
strike. The result is that individual exposures may
vary in direction of strike from N.—S. to E.—W.,
while in places, as in Bauchi province, the strike
may become regionally equatorial. A similar equatorial
divergence of the prevalent meridional strike has been
noted by M. Hubert’ in eastern Dahomey, but his
suggestion that the equatorial direction becomes pre-
dominant in Borgu and the Niger valley has been
found to be unsupported by local evidence. It is im-
possible to believe, moreover, that there can be any
connection, as suggested by M. Chudeau,’ between

1 Hubert, Mission Scientifique au Dahomey, 1908, p. 448+
2 Chudeau, Sahara Soudanais, 1909, p. 18.
110 NORTHERN NIGERIA CHAP.

this locally divergent strike of the gneisses and the
distribution of the overlying Cretaceous and Eocene
rocks.

The sedimentary origin of the first group is fairly
certain. The pebbly quartzites, quartz schists, schistose
grits, mica schists, slaty schists and phyllites represent
corresponding varieties of sandstones, grits and shales,
and frequently exhibit traces of their sedimentary origin
in the deformed pebbles and clastic grains which they
contain. The granular felspathic and micaceous
gneisses on the other hand are more highly recon-
structed, and afford in themselves little or no evidence
of a clastic origin. Their constant association and
alternation with the quartzites and schists make it
probable, however, that they represent the arkoses and
greywackes of the original sedimentary series. Many
of the green hornblendic and epidotic beds probably
also represent original gritty accumulations of chloritic
and epidotic character, while the quartz magnetite
schists of eastern Kabba correspond to ferruginous
grits or gritty ironstones of sedimentary origin. The
fine-grained crystalline limestones of Igbo, and the
course granular marble between Jakura and Wa,
similarly represent original clastic calcareous rocks
within the sedimentary succession. To what extent the
recurrence of belts of quartzites, phyllites and schists
in the western part of the Protectorate represents the
repetition of one or more belts is quite unknown. The
phyllites and schists are moreover everywhere un-
fossiliferous and the age of the original sedimentary
rocks is consequently undetermined. The foliation of
ll THE GNEISSES AND SCHISTS IIl

the reconstructed rocks is, as a rule, parallel with the
bedding, but the more micaceous schists frequently
show a more or less well-defined and oblique strain-slip
corrugation.

The alternation of belts of less and more highly
metamorphosed rocks in the west of the Protectorate
coincides to some extent with an alternation of belts
in which shear structures predominate, with belts in
which reconstruction is prevalent. The various
belts appear to pass insensibly into each other, but it
has been found impossible in the course of a rapid
survey to decide either to what extent shearing may
have everywhere preceded reconstruction, or to what
extent the varying degree of reconstruction in alternate
belts may represent a corresponding variation in the
intensity of the accompanying folding. All that can
be said with certainty is that the sedimentary series
as a whole has been subjected to a highly complex
folding accompanied by much shearing and reconstruc-
tion, and that while over the greater part of the
Protectorate the stresses have been for the most part
relieved by, or translated into, a molecular and
mineralogical rearrangement, there are certain belts in
which relief has been primarily obtained by mechanical
readjustment or shearing. Moreover, as in the re-
constructed areas there are certain beds which appear
to be more coarsely crystalline and less distinctly
foliated than others, so in the shear belts there are
certain beds which have assumed the character of
granulitic gneisses, while others in the immediate
neighbourhood have retained to a very large extent
112 NORTHERN NIGERIA CHAP.

their original clastic and gritty character. Most of
the reconstructed gneisses exhibit under the micro-
scope faint strain phenomena which, with the incipient
strain-slip foliation of the more micaceous schists, are
probably to be ascribed to regional stresses affecting
the whole series after the period of maximum recon-
struction.

Grey and purple sericitic phyllites with knots of
magnetite and pyrites are extensively developed in the
neighbourhood of Ngashki in the Niger valley, around
Anka and Bukwium on the borders of Sokoto and
Kontagora, and in the Zungeru belt in eastern Zaria
from Kato to Birnin Gwari and Koriga. In Kabba
and Nassarawa and southern Zaria their place is
taken by fine-grained quartz muscovite schists with
abundant magnetite. With the phyllites are associated
in the Niger valley and Sokoto province green
quartzose slaty schists (1195, 1325),' whose colouration
is due to recrystallised chloritic and hornblendic
material. Mr. Parkinson® has described similar slaty
schists from Southern Nigeria, In the neighbourhood
of Zungeru these green schists become softer and
show under the microscope (1563—4) ragged porous
or fibrous crystals and crystal aggregates of re-
constructed hornblende in a matrix of granulitic
quartz, felspar and magnetite, which encloses also
scattered grains of hornblende, biotite, chlorite and
epidote, as well as relics of original clastic grains of

1 The numbers in brackets refer to microscopic preparations in the
Imperial Institute Collection, NN.F.
2 Parkinson, Q./. G. S., Vol. LXIII, p. 315.
It THE GNEISSES AND SCHISTS 113

quartz and felspar. These rocks present a consider-
able resemblance to the ‘“‘ green beds” of the Scottish
Highlands.’ True quartzites are comparatively rare
and only at Kazaure do pure siliceous rocks attain any
extensive development. Elsewhere the rocks which
present the characteristic appearance of quartzite in
the field are usually more or less felspathic and
micaceous, and include schistose grits, micaceous
quartzites, quartz muscovite schists and granulitic
gneisses which show all the familiar stages in the
deformation of felspathic grits and sandstones. Some
of the white and pink granulitic gneisses, such as those
of Zungeru, may, however, be ultimatety proved to
have been originally of an eruptive character. A
characteristic feature of these rocks is the development
of tourmaline and sometimes of pyrites along the shear
and foliation planes as the result of later pneumatolytic
action. At Kuta a belt of coarse quartz muscovite
schist contains abundant sillimanite in sheaf-like
aggregates.

Mica schists in which biotite predominates are
common throughout and frequently carry garnet,
magnetite and staurolite in conspicuous crystals. In
the Igbo limestones the original impurities have re-
crystallised as tremolite, diopside, scapolite (122),
sphene, biotite, felspar, quartz and pyrites, while the
streaks of silicates in the limestone between Jakura
and Wa contain diopside, epidote, idocrase, felspar,
and quartz. In the latter limestone also, scales o1
graphite are common throughout and pyrites on the

1 Mem. Geol. Sur. Scotland, Expl. of Sheet 55, 1905, p. 13.
I
Tig NORTHERN NIGERIA CHAP,

margin. Amongst the reconstructed gneisses, which
show a remarkable and rapid variation in texture, the
paler-coloured felspathic rocks are usually rich in
orthoclase and microcline, and occasionally muscovite,
while the darker-coloured varieties, in which biotite
predominates, frequently carry garnet, sillimanite,
staurolite and in places also sphene, tremolite and
carbonates. Andalusite-bearing rocks are known from
certain localities, but kyanite gneisses and schists
have not been definitely recognised in place. The
local occurrence of kyanite on the river sands, how-
ever, points to its presence within the neighbouring
rocks. Calc silicate types are represented by the
tremolite schists of the Nassarawa tableland (668,
689), by a diopside tremolite schist from Borgu (1221),
a diopside and wollastonite-bearing rock with sphene
from Maibirro in the Niger valley (1192), a biotite
tremolite schist with calcite from Olle in northern
Kabba (879), and a diopside and scapolite-bearing
rock with sphene and green spinel from Atuka, near
Okuruku, in eastern Kabba (843). The epidote
hornblende gneisses of Boi in southern Bauchi (976)
contain much diopside and sphene, and are probably
of sedimentary origin, while relics of clastic felspar are
common in an epidote rock from Goshin Duchi a few
miles east of Boi (983). A similar clastic origin is
presumed for many of the epidosites and epidote
hornblende rocks associated with the sedimentary
gneisses in other parts of the Protectorate. The
quartz magnetite and quartz hematite schists include
coarse granular and fine-grained granulitic types (844,
UI THE GNEISSES AND SCHISTS 115

1370), the latter presenting considerable resemblance
to the itabirites of the United States. Their sedi-
mentary origin is presumed throughout and only in
the case of the massive quartz magnetite rock of
Okuruku (148), which is associated with a magnetite-
bearing epidiorite, is there any probability of an
igneous origin.

Two stages of alteration can be recognised among
the sheared trachytes of Bussa (p. 72). The least
altered types (1164, 1167) show fracturing of the
phenocrysts of felspar and the replacement of the
original ferro-magnesian minerals by fibrous uralite,
chlorite, epidote and calcite. The more altered types
(1166) are characterised by the production of abundant
white mica in the ground-mass and the development of
biotite, magnetite and carbonates from the original
ferro-magnesian material. Original vesicles of quartz
and calcite in these rocks have been deformed and the
quartz replaced by a mosaic of angular grains. A
sheared quartz-porphyry from Kanikoko (1206)
exhibits deformation and granulation of the pheno-
crysts of quartz and felspar and the abundant develop-
ment of white mica in the ground-mass. In the
altered dolerites of Ngashki (1175, 1176) the original
structures are almost entirely obscured by the extensive
production of granular epidote, calcite, uralite, chlorite,
magnetite, felspar and quartz. Knots of tourmaline
are common in these altered rocks. The types
grouped as amphibolites range from epidiorites to
hornblende schists and amongst them may be recog-
nised all the familar stages of saussuritisation and

[2
116 NORTHERN NIGERIA CHAP.

recrystallisation of original tonalitic, dioritic and
diabasic rocks.

It is probable, however, that amongst the amphibolites
are included rocks which were intruded at many different
periods during the metamorphism of the gneisses
and that to difference of age as well as to local
intensification of the metamorphism is to be ascribed
the variable degree of construction which the rocks
have severally undergone. The chlorite and _ talc
schists are to be regarded as basic intrusions which
had suffered considerable decomposition before being
subjected to metamorphism.

Amongst highly reconstructed rocks of doubtful
derivation, associated with the sedimentary gneisses,
are a garnetiferous quartz enstatite biotite granulite
from Atuka near Okuruku in southern Kabba (841)
and a garnet granulite from the adjoining village of
Kuturu (168) composed of labradorite, quartz and
garnet with a distinct centric structure. The garnet is
in spongy masses associated with a small quantity of
green pyroxene, sphene, apatite and iron ore. A
pyroxene granulite, from Againyi (823), consists of a
porous intergrowth of pale green pyroxene and green
hornblende, the former predominating, in a matrix of
clear labradorite. Sphene and ilmenite are also present
in irregular intergrowths as well as a little accessory
epidote and apatite. Another variety (832) contains
no amphibole and consists of pale green pyroxene and
garnet in a matrix of labradorite and quartz. A third
type from the same locality (821) is an epidote granu-
lite consisting of predominant epidote and garnet with
III THE GNEISSES AND SCHISTS 117

subordinate green pyroxene, sphene and ilmenite in a
matrix of labradorite. A pyroxene granulite from
Nassarawa province (854) shows ragged crystals of
diallage with quartz inclusions and rounded garnets
with inclusions of both quartz and diallage in a matrix
of coarsely granular quartz. A hornblende granulite
from the same province (859) consists of rounded
spongy garnets and radiate groups of actinolite fibres
with a little accessory ilmenite in a typical fine-grained
quartzo-felspathic mosaic. A remarkable biotite granu-
lite from Eri in eastern Ilorin (1056) contains in
addition to biotite and granular garnet as the pre-
dominate ingredients much sillimanite, staurolite and
andalusite in a matrix of untwinned felspar and quartz.

The harder gneisses of the second group are
subordinate in amount and irregularly distributed
throughout the micaceous and felspathic gneisses of
the first group. They consist of a series of much
granitised medium and even-grained biotitic and horn-
blendic gneisses which usually show a lenticular or
linear foliation but frequently also a ribboned or
banded and contorted character. In some cases the
banding is broad and only to be distinguished in the
field, while hand specimens present quite a homo-
geneous character. All variations may be found
between acid aplitic and basic hornblendic bands, and
knots and lenticular masses of more basic material are
common within the more acid types. As a rule the
banding is much interrupted by pale coloured granitic
material into which the lighter coloured bands seem to
pass imperceptibly. A striking feature is the presence
118 NORTHERN NIGERIA CHAP.

of a series of early pegmatite veins folded and foliated
with the gneisses. There is in fact every indication
that these banded rocks are of a primarily composite
character and represent either an originally sedi-
mentary or a differentiated igneous succession invaded
and injected by acid granitic material and pegmatite
veins in the deeper portions of the crust and subse-
quently subjected to a later folding, foliation and
recrystallisation. The foliation is in general vertical
and parallel with the banding. Under the microscope
the striated and banded gneisses exhibit all the
characteristic features of typical archzan rocks
(801, 846). They are composed of a granular
aggregate of quartz, felspar, hornblende or biotite with
sphene, apatite and iron ores as accessories. The
felspars are usually allotriomorphic and vary from
labradorite in the more basic to orthoclase and
microcline in the more acid rocks. The biotite occurs
in tabular flakes singly or in aggregates with the basal
plane well-developed but with ragged margins in the
prism zone, while the hornblende forms spongy
growths or irregular plates with embayed margins and
inclusions of quartz. Strain shadows are common in
the quartz and felspar but only traces of cataclastic
granulisation or of secondary micropegmatite are as a
rule recognisable. Van Hise is of opinion that the
strain phenomena and the vermicular quartz to be
observed in these thoroughly reconstituted gneisses are
due to the partial lagging of reconstruction behind
deformation. It is equally probable, however, that the

1 Van Hise, 7reattse on Metamorphism, 1904, p. 696.
Iq THE GNEISSES AND SCHISTS 11g

strain effects and micropegmatitic structures have
been induced after the period of maximum recon-
struction by later strains of lesser magnitude.

The mutual relations of the two groups of gneisses
are difficult todetermine. The actual contact between
the two has nowhere been found clearly exposed and
its character must therefore be to a certain extent
conjectural. The apparent irregular replacement of
the softer gneisses by members of the harder group
when traversed across the strike and the apparent
extension into the softer gneisses of tongue-like
masses from the larger areas of harder rock is
certainly suggestive of an intrusive character as
advocated by Mr. Parkinson*in Southern Nigeria and
Liberia. Upon this hypothesis the harder gneisses
would appear to correspond to an intimate mixture of
granitic and dioritic material, whose intrusion took
place during the folding and reconstruction of the
sedimentary gneisses. It is difficult, however, to
understand why these rocks should present in their
even-grained and closely foliated and banded character
such an entirely different aspect in the field from that
of even the earliest recognisable granitic intrusions
within the sedimentary gneisses and why they alone
should possess an early set of folded and foliated
pegmatite veins in addition to the later pegmatites
which are common to both groups of gneisses. All
the phenomena indeed are more readily explicable on
the assumption that the two groups differ in age, that

1 Parkinson, Q. J. G. S., Vol. LXIII, 1907, p. 308; Vol. LXIV, 1908,
Pp. 313.
120 NORTHERN NIGERIA CHAP.

the sedimentary gneisses were originally deposited
unconformably upon an earlier and probably archazan
gneissic or igneous complex and that the latter series
was refoliated and recrystallised during the recon-
struction of the former. The peculiar distribution of
the harder gneisses and their intimate alternation with
the softer series would then be due in part to the
original unconformability between the two groups and
in part to the irregular character and the varying
amplitude of the later folding to which both were
subjected. The abrupt replacement of the sheared
but little altered quartzites of the Niger valley by the
harder gneisses at Jebba, Wuru and Maibirro
probably indicates also a certain amount of faulting
and thrusting accompanying the folding. On account
of the subordinate and ill-defined character of the
distribution of the harder rocks no attempt has been
made to distinguish upon the map between the
archzean and the later sedimentary gneisses.

In the Sahara to the north, M. Chudeau! has
described the occurrence of archzan and sedimentary
gneisses whose mutual relations are similar to those
which prevail in Northern Nigeria. The archzan
areas are of comparatively small extent, and are
primarily distinguished, according to M. Chudeau, by
the presence of numerous domes and turtlebacks of
granite. This method of distinguishing between the
two groups, however, cannot be applied in Nigeria,
where intrusive granites are equally common amongst
both the earlier and the later gneisses. The meta-

! Chudeau, Sak. Soud., p. 2.
PLATE IX

 

yaaa here

aeRO NS

 

te

 

 

ON THE SUMMIT OF THE BAUCHI PLATEAU.

The Parade Ground at Bukuru.

 

 

ON THE PLATEAU LOOKING WESTWARD FROM BUKURU.
UI THE GNEISSES AND SCHISTS 121

morphic rocks of sedimentary origin attain a great
development in the Sahara’ and include quartzites,
phyllites, schists, gneisses and crystalline limestone
similar in type to those of Nigeria, and folded in a
similar complex manner along axes whose direction is
predominantly meridional. The decrease northward of
the intensity of the metamorphism, as advocated by
M. Chudeau, requires much further investigation in
view of the local occurrence of little altered rocks
within the Protectorate. M. Chudeau believes in the
original unconformability of the later gneisses upon
the archzean and points out, with M. Haug,’ the
analogy between the system of folding of the gneisses
of the Sahara and the Sudan, and the Caledonian
folding of the crystalline rocks of Scotland and
Scandinavia. He demonstrates the pre-Devonian age
of the sedimentary gneisses, and assigns them
provisionally to the Silurian on the strength of their
supposed continuity with the graptolite-bearing shales
of Tindesset* and Hassi el Kheneg.* The strati-
graphical evidence available, however, seems rather to
point to an unconformability between the shales and
the schists, and M. Flamand’ prefers to assign a pre-
Cambrian age to the whole series of crystalline schists
and gneisses.

In Dahomey, M. Hubert® has described a similar

1 Gentil in Doc. Sc. Miss. Sah., 1905, p. 721.

2 Haug, C. Rd. Ac. Sc.,7 Aug., 1905.

3 Haug in Doc. Sc. Miss. Sah., 1905, P- 753-

4 Flamand, C. Rd. Ac. Sc., 140, p. 954.

5 Flamand in Voinot, Budi. Com. Afr. Fr., 1908, p. 218.
6 Hubert, C. Rd. Ac. Sc., 146, 3 Feb., 1908 ; Miss. Sc. au Dahomey,

1908, p. 253.
122 NORTHERN NIGERIA CHAP.

complex of archzean and sedimentary gneisses in which
the latter clearly predominate. His separation as
Silurian of the quartzites and schists of Atacora from
the other metamorphic rocks appears, however, to be
unjustifiable. Quartzites, gneisses and schists of sedi-
mentary origin associated with granites and archean
rocks, are found also in West Africa, in French Guinea
and the Fouta Djalon,’ in Liberia,’ the Ivory Coast,’ the
Gold Coast,* Togoland,’ and Southern Nigeria,’ and
in Central Africa to the south and south-east of Chad,’
in the Kameruns,* and in the French Congo.’ Similar
rocks attain also a remarkable development to the
south of the equator.”

The comparision which M. Chudeau has drawn
between the strike of the gneisses and schists of the
Sudan on the one hand, and of the Scottish Highlands
on the other, may be further extended not only to the
petrographical character of the constituent groups of
the gneissic complex in West Africa, but also to the
respective relations of the various groups to each other,
and to the intrusive rocks which they enclose." Dr.

1 Chautard, Le Fouta Djalon, 1905.

2 Parkinson, Q. J. G. S., 1908, LXIV, p. 313.

3 Chevalier, Za G., XVII, 1908, p. 201.

* Lenz, G. M., 1877, p. 27; Knox, Geology of Africa, 1905, p. 93.

§ Von ‘Ammon, Geologie von Togo, M.H. Geog. Gessell. Miin., 1903,
I, p. 393.

6 Parkinson, Q. 7. G. S., 1907, LXIII, p. 308.

7 Courtet in Chevalier, L’A/r. Cent. Fr., 1908, p. 646.

8 Passarge, Adamaua, 1895, p. 312; Esch, Geol. von Kameruns, 1904,
p. 23.

9 Barratt, Ann. des Mines, VII, 1895.

10 Cf. Horwood and Wade, G. J, V, 6, 1909, p. 455.

u “The Geology of the North-West Highlands of Scotland,” Mem.
Geol. Sur., 1907, pp. 75, 214, 595, 607.
HI THE INTRUSIVE ROCKS 123

Voit’ has, moreover, arrived at similar conclusions in
the course of his investigation into the structure of the
crystalline complex of the northern Transvaal, the
constitution and mutual relationships of the Swaziland
system and the older granites and gneisses being closely
paralleled in the rocks of Nigeria.

Tue Intrusive Rocks.

Many of the thin bands of well-foliated augen and
granitoid gneiss enclosed within the metamorphic
series undoubtedly represent original granitic intrusions,
but these are so intimately bound up with the adjoin-
ing gneisses and schists, that no discrimination can yet
be attempted. Attention has been more particularly
directed in the field to those granitoid rocks which
form the prominent inselberge and isolated groups of
hills, and amongst them it has been found possible to
distinguish an older froma younger series of intrusions.
The older intrusive rocks consist very largely of granite,
while the younger intrusions include granitic, syenitic
and diabasic types with numerous associated dyke
rocks. To what extent the epidorites, amphibolites,
and granulites of the gneissic series represent more
basic intrusions associated with the older granites is
quite unknown.

(a.) The older Granites.

The older granites are never sharply marked off from
the adjoining gneisses, and invariably show a certain

1 Voit, Trans. Geol. Soc. S.A., 1905, VIII, pp. 106, 141.
124 NORTHERN NIGERIA CHAP.

amount of foliation in the field, and of cataclastic
deformation and reconstruction under the microscope.
They appear to have been intruded at different times
within the period of the evolution of the gneisses, and
the amount of reconstruction which they themselves
have undergone may be taken as a general indication
of their age. Vermicular micropegmatite is most
extensively developed in those schistose granites
which have stopped short of complete reconstruction
and which still afford abundant evidence of cataclastic
deformation. It may also occur, however, in small
amount in thoroughly foliated and _ reconstructed
granites, in which it is assumed to have been
developed, as in the case of the banded and striated
gneisses (p. 118), by minor crustal strains, after the
period of maximum reconstruction.

The most highly altered types form extensive
lenticular or phacolitic masses of well-foliated and
fairly coarse-grained biotitic and hornblendic gneisses
(849, 481), containing streaks and patches of darker-
coloured and finer-grained basic material. Under the
microscope they possess a coarsely granular and
thoroughly reconstructed character, and in the mutual
relations of their constituents present a considerable
resemblance to the banded gneisses of similar com-
position. The quartz and felspar show much later
straining with incipient granulisation and traces of
micropegmatite. These rocks have participated in all
the changes which the adjoining gneisses have under-
gone, and were apparently intruded before the period
of maximum reconstruction of the latter.
ur THE INTRUSIVE ROCKS 125

The least altered of the older granites (806, 1560)
are typically distinguished by the irregular batholitic
character of the intrusions and the partial and fre-
quently only marginal character of the foliation. They
sometimes have a tendency to become finer-grained
towards their junction with the gneisses, and they
usually enclose portions of the adjoining rocks and
vein and inject with granitic material the marginal
gneisses and schists. The inclusions may be of either
the harder or softer gneisses according to the character
of the rocks which the granite has invaded. In places
a parallel arrangement of the felspars appears to have
been induced through streaming during crystallisation.
The partial foliation is parallel in a general way with
that of the surrounding gneisses and schists. The
granites vary much in character from biotitic and horn-
blendic rocks with syenitic modifications to muscovite
and microcline granites and aplites. The quartz and
felspar are strained throughout and cataclastic granu-
litisation is common on the margins of the crystals.
Vermicular quartz is most abundant in the marginal
and more distinctly foliated portions. These rocks
would appear to have been intruded after the period
of maximum reconstruction of the gneisses, but before
the final cessation of stress and strain. In places, as
at Abuja, crush lines cross the granites, and in their
immediate neighbourhood the rocks show a higher
degree of reconstruction and a greater development of
micropegmatite in the matrix.

These later members of the older granites appear to
have produced little or no contact metamorphism in
126 NORTHERN NIGERIA CHAP.

the surrounding rocks. Brecciation and injection
structures on the other hand are very frequent. The
hard banded gneisses on the margin of the Abuja
granite, for example, are abundantly injected with
quartz and quartzo-felspathic material. Similarly at
Zwoll, in Bauchi province, a porphyritic biotite
granite has brecciated a series of banded and contorted
biotite and hornblende gneisses, and many of the en-
closed fragments are partially absorbed or minutely
injected with granitic material. The Okuruku granite
in southern Kabba, on the other hand, has invaded and
brecciated members of both the harder gneisses and
the softer series of biotite schists, magnetite schists
and amphibolites. In the neighbourhood of the in-
clusions the granite becomes knotted and richer in
biotite, hornblende, sphene and other minerals, while
the inclusions themselves are irregularly veined and
minutely penetrated by quartzo-felspathic material.
In every case it would appear that the rocks, which
the granites have brecciated and invaded, possessed
their gneissic or schistose character before the actual
intrusion of the granites, and that they, as well as the
larger inclusions, suffered little further change as the
result of the stresses and strains which brought about
the partial foliation of the granites. The gneisses as
a whole show strain phenomena, but only traces of
granulitisation and of secondary formation of micro-
pegmatite, while the granites show extensive marginal
formation of micropegmatite, together with intense
cataclastic deformation. It would seem indeed that these
granites were intruded after the period of maximum re-
11 THE INTRUSIVE ROCKS 127

construction of the gneisses, but before the final cessation
of stress and strain, and that while the gneisses which
had originated under conditions of maximum strain were
comparatively stable under similar strains of diminish-
ing intensity, the granites which had crystallised from
igneous fusion were in a condition of unstable equi-
librium with respect to the stresses and strains to
which they were subjected after crystallisation. The
gneisses, as it were, possessed a certain amount of
elasticity and transmitted the later strains with little
resultant deformation, while the rigid masses of granite
arrested those strains and suffered in consequence a
partial deformation. The production of a strain-slip
foliation in some of the more micaceous beds is
probably to be referred to the same period of differential
deformation of the granites. These later strains be-
came locally intensified along crush lines, and in the
case of the Abuja granite produced granulitisation
both of the granite and of the felspathised gneisses in
the neighbourhood of the crush line.

In addition to the two extreme types of the older
granites there are many elliptical masses of similar
material, elongated in a direction parallel with the
strike of the gneisses, which show a decided foliation
throughout, sometimes more and sometimes less intense
(48, 1223). Asa rule they are indistinctly marked off
from the adjoining rocks and preserve their normal
texture up to the margin of the intrusion. The
granites are predominantly biotite granites, more rarely
muscovite biotite granites, and the felspars are
frequently porphyritic. Under the microscope they
128 NORTHERN NIGERIA CHAP.

show a higher degree of reconstruction than the least
altered granites, but a less complete reconstitution than
the most highly altered types. The felspars vary from
oligoclase to microcline, and the plagioclases often show
basic interiors and zoned margins. Both the felspar
and the quartz show abundant strain phenomena, and
the felspars are usually partially surrounded by a
secondary fringe of vermiculate micropegmatite in
optically discontinuous grains. Frequently also the
felspars are corroded or irregularly penetrated by quartz
or micropegmatite, while the matrix consists largely ot
granular and partially recrystallised felspar, muscovite,
microcline and quartz. The darker patches within
these granites may be taken to represent portions of
the adjoining rocks caught up during intrusion and
partially absorbed, recrystallised and foliated with the
granites. These rocks may possibly be correlated in
the period of their intrusion with the least altered
granites and regarded as the smaller and therefore
more readily reconstructed representatives of the
larger partially foliated masses. On the other hand, in
the absence of the inclusions of adjoining gneisses
which form the characteristic feature of the least
altered granites, it is possible to regard them as of some-
what earlier origin and as having participated to a
considerable extent in the general reconstruction of the
gneisses themselves.

It seems probable indeed that the crustal movements
which brought about the metamorphism of the gneisses
were of a somewhat spasmodic character and spread
over a very considerable interval of time and that the
I THE INTRUSIVE ROCKS 129

intrusion of granitic and other igneous material took
place at intervals throughout the whole period. No
hard and fast line can therefore be drawn between the
highly reconstructed and gneissose granites and the
imperfectly or only partially foliated types, a complete
series of intermediate varieties being apparently
possible between the two extreme members of the
series.

(6) The Younger Intrusions.

1. Granites and pegmatites.

Amongst the later granites, which present for the
most part a batholitic habit, two types may be dis-
tinguished, differing in mineralogical composition and
probably also to some extent in age. The rocks of
the first type never show chilled margins, and were
evidently intruded while the adjoining gneisses still
possessed a comparatively high temperature. They
include non-foliated aplitic granites and pegmatites
usually rich in muscovite and tourmaline. The second
type includes riebeckite and biotite granites which are
sharply marked off from the adjoining rocks by felsitic
and fine-grained margins. The rocks of the first type
usually exhibit under the microscope a faint straining
of the quartz and felspar and were probably intruded
before the final cessation of the crustal movements
to which the reconstruction of the gneisses and the
foliation of the earlier granites were due. The
members of the second type, on the other hand,
are practically free from cataclastic phenomena and
evidently assumed their present position after the

K
130 NORTHERN NIGERIA CHAP.

cessation of movement within the crust. There is
no reason, however, to assume any great difference
in age between the two types or any marked discon-
tinuity in magmatic conditions. The same magma, of
a somewhat acid and alkaline character, was probably
present in the depths throughout the whole period of
intrusion, and the varying character of the products
may be taken as affording some clue to the nature ot
the differentiation within the magma itself.

The alkaline granites of the first type are pale-
coloured granular rocks composed almost entirely of
quartz, microcline, orthoclase, perthite, and acid plagio-
clase. Biotite and other ferro-magnesian minerals are
comparatively rare, while muscovite and tourmaline
are frequently abundant and in large primary crystals.
The quartz and felspar have a tendency to pegmatitic
intergrowth, and sometimes masses of graphic pegmat-
ite occur porphyritically in a normal quartzo-felspathic
matrix. The tourmaline and muscovite may occur
also as at Igbo in two generations, in large crystals and
in the ground mass. Frequently also these granites
possess a tendency to a coarsely banded structure, the
banding being due either to variation in size of grain
of the quartz and felspar or to variation in the abund-
ance of tourmaline and muscovite in successive bands.
These granites rarely form intrusions of any size, the
largest known being the tourmaline granites of Igbo
and Darroro, but even they are insignificant in com-
parison with the alkaline granites of the second type.

The pegmatite dykes and veins which are so abund-
ant throughout the gneissic series evidently belong to
I THE INTRUSIVE ROCKS 131

the same period of intrusion. Like the aplitic and
tourmaline-bearing granites they never exhibit fine-
grained margins at their junction with the gneisses.
They vary much in composition, and include graphic
granites, quartz-felspar pegmatites with biotite, mag-
netite or ilmenite, quartz-felspar pegmatites with
muscovite or tourmaline or both, and quartz-muscovite
pegmatites with or without tourmaline. At Eri there
are stanniferous pegmatites carrying quartz, muscovite
and cassiterite, but no tourmaline. The massive quartz-
reefs which frequently enclose portions of the surround-
ing schists and carry tourmaline, pyrites and sometimes
gold, are also to be referred to the same period of
intrusion. Inseparable from them and from the peg-
matites are the smaller veins of quartz and tourmaline
quartz and the schorl rocks of a foliated or striated
character which occur as a rule in association with the
veins of tourmaline quartz! The schorl rocks with
a gneissic habit in which the quartz is minutely granu-
litic and the tourmaline is in small crystals evidently
recrystallised and full of quartz inclusions, are probably
altered gneisses and schistose granites in which the
felspars have been replaced by quartz and tourmaline.
Traces of decomposed felspathic material are to be found
in every specimen, but no pseudomorphs in tourma-
line of felspar or of other minerals have been definitely
recognised. The striated schorl rocks in which the
darker bands are formed of finely fibrous tourmaline,
appear to arise also as modifications of the adjoining

1 Cf. Flett, “ Geology of Land’s End District,” Mem. Geol. Sur. Eng.
1907, P- 25.

K 2
139 NORTHERN NIGERIA CHAP.

rocks in the vicinity of the tourmaline quartz veins.
Sometimes a foliated rock may be traced through a
striated type into a massive tourmaline rock on the
margin of the vein in which the original structures
have entirely disappeared, and in which the original
minerals, including the quartz, have been entirely
replaced by finely fibrous tourmaline. In the quartz
veins, pegmatites and granites, on the other hand, the
tourmaline is in well-formed crystals of primary origin.
It would seem, therefore, that the pneumatolytic or
metasomatic formation of the schorl rocks was brought
about by emanations from the quartz veins and peg-
matites before the final consolidation of the latter.
The extensive development of tourmaline and pyrites
in the quartzites and schists of certain areas is also to
be ascribed to the circulation of mineralising vapours
and solutions throughout the adjoining rocks during
the same period. The remarkable absence of tin-
stone in the tourmaline pegmatites, together with its
appearance in pegmatites at Eri which do not carry
tourmaline, seems to point to the stanniferous peg-
matites having originated at a somewhat later date
than the normal tourmaline-bearing pegmatites. This
suggestion is supported by the occurrence of tinstone in
association with the soda granites of Bauchi province.

The alkaline granites of the second type are typically
distinguished by possessing fine-grained porphyritic
and felsitic margins which indicaté a considerable
difference in temperature between the granites and the
surrounding gneisses at the period of intrusion. To
this group are referred the biotite granite of the
m1 THE INTRUSIVE ROCKS 133

Anagoda hills in S. Nassarawa, the riebeckite granite
of the Gurkawa Hills in northern Muri, the biotite
granite of Bukuru and Negell, and the riebeckite
granites of the Kwandokaya Hills and of the Ningi-
Burra massif in Bauchi province, the riebeckite granite
of Fagam, Gadama and Galambi on the borders of
Bauchi and Kano, the riebeckite granite of Shira in
the sub-province of Katagum, and probably also the
Kailema granite near Jebba and the biotite granite of
Abara near Ngashki in western Kontagora. The
alkaline character of the original magma is reflected in
the nature both of the felspars and of the ferro-magne-
sians. The felspars are much kaolinised and consist
chiefly of tabular crystals of untwinned orthoclase
probably rich in soda, and of streaky perthitic inter-
growths of orthoclase and albite. Where enclosed in
quartz, the terminations of the crystals are frequently
idiomorphic. Microlites of riebeckite are common
inclusions and small plagioclases of an earlier growth
are frequently enclosed in the later felspars and in the
quartz. The quartz forms aggregates of irregular
grains showing faint strain shadows and has a great
tendency to form coarsely pegmatitic intergrowths with
the felspar. Where biotite alone is present, it is of a
normal greenish-brown colour. Riebeckite, however,
is the most characteristic ferro-magnesian, and occurs
for the most part in irregular plates moulded on the
felspars and sometimes enclosing small crystals of
felspar in poikilitic fashion. Occasionally, as in the
Shira granite, the riebeckite builds elongated crystals
more or less idiomorphic in the prism zone and
134 NORTHERN NIGERIA CHAP.

frequently intergrown with aegirine. Crystals of rie-
beckite over an inch in length are common in knots in
the Kila granite, while on the other hand the margin of
the Gurkawa granite is stippled with minute porous
crystals of the same mineral. Associated with the,
riebeckite in places are other blue and brown soda
amphiboles’ as well as green aegirine and a golden-
coloured mica, while zircon, apatite and iron ores are
constant but scanty accessories. Pyrites is sometimes
abundant in the porphyritic and felsitic marginal
rocks.

A remarkable feature of some of these later granites
is the occurrence in them of tinstone and numerous
sulphide ores. It would appear that in places these
later granites have been broken and fissured, and that
along these fissures vapours and solutions have risen
which have chloritised and mineralised the adjoining
rock and in part refilled the fissures with ore-bearing
pegmatite and vein stuff. In the Bukuru granite the
cassiterite is associated in the neighbourhood of Ngell
with pyrites, chalcopyrite, tetrahedrite, blende and
galena. Topaz and brown zircon are found accom-
panying the cassiterite in the tin-bearing alluvium at
Naraguta and elsewhere, and are probably also of pneu-
matolytic origin. The granites of the Kwandokaya
hills, of the Jengre and Limoro hills, of the Ningi-
Burra massif, and of the Gadama and Fagam hills also
yield in places a tin-bearing drift, and have probably
suffered, like the granite of Bukuru, a local fissuring

1 Cf Gentil et Freydenberg, Bull. Soc. Geol. Fr., 4th Ser., VIIL.,
1908, p. 44.
PLATE X

 

 

A WoRN VoLcaAnic HILL ON THE BAUCHI PLATEAU NEAR ZAMAGAN.

 

 

 

THE TWIN CONES OF KERENG FROM PANYAM
III THE INTRUSIVE ROCKS 135

and mineralisation. Tourmaline has not been defi-
nitely recognised as a product of these later emana-
tions.

Similar soda granites with microgranitic and felsitic
margins have been described by MM. Foureau, Gentil
and Lacroix’ from Zinder, by M.Chudeau ? from Mounio
and Goure, by M. Garde* from Machina and by M.
Hubert * from Dahomey, while Captain Freydenberg °
has noted the occurrence of a soda syenite with granitic
modifications at Melfi to the south-east of Chad.

2. Syenztes and Diorites

These rocks, which are by no means abundant, occur
as small bosses or intrusive masses within the gneisses
and schists. As a rule their junction with the sur-
rounding rocks is not exposed, and their relationship to
the later granites has not been definitely ascertained.
They should probably be regarded, however, as some-
what basic modifications or differentiation products of
the later granitic magma. Slight strain effects are
usually apparent in the quartz and felspar.

The low hills around the town of Bauchi are composed
of a coarse-grained augite syenite, in which orthoclase
felspar predominates in large twinned crystals with a

1 Gentil, C. Rd. Ac. Sc., 8 Aug., 1904; Foureau and Gentil, C. Rd. Ac.
Sc. 2 Jan. 1905 ; Lacroix, C. Rd. Ac. Sc. 1 May, 1905 ; Gentil, Doc. Sc.
Miss. Sah. 1905, p. 697-

2 Chudeau, Sak. Soud. 1909, p. 265 ; C. Ra. Ac. Sc. 1 July, 1907.

3 Garde, C. Rd. Ac. Sc. 149, 5 July, 1909, p. 43.

4 Hubert, C. Rd. Ac. Sc. 145, 1907, p. 764. ;

5 Freydenberg, Chad et Shari, 1908, p. 107; Gentil et Freydenberg,
Bull. Soc. Geol. Fr. {4), VIL, 1908, p. 44.
136 NORTHERN NIGERIA CHAP.

peculiar brownish tint and a resinous lustre. Under
the microscope (49) subordinate oligoclase is present
in smaller crystals, while the knots of darker minerals
are composed of intergrowths of violet-coloured augite,
green hornblende, brown biotite and iron ores. Quartz
is interstitial and occurs also in secondary vermicular
growths on the margins of the felspars. The accessories
are zircon and apatite, and the whole rock is much stained
with secondary limonite. A rock of similar appearance
from Kende to the east of Bauchi (69) is somewhat
more basic and may be termed a quartz augite-diorite.
The predominant felspar is a basic andesine, while the
ferro-magnesians are pale-coloured augite and green
hornblende in irregular plates and intergrowths. The
quartz is interstitial or intergrown with the felspar in
pegmatitic fashion. A similar rock from Kanna (1677)
contains much biotite in addition to the augite and
hornblende. The rock of Kogon Dutsi (1338) within
the walls of Kano is a basic augite diorite without
quartz, consisting predominantly of acid labradorite and
pale-coloured augite. Both the augite and felspar
have a tendency to schillerisation and the augite is
accompanied by, and in part intergrown with, green
hornblende, brown biotite and iron ores, while hypers-
thene is a scanty accessory. An augite-diorite from
eastern Kontagora (1302) contains a little interstitial
quartz and felspars varying from oligoclase to acid
labradorite. The ferro-magnesian minerals are much

intergrown and include pale-coloured augite, green
hornblende and brown biotite.
ur THE INTRUSIVE ROCKS 137

3. Porphyries, Porphyrites, Diabases and Basalts.

The later sills and dyke rocks are most abundant in
the central provinces and especially in Bauchi, eastern
Zaria and northern Nassarawa, but are somewhat
sparingly distributed throughout the remainder of the
Protectorate. They include quartz porphyries, ortho-
clase porphyries, mica and hornblende porphyrites,
diabases and basalts. In the central area the high
content in soda which characterises the more acid
types undoubtedly indicates a genetic connection
between the later soda granites and the dyke rocks,
although investigation has not yet proceeded far
enough to allow of the recognition of the major foci to
which the dyke rocks may be referred. Amongst the
quartz porphyries micro-granitic, granophyric and
felsophyric types are equally common. In the central
provinces riebeckite is frequent both among the
phenocrysts and in the ground mass, while elsewhere
biotite is the commonest coloured constituent. An
egirine granophyre occurs at Chikobo (1417) on
the borders of Bauchi and Zaria. Orthoclase por-
phyries are commonest in the central area and possess
typically a trachytic ground mass, of which riebeckite
and zgirine are frequent constituents. Augite syenite
porphyries are known from the Kudaru Hills in
eastern Zaria (1397) and from the vicinity of Limoro on
the borders of Bauchi and Zaria (1413). The latter
occurrence contains hornblende and biotite in addition
to the augite, as well as a small amount of quartz in
138 NORTHERN NIGERIA CHAP.

the ground mass. An extensive mass of granophyric
diorite porphyrite occurs in western Kontagora between
Auna and Bussa (1162). The felspars are turbid and
much epidotised and surrounded by a fringe of more
acid material which passes outwards into the grano-
phyric matrix, while smaller irregular crystals of green
augite and ilmenite and abundant minute plates of green
mica are also enclosed within the pegmatitic material.
A peculiar rock from Toro in Bauchi province (958)
may be termed a quartz diorite porphyrite, and presents
a certain affinity with the basic members of the
charnockitic series of the Ivory Coast." The pheno-
crysts have a tendency to aggregate in groups and
include rounded quartz grains, tabular crystals of
andesine and labradorite with inclusions of granular
augite, elongated crystals of hypersthene and irregular
plates of biotite much corroded by the ground mass
and enclosing grains of augite and apatite. The
ground mass is composed of granular green augite,
felspar and quartz, with much magnetite and apatite.
The felspar of the ground mass is frequently untwinned
and more acid than the phenocrysts, while the quartz
forms in places micropoikilitic plates enclosing the
other ingredients of the ground mass. As alkali-
syenite porphyries may be grouped the bluish-grey
trachytoid rocks of Kanikoko (1217—1219). The
phenocrysts include tabular plates of  sanidine,
microcline, microperthite and microcline-microperthite
and fairly well-formed crystals of diopside and enstatite,
much intergrown with brown mica and_ bluish

1 Lacroix, C. Rd. Ac. Sc. 150, 1910, p. 18.
mn THE INTRUSIVE ROCKS 139

amphibole. The ground mass consists of microlites of
alkali felspar and granules of the ferro-magnesian
minerals. Typical mica porphyrites with phenocrysts
of biotite and zoned andesines occur at Barazara (1274),
and between Dan Gerumfa and Gwashi (1276) in
eastern Kontagora. A hornblende porphyrite between
Naraguta and Tilde (956) is inconspicuously por-
phyritic and composed of allotriomorphic green horn-
blende with subordinate biotite and augite in a matrix
of acid plagioclase, orthoclase and quartz. A horn-
blende porphyrite from Borgu (1220) contains large
poikilitic crystals of augite and hornblende in a granular
matrix of labradorite, augite, hypersthene, hornblende
and iron ore. A somewhat similar rock from Bauchi
province (1602) contains large poikilitic hornblende
crystals in a matrix of granular augite, magnetite and
lath-shaped crystals of labradorite. A labradorite por-
phyrite from Toro in Bauchi province contains large
tabular phenocrysts of acid labradorite in a ground
mass of green augite, brown biotite, secondary green
hornblende and lath-shaped crystals of acid plagioclase.
The diabases and basalts of the central area are
particularly numerous round the margin of the Bauchi
plateau and the Nassarawa tableland, and probably
include intrusions of many different ages. Some of
the coarser-grained diabases present affinities with
gabbros in the idomorphism of their augite crystals
(47,1695). Others exhibit a typical ophitic structure
(962,985), while others are predominantly granulitic
(690). A hornblende diabase with pale green augite,
greenish-brown hornblende and deep red biotite occurs
140 NORTHERN NIGERIA CHAP,

in the Ruruma hills (1466) in eastern Zaria. Biotite
also accompanies the augite in an ophitic diabase from
the Kudaru hills (1390) in north-east Zaria. Uralite
diabases are fairly common, but olivine diabases (747)
are conspicuously rare. The basalts present few
features of interest and are typically compact, non-
porphyritic rocks with a holocrystalline, ophitic or
granulitic structure and free from olivine.

MM. Gentil’ and Chudeau? have described the occur-
rence of intrusive granites, pegmatites, porphyries,
lamprophyres, diabases and gabbros, throughout the
crystalline areas of the Central Sahara, and Dr.
Passarge*® has recorded similar intrusive rocks from
the northern gneissic region of Adamawa. Aé%girine
rhyolites and alkaline trachytes of an intrusive cha-
racter are known also from Zinder, Gabana, Hadj el
Hamis,* and M’Burao.2 M. Chudeau believes that
the alkaline granites of Mounio with their associated
hypabyssal types pierce the sandstones of the Tegama,
and would therefore refer all the known occurrences
of soda granite in Central Africa to a late Cretaceous
or Tertiary age. In Nigeria, however, there is little or
no evidence to support this view. The soda granites
are nowhere found piercing sedimentary rocks within
the Protectorate, and while it is possible that they may
have been originally intruded into rocks of Cretaceous

1 Gentil, in Foureau’s Miss. Sahar. 1905, p. 720.

2 Chudeau, Sah. Soud. 1909, p. 256.

3 Passarge, Adamawa, 1895, p. 382.

4 Garde, C. Rd. Ac. Sc. 5 July, 1909 (149), p. 433; cf Gentil and
Freydenberg, Bull, Soc. Geol. Fr. (4), VIII, 1908, p. 44; Gf also Suess,
The Face of the Earth, Vol. \V, Oxford Trans., 1909, p. 283.

5 Hubert, C. Rd. Ac. Sc. 1904 (139), p. 378.
II THE INTRUSIVE ROCKS 141

age which have now been removed, it is remarkable
that, with the exception of rare sills of dolerite and the
Tertiary pipes of basalt, no intrusive dykes or masses
of hypabyssal or plutonic material are to be found
within what remains of either Cretaceous or Tertiary
rocks within the Protectorate. Such intrusive rocks,
however, are particularly numerous within the crystal-
line areas, and especially in the neighbourhood of the
larger masses of soda granite, which are themselves
frequently pierced by marginal dykes of basalt and
porphyry. In view of the abundance of soda types
among the dyke rocks, moreover, it is hard to escape
the conclusion that the later non-foliated alkaline
granites of the second type (p. 132) with the associated
syenites, diorites and dyke rocks of acid, intermediate
and basic composition, all possess a certain genetic
relationship, and should be properly ascribed to one
and the same period of igneous activity. All the
facts, indeed, are more readily explicable on the as-
sumption of the pre-Cretaceous age of this period of
intrusion within the Protectorate. The stratigraphy
of Mounio and Koutous is somewhat doubtful, and
M. Chudeau’s section’ of the faulted margin of the
Goure granite does not indicate an actual transition
from the mica schists and quartzites into the sand-
stones and clays of the Tegama. M. Garde,’ more-
over, while indicating the occurrence of crystalline
gneisses to the north of Goure does not appear to
confirm M. Chudeau’s interpretation of this important

1 Chudeau, Sah. Soud. 1909, p. 267.
2 Garde, C. Rd. Ac. Sc. 149, 5 July, 1909, p. 43.
142 NORTHERN NIGERIA CHAP.

section. It should be remembered, however, that
even although further investigation may prove the
truth of M. Chudeau’s correlation, there is no reason
to believe that the intrusion and effusion of igneous
rocks rich in alkalis has been confined, as M. Chudeau
would suggest, to one particular period in the history
of the Sudan.

It is interesting to trace in a general way, and
subject to the limitations indicated above, the succes-
sive changes in the character of the igneous intrusions
from the earlier to the later granites and dyke rocks
on the hypothesis of a continuity in magmatic con-
ditions, or at least of a periodic renewal of activity in
the same igneous focus. The successive intrusions
may be tabulated as follows :—

1. Earliest well-foliated granites of intermediate
composition with numerous associated amphi-
bolites and epidiorites.

2. Partially foliated granites of both acid-alkaline and
intermediate character, with partially sheared
dyke rocks of acid, intermediate and _ basic
composition.

3. Aplitic granites and pegmatites, rich in muscovite
and tourmaline with associated reefs and veins
of quartz and tourmaline quartz.

4. Alkaline granites rich in soda with associated
syenites, diorites, and dyke rocks.

If the normal sequence of events within the period of
activity of any igneous focus be taken to be the succes-
sive manifestation of volcanic, plutonic and hypabyssal
III THE INTRUSIVE ROCKS 143

activity, there may perhaps be recognised in the
successive intrusions indicated above four periods of
igneous activity, each of which is now represented by
the products of the plutonic and hypabyssal phases
only, while the products of the accompanying volcanic
phases, if originally present, have been removed in
the course of denudation. The tendency to the pro-
duction of rocks rich in alkalis should be remarked as
a notable feature of the various periods of intrusion ;
and in this connection it is interesting to note that
Messrs. Horwood and Wade’ have likewise empha-
sized the alkaline character of many of the earlier
granitic intrusions to the south of the equator.

1 Horwood and Wade, Geol. Mag. V, 6, 1909, p. 455-
CHAPTER IV.

CRETACEOUS ROCKS.

Distribution : relation to crystalline rocks. The Cretaceous rocks of the
Benue valley : the succession around Awe ; the position of the salt-
bearing beds ; the Arofu and Akwana limestones and galena veins ;
the limestone-shales and brine springs of eastern Muri; the Muri
sandstones ; the Gateri grits; the limestones and galena veins of
the Kudu valley. The Cretaceous rocks of Yola and of the Gongola
valley : the Bima sandstones ; the Gongila limestone ; the rocks of
Gulani and Wuyo; the upper sandstones of Ture and Waja.
Classification of the Cretaceous rocks. The Cretaceous rocks of the
French Sudan, Southern Nigeria and the Kameruns.

No rocks of Devonian or Carboniferous age or of
any period preceding the Cretaceous have been
discovered within the Protectorate. The Cretaceous
rocks, moreover, are themselves represented only by
the upper members of the series, no deposits of
earlier age than the Turonian having been anywhere
definitely recognised. The Upper Cretaceous rocks
are confined within the Protectorate to the Benue
valley between long. 8°30’ E. and long. 12°15’ E.,
and to the valley of the Gongola between its con-
fluence with the Benue and lat. 11°15’ N. They form
the greater part of the plains of Muri and Yola, and

1 See Chudeau, Sak. Soud. 1909, pp. 47, 11, for pre-Cretaceous rocks

of the Sahara.
144
CH. IV CRETACEOUS ROCKS 145

of the narrow plain of the Gongola in Bauchi and
Bornu, but only around Ligri and Gateri and in
Wurkum, Tangale and Waja do they rise into ranges
of rounded or tabular hills. The rocks consist of a
well-bedded series of red and white sandstones and
grits, carbonaceous and calcareous shales, ironstones
and limestones, usually somewhat faulted and gently
folded into low anticlines and shallow synclines, and
in places pierced by intrusive masses of dolerite or
basalt. The original thickness is unascertainable,
partly on account of the folding and faulting to which
the rocks have been subjected and partly on account
of the thick covering of drift which obscures the rocks
for long distances and renders difficult or impossible
the correlation of the various exposures. In the west
the Cretaceous rocks are believed to pass unconform-
ably under the sandstones of the Lokoja series in the
neighbourhood of Udeni, but the actual junction has
nowhere been observed. How far westward they
extend under the Lokoja sandstones is also un-
determined. An exposure of white sandstones and
carbonaceous shales in the bed of a stream near
Akwacha in Bassa province seems to indicate that
they extend for a considerable distance west of Loko,
but that they do not reach the Niger is abundantly
evident from the absence of any trace of them in the
neighbourhood of the river below Lokoja.

To the north and to the south of the plains of
Muri, the Cretaceous sandstones give place im-
perceptibly to a crystalline floor. The actual contact,
however, has been found wherever examined to be so

L
146 NORTHERN NIGERIA CHAP.

much obscured by drift that it is impossible to say
whether any part of the margin is bounded by faults
or not. In the east the Cretaceous rocks pass under
the upper Benue sandstones and, so far as known, do
not reappear anywhere east of Yola. Similarly in the
Kudu valley they disappear under the sandstones of
Duguri and in the Gongola valley under the Gombe
sandstones to the west and north. To the east of
the Gongola between Bilaraba and Dusua they rest
upon a hummocky crystalline surface, while farther
south they pass behind Balbea under the Barbur basalt
plateau. To the west of Kwoia, however, their
junction with the crystalline rocks, although somewhat
badly exposed, has every appearance of being fractured,
while on the lower Gongola the relations between the

Cretaceous and the crystalline rocks to the east are
"such as to suggest most forcibly an extensive faulting
along the contact. Within the area covered by the
Cretaceous rocks inliers of granite and gneiss are
exposed around Arofu on the middle Benue, around
Tangalto and Chongwom in southern Bauchi and in
various places upon the narrow plain of the Gongola
and, while in some cases the crystalline rocks exposed
upon the plain of the Gongola have undoubtedly been
brought to the surface by faulting, it is at the same
time fairly certain that the earlier Cretaceous rocks
were deposited upon a highly irregular crystalline
floor, the more elevated portions of which have been
exposed at the surface in the course of denudation.
For the same reason also the apparent base of the
Cretaceous in the neighbourhood of these inliers of
Iv CRETACEOUS ROCKS 147

crystalline rock cannot be regarded as the actual
base of the series, which is at most very imperfectly
known.

Murti Province.

In Muri province a series of limestones and shales
definitely known to be of Upper Cretaceous and
Turonian age’ is exposed in western Muri around Awe
to the north and around Arofu and Akwana to the
south of the Benue. In eastern Muri, the same series
is found at Kumberi on the right bank of the Benue a
few miles above Amar. At Awe a sharp little anticline
runs E.N.E. along the north side of the town and brings
up coarse white felspathic grits and sandstones with
two bands of carbonaceous shales (Plate XV, Fig. 1).
It begins to the north-east of the town as a gentle arch
with its axis dipping gently westward. The intensity
of the folding increases rapidly in that direction until
the anticline passes into a fault with the downthrow
towards the north, but farther west the fold reappears
and speedily flattens out. The northern limb of the
fold is much more steeply inclined than the southern
and the beds are even in some places overturned. At
the same time the sandstone outcrop takes the form
of a bow with the concave side to the north, the
whole structure being evidently produced by a local
intensification of the folding. (A. L.)

To the north and south of Awe, there are synclinal
areas in which rocks higher in the series have been
preserved. From the various exposures in the neigh-

1 See Appendix II, Palgontology, p. 273.
148 NORTHERN NIGERIA CHAP.

bourhood the following approximate sequence can be
made out :

Soft white quartzose sandstones, often with calcareous cement.

Thinly-bedded light-coloured calcareous shales and sandstones with
bands of impure shelly limestone.

Greenish shales with ironstone bands and nodules.

White grits and sandstones and carbonaceous shales with brine
springs.

Base not exposed. (A. L.)

Grits and sandstones similar to the lowest beds seen at
Awe, with brine springs but without carbonaceous shales,
come up to the surface again along a line running from
Akiri to Azara and Ribi, but north of that again
comes another synclinal area, for between Azara and
the Ankwe river exposures of shales and limestones
are met with. Over the whole of this part of Muri
indeed the beds appear to be thrown into gentle
anticlines and synclines whose axes run approximately
E.N.E. A lower and essentially sandy division, often
yielding brine, appears along the cores of the anticlines
as at Azara, Akiri and Awe, while an upper, essentially
shaly division, is preserved in the intervening synclinal
areas. (A.L.)

Limestones are known to occur in the volcanic tract
on the Benue, south-west of Awe, while at Tunga wharf,
immediately south of Awe, a river section exposes the
lower sandstones striking E.N.E., and dipping north-
wards at 27°. At Arofu a small inlier of granite to the
east of the town is seen to be five-sixths surrounded by
silicified limestone with the remainder of its perimeter
concealed by marshy ground. An excavation proved
the limestone to rest directly on the granite and we are
therefore compelled to conclude that this granite forms a
knoll surrounded and at one time overlaid by the lime-
Iv CRETACEOUS ROCKS 149

stone. Whether similar relations hold good between
the other inliers of crystalline rocks in the neighbour-
hood and the limestone is not certain. The outcrop of
the limestones is a broad one, about half a mile across
in the vicinity of Arofu and still more to the south of
Akwana. The broad outcrop is accounted for partly
by the gentle dip, partly perhaps by gentle undulations
of the strata, but partly also by the thickness of the
limestone. What this is it is impossible to say in the
present state of .our knowledge, but it is certainly much
greater than that of the limestone bands known in the
neighbouring parts of the province. (A. L.)

The saltings of Arofu and Akwana bear witness to a
salt-bearing series underneath the limestones although
that series itself is nowhere exposed. Above the lime-
stones comes a series of shales, shaly sandstones and
ironstones with a few thin intercalated limestone bands.
This shaly series outcrops between Arofu and the
river and runs a little south of west to beyond Akwana.
The dip is about 1o° and almost north. At Shaii
however, twelve miles east of Arofu, similar shales dip
at 25° towards N. 40° E., so that the folding is some-
what variable. Around Arofu the limestones are
seldom seen in an unaltered condition, for almost all
the rock exposed is silicified. Thus the country is
crossed by innumerable dyke-like masses of silicified
limestone standing up several feet above the soil. In
the rising ground south of Akwana the silicified bands
give rise to several small cascades. Knots of galena
are common in the silicified limestone and in places as
at Arofu there are veins of galena and fluorspar. The
original structures of the limestone which was partly
150 NORTHERN NIGERIA CHAP.

foraminiferal but very largely oolitic and pisolitic have
been excellently preserved during the change. At
Arofu, however, a compact unaltered variety contains
imperfect remains of ammonites. It is possible that
these limestones which lie to the south of the Benue
may be on a somewhat different horizon from those of
Awe, but the presence of the underlying salt-bearing
series indicates that the general succession is the same.
(A. LL)

At Kumberi some miles above Amar there occurs
the following excellent riverside section of the limestone-
shale series, in which the subordinate character of the
limestone bands is very evident :

Occasional sandstone seen in the river bank :—
About 100 ft.—Fine-grained sandstone, mudstone and _ shales
alternating as below.
12, Sandstone.
About 50 ,, Shales.
2 ,, Good white limestone with numerous teeth, bones,
and phosphatic casts of lamellibranch and gastero-
pod shells. Ammonites.

» Shales.

1% ,, Shelly limestone.
» Shales.

2 ,,  Friable sandstone.

io ,, Shales with mudstone bands.
15 ,,  Blue-gray shales.
20 ,, Shales with mudstone bands.
2 ,,  Mudstone with large calcareous concretions round
ammonite shells.

5 »  Shaly sandstone.
Io ,,  Friable sandstone.
2 , Sandy shales.
Io ,, Soft, friable sandstones with shaly partings.

About 200 ,,  Fine-grained and soft sandstones, mudstones, and
shales alternating as above.
Occasional sandstones in river bank.

Total: 450 to 500 ft. Limestone: 3$ ft.
Strike uniformly N. 50° E. ; dip, 30°—35° S.E. (A. L.)
IV CRETACEOUS ROCKS 151

Farther east again scattered fragments of limestone
indicate the presence of the limestone-shale series in a
synclinal between Bomanda and Muri. An anticlinal
axis, running a few hundred yards south of Bomanda,
brings up a lower series of soft thinly-bedded calcareous
grits with partings of green calcareous marl along the
crest of the arch. Brine springs like those of Awe
rise through the northern limb. At Muri the lower
reddish grits are seen in full force and dip southwards
at about 60. A careful estimate of the thickness
exposed worked out at over 1,500 ft. though neither
the base nor the upper limit was seen. To the north
fragments of limestone are found in the swamps of the
Kudu valley to the west of Jebjeb and Gateri but the
the associated rocks have nowhere been observed.
(A. L.)

The white grits and sandstones and carbonaceous
shales of Awe and the calcareous grits and marls of
Bomanda represent the passage beds between the
upper limestone-shale series and the lower sandstones
exposed at Akiri, Ribi and Tunga wharf in the west
and at Muri town in the east of the province. The
weak brine which rises in springs through the passage
beds at Awe and Bomanda and even through the lime-
stones at Akwana appears to take its origin in the
upper part of the lower sandstone series. Brine
springs and surface incrustations are found also where
the lower sandstones outcrop at Jebjeb, Jebero, Jenoe,
and Langa in eastern Muri, at Akiri, Azara, Ribi,
Kanje and Abune in western Muri, and at Doya and
Keana on the borders of Nassarawa. These localities
152 NORTHERN NIGERIA CHAP.

occur immediately round the margins of the more
marked synclinal areas containing the remains of the
limestone-shale series, a fact which warrants the
assumption that the upper part of the sandstones under-
lying the limestones is impregnated with salt and
was originally accumulated under arid conditions.
Indications of the salt-bearing strata are also found at
Lafin Gisheri between Tunga and Ibi and at a place
of the same name between Shishi and Wurio to the
east of Ibi. In these localities we are justified in
assuming that the rocks immediately below the surface
belong also to the upper part of the lower sandstone
series.

To the north of the salt area in western Muri well
bedded sandstones are exposed in many places between
Lafia in Nassarawa province, and Wase and Bashar
to the north of Ibi. The prevailing type of rock is a
reddish grit or sandstone, frequently brick red, with
knots and spots of white felspathic material, every-
where unfossiliferous, and nowhere yielding any indi-
cation of salt impregnations. At Bashar thin beds
of white and red clay are interstratified with the sand-
stones. The rocks are usually inclined at a low angle
to the horizontal and appear to be thrown into a
series of gentle undulations. From their position
with respect to the salt-bearing beds and the lime-
stone-shale series, it may be assumed, although con-
tinuous exposures are wanting, that these rocks lie
conformably at or near the base of the sedimentary
succession in western Muri. Their thickness is un-
known, but if, as seems probable, they are to be
PLATE XI

 

 

Hivtocks oF Dritt ON THE BAUCHI PLATEAU NEAR Vom.

 

 

 

 

HILitocks oF DRIFT TO THE WEST OF NARAGUTA.
Iv CRETACEOUS ROCKS 153

correlated with the sandstones of Muri town which
underlie the limestones in the eastern part of the
province, they must be, according to Mr. Long-
bottom’s determination (p. 151), at least 1,500 ft.
thick, and they may well be more. The whole series
underlying the passage beds of Awe and Bomanda
and impregnated with salt in the upper part may
conveniently be termed the “ Muri sandstones.”

Upon the drift-covered plains of southern Muri are
found occasional detached exposures of sandstones and
grits, the majority of which probably belong to the
lower sandstone series. The presence of the “ Muri
sandstones ” underneath the limestones of Arofu has not
been demonstrated but, as already stated, the occur-
rence of brine springs at Akwana affords a considerable
presumption in favour of their occurrence. Whether
they outcrop in the unexplored Munchi country to the
south and south-west of Akwana is, however, quite
unknown.

In the north-eastern part of the province the “ Muri
sandstones” become more steeply folded, and in the
Jenoe, Ligri, and Gateri hills appear to be underlaid
by a series of very coarse-grained white felspathic grits
or arkoses. ‘The axes of the folds strike in a general
way a few degrees north of east, and the folding
appears to be most intense in the immediate neigh-
bourhood of Gateri where the grits are much hardened,
and in places set on end. On the western slopes of
the Gateri hills are white and red grits and sandstones,
the representatives of the “ Muri sandstones,” dipping
generally westward and apparently underlying the
154 NORTHERN NIGERIA CHAP.

fragmentary limestones of the Kudu valley. In the
Gateri hills, moreover, there are indications, as at Awe,
that the axes of the folds are not horizontal, but tilted
gently to the west, and the distribution of the upper
limestones in Muri province in elliptical areas or irregu-
lar centroclinals surrounded by the lower sandstones
clearly suggests a later transverse corrugation ofthea
whole series of gently folded rocks. It is probable,
therefore, that the limestones of the Kudu _vlley,
although originally occupying a much higher place
in the series than the Gateri grits, have reached their
present relatively low position, not so muchas the result
of faulting, but rather as the result of the irregular
folding to which the whole series has been subjected.
At the same time the occurrence of galena veins in
the swamps to the west of Jebjeb indicates that the
rocks of the Kudu valley, like those of Awe and Arofu,
have undergone a certain amount of shattering and
fissuring contemporaneously with the folding. Amongst
the fissure-veins may also be included the broad dykes
of limonitic ironstone which form conspicuous hillocks
around Akiri in western Muri.

Yola Province. (A. L.)

The limestone-shale series runs up the plain of the
Benue from Lau almost to Yola, and may even be
found eventually farther east than Yola. This series
occupies the lower ground and nowhere forms hills.
In addition to it there are sandstones of various kinds,
sometimes occupying the plain and sometimes building
IV CRETACEOUS ROCKS 155

up hills above the plain. The sandstones of the hills
are approximately horizontal and rest upon the lime-
stone-shale series. They will be referred to as the
‘Upper Benue sandstones.” The question of their
conformability or otherwise to the limestone-shales
will be discussed later (p. 188).

The limestone-shale series, being soft and easily
denuded, is very poorly exposed, and is generally
hidden by the river alluvium. Calcareous sandstone
and greenish yellow shale are seen near Lau, and south
west of Kunini large blocks and slabs of shelly lime-
stone a few inches thick lie scattered about over the
silt. An excavation at Kunini proved that the lime-
stone is in thin bands, 12 or 18 inches thick, inter-
calated between shales. The series is thrown into small
anticlines and synclines. Of one small anticline
noticed the strike of the axis was N. 10 E., one
limb being inclined at 20°, the other at 60°. The
shales are seldom seen but they give rise to a
characteristic soil which is easily recognised and which
leads to the discovery of limestone lumps and fragments
on further search. Low-lying country of this character,
with numerous slabs and lumps of limestone lying
about on the surface stretches up the Benue to the
vicinity of Namtari.

Similar areas of limestone-shales are found on the
Gongola between Kiri and Shillen and between Mada
and Kombo. The latter area runs up the plain of the
Maio Hawal, but for what distance isunknown. In both
areas the limestone is shelly and very fossiliferous and
there are no sections showing the shales or giving the
156 NORTHERN NIGERIA CHAP,

dips. The only natural section of this series which
was met with in Yola province was at Numan. Just
to the east of the village, white fine-grained sandstone
crops out and is followed by still finer sandstones and
mudstones on which the village itself is built. No
limestone appears in the section and only a little shale.
The dip is 10° towards N. 55° W. The mudstone is
usually reddish, but the fresher parts are greenish and
glauconitic-looking. Phosphatic nodules are found
in this material and also in lumps of shelly limestone
set up by the natives in Dong. A small inlier of Cre-
taceous limestone is exposed also between Jibaru and
Murki in eastern Yola to the north of the Bagele hills.

The thick grits and sandstones which emerge from
beneath the limestone-shale series in Muri province
are probably responsible for the bold escarpment
behind Wuduku, but in the absence of detailed
examination it is impossible to say if these infra-
limestone grits were ever deposited in Yola province,
and if, being so deposited, they crop out between
the limestone-shale series and the crystallines or are
faulted out. The problem, a simple one in itself, is
enormously complicated by the fact that the ‘ Upper
Benue Sandstones” rest upon the limestone-shales
and conceal their boundary with the crystallines.
Consequently, the relation of the Cretaceous rocks
to the crystallines is at present unknown.

The Cretaceous rocks floor the trench of the upper
Benue valley, while the plateau areas to the south
and, east of the Gongola, to the north also, are of
crystallines. It is improbable from the characters of
Iv CRETACEOUS ROCKS 157

the limestone-shale series that these beds were formed
in a narrow inlet running up into a land mass. On
the contrary they are fine-grained marine sediments
which were probably deposited in open water. Their
present position, on the floor of the valley, at a much
lower altitude than the crystalline plateaux north and
south must be explained as the result of tectonic
movements. The wrinkled character of the series is
consistent with this explanation, and in this connection
sections-in the neighbourhood of Kombo are suggestive.
There the broad channel of the Gongola, usually half
a mile wide, becomes suddenly constricted to less
than a hundred yards by a ridge of grits dipping at
50° towards S. 30° E. These grits pass under
limestone-shales to the south-east, and must there-
fore be correlated with the Awe and Bomanda
grits. When followed eastward, however, for only a
few miles, this prominent ridge of grits disappears,
and the limestone-shales are seen to approach to
within at least a few yards of the granite. This
strongly suggests that the limestone-shale belt running
up the Maio Hawal is faulted down to abut against
the granite. Ina similar way, it is believed that the
Upper Benue valley, to the east of its confluence with
the Gongola, was initiated as a tectonic valley. (A. L.)

Bauchi and Bornu.

“To the north as to the west of Gateri, a series of
white sandstones intervenes between the Gateri grits
and the limestones which outcrop in the swamps
158 NORTHERN NIGERIA CHAP,

between Putu and Tangalto. These limestones are
exposed in a very fragmentary manner, but the presence
of a narrow belt of the lower white salt-bearing sand-
stones in the midst of the limestones half-way between
Putu and Tangalto indicates here as elsewhere the
occurrence of the usual succession and an irregular
folding of the whole series. Approaching Tangalto
the Cretaceous rocks run out upon the crystallines as
white sandstones and quartzose conglomerates whose
horizon probably coincides with those of the Ture grits
to the east. In the hilly country to the east of
Tangalto and on the plains to the north, the inclination
of the Cretaceous rocks is in part due to a gentle
folding, and in part to an extensive faulting which has
in places on the Gongola plain brought up even the
base of the series and the underlying crystalline rocks
to the same level as the limestones. Around Ture
(Plate XIII, Fig. 1) and Awok, the varied dip of the
well-bedded sandstones indicates a gentle curving into
low domes and shallow basins, while a similar structure
is very evident at Gulani, to the east of the Gongola,
where the town is set within a circle of low hills which
possess a well-marked centroclinal dip. On the other
hand, the Wadi, Shinga, Bima and Gunna hills, are
separated by faults, and owe their greater northerly
inclination to the effect of a larger fault which is well
seen at Gunna on the left bank of the Gongola, and
on the track between Wadi and Wuyo, where the basal
sandstones of the Bima hills with the underlying
crystalline rocks are brought up to the surface of the
Iv CRETACEOUS ROCKS 159

plain. The faulting, like the folding, appears to be in
two well-marked directions at right angles to each other
and approximately N.N.W., and E.N.E., andit is prob-
able that there is here, as in the neighbourhood of Awe,
some intimate relation between the faults and folds, for
whose complete demonstration much more detailed
investigation would be required.

If the Gunna fault be taken as showing the base of
the Cretaceous, the succession in the Gongola valley
begins with a series of sandstones and grits at least
1,000 ft. thick. The basal beds are green and purple
earthy grits, composed of the debris of crystalline rocks
and containing large rounded fragments of granite and
pegmatite. These are followed by alternating bands
of red, white and purple grits, which pass into the
white and red sandstones and grits of the Bima and
Wadi hills. The marginal rocks, which overlie the
crystallines between Bilaraba and Dusua are white, red,
and purple grits, much broken and current bedded and
probably belonging to the same horizon as the lower
sandstones of the Bima hills. These ‘ Bima sand-
stones” are succeeded after an unknown interval by
the Cretaceous limestones which outcrop in many places
upon the plains to the east and to the west of the
Gongola, and are particularly frequent over the tract of
country which lies between Dukul and Deba Habe to the
west, and Wuyo and Gulani to the east of the river.
In one locality, a mile to the south of the village of
Gongila, between Nafada and Ashaka, the limestone is
clearly shown resting upon the lower series of white
160 NORTHERN NIGERIA CHAP.

and red sandstones and grits. Asa rule, however, the
rocks associated with the limestone, are badly exposed
and obscured by drift, while the shales which presumably
accompany the limestones have nowhere been observed.
At Gulani, the limestones pass conformably under a
series of coarse white and red grits and white, yellow
and brick red sandstones with intercalated bands of
clay and flaggy ironstones. With these upper rocks
the red and white sandstones, clays, and ironstones of
Wuyo present much lithological resemblance and
probably belong to the same horizon. Similarly at
Reme in the extreme south-east of Bauchi province
the limestones are overlaid by a well-stratified succession
of white and red sandstones, grits, and flaggyironstones,
which are at least 800 ft. thick, and form the escarp-
ments of the flat-topped hills of Waja. The whole
series becomes markedly ferruginous towards the
summit, and while the contact with the limestones
below is not actually exposed, there is no reason to
believe that it is other than conformable. These rocks
in Waja represent the highest known members of the
Cretaceous series, and it is they which are continued
westward by Tula, Awok, and Ture, and run out upon
the crystallines to ‘the east of Chongwom. Around
Awok and Ture these upper sandstones are distinctly
and variously inclined, but in Tula and Waja the dips
are so gentle as to be almost imperceptible. The white
grits and sandstones are usually unfossiliferous, but in
the neighbourhood of Ture and the Peak (Plate XIII,
Fig. 2), they contain much silicified wood from the
Iv CRETACEOUS ROCKS 161

presence of which a subsidiary argument may perhaps
be drawn in favour of their Cretaceous age. The
Gongola valley to the east and north-east of Waja
retains the faulted character which it exhibits to the
north, while the country which lies between the
escarpments of the Waja hills on the north, and the
Yam Yam hills fronting the Benue on the south, is
quite unknown and may contain representatives of
both granitic and sedimentary rocks.

From the various exposures described, the Cretaceous
series within the Protectorate may be tabulated as
follows :

 

Muri and Yola. Bauchi and Bornu.

 

Upper grits and

sandstones...... Sandstones, _ grits,
clays, and iron-
stones of Waja,
Ture, Gulani and

Wuyo.
Limestones ...... Turonian limestones and | Turonian limestones
shales of the Benue valley of the Gongola
valley.
Passage beds (white sand-
stone and carbonaceous
shales at Awe: calcareous
Lower grits and grits and green calcareous
sandstones...... marls at Bomanda).
Muri sandstones (upper part | Bima sandstones and
salt-bearing). grits.

Gateri grits.

 

 

 

No evidence of contemporaneous volcanic activity
has been found within the Cretaceous rocks of the
Protectorate. Intrusive sills of dolerite, however, have
been observed within the Cretaceous sandstones in

M
162 NORTHERN NIGERIA CHAP.

the neighbourhood of Awe, Bashar and Serakin Kudu
in Muri province, but they, together with the numerous
pipes and necks of basalt and trachyte which pierce
the Cretaceous rocks in the valleys of the Benue and
Gongola, are probably to be referred to some phase of
Tertiary volcanic activity (see Chapter VIII).

In the French Sudan limestones of Turonian age
have been described from the Damergou’ to the north
of Zinder, from Bilma to the north of Lake Chad,? and
from Tabankort, Tabrichet and Mabrouka® to the
south and west of the Adr’ ar’ des Ifor’as. The
occurrence in the Damergou of gypsiferous clays in
association with Cretaceous limestones has not been
paralleled in Northern Nigeria. On the other hand
the presence of a salt-bearing series within the
Cretaceous has not hitherto been recognised in the
Sahara. Any correlation of the lower grits and
sandstones of Northern Nigeria with the Lower
Cretaceous of the Tegama, as established by M.
Chudeau,* would, however, be premature, in view of
the absence of determinative fossils in both and the
marked lithological differences between the two. It
seems better for the present to avoid any definite
subdivision other than that indicated above and
to refer the whole series of grits, sandstones, clays,
ironstones and limestones provisionally to the Upper

1 De Lapparent, C. Rd. Ac. Sc., 135, 1903, p. 1298; Chudeau, Sak.
Soud., 1909, p. 89.

2 De Lapparent, C. Rd. Ac. Sc., 132, 1901, p. 388.

3 Chudeau, Sah. Soud., 1909, p. 91.

4 Ibid. p. 76.
IV CRETACEOUS ROCKS 163

Cretaceous. To the south of the Protectorate rocks
of a similar age have been described by Mr. Parkin-
son’ and Dr. Esch? from Southern Nigeria and the
Kameruns respectively.

1 Parkinson, “The Geology of the Oban Hills,” Q. 7. G. S., 63, 1907,
Pp- 314.
2 Esch, Geologie von Kamerun, 1904, p. 4.
CHAPTER V
EOCENE ROCKS

The Sokoto and Lokoja series: the nummulitic limestone of Sokoto ;
the upper ferruginous beds ; the pisolitic clay of Giro; the white and
pink clays of Kurukuru ; the partial colouration of the lower sand-
stones and clays ; the Lokoja sandstones and ironstones ; the piso-
litic ironstones of Mount Patti ; outliers of the Lokoja series. The
Duguri sandstones and grits: the clays of Pali, Kirifi and Deu ; the
Gombe sandstones ; the ironstones of the Tagum hills; the grits
and ironstones of Kerri Kerri; the age of the Duguri, Gombe and
Kerri Kerri sandstones. The Upper Benue sandstones : their rela-
tion to the Cretaceous and crystalline rocks of Yola; age of the
Upper Benue sandstones ; outliers of Eocene sandstones in Muri
province ; Tertiary history of the Upper Benue valley. The Eocene
rocks of the Upper Niger and the Kameruns. The stratigraphy
of the Chad area.

The dawn of the Eocene was marked by regional
upheaval, by the folding and fracturing of the
Cretaceous rocks and by subsequent intense erosion, as
the result of which the underlying crystalline floor
was again laid bare over the greater part of the
Protectorate. A period of depression, however, en-
sued, during which the sandstones, clays, limestones
and ironstones of the middle Eocene were extensively
and unconformably accumulated both upon the crystal-
line rocks and upon the worn and denuded edges of
the Cretaceous. The existence of this hitherto unsus-

pected unconformity between the Eocene and the
164
CH. V EOCENE ROCKS 165

Cretaceous introduces a new element of complication
into the history of the Sudan and the southern Sahara."
In the opinion of M. Chudeau® deposition was
continuous at least from the lower Turonian to the
close of the Eocene, while the early Eocene was
marked by a widespread transgression of the waters
over the Niger valley. The presence of the uncon-
formity, however, makes it evident that the known dis-
tribution of the Cretaceous cannot in any way be taken
to indicate the former limits of the Cretaceous sea.

The Eocene rocks within the Protectorate may be
conveniently classified into three groups :

1. The Sokoto and Lokoja series.

2. The Duguri, Gombe and Kerri Kerri sand-
stones.

3. The Upper Benue sandstones.

1. The Sokoto and Lokoja series.

The occurrence of fossiliferous limestones of Eocene
age at Kalfu, Tamaske, Garadimi and Toronkawa to
the north of Sokoto has been known since 1903.2. ~The

1 Cf. Suess, The Face of ithe Earth, Vol. 1V, Oxford Trans., 1909,
p. 89.

2 Chudeau, Sah. Soud., 1909, p. 104.

3 De Lapparent, C. Rd. Ac. Sc., 136, 1903, pp. 1, 118; Bather, Geol.
Mag., [5], 1, 1904, p. 292.

The Eocene fossils from Sokoto and Jega are similar to those
collected by Col. Elliot and Capt. Lelean from the Sokoto frontier, of
which accounts have been published by Dr. F. A. Bather (Geol. Mag.,
1904, p. 292, Plate XI) and by Mr. R. Bullen Newton (G. /., XXIV,
1904,:p. 522), who regard them as of Middle Eocene age. The
fossils consist principally of echinoids and internal casts of mollusca.
The latter are not sufficiently well preserved for exact determination.

From Sokoto numerous examples of Hemdaster sudanensis «(Bather
166 NORTHERN NIGERIA CHAP.

limestones have been found, however, to extend much
farther south and to be associated with sandstones,
clays and ironstones which are continuous with those
in the Niger valley from Ilo to Lokoja. One of the
finest sections of the limestone series is found in the
cliffs facing the river beyond Wurnu to the north-east
of Sokoto where the following succession may be
observed :

10 ft.—Dark red ferruginous grit on top.

10,, Ferruginous oolite.

30,, Soft, chalky, fossiliferous limestone with phosphatic nodules and

rounded lumps of hard and somewhat phosphatised limestone.
Io,, Calcareous clay.

80,, Blue shale, much obscured by landslips.

20,, Compact yellow calcareous clay, with efflorescence of gypsum.
40,, Red, yellow, green and black gypseous shales and clays.
50,, Black carbonaceous shales with radiating crystals of gypsum

alternating in thin bands with yellow ferruginous clays with
knots of ironstone ; efflorescences of alum and gypsum.

At Wurnu the same succession is represented by
red sandstones above and white, yellow and blue clays
and shales below, with fragments of limestone at the
foot of the slope indicating a thin band of limestone
intercalated probably near the summit of the shales.
Around Sokoto there is much earthy ferruginous
oolite on top passing downwards as a rule into well-
bedded red sandstones. Below the Wurnu gate,
however, there is an exposure of about thirty feet of
blue and white calcareous shales and clays with thin
bands of hard limestone 3-4 inches thick, numerous
were obtained, and also specimens of Lucina and gasteropods. At Jega
Hlemiaster sudanensis is also abundant, and a portion of Plestolampas

(probably P. Sakare, Bather) was obtained. The mollusca belong to
the genera Nautilus, Turritella, Voluta, Cardium, Lucina, Ostrea, etc.

(H. W.)
v EOCENE ROCKS 167

fossils and occasional fragments of gypsum. At
Alkamu, near Sokoto, a chalky limestone with nodules
and echinoids, associated with calcareous shales and
overlaid by earthy oolite, encloses rounded lumps of
harder nummulitic and crinoidal limestone which look
as if they had been originally washed into place.
This appears to be the first record of the occurrence
of nummulitic limestone in West Africa. A similar
hard nummulitic limestone is found as far south as the
neighbourhood of Jega and more detailed investigation
would probably reveal its presence in many localities
between Sokoto and Jega. The limestones, however,
no here form thick and massive beds, but appear to
occur always in thin bands or as nodules in calcareous
shales or clays. The occurrence of gypseous shales
below the limestones at Wurnu and Sokoto indicates
the earlier presence of arid conditions, but whether or
not the various exposures of limestone occur on one
and the same horizon has not been determined.
Neither limestones nor calcareous shales are known
from the immediate neighbourhood of the Gulbin
Kebbi below Sokoto.! There are, however, numerous
indications in the cliffs which bound the valley of a
lower lighter-coloured earthy series overlaid bya succes-
sion of gritty and ferruginous beds. At Tozo white
clays and earthy sandstones with thin bands of limonite
are covered by oolitic ironstone which is overlaid in
turn by hard red sandstone and pebbly ferruginous
grit between Tozo and Kantami. The escarpments

1 Fossiliferous limestone has, however, been reported from Yelu at the
confluence of the Dallul Mauri and the Niger valley.
168 NORTHERN NIGERIA CHAP.

of Gulma are composed of soft white earthy grit
below, becoming redder and more sandy towards the
top and capped by a layer of hard ferruginous sand-
stone. At Birnin Kebbi the lower massive white and
yellow earthy sandstones become mottled red and pass
into dark red ferruginous sandstones on top. At Giro
the lowest rock exposed is a yellowish pebbly grit with
intersecting silicified ribs which passes in places into
a friable white pebbly marl. This is followed bya
thick (100 ft.) bed of white clay, frequently stained red
along the joints and irregular cracks, almost every
specimen of which shows a pisolitic or concretionary
structure. Traced southward this bed becomes much
silicified in its upper part, with retention of the original
structure, and all stages may be traced between the
normal pisolitic clay and a pure silicified and somewhat
opalescent pisolite. Northward and eastward red and
yellow sandy beds and friable pebbly grits become
intercalated in the clay, while fragments of a fine-grained
and very ferruginous sandstone afford indications of the
former presence of ferruginous beds on top. Frag-
ments of a similar silicified clay are found as far south
as Marake where the prevailing rock is a brick red
earthy sandstone, in places spotted with felspathic knots.
At Kurukuru, near Ilo on the Niger, soft white and
pink clays are again prominently exposed under a cap
of ferruginous oolite. A pisolitic clay very similar to
that of Giro has been described by M. Hubert? from
Gaya on the Niger.

The sedimentary rocks run out upon the crystallines

1 Hubert, Mzss. Sc. au Dahomey, 1908, p. 384
v EOCENE ROCKS 169

as friable pebbly yellow sandstones at Shunga to the
east of the Niger, as a hard yellow silicified sandstone
at Bakinrua in Borgu to the west of the Niger, and
farther south as ferruginous sandstones and conglomer-
ates at Konkwesso and Kabe, and soft white earthy
sandstones on the Niger to the west of Warra. On
the plateaux throughout Sokoto province the prevailing
rock belongs to the upper ferruginous series of hard
red sandstones, grits and ironstones, the softer and
lighter-coloured rocks below being exposed for the
most part only in the cliffs which bound the river
valleys. The occurrence of outliers of still higher beds
upon the surface of the plateaux indicates that the
actual summit of the series has probably nowhere been
observed.

There can be little doubt that the partial colouration
of the lower beds, and to some extent also the
hardening of the upper sandstones, is due to some con-
siderable extent to the percolation of iron-bearing
solutions from above downwards. There is equally
little doubt that the oolitic ironstones are of primary
and not of secondary or metasomatic origin and that
the deposition of the ferruginous material took place
during the latest stage in the history of Eocene
sedimentation. All gradations indeed can be traced
between a pure oolitic ironstone and a ferruginous
sandstone with scattered oolitic grains of limonite.
M. Chudeau? insists that even where enclosed between
thick beds of clay, the oolitic ironstones are in every
case the product of the decalcification of limestone. He

1 Chudeau, Sah. Soud., 1909, p. 274.
170 NORTHERN NIGERIA CHAP.

has himself, however, supplied a sufficient answer to his
own argument in calling attention to the fact that the
limestones where now exposed never show any trace
of even a superficial alteration into ironstones and in
admitting, as he does, the truth of M. Hubert’s* con-
tention that the oolitic ironstones of the Niger valley
are nowhere accompanied by or traceable into lime-
stones of a similar character. The flints of Ansongo,’
moreover, like the nodules of Sokoto, indicate nothing
more than the local occurrence of limestone within the
Eocene accumulations.

The sandstones of southern Kontagora and of the
Niger valley below Jebba, which may be conveniently
grouped as the “ Lokoja series” from the locality of
their greatest development, represent the southward
continuation of the Sokoto sedimentary series and
more particularly of the sandstones, grits, conglomer-
ates and ironstones of the southern portion of the
series, lying below the confluence of the Gulbin Kebbi
and the Niger. The break in continuity at Warra is
more apparent than real and is due merely to the fact
that the Niger has entirely removed the sedimentary
rocks from its channel and thus exposed the underlying
crystallines. A well-marked difference in character
may be traced between the Eocene rocks of Sokoto
province and their southern representatives, a difference,
however, which is entirely due to a dissimilarity in the
earlier conditions of sedimentation. In the Sokoto
series there is a well-marked succession of marine and

1 Hubert, Miss. Sc. au Dahomey, 1908, p. 112.
2 Chudeau, of. cét., p. 275.
PLATE XII

 

 

 

A GRANITE MounT NEAR BaucHl.

 

 

A GRANITE MOUNT NEAR BAucul.
Vv EOCENE ROCKS 171

deeper water accumulations by shallow water and
lacustrine accumulations. Amongst the southern sand-
stones, however, there is no trace of a marine series, no
trace of limestones or of carbonaceous or calcareous
shales and even clays are conspicuous by the rarity of
their occurrence. The series throughout, which attains
at Lokoja a thickness of 1,000 feet, is a shallow water
accumulation of sandstones, grits, conglomerates and
ironstones, comparable to some extent with the upper
shallow water portion alone of the Sokoto series. The
resemblance indeed between the uppermost members
of both series is heightened by the prevalence in both
of oolitic and pisolitic ironstone, and it seems probable
that, in spite of their earlier dissimilarity, the conditions
towards the close of sedimentation in Eocene times
were identical over the whole area from Sokoto to
Lokoja. A further resemblance between the Lokoja
series and the rocks of the lower valley of the Gulbin
Kebbi is the frequent staining of the lower members
of the series by descending ferruginous solutions.
Wherever the lowest rocks of the Lokoja series are
exposed they are almost invariably light-coloured sand-
stones and conglomerates. The colourisation begins
along the joints and fissures and spreads inward as an
irregular pink or reddish mottling. Traced upward
the rocks gradually become uniformly coloured and the
tints gradually deepen until the rocks assume the
characteristic dull dark red or chocolate colour of the
uppermost members of the series. The staining in
places, owing probably to local differences in texture,
has reached a greater depth than in others with the
172 NORTHERN NIGERIA CHAP.

result that at certain points within the series the lower
lighter-coloured rocks appear to attain a less develop-
ment than in others. There is, however, to be observed
in places towards the upper portion of the series an
alternation of more and less ferruginous beds under-
neath the richly ferruginous cap of chocolate-coloured
sandstones and ironstones, while here and there inter-
calations of ferruginous beds are to be found even
within the lower lighter-coloured members of the series.
In northern Borgu, moreover, it is common to find the
basal conglomeratic beds richly ferruginous, a fact
which is probably to be explained as due to the
gradual extension of the marginal swamps during the
advent of shallow water conditions.

The outliers of the Lokoja series which lie to the
north and north-east of Kontagora belong to the
uppermost portion of the series and consist for the most
part of oolitic and pisoliticironstones. Immediately
south of Kontagora, soft white sandstones and earthy
grits are exposed in the gorge of a stream at Kagara.
Again at Sonko in a narrow canyon valley a fine-
grained hard ferruginous sandstone is intercalated
between beds of yellow gritty clay. Between Sonko
and Jebba, there is a great development of ferruginous
sandstones, ironstones and grits which extend also
over a large portion of western Nupe. In western
Kontagora, yellow grits and sandstones occur round
Auna, while at Shaffini yellow and reddish pebbly
sandstones form the base of the hills of ferruginous
grit’ which rise above the plain. At Kumboji the
rocks are red pebbly sandstones and ferruginous grits,
v EOCENE ROCKS 173

while at Chika a lower bed of yellow sandstone is
succeeded by red grit and ferruginous conglomerate.

On the Niger below Jebba, ferruginous sandstones
and gritty ironstones are exposed at Rabba on the left
bank, and red sandstones and pebbly grits at Shonga
on the right. At Share white pebbly sandstones and
conglomerates with thin bands of clay occur below the
ferruginous grits which form the summit of the tabular
hills. At» Padda, to the east of Pategi, the basal
beds are white conglomerates and sandstones, knotted
with fragments of felspar and passing upward into the
alternating series of white and reddish sandstones which
rise into the pinnacle peaks of Egbom. On the banks
of the Kaduna above Wuyo, white earthy sandstones
are frequently exposed passing upward in the isolated
hills through alternations of white and red sandstones
into hard ferruginous grit and ironstone. Throughout
southern and western Nupe, the rocks, where exposed,
are invariably red sandstones or ferruginous grits.
Between Kacha and Baro, however, the lower beds
are white or mottled red and pass upward into a
succession of red and white sandstones and grits. A
similar alternation occurs in the base of the outlying
Jakpara hills in northern Kabba which are capped by
red ferruginous grit.

From Baro southward along the Niger and eastward
into Nassarawa and Bassa, oolitic ironstones and earthy
limonites associated with ferruginous sandstones and
grits attain a greater development while the colouration
of the lower beds is in general much more complete.
At Baro a white or reddish sandy clay with pebbles of
174 NORTHERN NIGERIA CHAP,

quartz and kaolinised felspar is exposed at the base of
Mt. Gidda. This is followed by a thick mass of
oolitic ironstone covering the greater part of the slope,
in places much decayed and ribbed, banded and
knotted with concretionary limonite. The upper
portion of the hill is composed of red sandstone and
ferruginous grit, the uppermost beds being well banded
with coarser material, and enclosing pebbles of quartz
and felspar. At Lokoja the lowest rock’exposed at
the base of Mt. Patti is a soft white felspathic
sandstone with pebbles of quartz, kaolinised felspar
and pegmatite which occasionally accumulate into
conglomeratic bands. The greater part of the hill,
however, is composed of white sandstones and grits
indistinctly bedded and stained irregularly, and in
places to a considerable depth, with iron ore. In the
upper part of the hill the white sandstones give place
to ferruginous sandstones with concretionary knots of
earthy limonite and intercalated bands and irregular
lenticular patches of oolitic ironstone. The uppermost
150 feet are made up of oolitic, pisolitic and earthy
ironstones enclosing irregular masses of hard lustrous
concretionary limonite, while the summit is capped by
a pebbly ironstone composed of small rounded and
elliptical pebbles of compact ironstone cemented by
earthy limonite containing a few grains of quartz.’
The prolongation of the Lokoja series into Kabba,
Nassarawa and Bassa is accompanied by much
variation in the extent and thickness of the lower
lighter-coloured rocks, and in the proportions of

1 Cf. Gurich, Zezt. Deut. Geol. Gesell, XXXIX, 1887, p. 122.
v EOCENE ROCKS 175

ferruginous sandstone and oolitic ironstone in the
upper part of the series. Thereare also indications to
the north and east of Lokoja of the ironstones occupy-
ing in places a much lower horizon than they do in Mt.
Patti, as for example in Mt. Gidda where the iron-
stones are found onlya little way above theriver level and
at Amara on the Benue where a ferruginous conglom-
erate very similar to that on the summit of Mt. Patti
is exposed in the bank of the river. On the Benue,
the Lokoja series runs out unconformably and presum-
ably upon Cretaceous rocks in the Doma hills behind
Udeni which present the usual succession of white
sandstones below and red sandstones above. In Bassa
the Lokoja series, although not actually traced, is
believed to be continuous with the white and red sand-
stones and clays with plant remains exposed in the
neighbourhood of Idah and Igore on the borders of
Southern Nigeria. A small outlier of red and white
sandstones and earthy limonite, near Ojerami and
Akwi in southern Kabba, bears witness moreover to
the former extent of the Lokoja series to the west of
the Niger.

(2). Zhe Duguri, Gombe, and Kerrt Kerrt sand-

stones.

The post-Cretaceous rocks of eastern Bauchi and
Bornu, while more or less continuous from south to
north, may be conveniently divided into three groups,
the Duguri sandstones and grits, the Gombe grits and
clays, and the Kerri Kerri grits and ironstones. The
176 NORTHERN NIGERIA CHAP,

series throughout is a well-bedded succession of grits,
sandstones, clays and ironstones, usually lighter-coloured
below, and dark red and ferruginousabove. Although
everywhere unfossiliferous the series presents many
analogies with the Eocene rocks of the Niger valley,
and it is largely upon the strength of those analogies
that these eastern rocks are assumed to be also of
Eocene age. Their stratification throughout is
practically horizontal, though in a few localities a gentle
dip may be observed. Their junction with the under-
lying Cretaceous is believed to be unconformable, but
the actual contact has nowhere been observed. Their
total thickness, from the level of the Gongola at Nafada
to the summit of the Kerri Kerri plateau, is about
1,000 ft., and there is no reason to believe that they
elsewhere exceed this figure to any great extent.

In Duguri, the basal beds are not exposed, but in the
cliffs behind Tongolan there is an excellent section of
400 feet of white and purple grits capped by hard red
ferruginous sandstone, and banked against the crystal-
line rocks to the west. Between Tongolan and Yuli
there is an alternation of white and red sandstones with
occasional beds of gritty clay, while at Samia a series
of white sandstones and clays overlaid by red sand-
stones and grits is exposed in the cliffs which bound
the valley of the Yuli river. The boundary between
the Cretaceous and Eocene is very approximate, and
has been drawn provisionally a little east of Samia,
where the horizontal sandstones appear to give place
to sandstones possessing a distinct inclination to the
west and probably belonging to the inclined Cretaceous
v EOCENE ROCKS 177

series. Southward, the white grits of Duguri appear
to be largely replaced by red ferruginous sandstones,
which are well exposed around Tukkur to the east of
Kantana. On the plateau at Kantana, a thin series of
red sandstones with bands and streaks of flaggy limon-
ite, underlaid by white sandstones, pebbly grits, and
conglomerates, rests directly upon the crystalline rocks,
while the presence of outliers of hard red sandstone
on the summits of the hills around Kanna affords some
indication of the originally greater westward extension
of the series. The correlation of the various rocks in
Duguri and the Kanna district is rendered difficult
both by the rapid lateral variation in character of
individual beds and by the occurrence of much faulting
along the eastern margin of the plateau. The
distinction of a lower and lighter-coloured series from
an upper ferruginous series is less marked in Duguri
than elsewhere, the lower series being apparently in
great part an irregular succession of white and red
sandstones and grits.

Over the central plains of eastern Bauchi the
prevailing rock is a soft reddish grit in places quite
pebbly, in others passing into white and purple sand-
stones. Exposures are found mostly in the deep and
narrow channels which the streams have cut below
the surface of the plain. At Pali bands of white
gritty clay in every respect similar to the clays of
Kurukuru on the Niger (p. 168) are intercalated
amongst the sandstones, some of them containing
knots and lenticular patches of purer kaolin. At

Panguru rounded masses of earthy and oolitic iron-
N
178 NORTHERN NIGERIA CHAP.

stone are found in the surface alluvium, but it is
doubtful whether they are concretions in situ or
rolled fragments of an earlier deposit. A thin series
of soft white and red sandstones and earthy limonites
capped by hard red grit and possessing a dip of 10° S.
and belonging probably to the upper part of the series
is exposed immediately south of Putu. At Kirifi and
Deu on the Gongola, thick beds of white clay similar
to the clays of Pali are exposed below harder beds of
red sandstone and red ferruginous grit. Similarly at
Keffin Serakin Yaki, to the west of the Gongola,
banks of white clay occur as large lenticular patches
in reddish grit. Between Deu and Gombe white
sandstones and clays are frequently exposed in the
lower part of the cliffs which bound the river
valley, the upper part being invariably red sand-
stone or hard ferruginous grit. At Gombe a
characteristic section is exposed in the hill behind
the Residency. A coarse white clay with gritty and
sandy bands in its upper part and somewhat stained
with iron forms the lower slopes of the hill, while
on top are dark red sandstones and pebbly grits
passing in places into flaggy or oolitic ironstones.
The Gombe grits and clays are continuous within
the bend of the Gongola with the grits and ironstones
of the escarpments behind Tilde and Dukul which
bound the narrow plain of the Gongola in the extreme
east of Bauchi province. These eastern escarpments,
however, are much higher than the escarpments of the
west and the upper ferruginous series attains in them
a much greater development. At Dukul the thinly
v EOCENE ROCKS 179

bedded soft white sandstones which outcrop at the
base of the escarpment are covered by a thick series
of hard red grits with bands of flaggy limonite.
Around Tilde and Ribadu the ferruginous grits alone
are exposed, but at Birri to the north the lower series
is again exposed as thinly bedded white sandstones
under the usual ferruginous cap. To the east of the
Gongola, the Gombe series is continued in the low hills
of ferruginous grit, conglomerate, and ironstone around
Ligdar and Buni, and farther east in the sandstones
and ironstones of the broken hills which stretch from
Ndufa to Lua in southern Bornu. Around Ndufa
yellow and brick-red sandstones are exposed below
with ferruginous grits above, containing in places
scattered knots of hematite and streaks of lustrous
pisolite. At Lua the Tagum hills are entirely com-
posed of ferruginous grit enclosing in the upper layers
large knots, lenticles, and irregular masses of hard
pisolitic limonite similar in every respect to the
lustrous pisolite of Mt. Patti at Lokoja. Immediately
south of Koje the lower rocks run out upon the
crystallines in alternating bands of yellow sandstone,
coarse grit, and fine white clay somewhat stained with
iron ore.

In the Kerri Kerri country in western Bornu to the
north of the Gongola, the post-Cretaceous rocks are
magnificently exposed in the southern escarpments of
the Kerri Kerri plateau. The stepped cliffs of Kadi
consist of two thick and imperfectly stratified beds of
soft white earthy grit, passing in places into a coarser
pebbly grit and separated by a thin bed of red

N 2
180 NORTHERN NIGERIA CHAP.

ferruginous sandstone with streaks of limonite which
forms the floor of the step. The summit of the upper
bed is reddened and capped by a thin layer of con-
cretionary ironstone. The detached tabular hills
which fringe the plateau are either of the same height
as the plateau or cut down to the level of the inter-
calated bed of hard red sandstone (Plate XIV, Fig. 1).
In many cases the detached hills are stepped like the
escarpment of the plateau, and at times the upper grits
are represented merely by a conical peak set upon a
platform floored by the ferruginous band which
separates the upper and lower grits. Farther east the
prominent tabular hill behind Fika has a very similar
structure. The base is formed of white and brick-red
grits upon which is set a thick bed of white earthy grit
vertically jointed and bounded by precipitous cliffs.
A narrow ledge of hard red sandstone separates this
lower grit from an upper bed of similar character
somewhat stained with iron, whose gentler slopes are
covered with broken fragments of the red ferruginous
grit which caps the summit. Beyond Fika the
Potiskum road leads as far as Boza through the trench-
like intersecting valleys so characteristic of the margin
of the plateau with the rocks well exposed in the vertical
cliffs on either side (Plate XIV, Fig. 2). Almost in-
variably soft reddish grits are found below and white
earthy grits with bands and streaks of white and pink
clay above, the whole being capped at Boza by a
series of coarse red ferruginous grits. The stratifica-
tion which is indistinct in the lower part becomes more
marked towards the summit of the series and affords
Vv EOCENE ROCKS 181

indications in places of a very gentle inclination
towards the north. The upper ferruginous grits
frequently rise into low hills and mounds on the
surface of the plateau between Farsawa and Potiskum
and near Gojin they contain abundant pisolitic knots
of limonite, whose presence renders the grits very
similar in appearance to those of the Tagum hills in
southern Bornu.

To the west, the Kerri Kerri grits run out upon the
crystalline rocks in the neighbourhood of Hardawa, as
hard white conglomerates and grits, while to the north
and east they are gradually lost under the recent ac-
cumulations of blown sand and earthy drift. Between
Potiskum and Gujba, the surface rocks belong mostly
to the upper ferruginous series, the lower red and
white grits being exposed only in the base of the iron-
stone hills of Durua. The ironstones are very variable
in character and include richly ferruginous grits with
streaks of limonite, gritty pisolitic ironstones, pure
lustrous pisolitic ores and flaggy and earthy limon-
ites, the latter containing in places much decayed
and unrecognisable plant remains. East of Abakri
outcrops become rare and the last trace of the Kerri
Kerri rocks is found at Girboa in some scanty expos-
ures and broken fragments of ferruginous grit. In
central Bornu the only known occurrence of rock of
any kind is the outcrop of sandstone recorded by Barth
in the banks of the Maidugari river.’

It should be remembered that the assumption of an
Eocene age for the Duguri, Gombe, and Kerri Kerri

1 Barth, Central Africa, 1857, II, p. 368.
182 NORTHERN NIGERIA CHAP.

grits, clays, and ironstones rests entirely upon analogy.
They exhibit frequent resemblances to the Eocene
rocks of the Niger valley and more particularly to the
Lokoja series and to the southern portion of the Sokoto
series. They are throughout shallow water accumu-
lations, for the most part distinctly bedded, still
practically horizontal and presenting, like the rocks of
the Niger valley, a succession of a lower lighter-coloured
series by an upper and more richly ferruginous series.
The lithological resemblances are also particularly
striking. The earthy grits of Kerri Kerri can be
exactly paralleled at many points in the Niger valley and
in the valley of the Gulbin Kebbi, although in Kerri
Kerri they attain a much more extensive development.
The clays of Pali, Kirifi and Deu are similar in every
respect to the clays of Kurukuru on the Niger, while
the peculiar pisolitic ironstones and lustrous limonites
of Kerri Kerri and the Tagum hills are exactly similar
to those of Mt. Patti at Lokoja.

The assumption of an unconformable contact of the
Duguri, Gombe, and Kerri Kerri rocks with the under-
lying Cretaceous rests upon the practically constant
horizontality of the former and the practically constant
folding and faulting of the latter. Certain broad
resemblances, however, can be detected between the
uppermost and least inclined Cretaceous rocks of
Ture and Waja and the sedimentary series of Duguri,
Gombe, and Kerri Kerri. Like the latter the rocks of
Waja are of shallow water origin and show a gradual
transition from lighter-coloured sandstones below to
hard red ferruginous sandstones and ironstones above.
v EOCENE ROCKS 183

They are, however, asa rule more distinctly bedded and
inclined and much harder and more compact than the
Gombe and Kerri Kerri series, while in lithological
character they differ in the absence of intercalated clays
in the lower part and in the absence in the upper part
of the oolitic and pisolitic ironstones so characteristic
of the ferruginous series in the Kerri Kerri and the
Tagum Hills.

There is little doubt that in structural and litho-
logical characters the rocks of Duguri, Gombe, and
Kerri Kerri present a greater resemblance to the
Eocene rocks of the Niger than to the Cretaceous rocks
of Waja. The unfortunate absence of paleontological
evidence and of any decisive contacts with known
Cretaceous rocks is however to be greatly regretted.
On the whole it seems improbable that rocks so
distinctly inclined and so evidently undulating as the
Cretaceous of the Gongola valley should give place so
rapidly in the west and north to such an extensive
series of horizontal sandstones and ironstones as is to be
found in eastern Bauchi and Bornu. The entire
absence from the latter moreover of the pipes and necks
of basalt, so abundant in the Cretaceous of the Gongola
valley, is subsidiary evidence in favour of a difference
of age. It would seem indeed that, as in the case
of the Lokoja sandstones and the Cretaceous rocks
of the Benue, all the facts are much more readily
explicable on the assumption of an unconformity
between the Cretaceous and the Eocene in Bauchi
and Bornu.

The possibility of contemporaneous volcanic activity
184 NORTHERN NIGERIA CHAP.

during the deposition of the Eocene sandstones and
ironstones is discussed in Chapter VIII.

3. The Upper Benue sandstones. (A. L.)

Upon the Cretaceous rocks which occupy the Benue
plain in Yola province there rests a thick series of
sandstones which will be referred to as the “ Upper
Benue Sandstones.” The relation between these sand-
stones and their basement is extremely interesting and
yields valuable information as to the history of this part
of Nigeria.

The southern boundary of the sandstones is a very
irregular one. Thus on passing from Gidan Jauro to
Bamga the path proceeds over sandstones for a time,
then passes on to granite for a short distance, then on
to sandstone (an arkose) again and finally on to the
crystallines. North of Bamga the sandstone partly
wraps round a small hillock of granite. But in the
cliff-like sides of the Yendam Hills the evidence that
the sandstones have buried up an old and hilly land-
surface is very clear. Thus in Plate XVI a hill some
hundred feet high is seen to be composite. The bulk
of the hill (off the plate to the left) is granite, but its
base is hidden by conglomerates, which pass upwards
into pebbly sandstones. The latter are banked up
against the granite and overtop it, thus forming a
tabular hill. Many other sections in the district show
asimilar relation between sandstones and crystallines.
(Plate VI, Fig. 1.) There is here no question of a
faulted margin, but evidence on all sides that an older
v EOCENE ROCKS 185

and hilly surface has been buried up in sandstones. If
now one stands amongst these hills, there is the Benue
plain to the north, floored by the Cretaceous limestone-
shales, with the “ Upper Benue Sandstones” resting
upon them ; around are the composite hills with the
sandstone banked up against the granite, while to the
south is the crystalline plateau of southern Yola, with
the highest of its hills capped by sandstone. The
accompanying section’ is approximately correct, though
the maps will not permit of great accuracy.

Passing on towards Yola, there are crystallines at
Bikola and again beyond Jelima, but in the lower
ground between the two are pebbly sandstones and
conglomerates running up from the plain into the
crystalline area as a tongue. Here the present stream
course seems to occupy the same position as an older
drainage channel existing before the deposition of the
detrital rocks. The mass of the Gumba hills is almost
all of granite. The southern part, entirely of granite,
rises to 1,886 ft. above sea-level, but the cone of the
northern peak, 1,727 ft. high, is of sandstone which, as
in the case of the Yendam hills, must have been banked
against the granite at the time of deposition.

The observations made may be summarised by saying
that if the “ Upper Benue Sandstones” were stripped
off, so as to lay bare the underlying basement, no
great change in the physical geography would result.
Some detached hills and outliers would disappear, but
the essential features of the Benue plain with its
Cretaceous rocks and the crystalline plateau of southern

1 See Section IV on margin of coloured map.
186 NORTHERN NIGERIA CHAP.

Yola would still remain. The sandstones evidently
accumulated upon lower ground to the north, at first
abutting against the granite hills of the south but
eventually rising above them. The physical features
were buried up and have been exhumed by later
denudation with great modification in detail but with
the essential characters persisting throughout.’

The sandstones are found to run up the Benue’ plain
past Yola to Garua and they also extend some little
way north and north-west of Garua. The main spread,
however, appears to turn southward, and according to
German writers,’ they are found between Djerim and
Rei-Buba on the uppermost Benue, and also on the
hilly area to the west.

Bearing in mind this distribution of the sandstones
and their field-relations to the underlying basement,
there is seen to be an intimate connection between the
sandstones and the river, and it appears fairly certain
that the sandstones were accumulated in the valley
or valley-plain of an “Older Benue.” The outliers
of the Yendam Hills and the Bagele Hills at Yola,
which rise a thousand feet or so above the river, bear
witness to the former thickness of these accumulations,
now so largely removed.

The Upper Benue Sandstones cannot yet be sub-
divided even locally. No clay or shale bands have

1 The crystalline rocks at the base of the Bagele hills, mentioned by
Barth (Central Africa, Vol. 11, p. 478) may be taken to represent the
outcrop of a portion of the earlier hummocky floor which was buried
under the sandstones of Yola.

2 Passarge, Adamaua, 1895, p. 363. ; Edlinger, Miger-Tsad Expedition,
1904, Pp. 154.
Vv EOCENE ROCKS 187

been found which would serve as horizons. The
material does not vary much. The bulk is very
felspathic and has evidently been formed out of
granitic debris. At Bamga it is not always easy to
distinguish between the arkoses of the sandstone series
and the compacted granite sand at the base of the
hills. The base of the series may become con-
glomeratic and the sandstone is liable to be pebbly
even in the highest layers. Most of the rocks are
white or slightly stained with iron oxide, but there
are also intercalated layers of very ferruginous sand-
stone which occur as definite bands a few inches thick,
traceable across the entire section exposed. The
ferruginous character of these bands was determined
at the time of deposition, possibly by local concen-
tration of the heavier minerals. In addition to such
bands there are in places much thicker masses of
highly ferruginous grit occurring at what is locally the
base of the series.

Much of the sandstone is massive, without bedding
planes, and it tends to form caps to the hills with
vertical sides, fifty feet or more in height. Cross
bedding is beautifully exhibited in places in the lower
part of the series, especially in the Bagele Hills,
around Tagumbilli, and at Lamurde. The laminze
succeed each other in a perfectly regular manner
through considerable thicknesses of material, one set
of laminz being truncated and overlaid by another
set with a different inclination. Cross bedding is
frequently met with in the Cretaceous grits of the
Protectorate, where the laminz are oblique to the major
188 NORTHERN NIGERIA CHAP,

bedding planes. The cross-bedded sandstones of the
Upper Benue, however, are built up of sets of laminz,
indistinctly marked off from those above and below,
and without any true bedding planes at all. The
structure resembles in every way the cross bedding of
the Benue sandbanks, and in size of grain, in the
presence of occasional pebbles and even of pebbly
layers, and in the material itself, a coarse felspathic
sand, the sandstones closely resemble the sandbanks of
the present day (p. 15). The oblique lamination has
been likened to that of dunes, but the coarse size
of grain and the presence of pebbles indicate running
water rather than wind as the immediate cause.

The flat tops of the sandstone hills and the terrace-
like features on their sides show that the Upper Benue
sandstones have not been folded. They rest on the
Cretaceous limestone-shale series, which is folded in
Yola province as it isin Muri. This suggests that the
Upper Benue sandstones rest unconformably on the
Cretaceous and are therefore post-Cretaceous in age.
The actual boundary between the sandstones and the
Cretaceous was only met with in one place, between
Murki and Jibaru, about twenty-five miles north of
Yola. There a coarse, dark red grit rests directly on
Cretaceous limestone without any transition beds
between the two. Unfortunately the dip of the
limestone is not known, and therefore the evidence of
the contact is not conclusive. The immediate change
from limestone to unbedded ferruginous grit is easily
understood if the overlying series is unconformable
to the lower one, but it is not easy to account for it on
v EOCENE ROCKS 189

the view of a continuous sequence. This section is
regarded as strongly supporting the argument drawn
from the unfolded character of the sandstones.

Though the reliance to be placed on lithological
character is uncertain, so far as it goes the evidence is
all in favour of correlating the Upper Benue sand-
stones with the Lokoja series. It is true that the
oolitic ironstones so frequently met with in that series
are not known from the Upper Benue area, but the
soft friable sandstones and the ferruginous character of
much of the material strongly remind one of the
Lokoja series.

The above conclusions, and certainly the map of
this area, will require modification in details, for the
following reason. Two groups of sandstone are
known in the Benue area, one below the limestone-
shales and therefore Cretaceous, the other resting
upon the limestone-shales, in all probability unconform-
ably, and therefore post-Cretaceous. In the absence
of fossils from either group of sandstones, the only
method of determining the age of any particular
exposure is to prove continuity either with the sand-
stones passing below the limestone-shales or with the
sandstones resting upon the limestone-shales. This
would require careful work under the most favourable
conditions, and is out of the question in a preliminary
survey. Thus in the Yola province it may ultimately
prove that Cretaceous (infra-limestone) sandstones
have in places been mapped with the Upper Benue

sandstones.
In a few places in Muri Province there are sand-
190 NORTHERN NIGERIA CHAP.

stones having lithological resemblances to the post-
Cretaceous series. Near Mutum Biu, for example,
there is a porous, very ferruginous grit, breaking up
into small fragments, each coated with a skin of
limonite—characters exactly paralleled, in many locali-
ties, by the Lokoja series. Again at Loko, sixteen
miles north of Katsena Allah, there is a soft unbedded
pebbly sandstone which is much more like the Upper
Benue sandstones than the Cretaceous. It may yet
prove that on the widespread Cretaceous rocks of
Muri there are here and there patches of post-
Cretaceous sandstone, serving to link up the Upper
Benue sandstones with the Lokoja series.

In spite of such future modifications, it is believed
that the history of the Upper Benue can be already
sketched out as follows :

1. Crustal movements (folding and perhaps faulting)
dropped down the Cretaceous rocks below the
crystalline basement along the Lau-Yola line.

2. The soft character of the Cretaceous rocks
marked them out for rapid denudation, and an “ Older
Benue ” was established along this line with crystalline
plateaux north and south.

3. For some reason the detritus carried by the river
accumulated, and on consolidation it formed the Upper
Benue sandstones. The unstratified character of the
material and the absence of alluvial mud or clayey
bands indicates a rapid accumulation, probably under
somewhat different conditions from those now pre-
vailing. The sands were banked up against the
PLatTeE XIII

 

 

THE SANDSTONE HILLs OF TURE.

 

 

 

TURE OR TANGALE PEAK.
v EOCENE ROCKS 191

granites of the south and buried up at least the foot
hills.’

4. Later denudation has largely removed the sand-
stone and has exposed the Cretaceous floor again in
many places. (A. L.)

The great development of rocks of Eocene age in
the region of the Upper Niger has been sufficiently
emphasised by M. Chudeau.? The Niger sandstones
of Dahomey® are undoubtedly continuous with the
western members of the Sokoto series, and are pro-
perly ascribed by M. Chudeau to the Eocene. The
sandstones of the Upper Benue valley in the northern
territories of the Kameruns described by Dr. Passarge,*
are likewise continuous with the Upper Benue
sandstones of N. Nigeria, and therefore most probably
also of Eocene age. From the Southern Kameruns
Dr. Esch® has described Cretaceous and Eocene rocks
whose mutual relations are very obscure. The locally
folded character of the Cretaceous, however, suggests
an unconformity at the base of the Eocene. In
Southern Nigeria Mr. Parkinson’ has indicated the
occurrence of both Cretaceous and post-Cretaceous
rocks whose relations are at present unknown. The
clays and lignites of Asaba” may possibly, however,

1 Cf. Passarge, Adamaua, 1895, p. 390. Passarge did not recognise
the presence of Cretaceous rocks in the Upper Benue valley.

2 Chudeau, Sah. Soud., 1909, p. 97-

3 Hubert, Miss. Sc. au Dahomey, 1908, p. 399.

4 Passarge, Adamaua, 1895, p. 363.

5 Esch, Geologie von Kamerun, 1904, p. II.

6 Parkinson, “‘The post-Cretaceous Stratigraphy of S. Nigeria,’
Q. J. G. S., 63, 1907, p- 309. ’ Parkinson, of. cit.
192 NORTHERN NIGERIA CHAP.

have been accumulated contemporaneously with the
upper shallow-water portion of the Eocene of Northern
Nigeria.

M. Chudeau’s’ admirable attempt at the construc-
tion of a map of the central Sahara is somewhat
marred by his admittedly audacious method of deducing
the solid geology of certain areas from the average
depth of the wells. A striking example of the in-
accuracy thus introduced is the relegation by M.
Chudeau of the Eocene rocks of Sokoto to the Lower
Cretaceous. Another fruitful source of error is the
failure of M. Chudéau to recognise, doubtless through
the want of sufficiently suggestive exposures, the
possibility of an unconformity between the Cretaceous
and the Eocene in the Sudan. There is every reason
to believe that the erosion which followed the post-
Cretaceous elevation was active over the whole of the
Sudan, and that the greater part of the hummocky and
irregular surface thus produced was again under water
during the period of the middle Eocene depression.
Moreover, the deposits then accumulated were in turn
subjected to erosion during a subsequent movement of
elevation, with the result that the early Eocene surface
of crystalline and Cretaceous. rocks was again laid bare
over considerable areas. In view, therefore, of the
former probable extension of the soft sandstones and
ironstones of Kerri Kerri and the Tagum Hills over
the plains of Bornu, it is permissible to doubt the
accuracy of much of M. Chudeau’s suggested strati-
graphy of the Chad area. It seems more reasonable

1 Chudeau, Sak. Soud., 1909, p. 85 ; and map.
Vv EOCENE ROCKS 193

to regard the sandstones of Kanem and Manga as
Eocene rather than Lower Cretaceous, and to look
upon them as having been deposited, as in the case of
the Eocene rocks of the Gongola valley, upon an
earlier surface of Upper Cretaceous and crystalline
rocks now buried beneath the superficial accumulations
of Bornu. The rocks of Koutous and Alakhos, Ouame
and Tirminy’ present, moreover, characteristics which
ally them more with the Eocene rocks of the south
than with the Turonian of the Damergou, and it is
possible that even the southern escarpment of the
Tegama itself? where it overlooks the Damergou
should be referred to the Eocene. The red, white,
and yellow sandstones of Ennedi and of Snoussi on the
Upper Shari are probably also of the same age, and in
no way related (as suggested by M. Courtet*) to the
Karroo beds of South Africa. (J. D. F.)

1 Chudeau, Sak. Soud., 1909, p. 81 ef seg.

2 Barth, Central Africa, 1857, Vol. I, p. 531.
3 Courtet, C. Rd. Ac. Sc. 140, 1905, p. 162.
CHAPTER VI

SUPERFICIAL ACCUMULATIONS

The general absence of a deeply decomposed crust upon the rocks of the
Sahara and the Sudan. The drift of Hausaland and Borgu ; kankar ;
origin of the plains of Hausaland ; the surface ironstones ; origin of
the drift; Mounts Dala and Kogon Dutsi; the surface drift of the
Bauchi plateau ; conditions of formation of the surface ironstones ;
periods of maximum and minimum erosion ; periods of elevation and
depression of the crust ; the recent arid period. The drift of Bornu
and Katagum ; the absence of surface ironstones ; the “ firki ”-land
of eastern Bornu; the shelly marls of Kukawa; the conditions of
formation of the drift of Bornu; the early existence of swampy and
lacustrine conditions in Bornu ; regional oscillations of level in the
Chad area ; erosion of the floor of the present lake ; the cuvettes of
Manga. The drift of the Gongola valley. The drift of the Benue
valley. The ferruginous crusts of the flat-topped hills of the Lower
Niger and Benue.

No fossiliferous deposits of later age than Eocene
have been discovered within the Protectorate. M.
Chudeau* quotes the occurrence of Miocene shales at
Boutoutou ’ to the north of Gober and concludes that
the sea did not finally quit Central Africa until the
close of the Miocene. If, however, any deposits of
similar age were ever accumulated within the Protec-
torate, they appear to have been subsequently removed

1 Chudeau, Sak. Soud., 1909, p. 97.

2 De Lapparent, C. Rd. Ac. Sc., 26 Dec., 1904.
194
CH. VI SUPERFICIAL ACCUMULATIONS 195

and replaced by unconsolidated accumulations, most
probably of late Pliocene age, which now in places
cover Eocene, Cretaceous, and crystalline rocks alike.
These accumulations, which vary considerably in com-
position in different parts of the Protectorate, are of
continental and in part of lacustrine origin and repre-
sent the products of weathering and disintegration of
the crystalline and sedimentary rocks, sorted and rear-
ranged by the action of rain, river, and wind. Their
superficial portion now forms the surface soil which
except in swampy localities is characterised by the
small quantity of humus which it contains. M.
Chudeau* has remarked upon the absence of any deep
decomposition of the rocks in situ in the Sahara and
Sudan to the north of lat. 11°, and his remarks may
with justice be extended to the greater part of North-
ern Nigeria, where the original products of decomposi-
tion have rarely remained in place but have travelled
outwards for a variable distance from the parent rocks
and in places accumulated to very considerable depths.
This drifted or travelled character of the surface
alluvium may be typically observed round the margins
of the larger groups of granite hills. The disintegrated
debris rapidly accumulated during torrential rains at
the mouths of the narrow valleys or at the base of the
weathered slopes is gradually broken up and spread
out upon the plain during succeeding periods of less
intense fluviatile action.

1 Chudeau, of. cét., p. 273.
196 NORTHERN NIGERIA CHAP.

1. Hausaland and Borgu

The red sandy loam which covers the greater part
of the crystalline plains of central Hausaland and
Borgu, while predominantly of local derivation,
possesses for the most part a drifted or travelled
character, and in composition presents relatively little
affinity with the rocks which anywhere immediately
underlie it. A rude stratification may at times be
observed within the drift, but for the most part it
belongs to the category of ill-defined alluvium and
surface wash.’ Red earth and subangular quartz grains
in varying proportions naturally make up the bulk of
the deposit, but it contains also more or less worn and
weathered crystals of all the common rock-forming
minerals together with pebbles and fragments of
quartz, quartzite, granite, gneiss, amphibolite, and other
rocks which are naturally most abundant where the
drift is thinnest. Calcareous concretions similar to
the kankar of India are common in places where the
drift is predominantly earthy. They have, however,
nowhere been observed forming any continuous sheet
of sub-surface limestone, while, contrary to M. Hubert’s
suggestion,’ their distribution appears to have little
or no relation to the occurrence of crystalline lime-
stones within the schistose series. This composite
drift, while evidently resulting from the rearrangement
of weathered and disintegrated material, can frequently
be seen covering up and wrapping round smooth and

1 See Chamberlain and Salisbury’s Geology, 1905, p. 174.
2 Hubert, Mss. Sc. au Dahomey, 1908, p. 102.
VI SUPERFICIAL ACCUMULATIONS 197

little weathered surfaces of rock in the midst of the
open plain. The smaller inselberge moreover appear
to have little influence upon the composition of the
drift, which preserves its heterogeneous character up
to the base of the dome, and even encloses on the
margin sub-angular blocks and boulders of granite
detached at an earlier period from the surface of the
dome itself. In places, as on the high plains of Zaria
and Bauchi, a very considerable thickness of drift has
accumulated, and where locally it has been in part
removed the rocky floor below is hummocky and
irregular and as a rule remarkably free from any
evident decomposition. It is highly probable, indeed,
that the sandy loam with its heterogeneous composition
and its subangular pebbles of various rocks was slowly
accumulated upon an irregular surface and spread out
and levelled by wind and rain.* That it was accumu-
lated, moreover, under very different conditions from
those which now prevail is evident from the fact that
it is nowhere still in process of deposition upon the
open plains of Hausaland. On the contrary it is now
undergoing erosion, rearrangement, and gradual
removal by the rivers and streams which in many parts
of their course have not yet succeeded in exposing the
rock below. Its presence also to a remarkable depth
upon the watersheds and the loftiest plains makes it
highly improbable that such regional accumulation
could have taken place at the present elevation of the
central provinces. It would seem rather that there
has been within comparatively recent times a rearrange-

1 Cf Lenz, G. M., 1879, p. 172.
198 NORTHERN NIGERIA CHAP,

ment of the drainage system of the Protectorate,
brought about by a crustal movement of sufficient
intensity to transform the plains of Hausaland from
low-lying areas of accumulation into high-lying areas
of erosion.

Such an hypothesis serves also to explain the
present typical aspect of the plains themselves when
it is remembered that their gently undulating character
is due not so much to the smooth and even surface
of the underlying rocks as to the covering of drift
which has obscured all the minor irregularities of the
crystalline floor below. There can be little doubt that
the plains of Hausaland arose primarily as approxi-
mately base-levelled plains of erosion. There is,
however, no reason to believe that the actual surface
of the underlying rocks coincides in more than a
general way with that of the open rolling plains of
to-day. All the indications indeed point to quite the
opposite conclusion. The base-levelled plains appear
to have suffered some slight regional elevation and
erosion, and the consequent hummocky and irregular
surface has been in turn levelled up and buried in drift.
The plains as we know them, therefore, while primarily
plains of erosion, are in their more obvious character-
istics to some considerable extent plains of accumula-
tion.” The processes of erosion and accumulation
moreover, to which they owe their present aspect, are
for the most part the same as those which are now
active in these regions. The isolated hills and the

1 Cf Passarge, Rumpfflache und Inselberge (Kordofan-type), Zedt.
Deut. Geol. Gesell., 56, 1904, p. 193.
VI SUPERFICIAL ACCUMULATIONS 199

bare surfaces of rock frequently show evidence of
abundant pot-holing and of extensive fluviatile action.
Messrs. Andrews and Bailey’ have suggested that
a sub-aerial plain of erosion may in time, by means
of dry weathering and run-off, replace a tract of hilly
country at an altitude of even more than 3,000 ft.,
without the help of river erosion or planation. _What-
ever local influence these processes may have, however,
the possibility of such a result upon a regional scale is
exceedingly doubtful. The efficacy of dry weathering
indeed, as an agent of extensive erosion, is, in spite
of the able championship of Professor Walther,’
becoming more and more discounted with the progress
of research in the Sahara.®

A characteristic feature of the red sandy loam on
the high plains of Borgu, Zaria, and Bauchi is the
occurrence in places of a ferruginous cap or crust, which
frequently forms a continuous floor many acres in
extent. The ferruginous cap has arisen through the
cementation of the quartz grains and pebbles into
a hard resistant mass by means of hydrated ores
of iron originally deposited in the subsoil above ground
water level. The characteristic cellular or vesicular
character and hard lustrous surface of the ironstone
are due to the leaching out of the uncemented material
and the rearrangement and partial dehydration of the
iron ores upon exposure at the surface. Wherever,
therefore, the ferruginous cap is now exposed, it may
be assumed that the soil originally overlying it has

1 Andrews and Bailey, Q. /. G. S., Vol. LXVI, 1910, p. 228.
2 Walther, Das Gesetz der Wiistenbildung, 1900.
3 Cf Chudeau, Sak. Soud., 1909, p. 285.
200 NORTHERN NIGERIA CHAP.

been removed in the course of denudation. In
southern Bauchi and Zaria’ the vesicular ironstone
may at times be found forming low platforms raised
a few feet above the general level of the plain, which
is itself in places provided with a similar floor of iron-
stone. At other times where erosion has been more
intense it caps low flat-topped hillocks of drift whose
slopes are littered with fallen blocks and boulders of
gritty ironstone. Rolled pebbles of concretionary
limonite and subangular fragments of an_ earlier
ferruginous crust are frequently also characteristic
constituents of the surface soil. It is evident, there-
fore, that in addition to the period of formation of the
ferruginous crust which now in places forms the floor
of the plain, there has been at least one earlier period
of formation of gritty ironstone within the drift. It
may therefore be presumed that the drift was originally
of sufficient thickness to cover the highest platform
of ironstone of which traces still remain, and that the
ironstone platforms of lower levels were formed during
subsequent intervals in the later erosion of the drift.
In places fragments or masses of pebbly ironstone
of heterogeneous composition can be seen adhering
to bare and unweathered surfaces of granite, sand-
stone, and other rocks. Such occurrences are to be
regarded as relics of earlier sheets of ironstone formed,
it may have been only locally, when the drift was
thicker and the ground-water at a higher level than
it is at present.

1 Rohlfs evidently mistook the surface ironstones of Bauchi and Zaria
for rocks of sedimentary origin. Pet Mitt. Erg., VII, 1872, p. 64.
vI SUPERFICIAL ACCUMULATIONS 201

The clue to the origin of the drift is found within
the walls of Kano. The two flat-topped hills, Dala
and Kogon Dutsi, each 150 feet in height, are com-
posed almost entirely of soft and thoroughly decom-
posed rock, stained red towards the summit and
capped by a layer of vesicular ironstone (p. 90). The
presence of rolled fragments of an earlier ironstone in
the ferruginous cap indicates that the flattened
summits once formed the floor of the plain and were
themselves probably covered by an earlier sheet of
drifted alluvium. These hills bear witness, however,
not only to the extensive decomposition 2” sztw to
which the crystalline rocks were once exposed, but
also to the intensity of the subsequent erosion which
has left them as solitary relics of the earlier surface of
the plain. It is possible, indeed, that the formation of
such a sheet of weathered rock possessed a regional
character, and that in its later erosion is to be found
the explanation of the general absence of any deep
decomposition of the rocks zx s¢tw not only within the
Protectorate but also over the whole surface of the
central Sahara and Sudan. To the erosion of this
weathered crust is also to be ascribed the formation
of the hummocky and irregular surface upon which the
drift was afterwards spread out, and it is probable that
the greater part of the drift itself was derived from
the further erosion of those portions of the original
weathered surface which still remained above the level
of accumulation. No facts have been ascertained with
regard to the occurrence of true lateritic material either
in the original sheet of weathered rock or in the
202 NORTHERN NIGERIA CHAP,

drifted alluvium. There is some reason to believe,
however, that the surface ironstones in places contain
considerable quantities of free alumina.

It is possible that before accumulation began the
weathered rock had not been entirely removed from
the surface of the plains, and that portions of the
original sheet of decomposed material may there-
fore be preserved in places underneath the drift.
Moreover worn surfaces of the original weathered
rock may have been left practically devoid of any
covering of drift, and these surfaces, as around Aribi
and Gantam on the Nassarawa tableland, may have
been in course of time provided with a typical crust
of gritty and vesicular ironstone. The floor of the
plain of Kano around the two prominent hills probably
represents in this manner a platform cut in the earlier
sheet of weathered rock and covered with a ferruginous
crust. A similar origin should perhaps be ascribed
to the plains of Rauni which are characterised by the
great depth of their surface ironstones and the
presence of hillocks of similar composition which
recall the buttes of Djougou in Dahomey.’ Between
Kano and Katsina, moreover, the amount of drift
varies much from place to place, and appears to have
been locally very largely removed and replaced by
recent products of weathering and considerable ac-
cumulations of blown sand and clay which have
probably arisen to some extent through the rearrange-
ment of the earlier drift under the influence of the
winds. These recent accumulations are sometimes

1 Hubert, Miss. Sci. au Dahomey, p. 160, Plate VIII.
VI SUPERFICIAL ACCUMULATIONS 203

found resting upon older surfaces of cellular ironstone,
but are never themselves covered with a ferruginous
crust.

The red earthy drift which forms the detached flat-
topped hills upon the summit of the Bauchi plateau
(Plate XI, Figs. 1 and 2), while located for the most
part upon a crystalline floor, may possibly have
originated to a considerable extent through the
disintegration of the fragmental material of the
volcanic cones in the neighbourhood, and through
the rearrangement of the original weathering products
which may be presumed to have formed upon the
larvas of the Morrua plateau. There are, however,
few remaining traces of any earlier weathering of the
crystalline and igneous rocks preserved underneath
the superficial accumulations. For the most part the
latter rest upon smooth and comparatively unweathered
surfaces of rock (Plate XV, Fig. 2), while their travelled
origin is indicated not only by the presence of quartz
grains and granitic debris in the ferruginous cap, but
by the occurrence of tinstone in the drift throughout
the whole area. The tinstone is naturally most
abundant around Negell in the neighbourhood of its
centre of dispersion, but traces of it are to be found
even on the hills of Rukuba from which the drift itself
has now been almost entirely removed. There is
good reason to believe, indeed, that the Bauchi plateau
up to a comparatively recent date was continuous with
the central plains of Hausaland, and that it participated
in all the oscillations of conditions to which the latter
were subjected. It is probable, therefore, that the
204 NORTHERN NIGERIA CHAP.

plateau was at first covered with a sheet of decomposed
rock of variable thickness, by the subsequent erosion
of which the irregular surface was produced upon
which the drift was accumulated and spread out. It is
obvious, however, that the drift itself with its crust of
compact or vesicular ironstone is now undergoing
erosion, and that the present tin-bearing alluvium is
derived for the most part from the rearrangement of
the drift and only to a small extent from the denuda-
tion of the underlying rocks which is now again in
process. It is probable that, ‘during the earlier stages
in the erosion of the plateau drift, accumulation
continued upon the plains of Zaria and Nassarawa
round the base of the plateau, but any such action is
practically negligible under the present régime.

M. Hubert! in Dahomey, and Dr. Passarge? in
Adamaua, assign only a very subordinate place to the
formation of surface ironstones upon drifted alluvium.
They believe that the ironstones have almost always
formed within material which has arisen as the result
of the decomposition zz sztw of the rocks immediately
underlying.* M. Hubert’s insistence upon this point
of view has led him to suggest that the crystalline
rocks of the plains of Borgu were levelled before being
decomposed and covered with surface ironstones, and
that the plains themselves have preserved their present
character and elevation since the close of the Eocene.
It may be granted that the crystalline rocks of Nigeria

1 Hubert, Z7ss. Sct. au Dahomey, 1908, pp. 109, 123.
2 Passarge, Adamaua, 1895, p. 400.
3 Cf. also Mennell, G. 4., VI, 1909, p. 350.
VI SUPERFICIAL ACCUMULATIONS 205

were at one time deeply decomposed, but Mounts Dala
and Kogon Dutsi bear unmistakable testimony to the
subsequent intense erosion of this former crust of
weathered rock. In southern Bauchi and Zaria, more-
over, extensivesheets of surface ironstone can frequently
be seen capping typical gritty alluvium, and there can
be little doubt that within the Protectorate as a whole,
the formation of surface ironstone upon material
actually weathered zz sztu is the rarer phenomenon.
For the most part the ironstones rest upon and have
been formed within drifted and travelled superficial
material which has been accumulated, near or at base-
level, upon an irregular and hummocky surface, and
spread out in such a manner as to obscure all the
minor irregularities and to produce the present smooth
and even character of the plains of Hausaland. M.
Chautard* has noted the similar extensive formation
of surface ironstones upon the ancient alluvial plains
of Upper Guinea and the Futa Djalon.

The actual conditions of formation of the surface
ironstones are very problematical. Their association
with the older alluvium affords some reason for be-
lieving that their extensive formation in the past has
been accomplished under somewhat different conditions
from those which now prevail. It seems probable also
that the presence of surface ironstone as a ferruginous
cap upon drifted alluvium is an analogous phenomenon
to its occurrence upon material which has arisen,
as in Mounts Dala and Kogon Dutsi, through the

decomposition zz sztw of the rocks below. Drs.
1 Chautard, Le Fouta-Djallon, 1905, p. 126.
206 NORTHERN NIGERIA CHAP.

Hatch and Corstorphine’ believe that the surface
ironstones of South Africa have been formed very
largely as bog iron ores by the oxidation of ferruginous
solutions or by the deposition of the iron salts during
the evaporation of pools of stagnant water. Captain
Freydenberg® has noted the accumulation of
ferruginous clay on the northern shores of Chad, but
extensive sheets of ferruginous material comparable
to the platforms of surface ironstone have nowhere
been observed in process of formation upon the
surface of recent alluvium or of aeolian accumulations
under the present végzme of periodic rains. The
surface waters accumulated during the summer rains
are for the most part rapidly and completely drained,
and any probability of the formation at high altitudes
within the Protectorate of pan or bog iron ores upon
an impervious subsoil would appear to be prohibited
by the general open and porous character of the drift.
Moreover wherever true swamps, subject to partial or
complete annual desiccation, are to be found, surface
ironstones are typically absent, a waterlogged condition
of the subsoil being apparently unfavourable to the
deposition of the iron ores. M. Lacoin® believes that
in alluvial deposits such as those of the Shari and
Oubangui an enrichment in iron takes place in the
lower beds at the expense of the upper, and that the

! Hatch and Corstorphine, 7%e Geology of South Africa, 2nd Ed., 1909,
p- 330. Cf also Hatch, Mineral Resources of Natal, 1910, p. 73; Rogers
and Du Toit, Geology of Cape Colony, 1909, p. 390.

2 Freydenberg, Zchad et Chari, 1908, p. 21.

3 Lacoin, Bull. Soc. Geol. Fr., 15903, p. 484. Cf Foureau, Mss. Sah.,
p. 674 ef seq.
vI SUPERFICIAL ACCUMULATIONS 207

banks of ferruginous material, formed by sub-surface
evaporation and oxidation after the manner of the
“alios” of Landes,’ are afterwards exposed by the
removal of the overlying accumulations. Such an
hypothesis, however, is equally open to the objection
that the surface ironstones of Nigeria are most
typically found where the sub-surface drainage is most
perfect. Professor Walther * believes that the surface
ironstones are entirely the product of arid conditions,
and that their origin is similar to that of the protective
crust of the Libyan desert. While, however, there
can be little doubt that the hardening of the surface of
the ironstone and the production of the characteristic
varnish is the result of the partial dehydration of the
iron ores upon exposure to conditions of excessive
evaporation, it is difficult to believe that the occasional
rains and dews of an arid climate could suffice to
produce any extensive superficial accumulation of the
iron ores. MM. Chautard* and Hubert,‘ in view of
the sporadic distribution of the ironstones, would ex-
tend to their formation Sir T. H. Holland’s hypothesis ®
of the bacterial production of laterite under humid
conditions, an hypothesis, however, which still awaits
experimental verification. Dr. Passarge® is of opinion
that surface ironstones are formed under semi-arid
conditions where the aridity causes the rapid evapora-

! De Lapparent, Zraité des Geologie, 4th Ed., p. 333.

2 Walther, Das Gesetz der Wiistenbildung, 1900, p. 19.

3 Chautard, Le Fouta Djallon, 1905, p. 137; C. Rd. Ac. Sc, 146,
Pp. 239-

4 Hubert, Miss. Sc. au Dahomey, 1908, p. 199.

5 Holland, Geol. Mag., X, 1903, p. 59.

6 Passarge, Adamaua, 1895, p. 396.
208 NORTHERN NIGERIA CHAP.

tion of the occasional rains, while the high temperature
promotes rapid chemical weathering of the rocks, and
the excess of ozone and oxygen compounds in the
rains, together with the absence of reducing substances
in the soil, brings about the rapid oxidation and pre-
cipitation of the iron ores. Mr. Maufe’ believes that
the formation of surface ironstones (muram) in East
Africa is an immediate consequence of deforestation.
There is some reason to believe, however, that even
underneath a covering of vegetation the slow pre-
cipitation of iron ores in the subsoil may give rise to
the formation of ferruginous concretions which may in
time coincide to form a continuous layer. Where the
streams have trenched the deeply decomposed surface
of certain belts of schists in Kabba and Nassarawa
which support an abundant vegetation, it may be
observed that the iron shows a decided tendency to
accumulate in the upper portion. The solution of the
iron is brought about by the descent of water charged
with carbon dioxide and with organic acids, arising
primarily from the decomposition of the superficial
vegetation, while the subsequent rise and redeposition
of the iron ores above ground water level is accom-
plished during periods of less relative humidity. It is
conceivable that a similar action may take place
within alluvial deposits when covered with a rich
vegetation, and that a subsequent change in conditions
may bring about the more rapid evaporation of the
ferruginous solutions, the removal of the vegetation

1 Maufe, The Geology of East Africa, Col. Reps. (Miscell.), No. 45,
1908, p. 53.
vi SUPERFICIAL ACCUMULATIONS 209

and of the surface soil, and the hardening and polish-
ing of the crust into a typical surface ironstone. The
present irregular distribution of the ironstones may
have been conditioned by the amount of subsequent
erosion as well as by the original composition of the
drift, the content in iron of the circulating surface
waters, the abundance of the vegetation and the
character of the drainage, the free access of oxygen
to the subsoil being a necessary condition of their
formation.

Dr. J. M. Maclaren,’ Mr. F. P. Mennell? and Mr.
J. M. Campbell* have suggested an analogous
origin for certain laterites and ironstones of India,
Rhodesia and Upper Guinea respectively, and
postulate for their formation an alternation of wet
and dry seasons similar to the present régime.
Messrs. Mennell and Campbell are of opinion, more-
over, that the concentration of the ores upon definite
horizons to form the floors of successive platforms or
terraces may be explained as the result of a spasmodic
lowering of the ground water level under climatic
conditions similar to those which now prevail. While,
however, the erosion of the platforms themselves
within the drift may certainly be ascribed to this
cause, it is much more probable that, at least
in the case of Nigeria, the spasmodic activity in the
deposition of the iron ores has been brought about by
an alternation of humid and arid conditions, the

1 Maclaren, Geol. Mag. 3, 1906, p. 536.
2 Mennell, Geol. Mag. 6, 1909, p. 350.
3 Campbell, 7”. Just. MM. 19, 1910, p. 432.
210 NORTHERN NIGERIA CHAP.

formation of ironstone being most marked during
periods of gradual desiccation. It is well known that
the present ~égzme of periodic rains within the Sudan
represents a return to more humid conditions after a
period of aridity, and there is some reason to believe
that there have been many such climatic oscillations
in the past. Nothing is more probable, therefore, than
that certain periods of desiccation should immediately
follow the formation of certain platforms of erosion
within the drift, and that to the incidence of these
periods of desiccation is to be ascribed not only the
maximum deposition of the iron ores but also the
removal of the overlying alluvium and the hardening
of the surface of the ironstones. It is probably correct
to assume that an annual alternation of rains and
droughts similar to the present végzme is favourable to
the deposition of iron ores in the subsoil, and there is
every reason to believe that their accumulation is still
going on where conditions favourable to their forma-
tion are to be found. Under present conditions,
however, the amount of iron salts dissolved in the
ground water must be relatively less than it would be
at the close of a period of maximum humidity, and
it may therefore be presumed that in Northern Nigeria
the present is a period of comparatively slow ac-
cumulation of iron ores. There is indeed, as already
remarked, little or no evidence of any extensive forma-
tion of surface ironstone, since the beginning of the
present rég7me.

The ironstones must be exposed actually at the
surface before they can assume their characteristic
PuAtTe XIV

 

 

Doz1 Hitt, KERRI-KERRI.

 

 

A TRENCH-LIKE VALLEY NEAR LELE, IN KERRI-KERRI..
v1 SUPERFICIAL ACCUMULATIONS 211

lustrous carapace, and the removal of the vegetation
and of the surface soil can be accomplished only by a
climatic change. Mr. Campbell! in Upper Guinea,
and Mr. Maufe® in East Africa, would assign the
deforestation very largely to the influence of man, and
the subsequent removal of the soil to the agency of the
tropical rains. It is difficult to believe, however, that
the characteristic ironstone platforms of Hausaland
can possess such a comparatively recent origin, and
there can be little doubt that the highest platforms of
which traces still remain should be referred to at least
the later Tertiary period. Once formed, the hard
resistant crust may be covered by later alluvial or
zolian accumulations or by the products of disintegra-
tion and re-arrangement of the ironstone itself, upon
the return of more humid conditions. Wherever
covered by later deposits, however, the ironstone is
softer and lacks its characteristic varnish. Moreover,
where a scattered vegetation is now found creeping
over a surface of lustrous ironstone, it is frequently a
difficult matter to decide how much of the scanty soil
is a recent accumulation, and how much of it represents
the original covering of alluvium which had not been
entirely removed.

The formation of the surface ironstones of the plains
of Hausaland is thus by no means readily explicable.
Their origin is probably due, in part, to many different
causes, and their fragmental occurrence at various
levels, sometimes upon weathered rock, sometimes

1 Campbell, of. czz., p. 209. 2 Maufe, of. czt., p. 208.
3 Cf also Mennell, of. czz., p. 209.

P 2
212 NORTHERN NIGERIA CHAP.

upon unweathered rock, and sometimes upon drifted
alluvium, points to repeated formation and repeated
erosion at several different periods. It is believed
that, if thoroughly investigated, their distribution and
the distribution of the surface drift would afford some
clue to those repeated climatic and crustal changes to
which within comparatively recent times the surface of
the central Sudan has been subjected. The evidence
already detailed appears to be sufficient to establish
the following succession of events upon the plains of
Hausaland :—

(1) A period of minimum erosion during which the
superficial rocks were deeply decomposed to a variable
depth and covered with a ferruginous cap.

(2) A period of maximum erosion during which the
earlier sheet of decomposed rock was largely removed,
with the exception of such relics as Mounts Dala
and Kogon Dutsi.

(3) A period of minimum erosion and accumulation
during which the surface drift was spread out upon the
plains.

(4) The present period of erosion of the drift
during which, in places, successive platforms have
been cut in the drift and floored with concretionary
ironstone.

The cause of the alternation of these periods of
accumulation and erosion is probably to be sought in
crustal changes of a regional character. If a condition
of low relief be granted to begin with, a general
depression of the surface to the neighbourhood of base
level may be postulated during the periods of
VI SUPERFICIAL ACCUMULATIONS 213

accumulation, and a corresponding elevation of the
surface above base level during the periods of erosion.
The various periods indicated above may therefore be
termed respectively :—

(1) The first period of depression.
(2) The first period of elevation.

(3) The second period of depression.
(4) The second period of elevation.

The history of the earlier periods is somewhat
obscure and it is possible that there may have been
many minor oscillations of the crust during the first
period of depression and the first period of elevation.
It is possible also that the first period of depression
may have been represented merely by a general base
levelling of the surface through erosion, and that the
original sheet of weathered rock may have been
formed in part underneath sedimentary rocks which
were afterwards removed. The flat-topped _hillocks
of consolidated granitic grit and clay between Kano
and Kazaure may perhaps represent contemporaneous
accumulations during the first period of erosion, which
were themselves subsequently exposed to denudation.
There is some reason to believe, also, that there has
been within the various periods a minor oscillation in
climatic conditions. These minor oscillations would
naturally be most clearly recognisable within the
second period of elevation which is continuous with
and includes the present. There is little doubt that
the formation of the surface ironstones was favoured
by the successive occurrence of periods of maximum
214 NORTHERN NIGERIA CHAP.

evaporation, and it is highly probable that these periods
assumed at times a typically desert character, and that
the partially eroded surface of the drift was covered
up at intervals by zolian accumulations. One such
period at least immediately preceded the present more
humid conditions, and is clearly recognisable in the
worn and rounded dunes of the dead erg of northern
Hausaland. The dunes are now grassed over and
covered with scattered trees, but their origin is still
sufficiently indicated in their composition and general
outlines as well as in the characteristic banking of the
sand against rocky exposures. The surface soil and
the recent alluvium of the plains of northern’ Hausa-
land probably contain much wind-blown material, and
the swampy character of much of the surface of the
plains during the rainy season is probably to be in part
explained as the result of the interference of the
accumulations of this recent arid period with the earlier
system of drainage. At the same time, however,
it should be remembered that the erosion of the drift
has in most places not yet become very intense and
that the average slope of the plains of Hausaland
is as a rule so gentle that a considerable volume of
water must accumulate before a perceptible flow can
be established. Much swampland is found on the high
plains around and to the east of Zaria, where
Dr. Baikie’ first recognised the drifted character of
the alluvium.

1 Baikie, A Journey from Bida to Kano, 1866.
VI SUPERFICIAL ACCUMULATIONS 215

2. Bornu and Katagum.

A striking feature of the plains of Bornu and
Katagum and of the Gongola valley between Nafada
and the Yola border is the absence of any superficial
crust of vesicular ironstone. The drift which may
reach in Bornu a depth of more than 300 feet differs
considerably in composition from the characteristic
drift of Hausaland. Upon the open plains of Bornu
the drift is composed for the most part of a mixture
of white or yellow sand and light or dark grey clay.
A red ferruginous staining of the drift is comparatively
rare to the east and north-east of Gujba. The clays
in places yield irregular concretions of kankar and
small nodules of concretionary ironstone are dug from
the surface sands in the neighbourhood of Kukawa,
but no evidence has been anywhere obtained of the
formation or earlier existence of any continuous sheet
of vesicular ironstone. Well sections exhibit below
the surface alternations of sand and clay in beds of
very varying thickness... The sand varies much
in coarseness of grain and is in part angular and of
drifted fluviatile origin and in part well rounded and
of zolian origin, the latter apparently predominating
largely towards the north-east. The clays are finely
divided and flocculent in water and mixed with minute
grains of blown sand. In places they become darker
coloured from the inclusion of organic matter and pass
into the “firki” (p. 52) or so-called black cotton soil

1 Of. Freydenberg, Tchad et Chart, 1908, p. I.
216 NORTHERN NIGERIA CHAP.

of Chad and the lower Shari. Where exposed at the
surface, the clay becomes plastic and very tenacious
in the rains, but hard and brittle and much cracked
and fissured in the dry season. These clays are rich
in azote which contributes much to their fertility.’
This advantage, however, is counterbalanced by the
almost complete absence of lime, potash, magnesia,
and phosphoric acid, and by the presence of large
quantities of silicate of alumina and of salts of soda.
Fragments of broken shells of land snails and lacustrine
molluscs are common in the clays of eastern Bornu,
while thin beds of calcareous marl’ with abundant
remains of recent molluscs are intercalated among the
sands and clays of Mongonu and Kukawa. It is
evident that the conditions of accumulation of the drift
in Bornu were different from those under which the
drift of Hausaland was accumulated. The latter was
preeminently a terrestrial or sub-aerial accumulation
while the former in the finer-grained character of the
sand, the abundance of clay and the absence of pebbles
and of any intense ferruginous staining affords indica-
tions of having been deposited to a great extent
under water in a shallow lacustrine or swampy region.
It is probable, however, that the accumulation of the
drift of Bornu was, at least in the earlier stages, con-
temporaneous with the accumulation of the drift of the
plains of Hausaland and may therefore be referred
to a considerable extent to the second period of

1 Courtet, C. Rd. Ac. Sc. 140, p. 163.
2 Cf. Courtet, C. Rad. Ac. Sc. 140, p. 160; Garde, C. Rd. Ac. Sc. 148,
pp. 1616, 1698.
VI SUPERFICIAL ACCUMULATIONS 217

depression. No traces are left, however, upon the
plains of Bornu of the earlier periods of depression
and elevation, and it may therefore be presumed that
the surface upon which the drift was deposited was
entirely cleared of earlier accumulations during the
first period of erosion and that its minor irregularities
have been completely obscured by the later drift.
The second period of elevation which brought about
the erosion of the drift in Hausaland appears to have
resulted in comparatively little erosive action upon the
drift of Bornu. It is highly probable indeed that
Bornu retained its swampy and lacustrine and there-
fore receptive character to a comparatively recent
period and that the oscillations of less and more
humid conditions which probably prevailed during the
accumulation and erosion of the drift of Hausaland
are reflected in Bornu in the intermingling of zolian
and fluviatile and lacustrine material. The local
abundance of alkaline salts in the drift of Bornu may
also be taken as indicating an occasional and local
desiccation.

The presence of swampy and lacustrine conditions
in Bornu dates, therefore, from the second period of
depression and there is no reason to believe that there
has been any marked break in continuity between
these later Tertiary swamps and the present Lake
Chad. There is, however, no evidence that the
present lake or the former more extensive swamps in
any way represent the shrunken relics of the early
Tertiary seas. The later swamps indeed, with
which the lake is more or less continuous in point
218 NORTHERN NIGERIA CHAP.

of time, appear never to have reached any great depth
and to have been liable to repeated desiccation.
Desert periods may have changed them partially or
wholly into sand fields, but the return of humid con-
ditions constantly re-established their former character.'
It may be presumed also that during periods of excep-
tional rainfall the swamps became united into a shallow
lake of considerable extent which may even at times
have covered the greater part of central and Eastern
Bornu. There is no reason to believe, however, that
this was to any extent a normal condition of things, or
that the drift was primarily accumulated in a large
permanent lake. So far as known, marly beds occur
in Bornu only in the neighbourhood of the present
lake, and whatever the extent of the marginal swamps
may have been, the deepest and clearest water seems
always to have been confined to eastern Bornu. The
thinness and local character of the marls would seem to
imply, however, that the requisite conditions for their
formation were by no means common or universal.
Captain Freydenberg has described in sufficient detail
the former extension of the swamps to the north, east,
and south of Chad.

The character and thickness of the drift deposits
appear to indicate that Bornu has in the past formed
part of an area of predominant depression. The
shelly marl of Kukawa which lies at least fifty feet
above the present level of Chad, undoubtedly indicates
that the floor of the lake was at one time at a higher
level than it is at present. The long-continued

1 Freydenberg, Zchad et Chari, 1908, p. 63.
vI SUPERFICIAL ACCUMULATIONS 219

accumulation was probably conditioned at first by the
second period of depression and later by the gradual
uprise of the Congo watershed during the latest period
of elevation. In the neighbourhood of Kukawa, how-
ever, the low hillocks of drift show evident signs of
erosion, and it may therefore be presumed that the
present floor of the lake has been excavated out of the
earlier lacustrine and drift deposits. This erosion
which M. Garde’ would presumably ascribe entirely
to xolian activity, was probably in great part con-
ditioned by the continued relative subsidence of the
Bodele depression, the consequent eastward draining
of the lacustrine region and the establishment of the
Bahr el Ghazal as a waterway from west to east.
The lower relative level of Bodele has now been
definitely established, and M. Chudeau’s* arguments in
favour of the eastward flow of the Bahr el Ghazal may
be provisionally accepted until fuller information has
confirmed or contradicted them. Desert conditions,
however, followed close upon erosion. The worn and
rounded hillocks of drift around Kukawa were partially
buried in blown sand and the Bahr el Ghazal was
blocked by the action of the wind. On the establish-
ment of the present conditions the lake as we now
know it was formed and limited towards the west by
the line of sand dunes, now covered with abundant
vegetation, which stretches from Kukawa to the river
Yo along the margin of the lake. There is no reason,
however, to postulate the presence of an earlier lake

1 Garde, C. Rd. Ac. Sc. 148, pp. 1698, 1616.
2 Chudeau, Sah. Soud. 1909, p. 232.
220 NORTHERN NIGERIA CHAP.

actually on the site of the present Chad at a period
immediately anterior to the coming of the desert.

It may be presumed that during the period of erosion
which preceded the advent of the desert, shallow
watercourses were cut in the drift of Bornu and that
they were in part dismembered and filled up again
during the succeeding period of desiccation. One
such watercourse may be clearly traced from Murguba
to Maigumeri in central Bornu. The present channels
of the Yo, the Maidugari river, the Yedseram, and the
Shari were probably also established at the same
period. The cuvettes of Manga probably originated
at the same epoch and represent portions of earlier
watercourses detached and isolated by zolian accumu-
lations. The sites of the cuvettes may possibly have
been determined in part by the presence of springs in
the earlier river beds. While, therefore, there is little
reason to believe with Captain Freydenberg* that the
bottoms of the cuvettes represent detached portions of
the original floor of an extensive lake almost entirely
filled up with zolian accumulations, there is equally
little reason to believe with M. Chudeau’ that the
cuvettes have arisen through the local subsidence of
the underlying rocks brought about by the dissolution
of beds of soluble salts, hypothetically contained
within the sandstones of the Tegama below. M.
Chudeau’s objection that an approximately level
surface such as that of the plains of Bornu cannot be
produced under the influence of the wind is clearly un-

1 Freydenberg, Tchad et Chari, 1908, p. 61.
2 Chudeau, Sah. Soud. p. 84.
VI SUPERFICIAL ACCUMULATIONS 221

tenable in view of the known occurrence of extensive
level sandfields in modern deserts. Moreover, in
Katagum solitary dunes or isolated hummocks of blown
sand formed during the recent arid period may be
found alone in the midst of an open undulating plain.
There is some reason also to believe that the winds
which never attained any great intensity varied in
direction in different parts of the Protectorate. In
Bornu the dunes are elongated in a N.—S. direction
while in Katagum they are more generally E.—W.
and it is possible that a successive variation in the
direction of the winds over the same area may have
been responsible for much of the levelling of the
present surface of the plain.

ur The lacustrine conditions which prevailed over cen-
tral and eastern Bornu during the deposition of the
drift extended also for a considerable distance west-
ward through Katagum. The drift of Katagum is
very similar in character to that of Bornu and the
abundance in it of wind-blown material, as in the drift
of Bornu, bears witness to the constant struggle between
humid and desert conditions during the period of
its accumulation. The predominance of the latter at a
period immediately preceding the present is indicated
as in Bornu by worn and rounded dunes and banks of
sand. There is every reason to believe that Bornu
and Katagum have been for long on the margin of the
desert and that the history of the repeated advance and
retreat of the desert can be clearly read in the varied
character and composition of the drift.
222 NORTHERN NIGERIA CHAP.

3. The Gongola Valley

To the west of Gujba, thick accumulations of red
sandy loam effectually obscure the irregularities of the
topography of eastern Kerri Kerri. The drift has evi-
dently been largely derived from the disintegration of
the red sandstones and ironstones of Kerri Kerri, but
the surface of the original deposits has been in great
part rearranged by subsequent zolian action. Upon
the plateau itself the colian accumulations reach in
places a very considerable thickness. In the valley of
the middle Gongola to the south of Kerri Kerri there is
as in Bornu and Katagum, a remarkable absence of
surface ironstone. Around Nafada and southward upon
the narrow plain to the west of the Gongola the drift is
predominantly a red sandy loam. To the east of
Ashaka, however, the drift consists very largely of a stiff
tenacious black or dark grey clay, very similar in
appearance to the “firki” of eastern Bornu. This
material also covers large areas upon the central plain
of Bauchi to the south and south-east of Deba Habe
It is clear from the manner in which the red loam and
the dark coloured clay obscure the irregularities of the
surface and creep up the flanks of the sandstone hills
that the superficial accumulations are here also, as on
the plains of Hausaland, of drifted or travelled origin
and not primarily of the nature of material weathered
and disintegrated in situ. The local origin of the drift
may however be presumed. The red sandy loam of
the northern and western plains has been derived very
vI SUPERFICIAL ACCUMULATIONS 233

largely from the disintegration of the Kerri Kerri and
Gombe sandstones, while the clays of the east and south
have probably arisen in great part from the decomposi-
tion of the lavas of the Burra plateau. The original
depth of the drift is unknown, but must have been very
considerable. The Gongola in places has not yet
succeeded in cutting its way through the drift to the
rock below, while the highest portion of the plain which
is still buried in drift lies about 300 feet above the pre-
sent river bed. The total thickness, however, may well
have been much greater and there is every reason to
believe that what is now the valley of the middle
Gongola between Nafada and Gasi formed, along with
that portion of the central plain of Bauchi which lies
between Deba Habe and Putu, an area of special
accumulation throughout the second period of de-
pression and that the activity of the river and its
tributaries during the most recent period of elevation
has been directed mainly towards the removal of the
drift which had accumulated in the earlier valley.

4. The Benue Valley.

The alternation of the major periods of accumula-
tion and of erosion as established for the plains of
Hausaland was probably to some extent of a regional
character, although the relative amount of respective
depression or elevation may have varied much in
different parts of the Protectorate. The irregular
movements to which the Benue valley as a whole was
subjected during the latest period of elevation renders
224 NORTHERN NIGERIA CHAP.

the correlation of the superficial deposits with those
of the northern States a matter of considerable
difficulty. There is good reason to believe, however,
that the lower Benue valley and the greater part of
the provinces of Kabba and Ilorin were exposed
during the same period to very intense erosion, in
consequence of which the original drift deposits have
been almost entirely removed and the underlying
Eocene sandstones deeply trenched and worn. The
middle Benue, on the other hand, appears to have
been long a region of relative depression and
accumulation, and although platforms of surface iron-
stone may be found in places even on the plains of
Muri,’ the requisite conditions for its formation appear
to have been for the most part wanting. It is possible
that its absence may be due, as in Bornu and the
Gongola valley, to a prolonged water-logged condition
of the subsoil. Wherever, on the other hand, the
surface of a hillock of red sandstone was exposed
above the drift, there seems to have been a rearrange-
ment of the ferruginous material and a concentration
of the iron ores in the upper part which has given rise
upon exposure to a typical honeycombed limonitic cap.
The ferruginous crusts of the flat-topped hills and
plateaux of the lower Benue and the Niger have
a somewhat similar origin and have arisen in part
through the rearrangement and deposition in the
subsoil of the original iron of the sandstones and
oolites and in part, like the ferruginous conglomerate
on the summit of Mount Patti, through the cementa-

1 Passarge, Adamaua, 1895, p. 400.
PLATE XV

 

|

 

CRETACEOUS SANDSTONES AND SHALES AT AWE.

 

 

 

A FLAT-TOPPED HILLOCK OF DRIFT ABOVE NARAGUTA.
vi SUPERFICIAL ACCUMULATIONS 225

tion of travelled material of a similar composition.
Where the summits are bare and lustrous it may be
presumed, as in the case of the ironstone platforms
of Hausaland, that the surface soil, originally overlying,
has been removed in the course of denudation. At
Awe, on the middle Benue, a sheet of sintery calcareous
material appears to have been deposited upon the
upturned edges of the Cretaceous before the accumula-
tion of the drift.

Attention has been already directed (pp. 27, 77) to
the occurrence in Kabba, Nassarawa, and Southern
Zaria of belts of felspathic muscovite magnetite
schists whose deeply decomposed crusts support a
luxuriant vegetation. Where partially eroded, it may
be observed that the iron ores have a tendency to
accumulate in the subsoil, and it is possible that if the
overlying soil and vegetation were removed, the
subsoil might harden into a typical vesicular ironstone.
It is difficult to decide, however, to what extent the
decomposed crusts may be considered the result of
weathering under present conditions. It seems
probable in view of the absence of any deep decom-
position of the adjoining rocks that they may to a large
extent represent the irregular base of the earlier sheet
of decomposed rock to which the presence of Mounts
Dala and Kogon Dutsi bears witness upon the plains
of Hausaland and which may possibly have extended
at the same time over the remainder of the Protectorate.
In some places, moreover, as at Kanna, there is
evidence that the crystalline floor had been locally
and deeply decomposed as the result of differential

Q
226 NORTHERN NIGERIA CH. VI

weathering underneath the Eocene sandstones. <A
similar occurrence has been noted by M. Hubert" at
Youri in the Niger Valley.

Little consolidated accumulations of late Tertiary
age, frequently provided with a ferruginous cap like
the drift of Northern Nigeria, have been described
under the designation of ‘Benin Sands” by
Mr. Parkinson’? from Southern Nigeria, of ‘ Ossa
Sandstones” by Dr. Esch* from the Kameruns, of
“terre de barre” by M. Hubert‘ from Dahomey, and
of veg from the Northern Sahara by numerous French
authorities.° It is yet premature, however, to attempt
any correlation of these deposits with the drift of
Northern Nigeria.

1 Hubert, Mss. Sc. au Dahomey, 1908, p. 368.
? Parkinson, Q. /. G. S., 63, 1907, p. 309.

3 Esch, Geol. von Kamerun, 1904, p. 14.

4 Hubert, Miss. Sc. au Dahomey, 1908, p. 219.
> See Gautier, Sahara Algérien, 1908.
CHAPTER VII

TERTIARY CRUSTAL MOVEMENTS AND DRAINAGE CHANGES

Post-Cretaceous erosion in the Sudan; the Middle Eocene depression ;
western and eastern basins of sedimentation ; crustal oscillations of
the Middle Tertiary period; later Tertiary oscillations ; the first
period of depression ; the first period of elevation ; early drainage
system of the Protectorate ; the second period of depression ; lacus-
trine conditions in Bornu ; the second period of elevation ; flexuring
of the crust ; a- and 8-flexures ; differential elevation of the Nassarawa
tableland and the Bauchi plateau; deflection of the Gongola; de-
pression of the Chad area. Peculiarities of the watersheds and
river valleys of the Protectorate: explanation of the characteristic
features of the valleys of the Niger, Benue, and Gongola ; the origin
of inselberge; M. Hubert’s explanation of the hydrography of
Dahomey ; the period of formation of the ‘dallols” of Sokoto ;
correlation of the Tertiary crustal movements in the Sudan with
those of the Mediterranean area.

The close of the Cretaceous was marked by regional
upheaval, accompanied by fracturing and folding of the
crust and by subsequent intense erosion. The Cre-
taceous sandstones, shales, and limestones, which may
be presumed to have at one time covered the greater
part of the Protectorate, were largely removed from the
underlying hummocky and irregular surface of
crystalline rocks. The plateau of southern Yola, as
described by Mr. Longbottom (p. 32), and the
eastern cliffs of the central tableland of Kabba (p. 16),
would appear to have originated at this period. The

227 Q 2
228 NORTHERN NIGERIA CHAP.

final character of the post-Cretaceous drainage system
and of the early Eocene land surface is, however, very
imperfectly known. Mr. Longbottom believes that
there were earlier river valleys in the place of the
Upper Benue and Lower Gongola of the present day
(p. 190), and there is some reason to believe that there
was also an earlier river in the present valley of the
Lower Niger. At all events it is in these localities
that the greatest thickness of Eocene sediments is now
preserved, although there is little doubt that the later
crustal movements have also, to some extent, affected
their present distribution.

The movement of depression in the Middle Eocene
which resulted in the establishment of open sea in the
north-west and in the deposition of the marine beds of
Sokoto province, brought about also the gradual
submergence of the land surface and the predominance
of shallow water conditions over the greater part of
the Protectorate. In the earlier river valleys the
greatest thickness of sediments would naturally be
deposited, while only the ferruginous sandstones and
ironstones of the latest lacustrine phase would be
deposited over the higher lying portions of the early
Eocene land surface. The formation of the lava fields
of Bauchi and Burra was probably contemporaneous
with the latest phase of sedimentation. There is some
reason to believe, moreover, that during the greater
part of the period occupied by the movements of
depression, there were two major regions or basins of
sedimentation, a western and an eastern, separated by
a stretch of higher ground which extended from Zinder
VIL TERTIARY CRUSTAL MOVEMENTS 229

and the northern frontier of Hausaland to the southern
border of the Benue valley, and of which the Mur-
chison Range formed the only striking physical feature.
The thinning out of the Eocene sandstones to the east
of the Niger valley, on the middle Benue, and to the
west of the Gongola, lends some support to this hypo-
thesis. The accumulations within the western basin,
which was probably continuous westward with the
Atlantic, would then include the lacustrine series of
Southern Nigeria, the shallow water deposits of the
middle Niger, the marine limestones of Sokoto and
the sandstones of Dahomey and the Futa Djallon,
while the Duguri, Gombe, and Kerri Kerri sandstones,
the Upper Benue sandstones and their prolongation
into the northern Kameruns, together with the
ferruginous sandstones of the Upper Shari and the
Congo, would represent the accumulations within
the eastern basin. The outliers of Eocene upon the
Kanna hills and the relics of ferruginous sandstones
upon the plains of Muri indicate, however, that the
western and eastern basins became finally united, and
it seems probable that towards the close of Eocene
sedimentation, shallow water and lacustrine conditions
prevailed over the greater part of the southern Sudan.
Free communication may even have been established
at this time over Central Africa,! between the western
seas of the Upper Niger and the eastern seas of Lybia
and Egypt. There is no reason to believe, however,
that the lower marine facies of Sokoto ever extended
eastward much beyond its present limits.

1 Cf De Lapparent, C. Rd. Ac. Sc., 136, p. 1118.
230 NORTHERN NIGERIA CHAP,

There can be little doubt that the close of the
Eocene was marked by the cessation of the pre-
dominant movement of depression and the beginning
of those crustal oscillations which culminated in late
Pliocene or early Pleistocene times in the formation of
the Bauchi plateau and the establishment of the present
river system. No deposits of later recognisable age
than Eocene have been discovered within the Pro-
tectorate and it may therefore be presumed that until
the close of the Miocene, when the sea is believed to
have finally retired from the Sahara (p. 194), the
surface of the Protectorate remained near or at the
level of the sea. The predominant movement, how-
ever, was probably that of elevation, with the result
that the uppermost members of the Eocene suffered
some considerable erosion and were entirely removed
from the greater part of the surface of the central
provinces. The later Tertiary oscillations, which may
be conveniently grouped as Pliocene, began with a
negative or downward movement, which has already
been termed the ‘‘first period of depression ” (p. 213),
and during which the crystalline rocks of the central
provinces were deeply decomposed and probably also
covered with a layer of drift. The “first period of
elevation ” which followed was marked by a somewhat
irregular upheaval of the surface of the Protectorate.
The maximum movement appears to have been
attained in the east, where the Eocene and underlying
rocks were elevated in a low extended arch whose
axis formed the primary watershed and ran approxi-
mately from Eastern Yola to Zinder and Air. Asa
vit TERTIARY CRUSTAL MOVEMENTS 231

result of the erosion which followed the movement of
elevation the greater part of the sheet of decomposed
rock formed during the first period of depression was
removed from the surface of the central plain. The
crystalline areas assumed very largely their present
physical features and characteristic scenery. The
plains of Hausaland, however, were continuous with
the plains of Nassarawa and Muri across the site of
the Bauchi plateau and the Nassarawa_tableland.
The Murchison Range, the Wadai Hills, and the
Ningi and Kagoro massifs remained then as now
relics of a former erosion, and beyond acting as secon-
dary watersheds exerted comparatively little influence
upon the general system of drainage. The relics of
higher beds occasionally found on the sandstone
plateaux of the Niger may, however, be referred to
this period of erosion. The larger rivers probably
drained south-westward into Southern Nigeria and
Dahomey across the present valley of the lower Benue
and the Niger. The gorges of the Niger above
Lokoja and between Jebba and Yelwa clearly indicate
the much more recent origin of the present river
valley. In the east, however, along the watershed the
sedimentary rocks were deeply trenched and worn on
either side by the headwaters of the rivers. The
valleys of the middle Gongola and of the Upper
Benue present when compared with the Niger Valley
all the characteristics of a more ancient topography.
It seems probable indeed that towards the close of
erosion the rivers which drained westward over the
plains of Bauchi had already established the escarp-
232 NORTHERN NIGERIA CHAP.

ments of Kerri Kerri, the narrow plains of the middle
Gongola, and the cliffs of Waja and Tangale. An
earlier river, moreover, flowed westward from the
hills of Yola with its valley limited as now by the
highlands of Wurkum and Waja, which for a time
interposed a continuous barrier between the rivers of
Bauchi and the headwaters of the Benue. The
establishment of the gap at Kombo was probably
accomplished by a tributary of the Maio Haul towards
the close of erosion. To the east of the watershed the
plains of eastern and central Bornu were likewise
established at this period by rivers which probably
drained eastward and southward over the site of Chad
and the Shari valley into the Congo basin.

There followed, however, the “second period of
depression,” during which the drift was accumulated
upon the irregular surface of the plain. The maximum
movement would appear to have taken place in the
east in the region of the former elevation. It seems
probable that not only was the earlier watershed
depressed to such an extent that the lateral valleys in
Bauchi and Bornu were filled with drift to a depth of
400 to 500 feet, but that lacustrune conditions prevailed
farther east over the plains of Bornu and Chad and
the present valleys of the Logone and the Shari.
Another area of special depression was apparently
situated in southern Zaria and western Bauchi, where
the remains of a covering of drift 200 to 300 feet in
thickness forms a series of flat-topped hills on the
highest portion of the plateau. The older Benue
VII TERTIARY CRUSTAL MOVEMENTS 233

gravels, as described by Passarge* and Edlinger,? were
probably also accumulated at this period. The drain-
age in the earlier stages may be presumed to have
been, in general, towards the areas of maximum
depression, while the close of the period was marked
by the prevalence of conditions of accumulation and of
uncertain drainage over the whole surface. The in-
land seas of the Upper Niger, as described by MM.
Chevalier? Gautier and Chudeau,* should probably
also be referred to this period, but it should be re-
membered that, although they may have been at times
connected with the open sea to the west, there is, as
in the case of Lake Chad (p. 217), no reason to
postulate any kind of continuity between them and
the earlier Miocene or Eocene seas.°

Radical changes ensued upon the cessation of the
movement of depression and the return of a positive
movement of elevation in late Pliocene or early
Pleistocene times. It should be remembered, how-
ever, that the irregular upheaval of the surface during
the “second period of elevation” and the consequent
changes of drainage were in no sense catastrophic.
On the contrary, the movements and changes were
gradual, and possibly to some extent successive and
spread over a considerable interval of time. The
regional elevation of the Protectorate, with the excep-

1 Passarge, Adamana, 1895, p. 385.

2 Edlinger, Miger-Tsad Expedition, 1904, p. 157.

3 Chevalier, C. Rd. Ac. Sc. 15 April, 1901, p. 926.

* Gautier and Chudeau, Sah. Soud., 1909.

5 Of. Suess, The Face of the Earth, Vol. 1V., Oxf. Trans., p. 92.
234 NORTHERN NIGERIA CHAP.

tion of the middle Benue valley, to an average height
of 1,000 feet was accompanied and complicated by
a gentle flexuring of the crust into low arches and
shallow troughs along axes which ran approximately
W.S.W.—E.N.E. and N.N.W.—S.S.E. (see map,
p. 236). The two sets of flexures may be termed
respectively the a-flexures and the @-flexures, and it
may be presumed that they were produced for the
most part simultaneously and only to a small extent
successively by crustal movements, which were them-
selves contemporaneously functional. The irregular
elevation and depression of the surface which gave
rise to the present system of drainage may therefore
be looked upon as the result of the interference of the
two sets of flexures. Two axial arches of the a-series,
a northern (a,) and a southern (a,), are readily dis-
tinguishable within the Protectorate, the southern
being the more important and of the greater elevation.
The northern (a,) runs from Borgu over the high plains
of Kontagora, Sokoto, and Katsina towards Machina
and Zinder, and forms the watershed between the
Gulbin Kebbi and its tributaries on the one hand, and
the Kaduna and the Yo on the other. These rivers
may be presumed to occupy the shallow troughs on
either side of the axial ridge. The axis of the
southern arch (a,) runs from central Kabba through
Nassarawa and southern Bauchi into northern Yola,
and the Benue may be presumed to occupy the trough
to the south. The two a-arches are not strictly
parallel, but diverge somewhat towards the east. Of
the 8-flexures two axial arches are also distinguishable
VIL TERTIARY CRUSTAL MOVEMENTS 235

within the Protectorate, a central (@,) and a western
(B.), the latter being the more important of the two.
The central arch (8}) is of a very partial character, and
is recognisable only in the sinuous watershed which
runs northward between the two a-arches from the
summit of the plateau towards the Sokoto-Kano
frontier and separates the headwaters of the Kaduna
from those of the Yo. The western arch (8,) forms, in
part, the western watershed of the Niger, and runs
northward from the high plains to the south of Ilorin
approximately along the frontier of the Protectorate
to the neighbourhood of Nikki in Dahomey.

The arches throughout are asymmetrical in character,
and vary somewhat in elevation from point to point.
The sinuous character of the crests is probably due to
the mutual influence of the complementary forces
which produced the flexuring at right angles. The
intensity of the flexuring appears also to have varied,
and in the case of two intersecting flexures one or
other usually predominates. In the central region, for
example, the a-arches clearly predominate at their
intersection with the @-arch (@,), while in the west
the B-arch (@,) has evidently been the determining
factor in the establishment of the present course of
the Niger. The interference of the @-arch (@,) with
the western extension of the a-flexures is clearly
reflected in the repeated bending of the river. Where
the a-arches were crossed by the @-arch, dome-shaped
elevations of a regional character were formed, whose
effect may still be traced in the westwardly concave
curves which the Niger describes at Yelwa and above
236 NORTHERN NIGERIA CHAP.

Lokoja. Where the intervening a-trough, how-
ever, was crossed by the @-arch, the resulting curve
was concave eastward as at Jebba. The asymmetrical
position of the Niger valley indicates a shorter radius
for the western portion of the @-arch, while the
fact that the river was able to pursue a continuous
course across the a-arches and troughs makes it
sufficiently obvious that the 8-arch (@,) must have
reached originally a somewhat greater elevation than
the western portion of the a-arches. The influence of
the formation of the western @-trough, now occupied
by the Niger valley, may also be traced in the south-
ward deflection of the lower courses of the Kebbi,
Kaduna and Gurara. It is obvious also from the
height of the sandstone plateaux above Lokoja that
the greatest and perhaps most prolonged movement
of elevation in the Niger valley took place in the
region of the confluence of the Niger and the Benue.
This movement, moreover, was evidently sufficiently
slow to allow of the Niger cutting a continuous trench
across the rising arch, a result, however, which was
rendered possible only by the presence of sedimentary
rocks in the river bed. There is no reason to
believe with Gurich' that, during the formation of
their trench-like valleys in the region of the con-
fluence, the middle courses of the Niger and the
Benue were ever converted into a series of detached
basins or inland seas. It should be remembered
also that the relative elevation of the arches was for
the most part insufficient to produce any marked

1 Gurich, Zezt. Deut. Geol. Gesell., xxxix, 1887, p. 126.
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VII TERTIARY CRUSTAL MOVEMENTS 237

divergence from the apparent horizontality of the
sandstones in the Niger valley.

The symmetrical elevation of the southern a-arch
and the southward prolongation of the central @-arch
were modified and interrupted by the formation of
lines of weakness longitudinally along the former and
in the region of the intersection of the two arches.
The relative influence of the forces which produced
the flexures can be traced in the varying direction and
sinuous character of the lines of weakness. Along
these lines differential movements took place which
resulted in the disproportionate elevation of the
Nassarawa tableland and of the Bauchi plateau with
reference to the middle Benue valley and the northern
plains of Bauchi. On the north the fracturing of the
crust, as already described (p. 39), was confined only
to the central region, while to the west and east the
tableland and the plateau merged respectively into the
general slope of the arch. On the south, however, a
continuous line of fracture extended from western
Nassarawa by way of Darroro and Assab to Sura and
Angass in southern Bauchi. There is ‘no reason
to believe that the southern a-arch as a whole ever
reached the elevation of the Bauchi plateau or that
the plateau originated in any sense as a ‘‘horst,”*
separated from the adjoining tableland and the plains
of Nassarawa and Muri by the later differential
subsidence of the latter. On the contrary, the move-
ment appears to have been in one direction only,
and characterised by the differential elevation of

1 Cf Passarge, Adamaua, 1895, p. 377.
238 NORTHERN NIGERIA CHAP,

the plateau and the tableland and the lagging
behind of the lower plains of Nassarawa, Muri and
northern Bauchi. The trough of the Benue above
the confluence of the Niger affords clear evidence
indeed both of the comparatively stationary character
of the middle Benue valley and of the gradual relative
elevation of the Lokoja sandstones in the region of the
confluence.

In the east the prolongation of the northern a-arch
through Manga and the region to the north of Chad
extends beyond the limits of the Protectorate. The
southern arch, on the other hand, is prolonged as a
simple flexure of varying elevation through eastern
Bauchi into Yola province. In the trough between
the northern and southern arches, the river Yo occupies
the same relative position to the east of the central
B-arch as the Kaduna does to the west. The presence
in the east, however, of the former watershed of the
first period of elevation has introduced complications
into the otherwise simple relations of the a-axes and
troughs. It may be presumed that on the formation
of the southern a-axis and the differential elevation of
the Bauchi plateau, the river Gongola, like the Shidya
and the Delime, would have followed a general north-
easterly course and ultimately joined the Yo but for
the intervention of the higher ground along the earlier
watershed which diverted the river to the south. It
should be remembered that the whole of this region
had been deeply trenched and eroded during the first
period of elevation (p. 231) and that the earlier valleys
had been largely filled with drift during the second
vil TERTIARY CRUSTAL MOVEMENTS 239

period of depression. It seems probable, therefore,
that on the subsequent elevation of the southern
a-arch the Gongola on leaving the high plains of Bauchi
was able to make its way for long distances through the
earlier river valleys and stream courses and ultimately
to escape into the Benue valley through the gap at
Kombo. The trench of the Gongola above Gombe
may possibly be to some extent the product of recent
erosion, but there is little doubt that the plain of the
Gongola below Nafada was excavated at an earlier
period and is in no way to be regarded as the result of
the activity of the present river, whose energy has been
almost entirely directed to the removal of the drift,
which formerly obscured the hummocky surface of the
plain.

The prolongation of the southern a-axis into eastern
Bauchi appears to have been characterised by the form-
ation of a flexure of a flattened monoclinal type, which
resulted in the elevation of the plains of eastern Bauchi
and the middle Gongola to a height of 500 feet above the
valley of the Benue. The actual summit of the flexure
is probably situated in the vicinity of the rapids of
Kombo. The hydrography of northern Yola is very
imperfectly known and complicated by the presence of
the earlier watershed. It is probable, however, that
the present watershed between the Benue and Lake
Chad on the eastern frontier corresponds approxi-
mately with the prolongation of the a-axis, which here
resumes its normal character of an asymmetrical arch.
The last trace of the flexure may be recognised to the
east of the Mandara hills in the swampy watershed
240 NORTHERN NIGERIA CHAP.

between the Benue and the Logone. The configura-
tion of southern Yola suggests an ancient topography,
and its physical character is probably very similar to
that which prevailed at the close of the first period of
elevation. The Chad area to the north remained a
region of relative depression during all the later flexures,
and it seems probable that accumulation continued and
the escape southward of the surplus waters remained
possible until the final elevation of the Congo water-
shed along a parallel flexure to the south. The con-
temporaneous formation of the Bodele depression, how-
ever, brought about the establishment of the effluent of
Chadthrough the Bahr el Ghazal and the partial erosion
of the drift and lake deposits of Bornu. The subsequent
advent of arid conditions during the period immedi-
ately preceding the present resulted, as already
indicated (p. 219), in the diminution of the water supply,
the closure of the Bahr el Ghazal, and the restriction of
the lake to its present limits.

This attempted reconstruction of the more recent
hydrographical changes affords an explanation of many
of the more striking peculiarities in the physical
geography of the Protectorate. Attention has already
been directed to the fact that the larger tributaries of
the Niger and the Benue offer throughout their courses
a reversal of the normal sequence of mountain tract,
valley tract and plain tract. The Kebbi, the Kaduna,
and the Gongola rise upon lofty plains and flow for
long distances in broad sandy channels bounded by
imperceptible slopes until they enter, in their lower
courses, well-defined trench-like valleys bounded on
VII TERTIARY CRUSTAL MOVEMENTS 241

either hand by steep walls of rock. The watersheds
are marked by no ranges of jagged hills. On the
contrary, the lofty plains on which the rivers rise are
frequently more deeply buried in drift than the flood
plains of their lower courses. The rivers flow peace-
fully around and between the lofty granite domes which
rise abruptly from the upper plains, and even such
larger groups of hills as those of Ningi form merely
local centres of dispersion for the smaller streams.
Moreover, the hydrographical centre of the Protectorate
is not a rugged mountain mass, but an open treeless
plain, a plateau 4,000 feet in height, bounded by steep
cliffs on the south and west and provided with worn
and flattened hillocks of drifted alluvium perched in
places upon the very margin of the cliffs. A complete
reorganisation and rejuvenation of the drainage system
is clearly indicated, and it is possible only in some such
manner as that already described. The crust has been
flexured and fractured during a recent regional elevation,
and from the crests of the arches the consequent
streams have been thrown off to pick a course for
themselves over the drift-covered plains and between
the solitary hills and finally to unite to form the major
rivers in the bottoms of the shallow troughs. Dr.
Passarge’ has frequently called attention tothe youthful
age of the rivers of Africa, and his suggestion would
appear to be amply confirmed by the whole character
of the present river-system of Nigeria.

The sinuous course of the Niger within the Pro-
tectorate still represents in a general way the original

1 Passarge, Die Kalahari, 1904, p. 637.
R
242 NORTHERN NIGERIA CHAP,

adaptation of the drainage system to the tectonic
conditions. The diversity of scenery in the present
valley is, however, largely due to the influence of the
lithological character of the underlying rocks. There
is little doubt that at first the Niger flowed throughout
upon a sandstone surface, relics of which now lie from
500-1,000 feet above its present level, and that it
eraded its channel originally as a continuous, deep and
narrow trench. Complications first ensued when the
river succeeded in cutting through the overlying
sandstones between Yelwa and Jebba, and in reaching
the crystalline rocks below. The greater thickness
of sandstones below Jebba conditioned the cutting
back of the gorge between Jebba and Yelwa with
which the river is still occupied. The resistant
character of the crystalline rocks brought about the
formation of falls and rapids, while the consequent
lateral erosion at the head of the gorge gave rise to
the broad sandy plains between Yelwa and Ilo. Below
Jebba the prolonged elevation of the southern a-arch
brought about the continued trenching of the sandstones
above Lokoja and the lateral erosion of the banks in
Nupe and Ilorin, where the level of the river remained
stationary for considerable intervals of time. The
irregular degradation of the channel of the Niger
conditioned also the formation of the broad, flat-
bottomed valleys (dallols) of Sokoto and the narrow
canyon valleys of southern Kontagora, the dissection
of the sandstone plateaux of Nupe, the removal of the
Eocene rocks from northern Kabba and the cutting of
VII TERTIARY CRUSTAL MOVEMENTS 243

the lower gorge of the Gurara. Everything, indeed,
points to the recent erosion of the Niger valley, while
the rapids and falls of the Kaduna and the Gurara
beyond the limit of the sandstones and the ill-defined
valleys of their upper and middle courses clearly indi-
cate that they have only just begun to cut their way
backwards and downwards into the central crystalline
plains.

Compared with the Niger valley, the plains of the
middle and upper Benue present all the characteristics
of a more ancient topography, and it is probable that
they retain to a great extent the configuration which
they possessed at the close of the first period of
erosion. Only in its lower course has the Benue cut a
trench in the Eocene sandstones at all comparable
with the gorge of the Niger above Lokoja, and this
has probably been accomplished, as already explained
(p. 238), during the slow differential elevation of the
region of the confluence. There seems reason to
believe, also, that during the earlier stages of the more
recent erosion the Benue was provided with a greater
volume of water than the Niger, and that to this
influence is to be ascribed the greater imperfection of
the trench of the lower Benue and the removal of the
sandstones from the hummocky crystalline plain of
eastern Kabba. This increase of volume, however,
was probably only relative and contemporaneous with
the diminution of the Niger during the recent arid
period in the Sudan. The return of more humid
conditions, however, together with the capture of the

R 2
244 NORTHERN NIGERIA CHAP.

upper Niger by a tributary of the Taffassasset, as
described by M. Chudeau,' restored the activity of the
Niger and enabled it to cut its present channel in the
surface of the crystalline plains above and below
Lokoja.

The northern tributaries of the Benue, with the
exception of the Gongola, take their rise on the south-
ern border of the Nassarawa tableland and the Bauchi
plateau. Their headwaters alone, however, exhibit
evidence of any recent intense erosive activity.
Behind Jagindi and in the neighbourhood of Assab
the headwaters of the Modu river have trenched and
worn the margin of the plateau. The Wase river has
laid bare in Yergum and Angass the hummocky and
irregular slopes which separate the upper from the lower
plains. The headwaters of the Kudu river have cut
picturesque steep-sided valleys in the rocks of Duguri,
and narrow canyon-like trenches in the central plains of
Bauchi. In the Gongola valley, on the other hand,
the only traces of recent erosion are to be found in the
rapids of Baddera and Kombo and, in part, in
the imperfect trench which the river has cut in the sand-
stones between Gombe and Deu. From its source on
the plateau until it enters the plains to the east of
Gombe, the topography of the river valley recalls in
every detail the characteristic features of the valleys
of the Kadunaandthe Gurara. Nevertheless, although
of similar age and origin, the Gongola flows from
Nafada southward through a valley which presents all
the features of a more intense erosion than the Kaduna

1 Chudeau, Sak. Soud., 1909, p. 222.
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VII TERTIARY CRUSTAL MOVEMENTS 245

or the Gurara or even the Niger itself has been able
to accomplish in its lower course. It is difficult to
escape the conclusion that upon the rearrangement of
the drainage system and the establishment of the
present upper Gongola, the river entered to the east
of Gombe, an older river valley which had been
excavated during some former period of erosion. The
interlacing valleys of the margin of the Kerri Kerri
plateau may possibly have arisen during the latest
period of erosion, but if so, the streams which ex-
cavated them have never regained the activity which
they possessed before the last appearance of the desert
in the Sudan.

The isolated domes and kopjes (Plates III., XII.)
and detached groups of hills which form the most
striking feature of the higher plains are characteristic
also of all the older gneissic areas of Africa, and the
question of their origin has given rise to considerable
difference of opinion. The particular type of scenery
to which they give rise has been termed by German
writers the ‘Inselberglandschaft” (Plate XVII.,
Figs. 1, 2). Passarge’ sees in them the product of
arid conditions, and concludes that the surfaces which
they characterise assumed their present character for
the most part in early Mesozoic times when the
greater part of Africa was a barren desert. Bornhardt,’
on the other hand, believes that the inselberge have
arisen as the result of the superposition of several
cycles of erosion. There is, however, no reason to

1 Passarge, Rumpffidiche und Inselberge, Z. D. G. G., 56, 1904, p. 193.
2 Bornhardt, Deutsch Ost Afrika, Bd. VII, 1900, p. 37.
246 NORTHERN NIGERIA CHAP.

believe that this peculiar topography cannot arise
simply through an alternation of periods of weathering
and periods of erosion, brought about either by
a gentle oscillation of the crust or by a repeated base
levelling of the plains and rejuvenation of the drainage
system. A plane surface of granite and gneiss
subjected to long-continued weathering at base level
would be decomposed to unequal depths, mainly accord-
ing to the composition and texture of the various rocks.
When elevation and erosion ensued, the weathered
crust would be removed, and an irregular surface
would be produced from which the more resistant
rocks would project. Those rocks which had offered
the greatest resistance to chemical weathering beneath
the surface would upon exposure naturally assume that
configuration of surface which afforded the least scope
for the activity of the agents of denudation. In this
way would arise the characteristic domes and turtle-
backs which suffer further denudation only through
insolation and exfoliation. Their general elliptical
outlines, which Merrill? would ascribe very largely
to the influence of crustal stress and strain, are
probably in great part due simply to the modification
by weathering of original phacolitic intrusions. A
slight subsequent movement of depression would
suffice to cover with drift large areas of the irregular
surface between the domes and to produce the
characteristic topography of isolated hills rising,
abruptly from the level surface of the plain (Passarge’s

’ Cf. Harrison, J. B., Handbook of British Guiana, p. 87.
2 Merrill, Rocks and Sotls, 1897, p. 245.
VII TERTIARY CRUSTAL MOVEMENTS 247

Kordofan Type). That such indeed has been the
mode of formation of the kopjes of Hausaland can be
demonstrated within the walls of Kano. Kogon Dutsi,
the larger of the two flat-topped hills of diorite,
although deeply decomposed, still preserves in its
lower part detached boulders or cores of unweathered
rock. If the subsequent erosion had continued until
the weathered material had been entirely removed, the
flattened hill would have been replaced by a typical
kopje of loose boulders resting upon a smooth and
rounded surface of rock below. On the plains around
ample evidence can be found of the levelling of the
surface by means of the accumulation of drift. A
repetition of these conditions of formation would give
rise to an accentuation of the earlier domes and kopjes
and the formation of others of lower level. A similar
origin to that of the domes may be ascribed also to
the detached groups of hills and even to the larger
granite massifs like those of the Ningi, Ruruma,
Kagoro, and Vere Hills. There is no reason to
believe with Passarge’ that the latter partake in any
way of the nature of ‘‘horsts,” which have assumed
their present position through the differential sub-
sidence of the surrounding plains. Their flattened
though hummocky summits evidently bear witness to
an earlier regional level of erosion, but their character-
istic mode of occurrence is to be ascribed not to
marginal faulting, but to a succession of periods of
decomposition and accumulation and periods of erosion

1 Passarge, Adamaua, 1895, p. 377. Cf. also Suess, The Face of the
Earth, Vol. 1V, Oxford Trans., 1909, p. 283.
248 NORTHERN NIGERIA CHAP.

which has brought about the relative lowering of the
surrounding and less resistant gneisses and schists.

The pre-Cretaceous land surface, as exposed around
Tangalto, was marked like the present with domes and
inselberge. The pre-Eocene surface was somewhat
broken and irregular, but probably also characterised,
as in the Niger valley below Lokoja, by detached and
solitary hills. There is no reason, however, to suppose
that the actual pre-Cretaceous configuration of the
plains of Hausaland is still retained. It is much more
probable that domes and solitary hills have been
formed in the manner indicated at many different
periods, and are a characteristic product of sub-aerial
tropical weathering of a crystalline surface when
exposed to oscillations of level.

Dr. Passarge,’ in explanation of the structure of
Adamawa, has assumed the existence of two tectonic
directions, an E.—W. or Benue line, and a
S.S.W.—N.N.E. or Kamerun line, along both of
which extensive faulting has taken place at various
periods and in such a manner as to leave a numerous
series of isolated hills and ranges of hills standing out
as horsts upon the lower plains. According to him, also,
the Bagele and other hills of Yola have assumed their
present position through the subsidence of the sur-
rounding plains, while the Benue valley between Yola
and Garua is of tectonic origin, and bounded by faulted
margins tothe north and south. While, however,
there is some reason to believe that the Cretaceous

1 Passarge, Adamaua, 1895, p. 387. See also Suess, Zhe Face of the
Earth, Vol. IV, 1909, p. 280.
VII TERTIARY CRUSTAL MOVEMENTS 249

rocks of Yola have been faulted down against the
crystallines to the north and south, and that in pre-
Eocene times an earlier river occupied a tectonic valley
in the region of the upper Benue (p. 190), there is no
evidence to show that there has been a recurrence
of faulting on the upper Benue in post-Eocene times,
or that the slopes of any of the hills of “ Upper Benue
Sandstone” have been defined by later Tertiary or
recent movements. Passarge’s hypothesis is applicable
only to pre-Eocene topography, and cannot be extended
in explanation of those features of the upper Benue
valley which are of more recent origin.

M. Hubert’ has suggested in explanation of the
hydrography of Dahomey that the courses of the
present streams bear a direct relationship to the strike
of the gneisses and schists, and that the surface of the
colony has remained stationary since the close of the
Eocene. His hypothesis, however, is admittedly
inadequate to explain the transverse character of the
Niger valley. In Nigeria, moreover, all the principal
rivers without exception flow across the strike of the
gneisses, while the drift-covered character of the lofty
plains and of the watersheds and the nature of the
whole hydrographical system clearly indicate the
recent elevation of the present surface of the Pro-
tectorate. It is very probable indeed that Dahomey
has participated in all the recent crustal movements
which have affected Nigeria, and that the central
watershed of the colony corresponds with the west-
ward prolongation of the northern a-arch and the

1 Hubert, Miss. Sc. aw Dahomey, 1908, p. 443.
250 NORTHERN NIGERIA CHAP.

western f-arch of the Protectorate. A recent re-
juvenation of the drainage system is postulated, more-
over, by M. Chudeau’ in the French Sudan, by
Mr. Parkinson? in Southern Nigeria, and by Dr. Esch?
in the Kameruns, and it is improbable that Dahomey
should have escaped the general movement of eleva-
tion.

M. Chudeau‘* has recognised in the Sudan the recent
period of arid conditions of which traces are still
to be found within Northern Nigeria. He believes,
however, that the dallols were excavated during the
period of desert conditions by rivers which drew their
supplies from the mountains of Air. It is possible
that there may have been repeated alternations of
desert and humid conditions within the latest period
of erosion ; but it is clear in Nigeria that the dallols of
Sokoto were already excavated before the advent
of the latest arid period, and that the rivers which
formed them have not regained the activity which
formerly characterised them. Capt. Meynier’s sug-
gestion, quoted by M. Chudeau, that the rivers of
Hausaland turned their backs to the desert, though
picturesque, is little in harmony with the facts. The
courses they follow within the Protectorate were
defined long before the advent of the desert, and not
by any adaptation to climatic conditions, but by the
direct influence of the early Pleistocene crustal move-
ments which brought about the rejuvenation of the

1 Chudeau, Sak. Soud., 1909, p. 220.

2 Parkinson, G. /., XXIX., 1907, p. 56.
3 Esch, Geologie von Kamerun, 1904.

4 Chudeau, Sah. Soud., 1909, p. 220.
VII TERTIARY CRUSTAL MOVEMENTS 251

drainage system of Nigeria and the formation of
the Bauchi plateau. These movements were probably
also responsible for the establishment of the dallols
of Tahoua and the quaternary wadis of the northern
Sahara, as well as for the elevation of the plateaux
of Air and Adr’ar’ des Ifor’as. These movements,
moreover, were probably contemporaneous with the
later Tertiary movements in the Mediterranean basin
and in East Africa.

M. Chudeau" has pointed out the analogy between
the pre-Devonian and the post-Carboniferous move-
ments to the south of the Atlas and the caledonian
and hercynian movements to the north of the Alps.
In Nigeria and the Sudan some analogy may perhaps
be permitted between the general meridional strike
and vertical folding of the gneisses and schists and the
caledonian folding of Scotland and Scandinavia.
Of hercynian movements, however, there is little or
no trace in the Sudan, while the presence of an
unconformability at the base of the Eocene and the
absence of any later folding makes the post-Cretaceous
and early Tertiary movements in the Sudan more
nearly parallel with the sequence of events in northern
Europe than with the sequence in the Alps and the
Atlas. The period of maximum movement in the
Alps would appear to be represented in Nigeria and
the Sudan only by minor post-Eocene oscillations of
the crust, while the major movements in the Sudan
which gave birth to the present drainage system
appear to be contemporaneous with the later

1 Chudeau, Sah. Sowd., 1909, p. I.
252 NORTHERN NIGERIA CH. VII

Mediterranean stages of the Alpine movements.’
At the same time, however, it should be emphasised
that, while the movements may have been contem-
poraneous, there was probably little or no genetic
connection between them. The Tertiary period was
everywhere a period of great instability of the crust,
and the movements would appear to have varied both
in intensity and in kind, and to have been localised
now in one place and now in another, at different
periods of their history.

1 Suess, Zhe Face of the Earth, Vol. I. Oxf. Trans., 1904, p. 279% *
CHAPTER VIII

TERTIARY VOLCANIC ACTION

Absence of pre-Tertiary volcanic rocks within the Protectorate: two
periods of Tertiary volcanic activity. The early Tertiary period :
the Maradu vent; the nepheline basalts of Wase and Tangalto ;
the phonolites of Wase Rock, Tangale Peak and Bantaji; the
plateau lavas of southern Bornu, Bauchi and Nassarawa ; petro-
graphical character of the lavas ; early Tertiary lavas of the Sahara,
Sudan and Adamawa. The later Tertiary volcanic period: the
puys of northern Yola, the middle Benue valley and the Bauchi
plateau ; petrographical character of the lavas; petrographical
provinces.

It may be presumed that the intrusion of the
alkali granites and dyke rocks throughout the
Protectorate was accompanied in pre-Cretaceous times
by considerable superficial volcanic activity (p. 142).
M. Chautard? has, moreover, described the intercalation
of volcanic rocks in the Upper Cretaceous of Senegal.
All trace of pre-Tertiary effusive rocks, however,
within the Protectorate appears to have been removed
in the course of denudation. The fracturing and
folding of the crust at the close of the Cretaceous was
apparently accompanied in places by the formation of
mineral veins within the fissures, but no contempor-
aneous igneous activity has been definitely identified

1 Chautard, Bull. Soc. Geol. Fr., 4th Series, VII., 1907, p. 427.
253
254 NORTHERN NIGERIA CHAP.

within the Protectorate (p. 140). Within the Tertiary
era itself two separate periods of volcanic activity
may be recognised, one in the middle Eocene and
probably to some extent contemporaneous with the
accumulation of the Eocene sandstones within the
Protectorate, and one in late Pliocene or early
Pleistocene times and contemporaneous with the later
Tertiary oscillations of the crust. For the most part
the eruptions were of an isolated character and gave
rise to the formation of detached pipes, cones and
puys of igneous material. More rarely, as in southern
Bornu and on the borders of Bauchi and Nassarawa,
the extruded lavas united to form a continuous sheet
of volcanic rock, which covered a considerable area of
the underlying sedimentary and crystalline rocks.

The earliest outburst of volcanic activity appears to
have taken place towards the close of the post-
Cretaceous erosion or possibly in the middle Eocene
at a period contemporaneous with the accumulation of
the lower marine beds of Sokoto, and is represented
now by the extensive neck or vent of fragmental
material near Maradu in Sokoto province whose
levelling was accomplished during the later extension
of the middle Eocene sea. The greater number of
the boulders in the agglomerate are composed of a
microgranitic quartz porphyry with phenocrysts of
orthoclase, biotite and brown hornblende in addition
to quartz (1323). To the same period is probably
also to be referred the line of well-worn stumps of
basalt, phonolite and trachyte which stretches from
the Gongola valley westward through Tangale and
VIIE TERTIARY VOLCANIC ACTION 255

Angass to Namu in northern Muri. The Tangale
Peak (PI. XIII. Fig. 2) and the’ Wase Rock (PI.
V. Fig. 2), which still retain a portion of the original
flow attached to the rock in the vent, were probably
among the latest eruptions of. the series. The
intrusive dolerites of Bashar (41) and Awe (1014) may
be ascribed to the same phase of igneous activity,
while the Rock of Bantaji in Southern Muri may be
taken to represent contemporaneous volcanic action
to the south of the Benue. 7

In petrographical character the basaltic pipe rocks
are always olivine-bearing and usually porphyritic with
olivine and augite. Felspar is found only in the
ground-mass which at times contains a little intersertal
glassy base. The basalt of Wase Topa is remarkable
for the number and size of the nodules of olivine
which it encloses. A worn vent immediately south of
the town of Wase is filled with a fine-grained nepheline
basalt (32) containing glomeroporphyritic aggregates
of augite crystals and well-formed crystals of olivine.
Felspar is entirely wanting, the ground-mass being
composed of small rods of augite and granules of
magnetite set in a brown glassy base studded with
minute crystals of nepheline. A somewhat similar but
coarser-grained rock from Tangalto (1661) contains
large crystals of decomposed olivine and purple and
well-zoned augite in a holocrystalline ground-mass of
rods and granules of augite, magnetite grains, flakes of
biotite and abundant nepheline in well-formed and irre-
gular crystals. The nepheline was evidently the last
to crystallise, and to some extent takes the place of
256 NORTHERN NIGERIA CHAP.

matrix, being in part moulded upon the other constitu-
ents of the ground-mass.

The phonolite of the Wase Rock (31) is of a trachy-
toid type, containing columnar phenocrysts of sanidine,
ragged crystals of aegirine augite and scattered pseu-
domorphs after nepheline in a ground-mass consisting
predominantly of minute felspar prisms with a well-
marked fluxional arrangement, mingled with magnetite
grains and rods and granules of green pyroxene. The
phonolite of Tangale Peak (1665-6) contains pheno-
crysts of sanidine and soda pyroxene in a ground-mass
of a more orthophyric type, composed of minute
idiomorphic crystals of nepheline, imperfect prisms of
aegirine and aegirine augite and elongated microlites of
felspar which pass into an ill-defined felspathic matrix.
Traces of brown hornblende in irregular porous growths
may also be observed in the ground-mass. A similar
rock from the immediate neighbourhood of Tangalto
(1663)contains soda pyroxene, but no evident nepheline
in the ground-mass, and may be grouped provisionally
as atrachyte. The phonolite of Bantaji Rock is of a
more nephelinitoid type, with the ground-mass enclosed
in a somewhat intersertal manner between the abun-
dant but much decomposed phenocrysts of felspar.
With the felspar are associated as phenocrysts hypidio-
morphic crystals of aegirine and aegirine augite
frequently in zonal growths and smaller idiomorphic
and abundant crystals of somewhat weathered nephe-
line. The ground-mass is composed of lath-shaped
felspars, granular pyroxene and irregular patches of
analcime probably of secondary origin. The association
VulI TERTIARY VOLCANIC ACTION 257

of phonolite and nepheline basalt, observed in the
neighbourhood of Wase and the Peak, has not been
recognised around Bantaji.

The period of formation ot the lava fields in southern
Bornu and on the borders of Bauchi and Nassarawa
may be provisionally referred to the close of the
middle Eocene, on the strength of the apparent inter-
calation of a friable red sandstone amongst the lavas
in the escarpment of the Barbur plateau behind
Dukshi. The extensive erosion which the plateau
lavas themselves have undergone indicates, moreover,
that they are of no very recent age. The eastern
lava field is the more extensive of the two and perhaps
somewhat younger, so far as one can judge from the
less denuded character of the cones. The rich content
in iron of the upper part of the Eocene accumulations
may possibly have been conditioned to a considerable
extent by the distribution of much fragmental basic
igneous material upon the surface of the waters.

In petrographical character the lavas are basaltic
throughout and rich in olivine, and vary from felspathic
doleritic types to limburgitic varieties in which felspar
is greatly reduced in amount.’ Nepheline-bearing

! These rocks present in microscopical structure a decided resem-
blance to the Carboniferous lavas of the Bathgate Hills (Falconer,
Trans. Roy. Soc. Edin., Vol. XLV., 1906, p. 133) in Scotland. With
the exception that the doleritic types are somewhat less weathered,
the description and classification of the Bathgate rocks may be applied
almost word for word to these Tertiary lavas of Nigeria. Doleritic
rocks (Falconer, of. cé¢., Plate I., Fig. 2) with phenocrysts of augite and
olivine, and more rarely of felspar are common on the Morrua plateau in
eastern Nassarawa and along the base of the escarpment between Darroro
and Assab (928, 1573, 1630). Felspar is abundant in the ground-mass
and the augite occurs in granules, granulitic aggregates, small ophitic

s
258 NORTHERN NIGERIA CHAP.

types have nowhere been recognised, nor any effusive
rocks more acid than basalt. MM. Chudeau and
Gentil! have, however, indicated the occurrence of
aegirine rhyolites and phonolites, as well as of basalts,
tephrites and limburgites, amongst the older lavas of
Ahaggar and Air, which are probably of similar age to
those of Nigeria. Dr. Passarge® has described the
occurrence of basalt, augite andesite and phonolite on
the summit of the Shebshi hills on the borders of
Nigeria and the Kameruns. MM. Gentil and
Freydenberg*® believe that the aegirine porphyries
of Mounio and of Hadj el Hamis on the southern
shore of Chad are of volcanic origin. M. Garde,’
however, is of opinion that they possess an intrusive
character and belong to the hypabyssal phase of the
alkaline magma which gave rise to the Mounio and
Melfi granites.

The plutonic rocks of this early Tertiary volcanic
period are nowhere exposed within the Protectorate,

plates, or minute idiomorphic crystals between the felspars. The basalts
of Zammagan (1578) and Buratai (1640) show a typical fluxional arrange-
ment of the felspars (Falconer, of. cz¢., Pl. 1., Fig. 3). The basalt of
Kwoia (1654) exhibits an intimate mixture of felspar and augite in the
ground-mass (Falconer, of. cz, Pl. I., Fig. 4). The basalt of Assab
(934) contains scattered felspars with abundant minute granular agegre-
gates of augite, while a similar rock from Buratai and Dukshi (1641) con-
tains some residual brown glassy material and passes into limburgitic
varieties with phenocrysts of augite and olivine in an ill-defined microlitic
base.

1 Chudeau, Sak. Soud., 1909, p. 258; Gentil, Doc. Sc. Miss. Sah.,
1905, p. 726.

2 Passarge, Adamaua, 1895, p. 374. See also Downes, Geol. Rep.
Vola-Cross River Boundary Commission, 1910, p. 35.

3 Gentil and Freydenberg, Bud/. Soc. Geol. Fr, 4th Ser., VIII., 1908,
p- 35; Lacoin, C. Rd. Ac. Sc., 22 June, 1903.

4 Garde, C. Rd. Ac. Sc., 149, 5 July, 1909, p. 43.
Vill TERTIARY VOLCANIC ACTION 259

and hypabyssal types are almost unknown. The
doleritic sills of Awe and Bashar were probably in-
jected during one of the earlier phases of igneous
activity. Dr. Passarge’ has indicated the occurrence
of basaltic dykes in the sandstones of Adamawa and a
boss of nepheline syenite between Yola and Garua on
the upper Benue. The latter, however, more
probably belongs to the underlying crystalline floor.
M. Chudeau* believes that the alkali granites of
Zinder and Mounio have been intruded since the
close of the Cretaceous; but while there is every
reason to believe that the nepheline basalts and
aegirine rhyolites of Tertiary age drew their origin
from a magma rich in soda, there is, as already stated
(p. 140), no evidence within the Protectorate upon
which any immediate connection between the younger
soda granites and the Tertiary volcanic rocks can
be established. On the contrary, there would appear
to have been in the middle Eocene within the Pro-
tectorate merely a renewal of volcanic activity from
the same alkaline source from which the pre-
Cretaceous granites and dyke rocks originated. If,
however, further investigation should confirm M.
Chudeau’s suggestion of the Tertiary age of the
granites and porphyries of Zinder, Mounio and Goure,
these rocks may then be taken to represent the
plutonic and hypabyssal phases of this middle Eocene
period of igneous activity.

To the later Tertiary period ot volcanic activity,

1 Passarge, Adamaua, 1895, pp. 363, 384.
2 Chudeau, Sak. Soud., 1909, p. 266.
260 NORTHERN NIGERIA CHAP.

which may be referred to the close of the Pliocene
and which perhaps also extended into the early
Pleistocene, are to be assigned the puys of Kereng
(Plate X, Fig. 2) on the southern margin of the Bauchi
plateau, the puys of Song and Mboi (Plates VI, Fig. 2 ;
VII, Figs. 1, 2) in northern Yola, and somewhat doubt-
fully also those of the Awe district on the middle Benue
(Plate V, Fig. 1). The puys of the Kereng group are
remarkably perfect and exhibit steep crater walls of
fragmental material breached by a single short flow of
olivine basalt. Elsewhere on the plateau also, as
between Vom and Bukuru, there are small puys with
breached craters which are probably of a similar recent
age. From the cliffs of Assab, moreover, later flows
of lava may in places be seen on the worn slopes of
the plateau edge, and there is every reason to believe
that the erosion of the drift and of the margin of the
plateau was considerably advanced before the final
close of volcanic activity. The presence of craters
and the local character of the associated flows serve
to distinguish these later products of igneous activity
from the earlier lavas of the plateau. A similar super-
position of later volcanic material upon earlier lavas
has been observed by M. Chudeau' in the Ahaggar
and in Air. Unlike the central Sahara, however,
there is in Nigeria no reason to believe that there has
been any actual continuity in volcanic action between
the earlier and the later periods.

In Yola province the Mboi Hills are crossed by a
line of small craters four or five miles long, running

1 Chudeau, Sak. Soud., 1909, p. 361.
PLATE XVIII

 

 

 

 

THE SALT-FIELDS OF AWE; VOLCANIC HILLS IN THE BACKGROUND.

 

 

 

 

AKIRI SALTINGS.
VIII TERTIARY VOLCANIC ACTION 261

roughly in a N.W.—S.E. direction. To the south-
east between the Mboi Hills and Song the line is
continued by a number of hillocks of basalt for a few
more miles, but how far it extends to the N.W. is
not known. Only a relatively small amount of basalt
was erupted from these vents. In the case of the
largest crater with a crater floor of 250 yards in
diameter the volcanic material was not sufficient to
conceal the granite through which it came. The
granite was broken away during the eruption so as to
form a cliff extending one-third round the crater, while
the other two-thirds is formed of agglomerate and tuff
with very many fragments of granite. The crater
thus resembles a swallow’s nest attached to its support.
With one exception, where the wall is entire, all the
craters were breached by a lava flow. They are in
excellent preservation, and the cliff-like walls, with
insignificant talus heaps at their bases, indicate a very
recent origin. (A. L.)

The vents on the plain to the south-east are not
marked by craters or by fragmental materials, but by
mounds of basalt less than fifty feet high spreading
out into lava flows, which cover most of the surface
near by. Here the eruptions seem to have consisted
in a much quieter extrusion of lava alone. The
basalts are all vesicular and very commonly quite
light and cellular. (A. L.)

The basalts of the Benue plain likewise form low
hillocks or mounds with no tuff or fragmental material
tobeseen. Generally there is no lava flow proceeding
from them, and the extrusion of quite a small quantity
262 NORTHERN NIGERIA CHAP.

of lava seems to have sufficed to relieve the pressure.
Kaddemi Hill is an exception; an old basalt flow
leads from it for two to three miles to the south-east.
(A. L)

All the basalt flows around Awe are raised consider-
ably above the level of the plain, and protect the
limestone shales below from denudation, though else-
where the shales are very badly exposed. In conse-
quence the flows rest on “ pedestals” from thirty to
fifty feet in height. Assuming that the lava chose the
level surface of the plain rather than ridges upon it, it
follows that since the eruptions around Awe there has
been a general lowering of the surface by that amount.
From this it appears that the Awe eruptions were not
quite contemporaneous with those of Mboi, for at the
latter place only a small amount of talus has been
broken off from the crater cliffs. (A. L.)

The ash cones and puys of the middle Benue are
much more imperfectly preserved than those of Kereng
or Mboi and are certainly considerably older. Their
comparatively recent age is presumed, however, as in
the case of the later volcanic period in Air and Tibesti,'
from the presence of thermal springs in the immediate
neighbourhood. It seems probable that they were
established as the result of the crustal movements
anterior to the accumulation of the drift, while the puys
of Kereng and Mboi owe their origin to the differential
movements of the latest period of elevation.

In petrographical character these later rocks are
very similar to the earlier Tertiary lavas. All are

1 Chudeau, Sak. Soud., 1909, p. 264.
VII TERTIARY VOLCANIC ACTION 263

basalts rich in olivine and augite and varying in the
same locality from types with abundant felspar in the
ground-mass to thoroughly limburgitic’ varieties (12)
from which felspar is entirely wanting. The ash of
the Kereng puy is remarkable for the number and size
of the rounded augite crystals and olivine nodules
which it contains. Recent flows of olivine basalt and
limburgite are known also from Ahaggar and Air * and
from the Kameruns.* M. Chudeau* has described
rhyolites from Inzize to which he assigns a later
Tertiary age, Dr. Passarge° has noted a nepheline
basalt from an isolated cone of recent origin in the
Benue valley between Yola and Garua, and Dr.
Esch’ has described nephelinites and leucitites from
the Kamerun Mt. which is still periodically in active
eruption. No rocks of similar composition, however,
have been recognised amongst the products of the
most recent volcanic period within the Protectorate.
MM. Chudeau’ and Chautard,* following M. Lacroix,°
have suggested that the alkaline rocks of North Africa
may be grouped into three petrographical provinces, a
western province including the Azores, Canaries, Cape
Verde and Senegal, a central province including
Ahaggar, Inzize, Air, Zinder and Mounio, Chad and

1 Cf. Falconer, Trans. Roy. Soc. Ed., XLV., 1906, Pl. I, Fig. 6.

2 Chudeau, Sah. Soud., 1909, p. 361.

3 Esch, Geologie von Kamerun, p. 40.

* Chudeau, of. ctt., p. 259.

5 Passarge, Adamaua, 1895, p. 384.

6 Esch, Sitz. Ber. Ak. Wiss. Berlin, 1901, p. 277.

7 Chudeau, of. cét., p. 268.

8 Chautard, Bud?. Soc. Geol. Fr., 4th Ser., VII., 1907, p. 427.

9 Lacroix, C. Rd. Ac. Sc., 24 May, 1899, p. 13533; 1905, 140, p. 22.
Nouv. Arch. Mus., 4th Ser., IV.,fp. 156; V., p. 246.
264 NORTHERN NIGERIA CH. VIII

the Shari valley, the Kameruns, and Dahomey, and an
eastern province including Abyssinia, Arabia and
Somaliland. Upon this hypothesis the alkaline rocks
of Northern Nigeria belong to and complete the
central province of Lacroix, as extended by M. Chudeau.
It is probable, however, that this central province
includes intrusive and volcanic rocks of many different
ages, and that alkaline types have been a characteristic
product of differentiation from the earliest times to the
present day, (p. 142). There is, moreover, every
reason to believe that the progress of investigation will
reveal many connecting links between the various
provinces, which are themselves somewhat too exten-
sive and comprehensive to warrant their recognition as
such. A petrographical province in the stricter sense of
the term may perhaps be set up to include the alkaline
plutonic rocks of Bauchi province and their associated
hypabyssal types, but there can be little doubt that the
general alkaline character of the igneous rocks of
northern Africa, to which Lacroix has given expression,
may be quite sufficiently indicated by emphasising
their natural classification within the Atlantic branch of
igneous rocks.’

1 Cf Prior, Min. Mag., 1903, XIII, p. 228; Harker, Wat. Hist. of
Lgneous Rocks, 1910, p. 91.
APPENDIX I

MINERAL RESOURCES
Salt—Iron—Gold—Monazite—Galena—Tinstone.

DetaILeD information respecting the principal
mineral resources of Northern Nigeria will be found
in Professor Dunstan’s Reports on the Results of the
Mineral Survey." The following is a brief summary
of the more important facts.

(1). Sadt.

Salt has long been a staple article of inter-tribal
commerce on the middle Benue, and its manufacture
has in the past been extensively carried on in the
province of Muri. The introduction of European salt
has, however, adversely affected the native industry,
and salt-making is now confined only to those localities
in which the natural conditions are most favourable.
In Muri province the salt is prepared by the con-
centration and evaporation of the waters of weak brine
springs which are distributed over a western and an
eastern area. In the western area the town of Awe is
the centre of the industry, while Akiri and Azara are
subordinate in both production and population. (Plate
XVIII, Figs. 1, 2.) Keana on the Nassarawa border
forms the western limit of the salt-producing area,

1 Dunstan, Col. Reps. (Miscell.), Nos. 32 (1906), 46 (1908), 47 (1908).
A fourth report on the results of the Mineral Survey will shortly be
issued.

265
266 APPENDIX I

while Akwana to the south of the Benue marks its
southernmost extension. In addition to these towns
which still manufacture a surplus for export, salt-
making for local purposes is carried on at Kanji,
Doya, Abuni, Ribi and Arofu within the same area.
At a former period also salt was made at Lafin
Gisheri, between Tunga and Ibi, and this locality may
be taken to mark the eastern limit of the salt area.
In eastern Muri the salt-producing district is of less
importance than that in the west. The centres of the
industry are Bomanda and Jenoe, but small quantities
of salt are also prepared at Jebjeb, Jebero and Langa.
With regard to geological occurrence it is believed,
as already indicated, that the weak brine from which
the salt is made in Muri province is located within
the upper part of the ‘‘Muri sandstones” and im-
mediately underneath the passage beds and the
Turonian limestone. Mr. Longbottom found that at
Awe the springs supplied from the sandstones of the
passage beds are entirely free from salt and cease
flowing before the end of the dry season, while the
neighbouring brine springs which rise from rocks lying
below the surface drainage maintain a constant flow
throughout the year. Moreover, wherever the shaly
bands within the passage beds were pierced by bore-
holes, the brine rose with a steady flow under
considerable pressure. The sandstones and _ grits
underneath the passage beds appear to be saturated
with weak brine which is retained, as in a reservoir,
by the overlying shales. It is believed that the
western and eastern salt-bearing districts form
detached and irregular synclinal areas affected by a
subordinate folding. The brine springs at Awe,
Azara and Bomanda are especially associated with the
subordinate anticlinal axes along which the salt-
bearing beds within the synclinals approach the
surface. Some of the minor salt towns, such as
Ribi, Keana and Jenoe, are probably located on or
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APPENDIX I 267

near the outcrop of the salt-bearing beds. Wherever
the brine springs are found, bubbles of a colourless
gas, probably carbon dioxide, rise with the water.
Calcareous incrustations round the orifices of the
springs are found at Awe and Jebero. Some of the
springs of Awe are, moreover, slightly thermal and
possess a temperature a few degrees above sun heat.
This is probably to be correlated with the recent
volcanic action in the neighbourhood.

The present springs rise in stream courses and are
unavailable during the rainy season. Boring, however,
within the synclinal areas would afford a copious and
continuous supply. Professor Dunstan has analysed
the salt of various localities and discussed the
possibilities of increasing the native output. The
general weakness of the brine, however, would appear
to be unfavourable to European exploitation.

Salt is won from brine pools in south-eastern Bauchi
over an extensive belt of country which stretches
northward from the Pero Hills and passes to the east
of Chongwom and Tangalto. The pools are presum-
ably fed by springs and the salt is said to be abundant
and easily prepared. The whole area, however, is
very imperfectly known and largely unexplored.
Scanty incrustations of natron, utilised by the local
herdsmen, are known from the Gongola valley in the
neighbourhood of Nafada.

In Bornu salt is made from the ash of the siwak
tree (Salvadora persica) which grows abundantly on
the ancient dunes which fringe the western shore of
Chad. The slaves of Mongonu and Musara prepare
salt also from the ash of three varieties of grass,
‘‘pagam, kalaslim and kanido,” which are found in
the immediate neighbourhood of the lake. Over the
whole of central Bornu the waters of the wells are
charged with salts of soda in very varying amount.
The ancient alluvium of Bornu is evidently impregnated
with soda, and incrustations are found in places upon
268 APPENDIX I

the surface of desiccated swamps. Natron pools,
similar to those of Manga and presumably fed by
springs, are unknown in central Bornu.

In Sokoto province incrustations of salt are found
in the dry season at Zauro in the valley of the Gulbin
Kebbi, and natron (kungwa) occurs in a similar manner
between Gulma and Argungu. Knots and streaks of
gypsum are common in the shales and clays around
Sokoto, while efflorescences of gypsum and alum are
found on the cliffs of Wurnu to the north-east. Scanty
incrustations of natron are found upon desiccated
swamps in many localities in the provinces of Sokoto,
Kano, Zaria and Ilorin, but never in sufficient quantity
to give rise to even a native industry. Hausaland has
been in the past supplied with salt and natron from
Asben, Bilma and Manga in the French Sudan.
European salt, however, is rapidly replacing the native
article, and many caravans now bring only natron from
the north to the markets of Kano.

(2). Lron.

As in the case of salt, so in the case of iron, the
native manufacture has been very largely superseded
by the importation of European bar-iron. Only in
the more inaccessible districts or in those places where
the ore is abundant do the natives still smelt the local
ironstones in their primitive fashion. The surface iron-
stones were at one time generally utilised throughout
the Protectorate as'a source of iron. The magnetite
sands are still washed and smelted by the pagans of
the Mumuye hills in eastern Muri, while in northern
Nassarawa the Koro tribe around Kao is still noted
for its proficiency in the manufacture of iron from the
local limonitic ores which occur within the schists in
veins of varying thickness.1 Similar ores occur in

1 Sir William Wallace has reported an extensive native iron industry at
Fawa in Katsina, where the ore appears to occur in a similar manner to
that in the neighbourhood of Kao.— G. /., VIII., 1896.
APPENDIX I 269

veins in the sandstones around Akiri in western Muri,
but are no longer utilised by the natives. The oolitic
and earthy ironstones of sedimentary origin and of
Eocene age give rise to an extensive native industry
around Akwi and Ojerami in central Kabba, around
Mahorro in eastern Kontagora, around Aliero in
southern Sokoto, and around Kantana in southern
Bauchi, as well as in the Kerri Kerri country in
western Bornu and in the Tagum hills in southern
Bornu. So far as European exploitation is concerned,
the sedimentary ores of Mt. Patti and the lower Niger
are most favourably situated for transport. The ores,
however, while abundant, are of a somewhat low
grade character and relatively rich in phosphoric acid.
Magnetite and hematite schists are extensively de-
veloped in eastern Kabba, but their composition
would render necessary costly crushing and separating
processes before the ores could be available for export.’

(3). Gold.

Traces of gold have been found in some of the
quartz veins which are so widely distributed through-
out the Protectorate, but no payable reefs have yet
been discovered. Small quantities of free gold occur
in the streams between Koriga and Birnin Gwari in
northern Zaria and around Tagum in southern Muri.
In Zaria the gold is evidently located within the
northern prolongation of the Zungeru belt of slates
and schists, and further exploration may possibly lead
to valuable discoveries. All the slaty belts already
described within the Protectorate are, indeed, worthy
of careful prospecting for gold. Small quantities of
gold are also found associated with cassiterite in some
parts of Bauchi province.

1 In Zhe Iron Ore Resources of the World, Vol. I1., 1910, p. 1029, Dr. J.
W. Evans has given a 7ésumé of the results of the investigations of the
Mineral Survey into the extent and value of the ferruginous deposits of
Northern Nigeria.
270 APPENDIX I

(4). Monaztte.

Monazite is widely distributed throughout the Pro-
tectorate, and appears to be a fairly constant constituent
of the gneisses and schist. Small quantities are con-
tained in almost every river and stream within the
crystalline areas. It has been found most abundantly
in central Kabba and in northern Nassarawa, but, so
far as known, it occurs nowhere in sufficient quantity
to afford any hope of profitable European exploitation.

(5). Galena.

A slightly argentiferous galena occurs in veins within
the Cretaceous rocks around Arofu and Akwana in
western Muri, and in the Kudu valley to the west of
Jebjeb in northern Muri. In the Arofu district the
galena is associated with fluorspar and calcite, and the
formation of the veins has been accompanied as already
described by much silicification of the adjoining lime-
stones. The Arofu galena is excavated by the natives
for use aS a cosmetic, and from time to time small
pockets of silver are discovered within the veinstuff.
To the west of Jebjeb the galena is no longer dug by
the natives, and the old workings are now levelled
and grassed over. The galena appears to have been
associated with quartz, hematite and blende, but there
is no evidence of silicification of the country rock.

(6). Cassttercte ( Tznstone).

Tinstone is the most valuable asset of the Pro-
tectorate from the point of view of mineral resources.
Its occurrence in western Bauchi was known to the
natives long before the advent of Europeans. Recent
investigation, however, by the Mineral Survey has
proved its presence over considerable areas in widely
separated localities within the Protectorate. The most
extensive area over which tinstone is found in the
APPENDIX I 271

surface alluvium occurs in western Bauchi, and in-
cludes the summit of the plateau and the greater
part of its northern margin. The alluvial deposits
of Naraguta, which lie within this area, were originally
developed by the Niger Co., but have now been
acquired by the Consolidated Gold Fields, Ltd. Else-
where, however, tinstone becomes equally abundant,
and there is little doubt that further investigation will
reveal many localities within this extensive area in
which alluvial workings may be profitably carried on.
Several syndicates indeed are now engaged in ex-
ploiting certain portions of the tinfield. In the
neighbourhood of Ngell the tinstone, accompanied by
sulphide ores of copper, zinc and lead, occurs, as
already described, in part as a pneumatolytic modifica-
tion of the Bukuru granite, and in part as a true lode
or pegmatitic formation. This particular occurrence
is being developed by the Niger Co., but there is
every reason to believe that similar occurrences will
be found throughout the area as investigation proceeds.

Apart from this extensive tin-field in the centre of
the Protectorate, cassiterite is also found in Bauchi
province in many places throughout the Ningi and
Burra hills, and detailed prospecting will probably here
also reveal several payable localities. The completion
of the Baro-Kano railway * within the next two years
will afford an easy means of access to the tin-producing
areas of Bauchi, and will at the same time largely
overcome the difficulty of transport which is at present
the greatest obstacle in the way of the development of
the tin fields.

Beyond the limits of Bauchi province small quantities
of tinstone have been found in the neighbourhood of
Gadama and Fagam on the borders of Bauchi and
Kano, around Gantam and Aribi on the Nassarawa
tableland as well as on the eastern slopes of the Vere
hills in Yola, the western slopes of the Shebshi hills

1 And the branch line to Leri in Zaria province.
272 APPENDIX I

in southern Muri, and in the neighbourhood of Eri
in eastern Ilorin. In the latter locality the tinstone
was found to be derived from a richly stanniferous
pegmatite vein, but the actual extent and possibilities
of the occurrence are as yet unknown. The same
may be said also of the other localities indicated, and
there can be little doubt that all of them are worthy
of further investigation. Tinstone has been reported
to occur abundantly in the Mada country in eastern
Nassarawa, but this discovery likewise awaits con-
firmation.
APPENDIX II

THE PALZONTOLOGY OF THE UPPER CRETACEOUS
DEPOSITS OF NORTHERN NIGERIA

By HENRY Woops, M.A., University Lecturer in Paleozoology,
= Cambridge

THE fossils collected by Dr. J. D. Falconer anc
Mr. A. Longbottom from the Upper Cretaceous
deposits of Northern Nigeria include Fishes,
Ammonites, Gasteropods, and Lamellibranchs. The
localities from which these fossils were obtainec
are: Awe, Deba Habe, Jibaru, Gongila,’ Gulani
Kumberi, Kunini, and Reme. At present the number
of species which can be identified is comparatively
small, but the collection is sufficient to show that unde
more favourable conditions a large and importani
fauna could probably be obtained from the deposits o
this region.

Teeth, vertebre, &c., of fishes were collected a
Kumberi and Jibaru, and have been examined by
Dr. A. S. Woodward who identifies them a:
Gigantichthys,a genus which is known from the Chalk
of Egypt and the Sahara.27 Ammonites have beer
found at Gongila, Reme, Kunini, and Kumberi, anc
they show that the deposits are of Turonian age—

1 The occurrence of Turonian fossils at this locality has been recordec

by G. C. Crick, Geogr. Journ., Vol. XXIV., 1904, p. 522, footnote 1.
2 Dames, Sitzungsber. Ges. nat. Freunde, Berlin, 1887, pp. 69, 137.

273 7"
af
274 APPENDIX II

probably Lower Turonian. The Ammonites bel
to the genera Vascoceras, Mammites (Pseudasprdocer.
and Hoplitordes. Vascoceras is confined to
Turonian. Pseudaspidoceras is mainly of Turon
age. The species of Hoplitoides belongs to the sect
of that genus which occurs in Turonian deposits. 1
species of Vascoceras and Mammites (Pseudaspidocer
found in Nigeria are closely allied to forms wk
occur in the Lower Turonian of Northern Africa ;
the Iberian peninsula.

The larger number of the Gasteropods and Lam
branchs were found at Awe, but no Ammonites w
obtained at that locality ; these fossils, so far as t
can be identified, do not give any definite evide
that the deposit at Awe is of earlier age than
Turonian.

At Deba Habe Ostvea (Exogyra) olistponer
Sharpe, is abundant and is the only fossil obtainec
that place. In Portugal that species occurs in kt
Turonian and Cenomanian deposits. In Nigeriz
has also been found at Gongila, where the Turor
floplitoides occurs. So that it is probable that
deposit at Deba Habe is of the same age as the on
Gongila.

At Gulani Ostrea prelonga, Sharpe, is abund:
but no other fossil was found at that locality.
Portugal O. prelonga occurs in the Bellasian—
horizon which is believed to come between the Ap
and the Cenomanian. The same species is found :
similar level in Tunis and Algeria. The occurre
of this one species can, I think, hardly be taken
sufficient evidence that the deposit at Gulani is
Bellasian age, since it is not unlikely that, as is
case with O. (Exogyra) olisiponensis, this form 1
recur at later horizons when a favourable facies
deposit again appears.

At present, then, we can state that the deposit
which Ammonites occur are of Turonian age, and |
PALZONTOLOGY 275

there is not sufficient evidence to show that beds of
earlier age are represented.

The fauna of the Turonian deposits of Northern
Nigeria resembles closely that found in beds of similar
age in Portugal, Tunis, and Algeria. This is shown
especially by the Ammonites and oysters. At present
the genus Vascoceras is known only from Portugal,
Spain, Algeria, Tunis, Egypt, Nigeria and Brazil.
Hopltordes occurs in Algeria, Tunis, Nigeria, the
Kameruns, and probably in Egypt. The species of
Pseudaspidoceras found in Nigeria is allied to forms
found in Portugal, Tunis and Brazil. The oysters
likewise belong to species characteristic of Northern
Africa and South-western Europe, and one of them
has also been found as far south as Angola. The
Ammonites also show, as Pervinquiére has already
pointed out is the case in Tunis, that the fauna is
related to that found in the Upper Cretaceous of
Brazil.

Amongst other places in West Africa, Cretaceous
deposits have been found in the Kameruns, and are
regarded by Solger as of Upper Turonian and Lower
Senonian age, but by Harbort’ they are referred to
the Emscherian (Lower Senonian). They certainly
appear to be of later date than the Nigerian deposits
with which they are connected chiefly by the presence
of Hophtozdes.

Until the fauna of the Nigerian Cretaceous is more
completely known any further discussion of its
relationship to the faunas of other areas must be
postponed.

The list on the following page shows the distribu-
tion of the species found in Nigeria, and is followed
by paleontological notes and descriptions of some of
the species.

1 Guillemain and Harbort, “Profil der Kreideschicht. am Mungo,”
Abhandl. a. k. preuss. geol. Landesanst. N.F., Heft 62, 1909, p. 405.

T 2
276 APPENDIX I

 

Awe.
Deba Habe.
Gongila.
Gulani
Kumberi.
Kunini
Reme,

 

Nuculana, sp. 6. 6. eee ee ee ee
Trigonoarca, sp... 1 6 ee ee ee ee
LHLUZOHIA; SDs. se He
MOdIO1G: SPs vse wk a ve te GR ig
Pecten (Neithea) guinguecostatus, Sow... .
Lima (Mantellum), sp. . 2... 2. 2 eee
Ostrea prelonga, Sharpe .....+....
» (Exogyra) olisiponensis, Sharpe aw
Gervillia (Pseudoptera), sp... ......
Astarte awensis,sp.nov. .........
EUCiHaySp. «3s a Se OO GS
Cardiumy SDs sc: i a RH eS
COPA SD. coo as A ie OO
Pseudomelania, sp... 1... 5... ee ee
UGE ICEL, SDs 6 sh. 55 ae age bat ig! was ak ORS
Semifusus africanus, sp.nov... .... 6. =
Vascoceras nigeriensis, sp.nov... .....
” gongilensis, sp.nOv.. ......
Mammites (Pseudaspidoceras), sp. .....
Hoplitoides nigeriensis, sp.nov. ..... .

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LAMELLIBRANCHIA.

NUCULANA, Sp.
Plate XIX., Fig. 4.

An internal cast resembles in form VV. Maria (d’Orbigny), but in
the absence of the shell the species cannot be identified.

Locality —Kumberi.

TRIGONOARCA, sp.
Plate XIX., Figs. 1-3.

Several specimens of TZyigonoarca were found, but are not
sufficiently well-preserved for specific identification. In general -
form they resemble some examples of 7. ¢richinopolitensis (Forbes) !
from the Trichinopoli Beds of Southern India.

Locality.— Awe.

1 Stoliczka, Cret. Fauna S. India, 1871, p. 353, Pl. XVIII. Figs. 12,
14; Pl. XIX.,, Figs. 2, 3; Pl. XX., Figs. 2, 8, 9, 10.
PALEONTOLOGY 277

TRIGONIA, sp.

Two specimens of a species belonging to the Scabre section of
Trigonia are in the collection, but are not sufficiently well-preserved
for identification.

Locality.— Awe.
Mopiota, sp.
Examples of a small form of Aodiola occur at Awe.

PEcTEN (NEITHEA) QUINQUECOSTATUS, Sowerby.
Three specimens with the shell preserved were found at Awe.

Lima (MaNTELLuUM), sp.

An imperfect specimen from Awe resembles Zima (Mantellum)
gaultina, Woods.1
OSTREA PRELONGA, Sharpe.
Plate XIX., Figs. 5-8.
1850. Ostrea prelonga, D. Sharpe, Quart. Journ. Geol. Soc.,
VI, p. 187, Pl. XX., Fig. 4.
« 1869. Ostrea prelonga, H. ‘Coquand, Mon. Ostrea. Terr. Crét.,
p. 169, Pl. LXVI., Figs. 1, 2.
1890. Ostrea prelonga, A. Peron, Moll. Foss. Terr. Crét. Tuniste,
p. 110, Pl. XXIII., Figs. 1-6.

                                                

Ostrea, agreeing closely with O. prelonga, Sharpe, were found.
O. pentagruelis, Coquand,? is considered by Peron to be only a
very old individual of O. prelonga.

This species occurs in the Bellasian of Portugal. In Algeria and
Tunis it is characteristic of beds which occur below the Cenomanian,
and are referred by Peron to the Upper Albian.

Locality,—Gulani.

OsTREA (ExOGYRA) OLISIPONENSIS, Sharpe.
Plate XX., Figs. 1-3.

1850, Lxogyra olisiponensis, D. Sharpe, Quart. Journ. Geol. Soc.,
VL, p. 185, Pl. XIX., Figs. 1, 2.

1862. Ostrea Overwegi, H. Coquand, Géol. pal. rég. sud. prov.
Constantine, p. 226, Pl. XIX., Figs. 1-6.

1862. Ostrea Coguandi, Julien, in Coquand, zd7d., p. 324,
Pl. XXXIIL., Figs. 10-12.

1 Mon. Cret. Lamell. England, Vol. 11., 1904, p. 31, Pl. V., Figs.
16-20.
2 Mon. Aptien de PEspagne, 1865, p. 166, Pl, XXVL., Figs. 1, 2.
278 APPENDIX II

1869. Ostvea olisiponensis, H. Coquand, Mon. Ostrea. Terr.
Crét., p. 125, Pl. XLV., Figs. 1-7.

1869. Ostrea Overwegt, Coquand, did., p. 140, Pl. XLIV.,
Figs. 1-9 ; Pl. XLVL, Figs. 14, 15.

1873. Ostrea olisiponensis, L. Lartet, Ann. Sct. géol., Vol. III,
p. 59, Pl. XI., Fig. 1.

1882. Lxogyra oltstponensts,G. Seguenza, Atti d. R. Accad. det
Lincet, Ser. 3; Mem. Scien. Fis. Math., Vol. XII., p. 180,
Pl. XVIL., Fig. 2.

1882. Lxogyra oxyntas, Seguenza, ibid, p. 178, Pl. XVIIL,
Fig. 1.

1888. Ostrea olisiponensis, P. Choffat, Mém. Soc. Phys. et & hist.
nat. de Geneve, XXX., 2, p. 95.

1891. Ostrea olisiponensis, A. Peron, Moll. Foss. Terr. Crét.
Tunisie, p. 114, Pl. XXIIL, Figs. 14-18.

1902. Ostrea (Exogyra) olisiponensis, P. Choffat, Faune Crét.
Portugal, Vol. I., Ser. 4, p. 166, Pl. VI., Figs. 17-19.

1903. Ostrea olisiponensis, R. Fortau, Bull. Instit. Egypt., Ser. 4,
Vol. IV., p. 283, Figs. 3-5.-

1905. Ostrea (Exogyra) olisifonensis, P. Choffat, Géol Col.
Portug. a’ Afrique. If, Nouvelles données sur la zone
littorale d’ Angola, p. 44, Pl. I., Figs. 4, 5.

Remarks.—This species is represented by numerous examples, in
a few of which the surfaces of the shell are well-preserved and show
a few coarse ribs. Sharpe and other writers have noted the great
variability in the ribbing of this species. The Nigerian specimens
agree with the varieties which possess only a few ribs. Peron,
Choffat, and Fortau have discussed fully the affinities and synonymy
of O. (Exogyra) olisiponensis. This species is common in Northern
Africa and Portugal ; it occurs in the Cenomanian of Algeria, Tunis,
Egypt, and Palestine ; in Portugal it is found in both the Upper and
Lower Turonian, as well as in the Cenomanian, wherever the
deposits are of the marly facies. South of Nigeria this species has
been discovered in the province of Angola.

Localities.—Deba Habe and Gongila.

GERVILLIA (PSEUDOPTERA), Sp.
Plate XX., Figs. 4-6.

There are several internal casts resembling in form G. (Pseudop-
tera) anomala (Sowerby), but there is no evidence to show whether

' For figures see Woods, Mon. Cret. Lamell. England, Vol. 11., 1905,
p. 64, Pl. IX., Figs. 2-4. Compare also d’Orbigny, Pal. Frang. Terr.
Crét., Vol. III., 1846, p. 478, Pl. CCCXCII., Figs. 1-3. When describing
this species I overlooked Guéranger’s statement that he had seen speci-
mens showing ligament pits ; from the presence of those pits it is evident
that this species cannot belong to Péervza. It seems probable that
PALEONTOLOGY 279

radial ribs were present on the shell or not, and the species cannot
be determined at present.

Specimens from the Cenomanian of the neighbourhood of Tebessa
(Algeria) have been identified with Sowerby’s species by Coquand,!
and Peron? states that it is abundant and well-preserved at that
locality.

Locality —Awe.

ASTARTE AWENSIS, Sp. nov.
Plate XX., Fig. 7.

Description.—Shell rather small, moderately convex, with the
postero-dorsal part somewhat compressed, outline subquadrate or
subtriangular, very inequilateral. Anterior margin slightly concave ;
ventral margin convex ; posterior margin short, truncated, forming
an obtuse angle with the long, slightly convex postero-dorsal margin.
Umbones pointed, rather prominent. Lunule large, ovate, smooth,
with a sharp edge. Escutcheon large, deep, with a sharp edge.
Ornamentation consists of about fourteen broad, prominent con-
centric ribs, which are marked by fine concentric lines. Length,
8-25 ; height, 7 mm.

Affinities.—In the character of its ornamentation 4. awensis
resembles several small species of Astarfe found in the Cretaceous
rocks. It is more inequilateral, more elongate, and has the posterior
margin more distinctly truncated than in 4. subsimilis, J. Bohm.®
In similar respects it differs from A. griesbachi, Woods,* from
Pondoland.

Remarks.—Numerous casts of this species occur in ferruginous
nodules.

Locality. Awe.

LUCINA, sp.
Plate XX., Figs. 8, 9.

Description.—Shell nearly orbicular, convex, slightly inequivalve ;
height and length nearly equal. Anterior and ventral margins
rounded ; posterior margin truncated, forming an obtuse angle with
the straight or slightly convex postero-dorsal margin. Umbones
rather prominent. Ornamentation consists of regular, concentric

Pseudoptera should be regarded as a sub-genus of Gerviliia. Guéranger,
Album Paléont. dela Sarthe, 1867, pp. 17, 20, Pl. XXIL., Figs. 9, 10;
Pl. XXV., Figs. 10, If.

1 Géol. et Pal. de Constantine, 1862, p. 292.

2 Peron, Moll. Foss. Terr. Crét. Tunisie, 1890, p. 238.

3 “Kreidebild. des Fiirbergs u. Sulzbergs,” Paleontographica,
XXXVIIL., 1891, p- 74, Pl. IIL, Fig. 8. ;

4 Ann. S. African Mus., 1V., 1906, p. 300, Pl. XXXV., Figs. 18, 19.
280 APPENDIX II

lamellar ribs separated by broad, flat interspaces which are marked
by fine, concentric lines. Length, 11 mm. ; height, 11°5 mm.

A ffinities.—In general form, and in the character of its ornamenta-
tion, this species resembles one of the varieties of Lucina fallax,
Forbes, described by Stoliczka! from the Utatir Group, but the
umbones are more prominent, and the postero-dorsal angle is more
distinct. It also resembles Z. sahkarica, Quaas,? and some forms of
L. subnummismalis, d’Orbigny.®

Locahity.—Kumberi.

CaRDIUM, sp.
Plate XX., Fig. 10.

In the possession of numerous radial ribs and in the general form
of the shell, some internal casts resemble Cardium cenomanense,
d’Orbigny,* but the valves are less convex.

Locahity.—Awe.

CORBULA, sp.

Specimens of Corbula resemble C. elegans, Sowerby,> in the
character of their ornamentation, but the posterior part of the shell
is more produced.

Locality. Awe.

GASTEROPODA.

PSEUDOMELANIA, Sp.
Plate XXI., Fig. 1.

Several specimens of a small gasteropod resemble Psexdomelania
fallary?, Peron and Fortau,® from the Cenomanian of Egypt, but
they are of much smaller size, being from 8 to 13 mm. long. The
surface of the shell is smooth, except for slightly curved growth-
lines, and, on the base, spiral grooves.

Locality,— Awe.

eh Palaont. Indica, Cret. Fauna S. India, 111., 1871, p. 256, Pl. XIV.,
ig. 7.

* Paleontographica, XXX., 2, 1902, p. 214, Pl. XXIV., Fig. 7.

3 Ravn, Mollusk. Danmarks Kridtafl. [. Lamellibr., 1902, p. 129,
Pl. IV., Fig. 21.

4 Pal. Frang. Terr. Crét., U11., 1844, p. 37, Pl. CCXLIX, Figs. 5-9.

5 Woods, Mon. Cret. Lamell. England, Vol. 11., 1908, p. 216, Pl.
XXXIV., Figs. 23-28.

° Bull. Institut Egypt. Ser. 4, Vol. VI., 1903, p. 270, Pl. L., Fig. 22.
PALZONTOLOGY 281

TURRITELLA, Sp.
Plate XXI., Fig. 2.

A species of TZurritella resembles 7. Choffatt, Thomas and
Peron,! from the Turonian of Tunis. The anterior part of each
whorl is bent at an angle with the large flattened posterior part, and
the ornamentation consists of four strong spiral ribs, one of which
occurs at the angle, giving the appearance of a carina. On the later
whorls the ribs become granular or tubercular. The ribs are much
coarser than in Z. Choffatt.

Locahity.—Kumberi.

SEMIFUSUS AFRICANUS, SP. nov.
Plate XXI., Figs. 3~5.

Description.—Shell subfusiform. Spire’shorter than the last whorl,
consisting of about five whorls. Whorls carinate, the carina being
more or less distinctly nodular. Posterior part of the whorls
flattened, much larger than the anterior part in the spire. Anterior
part of last whorl convex. Ornamentation consists of narrow spiral
ribs with flat interspaces crossed by growth-lines ; on the later whorls
the ribs become divided up into rows of elongated tubercles.

Remarks.—This species, which is represented by several imperfect
specimens, shows some resemblance to Lagena nodulosa, Stoliczka,?
and Z. secans, Stoliczka,? from the Ariyaltir Group, and also to
Serrifusus dakotensis vax. vancouverensis, Whiteaves,* but possesses
one carina only.

Locality.—Awe.

CEPHALOPODA.
Genus—VascoceRas, P. Choffat.
(Faune Crét. Portugal, I., 1898, p. 51.)
VASCOCERAS NIGERIENSIS, sp. nov.
Plate XXI., Fig. 6; Plate XXIL, Figs. 2, 3.

Description.—Shell inflated, rounded, subglobose. Whorls thick,
largely embracing ; umbilicus deep, rather more than a third of the

1 Moll. Foss. Crét. Tunisie, 1889, p. 47, Pl. X1X., Figs. 13, 14.

2 Cret. Fauna S. India, Vol. 11., 1867, p. 137, Pl. XL, Fig. 18.

3 Jéid., p. 138, Pl. XL, Figs. 19, 20. .

4 Mesozoic Fossils, Vol. 1., 1879, p. 119, Pl. XV., Fig. 5. Compare also
Woods, Aun. S. African Mus., Vol. 1V., 1906, p. 324, Pl. XL. Figs. 5, 6.
Newton, Zvans. Roy. Soc. S. Africa, Vol. 1., 1909, p. 28, Pl. IX., Fig. 6.
282 APPENDIX II

diameter of the shell, with nearly vertical walls, the umbilical margin
subcarinate, without tubercles. Flanks curving gradually from the
umbilical margin and not limited from the rounded periphery.
Surface of shell with growth-rings.

Sutures: Saddles large, broad, and low; external saddle unsym-
metrically divided and with small minor divisions; first lateral
smaller than the external saddle, more rounded, less divided, with
the outer margin sloping and the inner margin nearly perpendicular ;
second lateral saddle broad, only slightly divided. External lobe
deeper than the first lateral lobe ; the latter is small with one main
division ; second lateral lobe smaller, with two points.

Q) @)
Diameters . 44 2 4. -e we we ees 88 93mm.
THICKNESS: ec ae ee - 58 54
Height of last whorl. ....... 37 34
Width ofumbilicus ........ 30 33

(1) Reme. (2) Kunini.

Affinities —This species resembles the thicker forms of V. durandi
(Peron and Thomas),! but the walls of the umbilicus are steeper, the
umbilical margin is without tubercles, and the external and first
lateral saddles are broader and not so high. In general form, and in
the absence of tubercles at the umbilical margin, V. migeriensis
resembles V. amierensts, Choffat,2 but the whorls embrace to a
larger extent, and their sides are less flattened ; there are also some
differences in the suture. In the form of the umbilicus, and in the
breadth of the saddles, this species resembles V. harttiformis,
Choffat,? but the shell is much less thick. Another similar form
but with a thicker shell, is Y%. Aarti, Hyatt,* from Brazil.

Localities—Reme and Kunini.

VASCOCERAS GONGILENSIS, sp. nov.
Plate XXI., Fig. 7; Plate XXII., Fig. 1.

Description —Shell moderately inflated. Umbilicus less than a
quarter of the diameter of the shell, with vertical walls and sub-

1 Moll. Foss. Crét. Tunisie, 1889, p. 27, Pl. XVIII., Figs. 5-8. Peron,
Amm. Crét. suptr. Algérie, 1896-7, p. 44, Pl. 1V., Fig. 1; Pl. V., Fig. 1;
Pl. XVIL., Fig. 5. Pervinquiére, Paléont. Tunistenne, Ceph. secondatres,
1907, p. 332, Pl. XXL, Fig. 1. V. Douvillet, Choffat, Faune crét.
Portugal, Vol. 1., 1898, p. 59, Pl. X., Fig.6; Pl. XL, Figs. 2-5 ; Pl. XXL,
Figs. 13-16.

2 Choffat, zé¢d., p. 61, Pl. XII, Figs. 1, 2; Pl. XIII., Figs. 1, 2;
Pl. XXL, Figs. 17-21.

3 Ibid, p. 61, Pl. XII, Fig. 3; Pl. XIII, Figs. 3-6; Pl. XXI.,
Figs. 22-24.

4 “Contrib. Paleont. Brazil,” Archiv. Mus. Nac. Rio de Janeiro, VIL,
1887, p. 226, Pl. XIX., Figs. 1, 2; Pl. XX., Fig. 3. Hyatt, “ Pseudo-
ceratites of the Cretaceous,” U. S. Geol. Survey, Mon., XLIV., 1903,
p- 103, Pl. XIV., Fig. 16.
PALEONTOLOGY 283

carinate margin. Flanks somewhat compressed. Periphery
flattened. Inner whorls with strong ribs on the flanks and promi-
nent tubercles at the umbilical margin and at the limit of the flanks
and periphery ; on the last whorl the ribs and tubercles gradually
become obsolete.

Sutures: External saddle broad, subquadrate, with small
divisions ; first lateral saddle broad, rounded, divided unsymmetri-
cally by a small lobe ; second lateral saddle subquadrate ; one small
auxiliary saddle on the flanks. External lobe deep and larger than
the first lateral lobe, which has only small divisions ; second lateral
lobe small, its lower margin with pointed divisions.

Diameter : @ 2 6 #4 % 3 @ 3 108 mm.
PRICKMESS co. ah ae a we 57 95
Height of last whorl . . . .. 52) 55
Width of umbilicus ..... B53

Affiinities—This species resembles V. sudconciliatum, Choffat,}
from the Turonian of Portugal, but the ribs and tubercles become
obsolete at an earlier stage, the umbilicus is smaller, the divisions in
the external saddle are less deep, the first and second lateral saddles
are more rounded, and the first lateral lobe is narrower. V. gongi-
Jensis also resembles some forms of V. cauvini, Chudeau.*

Locality.—Gongila.

Genus—Mamm TEs, Laube and Bruder.
(Paleontographica, XXXIII., 1887, p. 229.)
Sub-genus—PSEUDASPIDOCERAS, Hyatt.

( Pseudoceratites of the Cretaceous,” U. S. Geol. Surv. Mon.,
XLIV., 1903, p. 106.)

MAMMITES (PSEUDASPIDOCERAS), SP.
Plate XXIII., Figs. 1, 2.

In the collection there is one specimen of Mammites (Pseudaspi-
doceras) ; it resembles the form figured by Choffat® under the name
Acanthoceras (?), cf. Footeanus (Stol.), from the Turonian of Portugal,
but differs in having a smaller umbilicus and less distinct siphonal
tubercles. The sutures are not shown in the specimen from
Nigeria.

1 Faune crét. Portugal, Vol. 1., 1898, p. 64, Pl XV, Figs. 1-3;
Pl. XVL., Fig. 4; Pl XXII, Figs. 28-31.
a te Anon du Damergou (Sahara méridional),” Budl/. Soc. géol. de

France IX., 1909, p. 68, Pls. I., I. Ill. ;
oe ordt. Pou, Vol. 1, 1898, p. 66, Pl. XVI., Figs. 9, ro ;

Pl. XXIL, Figs. 3, 4
284 APPENDIX II

The Portuguese form differs from A. footeanus, Stoliczka,! by the
absence. of secondary ribs on the siphonal region of the inner whorls,
and by the forward inclination of the ribs between the lateral
tubercles and the siphonal tubercles.

Other allied species are MM. (Pseudaspidoceras) salmuriensis
(Courtiller) var. dyzacenica, Pervinquiére,? from the Lower
Turonian of Tunis, and MZ. (Pseudaspidoceras) Pedroanus (White),®
from Brazil.

Locality.—Gongila.

Genus—Hop .itoipEs, A. von Kcenen.

(“Nachtrag Foss. Unter. Kreide Mungoin Kamerun,” Adhandl. d. kh.
Gesellsth. d. Wiss. Gottingen, Math.-Phys. Ki., NF. Band 1,
1898, p. 53. Emended F. Solger, oss. Mungokreide in
Kamerun, 1904, p. 127; L. Pervinquitre, Etudes Pal. Tunis,
L. Ceph., 1907, p. 215.)

HOPLITOIDES NIGERIENSIS, sp. nov.
Plate XXIII., Fig. 3; Plate XXIV., Figs. 1-5. Text-figure 1.

Description.—Shell discoidal, compressed, with truncated peri-
phery. Whorls largely embracing, with the flanks slightly or
moderately convex, the greatest convexity being at a short distance
from the umbilical margin. Umbilicus small, or very small, about
one-seventh of the diameter of the shell, its sides nearly perpen-
dicular. Periphery usually rather broad, bounded on each side by a
prominent rounded carina ; the prominence of the siphuncle gives
rise to a median rounded ridge between which and the carine the
shell is concave.

In fully-grown individuals the shell is smooth, but in smaller
examples the flanks bear a few strong, rounded ribs, which curve
slightly forwards near the periphery; the larger ribs start from the
umbilical margin, and one or two smaller ribs may be intercalated on
the flanks. Where the ribs join the carina the latter may become
more or less distinctly tuberculate. Usually the ribs become obso-
lete when the shell reaches a diameter of about 50 mm., but
occasionally they persist on larger individuals.

Sutures: External saddle broad, rather low, with a variable
number of small divisions. First and second lateral saddles similar

1 Palaont. Indica, Ceph. Cret. S. India, 1864, p. 101, Pl. LIL, Figs. 1, 2.
Kossmat, “ Siidindische Kreideformat.,” Beztr. Pal. Geol. Osterr-ungarns
u. a. Ortents, XI., 1897, p. 20. Petrascheck, “Amm. sachsich. Kreide-
format., zézd., X1V., 1902, p. 144. Pl. IX., Fig. 1.

2 Etudes Paléont. Tunisienne, I. Ceph. Second., 1907, p. 315, Pl. XIX,
Fig. 1.
Pe Contrib. Paleont. Brazil,” Archiv Mus. Nac. Rio de Janeiro, VII.
1887, p. 212, Pl. XXII., Figs. 1, 2.
PALEONTOLOGY 285

to, but distinctly smaller than the external saddle ; each has usually
some small divisions, but in some cases these are absent, and the
saddle is then rounded. One or two auxiliary saddles may occur.
External lobe deep, sometimes nearly as wide as the space between
the two carinz. First lateral lobe usually rather narrower and not
so deep as the external lobe, with more or less numerous small
divisions. The second lateral lobe is similar to, but smaller than
the last.

(1) (2) (3) (4) (5) (6) (7) (8)
67. 68 62 57

Diameter ...... IIo 6950084 44 mm.
Thickness ...... 47. 42 34 28 28 27 28 20 y
Height of lastwhorl. . 6: 49 45 37 38 38 34 25 y
Width ofumbilicus. . 15 5 Io 10 7 65 8 6,

(1—8) From Gongila.

 

5

Fic. 1.—Hoplitoides nigeriensis, sp. nov. Gongila. Sutures of six specimens.
Natural size.

Affinities.—This species appears to belong to the bicarinate group
of Hoplitoides. In general form it resembles ZH. muntert,
Pervinquitre,! from the Lower Turonian of Tunis, but the whorls,
are thicker, the flattened periphery is broader and shows a distinct
siphuncular ridge. The sutures are similar to those of A. munieri,
but are symmetrically placed, and the first lateral lobe is relatively
narrow. The ribbing of the smaller specimens is similar to that of
Hoplites ingens, v. Koenen em. Solger.?

1 Etudes Pal. Tunis, 1, Ceph., 1907, p. 217, Fig. 83, Pl. X., Figs. 1, 2.
2 Solger, Foss. Mungokreide in Kamerun, 1904, p. 137, Pl. V.,
Figs. 8, 9.
286 APPENDIX II

In general form, &. nigeriensis is similar to Heterotissotia neocera-
toides, Peron,! from the Lower Senonian of Algeria and the Upper
Turonian of Tunis. Both possess a broad, flattened periphery with
a keel on each side and a prominent siphuncular ridge, but in
fT, neoceratoides the ribs are retained to a later stage. The figures
given of the suture of Peron’s species are not satisfactory, and Iam
indebted to Dr. L. Pervinquitre for comparing figures of the sutures
of Hoplitoides nigeriensis with the type of Heterotissotia neoceratoides
which is now in the Sorbonne. Dr. Pervinquitre states that the
differences in the suture are too great to allow of these two species
being referred to the same genus.

Remarks.—The sutures of Hoplitoides nigertensis vary considerably
in appearance on account of the difference in the number and size
of the small divisions of the saddles. A somewhat similar variation
is seen in the sutures of HZ. imgens, v. Koenen, em. Solger, and
HT. munieri, Solger. Variations also occur in the thickness of the
whorls, the breadth of the periphery, the size of the umbilicus, and
the period at which the ribs become obsolete. In one specimen,
which is less thick than the other, the siphuncular ridge is absent.

This species is represented by numerous specimens, all of which
are internal casts or have only a small portion of the shell preserved,
and in nearly all cases the sutures are clearly exposed.

Locality —Gongila.?

1 Amm. Crét. supér. de 0 Algerie, 1897, p. 82, Pl. XVI. Figs. 9, 10;
Pl. XVIIL., Fig. 20. Pervinquiére, Etudes Pal. Tunis, I, Ceph., 1907,
p- 379, Pl. XXIIL., Fig. 7.

2 Specimens of Hoplitoides have also been found at Reme, but are
not sufficiently well-preserved for specific identification. An imperfect
Ammonite from Kumberi resembles in the form of its shell and in the
general character of the sutures Cozlopoceras Jlesseli, Briiggen, Neues
Jahrb. tir Min., etc., Beil.-Band XXX., 1910, p. 734, Plate XXIX.
PLATE XIX

 

SCA.

CRETACEOUS MoLLU

del.

T. A. Brock,
Fics.

”

1-3.

4-6.

8, 9.

10.

PLATE XX

Ostrea (Exogyra) olisiponensis, Sharpe. Deba Habe.
Left valves. (Page 277.)

Gervillia (Pseudoptera), sp. Awe. Internal casts. 4, 5;
left valves ; 6, right valve. (Page 278).

Astarte awensts, sp. nov. Awe. Right valve, drawn from a
wax impression of an”external cast. x14. (Page 279.)

Lucina, sp. Kumberi. 8, right valve; 9, dorsal view of
the same. x14. (Page 279.)

Cardium, sp. Awe. Internal cast of right valve. The
marginal part of the valve is imperfect. (Page 280.)
Plate XX

    
     

CRETACEous Mo.tusca,
Diy Brock, del,
Fics. I
” 2.
» 3-5
7 6.
a 7-

PLATE. XX

Pseudomelania, sp. Awe. x1}. (Page 280.)
Turritella, sp. Kumberi. x14. (Page 281.)

Semifusus africanus, sp. nov. Awe. 3, drawn from a wax
impression of an external cast; 4, portion of the orna-
mentation of 5, x6. (Page 281.)

Vascoceras nigeriensis, sp. nov. Reme. (Page 281.)

Vascoceras gongilensis, sp. nov. Gongila. Internal cast. .
(Page 282.)
PLATE XXI

ey

 

CRETACEOUS MOLLUSCA.

T. A. Brock, del.
PLATE XXII

Fics. 1. Vascoceras gongilensis, sp. nov. Gongila. Siphonal view of

Fig. 7, Plate XXI. (Page 282).

» 2,3. Vascoceras nigeriensis, sp. nov. Kunini. Two views of the

same specimen. (Page 281.)
PLATE XXII

 

EOUS MOLLUSCa.

ETAC

Cr

del,

2

T. A. Brock,
PLATE XXIII
Mammites (Pseudaspidoceras), sp. Gongila.
the same specimen. (Page 283.)

Fics. 1, 2. Two views of

3 3. Hopltitoides nigeriensis, sp. nov. Gongila. (Page 284.)
 

CRETACEOUS MOLLusca,

T. A. Brock, d 1
PLATE XXIV

Fics. 1~5. Hoplitoides nigeriensis, sp. nov. Gongila. 14, siphonal

view of Fig. 3, Plate XXIII; 4, siphonal view of Fig. 3.
(Page 284.)
PLATE XXIV

 

CRETACEOUS MOLLUSCA.

del.

’

Brock

T. A.
 

  
INDEX
 
INDEX OF AUTHORS

Alexander, Boyd, 2, 13, 31, 45, 55
Allen and Thomson, 2

Ammon, A. von, 122

Andrews and Bailey, 199

Baikie, W. B., 2, 214

Bailey, see Andrews

Barratt, J., 122

Barth, H., 2, 52, 58, 89, 106, 181,
186, 193

Bather, F. A., 165

Bohm, J +» 279

Bormhardt, W., 18, 245

Briggen, 286

Campbell, J. M., 209, 211
Chamberlain and Salisbury, 196

Chautard, J., 122, 205, 207, 253,
263

Chevalier, A., 122, 233

Choffat, P., 282

Chudeau, R., 109, 120, 122, 135, 149,
141, 144, 162, 165, 169, 170,

191-5, 199, 219, 220, 233, 244,
250, 251, 258-60, 262, 263, 283;
see also Gautier

Clapperton, see Denham

Coquand, H., 277, 279

Corstorphine, see Hatch

Courtet, H., 106, 122, 193, 216

Crick, G. C., 273

Crowther, S. A., 2

Dames, 273

Denham and Clapperton, 2, 90
D’Orbigny, 278, 280

Downes, W. D., 104, 258
Dunstan, W. R., 92, 96, 265
Du Toit, see Rogers

Edlinger, W., 186, 233
Esch, E., 122, 163, 191, 226, 250, 263
Evans, J. W., 269

 

289

Falconer, J. D., 257-8, 263, 273

Flamand, G. B. M., 121

Flett, J. S., 131

Forteau, see Peron

Foureau, F., 135, 206

Foureau and Gentil, 135

Freydenberg, H., 135, 206, 215, 218,
220; see also Gentil

ards eis 135, 140, I41, 216, 219,

25

Gautier, E. F., 226, 233

Gentil, L., 121, 135, 140, 258

Gentil and Freydenberg, 106, 134, 135,
140, 258

Guéranger, 279

Guillemain and Harbort, 275

Gurich, G., 174, 236

Harker, A., 264

Harbort, see Guillemain

Harrison, J. B., 246

Hatch, F. H., 206

Hatch and Corstorphine, 206

Haug, E., 121

Holland, Sir T. H., 207

Horwood and Wade, 122, 143

Hubert, H., 69, 109, 121, 135, 140,
168, 170, I91, 196, 202, 204,
207, 226, 249

Hyatt, 282

Knox, A., 122
Kossmat, 284

Lacoin, L., 206, 258

Lacroix, A., 135, 138, 263

Laird and Oldfield, 2, 6

Lander, R. and J., 2

Lapparent, A. de, 162, 165, 194, 207,

229
Lenfant, Capt., 2, 8
Lenz, O., 122, 197
290

Longbottom, A., 13-16, 20, 22, 33-5,
87, 96, 98, 103-6, 147-51, 153,
154-7, 184-91, 227-8, 261-2, 273

Lugard, Sir F. D., 2

Maclaren, J. M., 209

Maufe, H. B., 208, 211
Mennell, F. P., 204, 209, 211
Merrill, G. P., 246

Newton, R. B., 165, 281
Oldfield, see Laird

Park, Mungo, 2

Parkinson, J., 81, 112, 119, 122, 163,
191, 226, 250

Passarge, S., 2, 122, 140, 186, I9I,
198, 204, 207, 224, 233, 237, 241,
245, 247, 248, 258, 259, 263

Peron, A., 279, 282, 286

Peron and Fortau, 280

Peron and Thomas, 281, 282

Pervinquiére, L., 282, 284-6

Petrascheck, 284

Prior, G. T., 264

 

INDEX OF AUTHORS

Quaas, :280

Rogers and Du‘Toit, 206
Rohlfs, G., 200

Salisbury, see Chamberlain

Solger, F., 285

Stroliczka, 276, 280, 281, 284

Suess, E., 140, 165, 233, 247, 248, 252

Thomas, see Peron
Thomson, see Allen

Vandeleur, S., 7
Van Hise, C. R., 118
Vogel, H., 2

Voit, F. W., 123

Wade, see Horwood
Wallace, Sir W., 2, 268
Walther, J., 199, 207
Whiteaves, 281

Whitlock, G. F. A., 32
Woods, H., 166, 273, 277-81
Woodward, A. S., 273
GENERAL INDEX

Abuja: the Rock, 27
granites and gneisses of, 99
Alpine movements in Sudan, 251
Ansongo, flints of, 170
Arofu : Cretaceous rocks of, 148
saltings of, 149, 266
silicified limestone of, 149
galena veins of, 149
Augite-syenite, 135
Awe: brine springs of, 148, 266
Cretaceous rocks of, 146
volcanic hills of, 31, 260, 262
Axes of elevation : 234

Bagele hills: 14, 34, 186
Barbur basalt plateau, 146, 257
Baro, 4, 173
Basalts, 139
of Sahara, 140
of Tertiary age, 253
nepheline basalts, 255
plateau basalts, 51, 100, 257
Bassa: scenery of, 25-6
crystalline rocks of, 82
Bauchi plateau, 3, 38-43
summit of, 40
limits of, 41
scenery of, 42
volcanic hills of, 42
drift deposits of, 43, 203
former continuity with plains of
Hausaland, 203
elevation of, 237
not a horst formation, 237
Bauchi province, scenery of, 50
eastern plains of, 44
crystalline rocks of, 101
intrusive rocks of, 102, 133
Benue, watersheds of, 3
tributaries of, 10
scenery of, II
volcanic tract of, 12
plain of, 13
sandbanks of, 15
drift of Benue valley, 223

 

Benue, antecedent character of theupper
and middle Benue valley, 231, 243
Bida, 24
Bima, hills, 50
sandstones, 161
Borgu, scenery of, 20
crystalline rocks of, 69
drift of, 196
Bornu province, scenery of, 50-56
sandstones of, 50, 179
volcanic plateau of, 51
northern plains of, 52-3
crystalline rocks of, 106
drift of, 215
area of predominant depression, 218
dry water-courses of, 220
Bussa, 8, 9, 19, 71

Calc silicate rocks, 114

Carboniferous rocks of Sahara, 144

Cassiterite, see Tinstone

Chad, lake, 2, 52
crystalline rocks near, 107
stratigraphy of rocks around, 192-3
ferruginous clay on shores of, 206
alluvial deposits of, 215
shelly marls of, 216, 218
former greater extent of, 217
not continuous with Eocene seas, 217
excavation of present floor of, 219
climatic changes in Chad area, 219,

240
depression of Chad area, 216, 217, 240
Clays,
of Giro, 168
of Kurukuru, 168
of Pali, 177
of Kirifi, 178
of Deu, 178
of Gombe, 178
Climate, changes of, in Sudan, 210
in Hausaland, 214
in Chad area, 219
favourable to formation of surface
ironstones, 219

1
292

Cretaceous rocks, distribution of, 144
relation to crystallines, 146
of Muri province, 147
of Yola province, 154
of Bauchi and Bornu, 157
folding of, 147, 154, 158
classification of, 161
of French Sudan, 162
of Southern Nigeria, 163
of Kameruns, 163
paleontology of, 273 ef seg.
Crustal movements, see Movements

Dala, see Mt. Dala
Dallols, 61, 242, 250, 251
Desert periods in Nigeria, 214, 217
recent arid period, 210, 214, 219, 240
Devonian rocks of Sahara, 144
Diabase, 139
Diorites, of Bauchi, 136
of Kano, 136
of Kontagora, 136
diorite porphyrites, 138
Drainage system, recent rearrangement
of, 198, 213, 233, 240
Drift, 195
of Hausaland and Borgu, 196, 199
ferruginous crust of, 199
origin of, 201
of Bauchi plateau, 203
of Bornu, 215
of Katagum, 221
of Gongola valley, 222
of Benue valley, 223-4
of Sahara, 226
Duguri, canyon valleys of, 48
sandstones of, 175
Dunes, ancient, 53, 58, 214

Eocene rocks of Northern Nigeria, 164

unconformable upon Cretaceous, 164,
175

of Sokoto province, 165

of the Niger valley, 169

conditions of accumulation of, 171

of Kontagora, 172

of Lokoja, 174

of Nupe, 173

of Bassa, 174

of Nassarawa, 174

of Kabba, 173, 175

of Duguri, Gombe and Kerri Kerri,

175
age of, 181
unconformity
182-3

of Yola, 184

of Muri, 189

of Upper Niger, 191

of Kameruns, 191

upon Cretaceous,

 

GENERAL INDEX

Eocene rocks of Southern Nigeria, 191
basins of sedimentation, 228
probable extension over

Africa, 193, 229

Central

Faulting, of Cretaceous rocks, 145, 147,
154, 157, 158
of margin of Bauchi plateau, 237
on Upper Benue, 190
Ferruginous crust of drift deposits, see
Surface ironstones
Firki of Bornu, 52, 215

Galena, of Arofu, 149, 270
of Kudu valley, 154, 270
Gateri Hills, 46, 48, 153
grits of, 153
Gneisses, softer and harder, 69, 108
replacement of softer by harder in
Niger valley, 74, 120
in Kabba and Ilorin, 80, 84
near Abuja, 99
in Bauchi, 102
relations of harder and softer, 119
of Sahara, 121
of West Africa, 122
of Transvaal, 123
meridional strike of, 109
of sedimentary origin, 110
mecamorphism of, III
Gold, in Northern Zaria, 96, 269
in Southern Muri, 269
in Bauchi, 269
Gombe, grits and clays of, 175, 178
Gongola, plain of, 14, 33, 47
valley of, 46, 50
drift of, 222
antecedent character of middle
Gongola valley, 231, 244
Granites, 123
petrography of older, 123
of younger, 129
soda granites, 102, 130, 135, 140
age of younger, 140
periods of intrusion of, 142
Granulites, 116

Hausaland, provinces of, 3
scenery of, 21, 35
plains of, 21, 36, 198
drift of, 196 e¢ seg.
surface ironstones of, 199
origin of present aspect of, 198, 246
periods of elevation and depression
of, 213

Ibi, 12
Tlo, 4
GENERAL

Tlorin, orographical structure of, 16
great plain of, 19
crystalline rocks of, 75
Inselberge of Kabba, 17
of Borgu, 20
of Kontagora, 22
of Nassarawa, 27
of Muri, 31
of Yola, 35
of Zaria, 36
of Bauchi, 44
of Kano, 56
of Sokoto, 60
origin of, 201, 246
Inselberg landscape, 18, 245
Intrusive rocks of Bauchi province, 102
petrography of, 123
older granites, 123
younger granites, 129
pegmatites, 129
syenites and diorites, 135
porphyries, 137
basalts, 137
Iron sands, 268
Ironstones, crystalline, 78, 81, 110,
114, 269
Cretaceous, 154, 160
Eocene, 164, 269
of Sokoto, 166
of Kontagora, 172
of Baro (Mt. Gidda), 173
of Lokoja (Mt. Patti), 174, 269
of Kantana, 177
of Panguru, 178
of Tagum hills, 179
of Kerri Kerri, 180
See also Surface ironstones

Jakpara hills, 18
Jakura and Wa, limestone of, 66, 78,
110, 113
Jebba, 7 e7 seg.
gorge of the Niger above, 7
Ju Ju Rock of, 8, 70
quartzites of, 70

Kabba, orographical structure of, 16
central tableland of, 16
scenery of, 17, 37
crystalline rocks of, 77 e¢ seg.
Kaduna, scenery of, 24, 36
tributaries of, 36
gorge at Zungeru, 35-6
in axial trough, 234
Kano, province of, 56-8 . :
Mts. Dala and Kogon Dutsi, 58,’ 90,
136, 201, 247
crystalline rocks of, 89
drift of, 196

 

INDEX 293

Karakai quartzites, 60, 88
Kara river, 92
Katagum, 57
drift of, 221
Kato phyllites, 95
Katsina, scenery around, 59
granites of, 89
granite surface rock, 89
sandstones of, 89
Kazaure, blue quartzite of, 58, 89-90
Kerko hills, granite massifs of, 37
Kerri Kerri, plateau of, 54
trench-like valleys of, 56
rocks of, 179
ironstones of, 181
Kilba hills, 35, 105
Kogon Dutsi, see Mt. Dala
Kontagora, 21
scenery of, 22
crystalline rocks of, 91, 92
sandstones of, 170
Kurefi, 89
Kwaba hill, 33

Lake Chad, see Chad
Limestone, crystalline, between Jakura
and Wa, 66, 78, 110
at Igbo, 82
origin of, 110
petrography of, 113
Turonian, of Muri province, 144, 147
of Awe, 147
of Kumberi, 150
of Arofu, 149
of Yola, 155
of Gongola valley, 159
of Gongila, 169
of Reme, 160
of Sudan, 162
paleontology of, 273 ef seg.
Eocene, of Sokoto, 165
nummulitic, 167
Lokoja, 2, 6, 82, 174
crystalline rocks of, 82
sandstones and ironstones of, 174
Loko, I1

Mada hills, peaks of, 30
Magnetite schists, 78, 81, I10, 114
Manga, 238
Maradu, volcanic agglomerates of, 60,
88, 254
Mahorro, ironstones of, 22, 172, 269
Maibirro, quartzite hills of, 21, 73
Malenda river, granites and quartzites
of, 21
Metamorphism, absénce of contact
metamorphism in Kabba, 83
variation in alternate belts, 111
of granites, 123
294
Mineral resources of Northern Nigeria,

205
Miocene rocks of Sudan, 194
Monazite, 270
Morrua, plains of, 29
Mts. Dala and Kogon Dutsi, 58, go,
QI, 201, 205, 212, 225, 247
Mt. Patti, 6, 11, 174, 269
Mt. Purdy, 6
Movements, crustal, post-Cretaceous,
164, 227
Tertiary, 212, 227 et seq.
alternate periods of elevation and
depression, 213, 230
flexuring of crust, 234, 241
elevation of Bauchi plateau, 237
Alpine movements in Nigeria, 252
Mumuye-Manna plateau, 32, 104
Murchison hills, 2, 12, 31, 103, 231
Muri, great plain of, 12, 30
sandstones, 153
crystalline rocks of, 30, 103
Cretaceous rocks of, 145, 147
volcanic hills of, 31, 262
Muri sandstones, 153

Nassarawa, province of, 26
scenery of, 27-30
central plain of, 28
northern tableland of, 29, 39
crystalline rocks of, 100
Nepheline basalt, 255
syenite, 259
Nigeria, Northern, area of, 1
boundaries of, 1
provinces of, 2
headquarters of, 2
physical features of, 2
hydrographical systems of, 3
hydrographical centre of, 3, 40
recent origin of river system of, 240-

243

crystalline rocks of, 63

Cretaceous rocks of, 144

Eocene rocks of, 164

superficial accumulations of, 194

mineral resources of, 265

Niger, the, 4 ef seg.

watersheds of, 3, 4, 19, 36

tributaries of, 5

gorge above Lokoja, 7

sandstone plateaux of, 7

gorge between Jebba and Yelwa, 8

rapids of, 9

establishment of present course of,
241

relation of scenery to character of
rocks, 242

recent origin of Niger valley, 243

 

GENERAL INDEX

Ningi hills, 44
Ningi massif, 102
Nodules, phosphatic, in Turonian lime-
stones, 156
in Eocene limestones, 166
Nupe, scenery of, 23
crystalline rocks of, 98

Odouape, granite and gneisses, 80
Olle, 114
Okoro, 77
Okuruku granite, 126

quartz magnetite rock of, 81, 115
Okwa river, 28
Orissa hills, 19, 76

Petrography, of gneisses and schists, 108
of intrusive rocks, 119
of early Tertiary lavas, 254
of later Tertiary lavas, 262
petrographical provinces, 263
Phonolites of Northern Nigeria, 256
Phyllites, of Bussa, 71
of Ngashki, 73
of Sokoto, 86-8
of Zungeru belt, 93-5
petrography of, 112
Porphyries, 137
Porphyrites, 138-9

Quartzites, of Jebba, 70
of Maibirro, 73
of Lukke, 78
of Kazaure, 89
of Zungeru, 93
petrography of, 113

River system of Northern Nigeria
recent origin of, 233, 241

Salt, 265
in western Muri, 148
in eastern Muri, 151
between Putu and Tangalto, 158
vegetable salt of Bornu 267
Shappa hills, 19, 76
Shebshi hills, 30, 32
Silurian rocks of Sahara, 121
Sokoto, province of, 60
dallols of, 61, 242, 250
crystalline rocks of, 86
Eocene rocks of, 165
Superficial accumulations of Nigeria,

194
of West Africa, 226
GENERAL INDEX

Surface ironstones of Borgu, 20, 199
of Bauchi and Zaria, 199
platforms of, 200
occurring upon drifted alluvium, 205
mode of formation, 205-211
period of formation, 211
absence in Bornu, Katagum and
Gongola valley, 215
vesicular character of, 199
lustrous surface of, 199
irregular distribution of, 209
Syenites of Bauchi, 135
Syenite porphyries, 138

Tabachi, 73
Tagum hills, 52, 179
Tangale hills, 47, 48
Peak, 49
Tinstone, in eastern Ilorin, 77, 131
in eastern Zaria, 98
in Bauchi, 103
in pegmatites, 131
in alkaline granites, 134
in plateau drift, 203
economic development of, 270
Tongolan, 176
Tourmaline, in quartzites, 70
in quartz veins, 72, 73
in pegmatites, 76, 82, 99
in granites, 85, 99, 130
in slaty schists, 88
associated with younger granites, 129
schorl rocks, 131
Trachytes of Bussa, 72, 115
Traverses, typical, 64
Ture Peak, 49

Upper Benue sandstones, 155, 184
relation to crystalline rocks, 184
unconformable upon Cretaceous, 188
cross-bedding in, 187
mode of formation, 187, 190

Valleys, canyon, of Bauchi, 46, 244
flat-bottomed valleys of Sokoto, 61,
242
shallow valleys of Borgu, 20
of Hausaland, 22, 57
canyon, of Kontagora, 23, 242
canyon of Duguri, 48, 244

 

295

Valleys —continued
trench-like, of Kerri Kerri, 56
interlacing valleys of Kerri Kerri,
56, 245
Vere hills, 14, 34, 105, 247
Volcanic hills of Muri, 12, 31, 260
of Yola, 13, 35, 260
Barbur volcanic plateau, 51, 257
volcanic agglomerate of Maradu, 60,
88, 254
Morrua volcanic plateau, 100, 203
absence of pre-Tertiary volcanicrocks,
253
character of Tertiary volcanic erup-
tions, 254
early Tertiary volcanic period, 254
later Tertiary volcanic period, 259

Wase river, 39, 45
Wase rock, 31
phonolite of, 256
Watersheds, primary, 3, 36, 40
character of, 36, 40, 241
Weathering: absence of weathered
crust upon rocks of Sudan, 195
dry weathering not a potent factor
in denudation, 199
former sheet of weathered rock in
Nigeria, 201
Wuru, Great Rapid of, 8, 9
Wurkum hills, 30

Yo river, 4, 234

Yola, eastern, 230
scenery of, 32-5
southern plateau of, 32, 104, 227
volcanic hills of, 13, 35, 260
crystalline rocks of, 103
Cretaceous rocks of, 154
Eocene rocks of, 184

Zaria, province of, 35
scenery of, 37
hills of, 36
crystalline rocks of, 93-98
plains of, 38
vesicular ironstone of, 200
drift of, 197

Zungeru, 2, 35
quartzites and schists of, 93

ERRATUM.

p- 203, line 13, for ‘‘larvas ” read ‘* lavas.”

RICHARD CLAY AND SONS, LIMITED, BREAD STREET HILL, E.C., AND BUNGAY, SUFFOLK.