Yale Peruvian expeditions, 1911-1915,
Publications no. 21.

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[From The American Journai, op Science, Voi,. XXXVI, Sept., 1913.

GEOLOGIC SKETCH of TITICACA ISLAND and
ADJOINING AREAS.
By Herbert E. Gregory.

Results of the Peruvian Expedition of i 9i 2, under the auspices
of Yale University, and the National Geographic Society.

THE PERUVIAN EXPEDITION OF 1912
UNDER, THE AUSPICES OF
YALE UNIVERSITY 8b THE NATIONAL GEOGRAPHIC SOCIETY
HIRAM BINGHAM, .DIRECTOR

LAKE TITICACA 8c VICINITY

Am. Jour. Sei., Vol. XXXVI, Sept., 1913.

Plate I (Fig. 1).

THE

AMERICAN JOURNAL OF SCIENCE
[FOURTH SERIES.]

Art. XXIII. — Geologic Sketch of Titicaea Island and Adjoin
ing Areas ; by Herbert E. Gregory.* With Plate I.
Introduction.
The great Andean Plateau of southern Peru and northern
Bolivia, the " altiplano," has a width in the Titicaca region of
approximately 50 miles. Though possessing in itself relief
exceeding a thousand feet, its plateau features are well brought
out when the lofty ranges of the Cordillera Real and the
Maritime Andes, between which it is hung, are taken into
view. The bordering range on the northeast maintains a
height of over 17,000 feet for a distance of 200 miles and
reaches at Sorata (Illampn) a point 21,520 feet (Conway) above
sea level. The western border of the plateau is a wide moun -
tainous highland crossed by the railroad at 14,666 feet, and
maintaining an average elevation in southern Peru of nearly
14,000 feet. As shown by Bowman, the Maritime Andes is a
dissected peneplain and represents a mountain range which
may have exceeded in height the present eastern Cordillera.
Occupying an irregular depression in the high plateau,
between "lat. 15° 20' S. and 16° 35' S. lies Lake Titicaca at an
elevation of 12,500 feet above sea level. The lake is roughly
rectangular in shape, one hundred miles long, and with an
extreme breadth of thirty-eight miles, f
Its superficial area, calculated by planimeter from the best
available maps, is approximately 4,000 square miles, and the
length of the shoreline probably exceeds 500 miles.J Properly
speaking, there are two lakes, connected by the rock-walled
straits of Tiquina, five-eighths of a mile wide. The lower
* Geologist, Peruvian Expedition of 1912.
f The figures are from LeMaire. No complete instrumental survey of the
lake has yet been undertaken. j<f""">
% The figures given by Paz Soldan (270 mil4^TO<I^.,e€)ijJjflin other writers
are manifestly too small.

Am. Jour. Sci. — Fourth Series, Vol,. XXXVI, No. 213. — September, 1913.
13 ~~

iQ&Gn±fy .gjttfyin oih
XVI, No. 213.— Septem

188 II. E. Gregory — Geologic Sketch of
lake (Lago Pequeno) is shallow, with gently sloping bottom
flats and large areas of low shore from which rise rock knobs
and hogbacks of moderate height. The main lake (Lago
Grande) reaches a depth of over nine hundred feet and is
bordered by abruptly descending under-water shelves. Twenty -
iive tributaries, all small and greatly fluctuating in response to
seasonal precipitation, supply the lake. Its surplus waters are
carried by the Desaguadero into the salt Lake Poopo, thus
forming a chain of fresh- and salt-water bodies like the Sea of
Galilee-Jordan River-Dead Sea of Palestine and Utah Lake-
Jordan River-Great Salt Lake of Utah. Thirty-six islands
rise above the surface. The largest of tliese, Titicaca, has
given its name to the lake, and as the Island of the Sun, shares
with Koati (the Island of the Moon) and Tiahuanaco, a posi
tion as a center for archaeological and historical research.
Physiography.
The Lake Floor. — The soundings made by LeMaire* and by
Agassiz,f supplemented by scattered data, are sufficient for the
construction of a bathymetric map of the basin now occupied
by the waters of Titicaca. (See fig. 1, Plate I.)
It will be noted that Lago Pequeno is, properly speaking, not
a part of the depression holding the waters of Titicaca. Its
floor is remarkably flat, less than one-tenth of its area reaching
a depth exceeding 20 feet ; and a fall of ten feet in water level
would expose about one-fifth of its bed, and effectively impede
navigation. Lago Grande is seen to occupy a rectangular
basin with abruptly ascending edges on three sides, and with a
slope from southwest to northeast. The southeastern extrem
ity partakes of the nature of a canyon, — Tiquina is a sharp-cut
valley included between steeply sloping rock walls. The islands
of Titicaca (fig. 2), Koati, and Soto are mountains, rising respec
tively 1,400, 1,500, and 1,300 feet above the basin floor, while the
archipelago facing the coast at Escoma includes stacks and pin
nacles, erosion remnants, rising above a slightly submerged
platform. There are no indications that the tiny islands adjoin
ing Titicaca Island form steps in a submerged causeway unit
ing Copacabana with the Bolivian mainland at Huaicho, as
surmised by Bandelier, and no proof that the straits of Tiquina
have been opened by faulting or torrent erosion since the lake
attained its present dimensions, as is implied by various writers.
How much of the shallowness of the bays of Puno, Rames and
Achacache and of Lago Pequeno is due to waste furnished by
* Les Lacs des Hauts Plateaux de L'Ame'rique du sud, Paris, 1906.
+ Hydrographie sketch of Lake Titicaca, Proc. Am. Acad. Arts and Sei
vol. xi, 1875-76.

Titicaca Island and Adjoining Areas. 189
the tributary streams, and how much to original depression, is
impossible to determine, but it is significant that bays of great
depths and precipitous shore fronts as Yampupata, Tiquina,
Huaicho, Conina, and Huancane do not furnish an outlet for
debris-laden streams of large size. Soundings so far avail
able fail to indicate under-water channels or canyons whose
orientation may be determined. That the basin, somewhat
extended, is a warped, downfaulted area, is suggested by the
Fig. 2.

i 3
j Titicaca 'JJ
fi Island U
ft  Jfjfa  U

Fig. 2. Section across Lake Titicaca from Carabuca to Pomata showing
mountainous character of Titicaca Island.
rectilinear quality of shore and island borders. It would appear
also, from the character of the under-water slopes, that the
topography had reached a stage of early maturity before the
advent of structural movements which prepared the basin for
filling by water.
The floor of the lake basin, in its deepest part and frequently
near shore, was found by Agassiz* to be covered with " thick
mud, the finest possible greenish black silt containing few frag
ments of shells— the mass being probably several feet thick."
In a few localities sandy, shelly, and rocky bottom was found.
The bed of Lago Pequeno appears to be covered with sand.
Professor Thoulet analyzed three samples obtained by LeMaire,
the first from Lago Pequeno near shore at Chillilaya, the
second from a depth of 741 feet, the third from near shore at
Huaicho on Lago Grande. The gray slime from Chillilaya
contained microscopic fragments of siliceous spicules and dia
toms, black, ferruginous, combustible specks (coal?), brick-
colored particles, minute angular quartzes, black magnetic
grains and sparsely distributed obsidian, pumice,_ hornblende,
olivine, pyroxene, and mica. Percentage calculations of these
samples gave : sand and plant fragments 13 ; calcareous slime 3 ;
non-calcareous slime 13 ; calcareous mud 59 ; organic residue
12. Both entire and fragmentary shells were recovered. The
sample from deep water gave in parts per 100 : sand, etc. 3 ;
* Proc. Am. Acad., vol. xi, p. 284, 1875-76.

190 H. E. Gregory^Geologic Sketch of
slime 78 ; calcareous mud, a trace ; organic residue 18 ; inde
terminable 2. This sample contained the same minerals as
were found in Lago Pequeno and differs only in the absence
of lime and greater abundance of globular diatoms. Erom the
Huaicho dredging were obtained iron-coated grains of quartz
" resembling the sands of Sahara," and a few volcanic frag
ments. Thoulet's studies show that the deeper parts of Titi
caca are mantled with organic materials, chiefly diatoms,
mingled with siliceous and calcareous (in Lago Pequeno)
grains, minute fragments of minerals either wind-worn or vol
canic, rarely meteoric. Near shore sand, plant fragments, and
small shells occur.
As pointed out by Agassiz, the peculiar physical conditions
of the lake bottom combined with high elevation and high
temperature of water should tend to the specialization of
genera, — a result which does not occur. The absence of unique
forms and the poverty of species are remarkable. The two
genera of fish and the mollusks belong to widely distributed
fresh-water types. The Crustacea, however, have for their
nearest relatives marine forms. An interesting fact pointed
out by Orton is that one of the fishes, Trichomycterus dispar,
occurs also in the Rimac and Guayaquil rivers.
Lake Water. — The temperature of the water, under the
influence of the tropical sun and of the rarefied atmosphere, is
remarkably uniform at all depths. Of thirty-four measure
ments made by Agassiz in which the temperature of the water
at the bottom was compared with that at the surface and that
of the air, the difference between bottom and surface was
3°-4° ; the bottom temperature being 54°-55° (one reading
51° at 618 feet), while the surface temperatures were 56°-57°.
Only one much larger range, 6-5°, was noted. At the same
time (January 1st to March 5th) the temperature of the air
ranged from 42°-44° early morning to 55°-63° during the
hottest part of the day ; extremes of 47° (cloudy) and 67° (very
bright) were observed.
The mean of twenty-nine records taken by LeMaire from
depths between 11 feet and 925 feet* give a value of 5L51° F.,
the highest reading being 52-52° F. at 79 feet and 607 feet, and
the lowest 48-92° F. at 11 feet, 49-64° F. at 160 feet, and
49-46° F. at 740 feet. A grouping of LeMaire's thermometric
observations indicates an increase from surface to 492 feet,
reaching a maximum between 500 and 650 feet, followed by
a slight decrease to the lowest depths. The temperatures of
* This is the greatest depth obtained by soundings. In Marie E. Wright's
elaborate book "Bolivia" (1906) is an illustration of the loose statements
frequently found in print: ''Its depth varies from 250 feet to 1500 feet,
and there are places where it is unfathomable" (p. 243).

Titicaca Island and Adjoining Areas. 191
the surface waters during July, during the time the above deep
water temperatures were recorded, gives a mean of 52-06° F.
The mean temperature of the air, including all hours of the
day during the same period, was 45-32° F. It thus appears
that the temperature of the surface water averages higher than
that of the overlying air in summer as well as in winter.
These records of water and air, though manifestly inadequate
for meteorological discussion, are sufficient to show that freez
ing temperatures are rare, that ice forms only in narrow bays
and then infrequently, and that accordingly the effect of frost
in disintegrating rock either in contact with waves or with air
is reduced to very low terms. Moreover the diurnal range of
temperature is insufficient to aid greatly the disruption ofrock
masses, conditions which do not hold for the surrounding alti-
plano. The water of the lake is fresh and palatable. Raimondi's
analysis showed but a trace of saline matter and the analysis of
three samples by Malliere gave 1*07 grams per liter of mineral
content, of which -465 of a gram was chloride of sodium. The
slightly disagreeable taste of samples taken near shore is due,
according to Barranca, to the presence of magnesium and
bicarbonate of lime formed by the action of carbonic acid
liberated by the decomposition of Myriophillum and totora,
which flourish in the shallower bays. The water is clear, even
in the rainy season when mud from streams discolors shore
areas, and its transparency is little less than Geneva and Tahoe.
The outflow of the lake (the Desaguadero, 45 meters wide, two
to seven meters deep) is, according to Reck,* 4-822 cubic
meters per minute. Evaporation amounts to five millimeters
per day.f
Fluctuation in Level. — The dimensions of the present
Titicaca are, as previously stated, one hundred miles by thirty-
eight miles, with a superficial area of approximately 4000
square miles. That it formerly had a somewhat greater ex
panse seems to be sufficiently attested by historical and geo
logical observations. Tovar;): observes that cultivated fields
now occupy small portions of exposed lake bottom at Guarisco,
Acora, and Llave, that disputes regarding the ownership of
reclaimed land at Capachica and Pusi are listed in local court
records, and that in 1877 the waters of the lake reached the
suburbs of Puno, now five "cuadras" (city blocks or squares)
distant. The ancient ports of Huancave, Moho, Conima,
Ancoraimes, and Achachaci are now two to three kilometers
* Geog. Soc. de Lima, Tomo X.
t Prado, Bol. Soc. Geog. de Lima, Tomo I, 1892.
% Bol. Soc. Geog. de Lima, Tomo I, 1892.

192 II. E. Gregory — Geologic Sketch of
inland. Agassiz states* that Lake Arapa and several lakes
near the west shore are outliers of an ancient water body, and
that the plain north of Lampa "only 100-150 feet above the
lake . . . was one sheet of water." ".The terraces of the
former shores are still very distinctly seen." Tovar also
records the tradition that Lake Umayo, now fifteen miles
distant and fifty feet more or less above the Titicaca level, was
formerly part of Titicaca and that the plains about the north
west end of the lake were formerly less extensive. Yiscarraf
states that within historical times the peninsula of Copacabana
was an island. La Puente,:]: Zundt,§ Posnansky,| Markham,!"
and Conway** accept the general view first stated by Orton,fT
that the waters of the lake were vastly more extensive and sur
rounded Tiahuanaco within historical times. £:{:
When the Titicaca coast is examined it appears that the data
presented by Tovar have little significance. Most of the places
mentioned adjoin very shallow waters which are gradually being
reclaimed by stream-borne sediments (fig. 3). This is particu
larly true of the areas mentioned by Agassiz, in which the
Lampa and Rames are aggrading their beds and carrying sedi
ment forward to form deltas. Squier appreciated this fact and
remarks that " the region around the mouth of the Rames is a
kind of delta, very low and level, interspersed with shallow
pools as if but recently half rescued from the lake by deposits
from the river." That the lake level has been eight to twelve
feet higher than to-day is shown by the whitish band of
deposited salts and discolored rock which decorates the bases
of rock islands. While in part the evidence of the height
reached by breakers, this horizontal band strongly suggests a
former level below which the waters have sunk within prob
ably a few decades. The annual fluctuation in lake level is
approximately 4 feet, and so shallow is the bottom in places
that hogs may feed several hundred feet from shore. In the
absence of quantitative measurements and of definite locations
of ancient shore lines, the conclusion of Tovar that the lake is
" regularly diminishing " in a " surprising manner " is not
justified. *Proc. Am. Acad. Arts and Sei., vol. xi, 1875-76.
f Copacabana de loslncas, La Paz, 1901.
% Bol. Soc. Geog. de Lima. Tomo I, 1892.
§ Op. cit.
|| Bol. oficina Nacional de Estadistica de Bolivia, 1911.
IT Geog. Jour., October, 1910.
** Climbing and Explorations in the Bolivian Andes, 1901.
ft The Andes and the Amazon, 1876.
XX In a paper presented by Professor Bowman before the Association of
American Geographers, December, 1912, and later to be published, the r61e
played by Lake Titicaca in the history of ancient Tiahuanaco is discussed in
detail.

Titicaca Island and Adjoining Areas.

193

Berglalund reports* that during twenty- three years' residence
at Desaguadero the annual fluctuation reached five or six feet
and that the level in 1906, following four years of deficient
rainfall, was considerably lower than in 1909. Such variations
are not uncommon in lakes of the world, even in humid regions

Fig. 3.

Fig. 3. Bay of Puno, showing a typical portion of the deltas extending
into Lake Titicaca from the northwest.
marked by climatic regularity. A seasonal or cyclical change
in climate, taken in connection with river-borne sediments, is
sufficient to account for all authentic facts so far reported,
without involving a hypothesis regarding the geological history
* Geog. Soc. de Lima, Tomo X.

194 II E. Gregory — Geologic Sketch of
of the lake. Until long-term, continuous records are available,
it seems best to assume that Titicaca, in common with other
water bodies, rises and falls in response to the increased and
decreased precipitation which characterizes climatic cycles, the
existence of which has been demonstrated for other parts of
the world. The hypothesis of progressive diminution through
centuries of time would accordingly be discarded.
Former Extent. — That Titicaca is the diminished represen
tative of a vast interior sea which covered the altiplano in
northern Bolivia and southern Peru, is claimed by nearly all
students of this region. Thus, Agassiz states,* " Lake Titicaca
itself must have, within a comparatively very recent geological
period, formed quite an inland sea. The terraces of its former
shores are everywhere most distinctly to be traced, showing
that its water level must have had an elevation of 300 or 400
feet at least higher than its present level." Le Mairef accepts
Agassiz's conclusions, supplemented by the existence of an
ancient beach line in the Poopo basin, first observed by Mus
ters,;]: and concludes that Titicaca and Poopo are parts of one
interior sea covering the region between 15° and 21° south lat
itude, including La Paz and Oruro. The outlet was supposed
to be through the present La Paz river into the Atlantic.
" The largest lake in the world fed the largest river in the
world." " Within historical times the Desaguadero has been
reduced from a wide strait to its present dimensions." La
Puente § holds the same view but mentions no evidence
bearing on this point. Posnansky| believes that Titicaca is a
remnant of an enormous salt sea separated from the ocean by
uplift and drained through the eastern Cordilleras by a passage
prepared by a cataclysmic rupture of its barrier.. As if this
were not sufficient proof of the power of the " titanic forces of
nature," Posnansky states that the region was again flooded by
waters from Lagunillos freed by the rupture of massive rock
walls, — a disaster which destroyed the civilization represented
by Tiahuanaco ! Zundt's original viewsT were in harmony
with those of Posnansky and required the elevation of strata
to a height of 13,000 feet without destroying their horizontal-
ity. The steep faces of the mesas were considered the work of
waves. Zundt's later interpretation** is based on the hypoth
esis of a late Tertiary river, " Rio Titicaca," which extended
from Sicuani, Peru, to Ulimani, Bolivia, via La Paz. This
*Proc. Am. Acad. Arts and Sei., vol. xi, 1875-76, p. 288.
f Lagos de Los Altiplanos, pp. 153-154. La Paz, 1909.
JGeog. Jour., xlvi, 1871-77. § Op. cit., 1892.
| Bol. officina Nacional de Estadistica de Bolivia, 64-66, La Paz 1911
pp. 689-702.
f Appendix, D'Orbigny, 1907.
**Boi. Estadistica, 67-69, 1911, and 70-72, 1912.

Titicaca Island and Adjoining Areas. 195
ancient channel was blocked by alluvium and glacial debris,
thus isolating the present Titicaca. The ancient level of the
original lake was not much above the present, and is marked
on the rocks at the straits of Tiquina. Duenas* expresses the
view that ancient Titicaca may have extended into the Depart
ment of Cuzco. These views are only less extreme than the
conclusion of Ortonf that the " depression holding Lake Titi
caca is apparently a volcanic basin; fragments of lava, porphyry,
and jasper are scattered around and towers of igneous rock
protrude through the sedimentary strata."
It will be noted that the conclusions of Le Maire, Posnansky,
and others rest on the assumption that the hypothetical Titicaca
had its outlet through the La Paz canyon, an assumption neg
atived by the fact that the deposits at La Paz are of later date
than the lake basin, and the gorge itself is in large part post
glacial and recent. The existence of the hypothetical " Rio
Titicaca" of Zundt, flowing in a wide valley or canyon sunk
1000 feet below the altiplano, is supported by no evidence
from the lake bed, the altiplano, tlie valley of La Paz river,
or from the upper part of the' supposed valley now exposed to
view in the region between Huancani and Sicuani. The enor
mous lake which is supposed to have occupied the basin between
the two Andean ranges is believed by Posnansky to have been
a detached portion of the sea elevated 12,000 to 13,000 feet
without affecting the attitude of the Mesozoic strata. Points
urged by Posnansky in favor of the marine origin of the basin
are deposits of salt at several localities, deposits of sediments
at La Paz and on the altiplano, and the marine affinities of
the fauna of the lake. The first two points have little signifi
cance, since salt is a constituent of the country rock, and the
sediments at La Paz are river deposits, not marine pr even
wholly lacustrine.;]:
The lake fauna exhibits in part a marine facies, but is not
necessarily of direct marine origin. § The fish are fresh-water
forms, with marine affinities ; the mollusks, copepods, Daph-
nids, and ostracods are fresh-water forms ; the amphipods pre
sent a marine aspect, but nothing definite may be said of their
origin. The only true marine species mentioned by Posnansky,
the hippocampus, is not found in the extensive collections of
Agassiz and Le Maire. The presence of this species in the
lake, a conclusion based on a specimen given to Posnansky by
an Indian fisherman, and now in the private museum of the
collector, requires further confirmation.
* Bol. Cuerpo de Ing. de Min., No. 53, Lima, 1907, p. 25.
I The Andes and the Amazon, 1876.
X See Gregory: The La Paz Gorge, this Journal, vol. xxxvi, pp. 141-150.
§ For data concerning the habitat of the Titicaca fauna, I am indebted- to
my colleague, Professor Petrunkevitch.

196 E. E. Gregory — Geologic Sketch of
In this connection Agassiz's statement, quoted above, that
" the terraces of its [Titicaca] former shore line are everywhere
most distinctly to be traced," at "an elevation of 300 or 400 feet
at least higher than its present level," deserves attention. Such
high level terraces were not observed by the writer at Puno,
Guaqui, Tiquina, Yampupata, or on Titicaca Island,— a fact
which surprised me not a little, since I had assumed that such
evidences of higher level were to be found on all sides. The
shale, sandstone, and limestone, tilted at various angles and of
different degrees of firmness, fretted by waves of considerable
power, especially during the southern winter, would be expected
to produce unmistakable rock benches, and the low-lying bor
ders of parts of the lake offer favorable opportunities for beach-
making. Moreover, the conditions for preserval of the shore
forms in a semi-arid climate and where freezing is unusual are
favorable. This does not prove, of course, that no such evi
dences of high-water level exist, for no detailed survey has as
yet been made ; but raised terraces are not " distinctly to be
traced." In fact, no rock shelf or raised beach has been mapped
or described, and there is no direct evidence of former high
levels except for the relatively slight fluctuations discussed
above. It is significant that La Puente, who stoutly affirms
the former existence of a vast interior sea, made a traverse of
the lake borders and visited many islands without recording
the presence of ancient shore form's, and that Bowman in 1908
saw no signs of raised terraces.*
It will be noted that the argument against the presence of
an ancient interior sea of vast dimensions rests chiefly on evi
dence of a negative value, and in the absence of topographic
maps and of detailed physiographic studies must remain so.
The problem involves the unraveling of the geologic history
of the entire plateau region. From the data at hand it appears
that the great interior depression, itself a plateau, owes its
existence to faulting as implied by Bowmau,f and that the
downfaulted area was given its, relative position after uplift
and peneplanation of both the eastern and the Maritime Cor
dilleras in early Tertiary time. It is also probable that the
floor of the sunken area was further modified by warping and
selective faulting which produced a number of secondary
depressions at considerable depths below the general floor.
It is reasonable to suppose that such a downfaulted, warped
surface would be occupied by a number of lakes, whose extent
and permanency and degree of salinity would bear direct rela
tions to the original topography, abundance of waste and
climatic fluctuations. * Private communication.
f This Journal; vol. xxviii, 1909.

Titicaca Island and Adjoining Areas. 197
Titicaca Island. — Titicaca Island is a representative of a
large class of elevations including hogbacks, eroded folds,
mesas, igneous masses, and probably fault blocks, which pro
ject above the general floor of the great interior basin or pla
teau. In common with its companions it has reached a mature
stage of development and is, in brief, a residual prominence
now partly submerged in the waters of a lake.
In outline Titicaca Island is very irregular (fig. 8). Five
large bays set deeply into the land, in addition to ten or twelve
other bays of one-fourth mile or less in width which scallop
the island's border. Although the island has an area of 102
square miles, with an extreme length of only seven miles, and
width nowhere exceeding three miles, the length of the coast
line' is 33 miles. Only at the southwest, where the sandstone
ridge of Kakayo-Kena forms an unbroken wall for nearly five
miles, does the coast assume a rectilinear quality.
The dominating feature of the island's surface is a backbone
or central ridge, extending from Bilcokyma to Sicuyo, a distance
of about seven miles, and following the direction of strike of
the sedimentaries which compose it. On the northeast the
Kea Kollu dome, extending far into the lake, assumes a com
manding position, and on the southwest the long, straight
ridge of Kakayo-Kena, culminating at Chullun-Kayani with an
elevation of 800 feet, constitutes a conspicuous feature of the
landscape. At the north the peninsula of Marcuni, tied to the
land by the low isthmus of Challa, is a prominent feature when
viewed from the lake. Approximately two-thirds of the
island maintains a height of 400-500 feet, a few small areas
are over 700 feet, and at Palla-Kasa a barometer reading of
13,330 feet, 830 feet above lake level, was obtained. This is
probably the culminating point on the island, and Squier's
figure, 2,000 feet, for the hills back of Challa is clearly an
error. Back from the shore the surface has little sharp relief;
cliffs and precipices and deeply cut chasms, except those
formed by differential erosion of strata, are absent. Rounded
ridges, flattened domes, flat saddles', and graded slopes form
the surface, but not to the exclusion of minor steep rock
slopes developed on the edges of tilted strata. In fact dip
slopes and cuesta fronts in many places determine the topog
raphy and point to structural control of subordinate features.
The valleys separating the rounded heights are broad V-shaped,
frequently nearly flat, and the divides are everywhere incon
spicuous. Only in their lower courses do the stream channels
become steep-walled ditches and then only where wave-worn
headlands have destroyed previously established grades. In
short, the topography is mature or post-mature and youthful
features are exceptional. (See figs. 4, 5 and 6.)

198

H. E. Gregory— Geologic Sketch of

The coast shows everywhere signs of vigorous erosion ; head
lands of bare rock, rising 100-300 feet above water, are numer-

Fig. 4.

Fig. 4. General view of the Peruvian shore of Lake Titicaca.

Fig. 5.

*S*9^SS

^tJm*1***"

r.T*^.!!1***'

Fig. 5. Bay of Challa, Titicaca Island, showing beach and quality of hill slopes.

Titicaca Island and Adjoining Areas.

199

ous, and the short stretches of crescent beach are piled high
with gravel. (Figs. 6 and 7.) The longer beaches, as at South
Yumani and Challa, are built of fine materials with flat gradi
ents and in more sheltered places luxuriant fields of reeds
Fig. 6.

vsmr^.'^fi^r^.. '"jCpc.

Fig. 6. Kona Bay at South Yumani, showing beach, hill slope, and
quality of the short drainage channels.

{totora) are found. The Marcuni peninsula is tied to the land
by a double-faced, wave-made beach. A traverse of the strand
involves clambering over jutting rocks, climbing precipitous
headlands, and walking on beaches of yielding sand. Most of
the headlands plunge into deep water and the low sand beaches

200

H. E. Gregory — Geologic Sketch of

which occupy sheltered coves slope gently lakeward for a few
feet only to drop abruptly into the depths. The one hundred-
foot bathymetric contour lies very close in-shore, except to the
northwest, where the under-water platform forms a foundation
for six islands, the largest only a little over a square mile in
area, and all within two miles of Titicaca itself.
The agencies concerned in molding Titicaca are none of
them vigorous except the waves, which are very efficient tools,

Fig. '

Fig. 7. Ahyjadero Bay, Titicaca Island, showing beach, lake cliff, and
terraced fields (ande.nes). The strata exposed are limestones of Pennsyl-
vanian age and mark the northwest side of the Ahyjadero fault. E. C.
Heald, photo.
particularly during the southern summer. Chemical decom
position is favored by continuously moist atmosphere- stream
erosion is checked by infrequency of rain and by flat gradi
ents, which is offset only in part by the severity of sudden
showers. The peeling of rocks occasioned by diurnal chano-es of
temperature is little in evidence, owing to a nearly constant
temperature which, influenced by the lake, maintains a mean
of about 55° and very rarely drops below freezing. The
waves, however, are vigorously attacking the shores 'and by
selective erosion have developed dikes of' sandstone by remov
ing the less resistant shales, and here and there have sur
rounded masses which stand as stacks and skerries.

Titicaca Island and Adjoining Areas. 201
Structure.
The meager and disconnected geological mapping resulting
from studies of Titicaca is an insufficient basis for the discus
sion of structural detail, and has allowed the perpetuation of
such notions as that the basin is igneous in origin and that
" smoldering fires still keep the waters warm ;" that the Straits
of Tiquina resulted from a volcanic eruption ; that the coal is
Tertiary ; that the succession of strata and the age of the rocks
are identical with those represented in the Alps, etc. The inves
tigations of Forbes and D'Orbigny are, however, sufficient
to indicate that the strata, Devonian and Carboniferous in age,
have been thrown into folds, the truncated edges of whose
limbs are responsible for the innumerable rounded hogbacks
which form such conspicuous features of the landscape.
The basin of Lago Grande has the appearance of a
"graben" — one or more down-sunken fault blocks bordered
in places by escarpments, elsewhere by areas of steep faulting.
Faults are present in large numbers, but their length and
amount of displacement and structural control are as yet un
known. In a section extending from Achacachi to La Guardia,
entirely across the lake basin, Forbes encountered volcanics
and highly contorted Devonian (D'Orbigny) strata, presumably
cut off from overlying strata by a fault, the Carboniferous
dipping westward until the Straits of Tiquina are reached,
then dipping eastward across Copacabana. The straits are de
scribed as the locus of a fault, a "broken arch." Agassiz
believed the Carboniferous to consist of a series of rather
limited elongated basins with axes (determined by Forbes)
running northwest-southeast. " By a series of such faults [as
at Tiquina] , more or less prominent, the successive basins^of
Carboniferous .... have been separated."*
Structurally, Titicaca Island is a continuation of Copacabana
peninsula. The strata are alike in composition, exhibit the
same folds and nearly identical strikes and dips. This con
nection is well shown by a narrow sandstone hogback which
projects as a cape from Copacabana and terminates in a line of
islands, progressively decreasing in size. On Titicaca Island,
the same bed apparently is included in the strata carried north
west along the line of strike. With the exception of the
rounded knobs and eastward-facing cliffs carved by waves from
the limestone, the whole surface of the island is formed of
more or less modified hogbacks facing southwest and exhibit
ing the influence of structure. From a structural standpoint
the island may be considered as a group of eroded, folded
strata, drowned by the waters of the lake. The northwest-
* Agassiz, p. 283.

202 H. E. Gregory — Geologic Sketch of
southeast trend of the ridges is characteristic. At Challa .the
strike is NT. 60° ; at Ahyjadero (Pucara) the strike is N. 55°-60°
W. ; and measures between N. 40° W. and N. 60° W. were taken
at several localities. For Yampupata the figures are the same.
Near South Yumani where the strata are faulted, N. 25° W. and
N. 20° W. were measured, and at a few places, as on the ridge of
Kuru-pata where a strike of 1ST. 20° W. becomes in half a mile
N. 40° E., the presence of minor horizontal and vertical folding
is demonstrated. In addition to the faults traced by K. C.
Heald and the writer and indicated on the map (fig. 8), there
are many minor dislocations which are of economic importance,
but only one so far observed has interrupted the stratigraphic
succession to any considerable degree. The Ahyjadero-Kona
fault has offset the strata for nearly one-half mile.
Economic.
The presence of coal at Yampupata and on Titicaca Island
is mentioned by Forbes (1861) but was doubtless recognized at a
much earlier date, since the absence of fuel other than llama
dung for domestic purposes, as well as for smelting and for
making steam, encouraged a search for mineral fuels. Agassiz
(1875) found the mine at Yampupata producing "30 tons of
coal per day," "of fair quality." More recent studies of these
deposits were made by engineers in the employ of the Peruvian
corporation and by Dereims, who reported a narrow band of
coal running the length of the island.
The principal coal-bearing shales and sandstones traverse the
island from South Yumani to Taana Bay as a belt ten to fifty
feet in width, a limited proportion of which is of commercial
value. The coal occurs in lenses and overlapping layers inter
leaved with argillaceous and sandy shales. Bands of true coal
from a few inches to more than two feet iu thickness were ob
served at South Yumani and northwest of Challa. The con
ditions of original deposition as well as field observation
indicate that the maximum thickness of a given stratum of
true coal will probably not exceed three feet and that such
beds will vary greatly in linear extent. It is improbable that
workable beds over three feet in thickness, continuous for
more than 300 or 400 feet, will be found on the island. In
several places examined, the coal lenses have much smaller
dimensions. Three exposures bordering South Yumani Bay show re
spectively : (1) 14 feet of carbonaceous shale with abundant
thin streaks of impure coal of no value. (2) At a prospect
hole, 10 feet more or less of carbonaceous shale contains beds
of coal three inches to three feet thick, exceedingly variable in

Titicaca Island and Adjoining Areas. 203
thickness, extent and quality. One two-foot coal bed is fully
half shale. The coal-bearing beds are overlaid by 6 feet of
cross-bedded sandstone and underlaid by 30 feet of shale with
lenses of sandstone. (3) Between South Yumani and Bil-
cokyma the section from bottom upwards is :
1. Shale with \" to 1' lenses of coal  15 feet
2. Sandstone     4 «
3. Shale    2 "
4. Sandstone  3 «
5. Carbonaceous shale with \"-2" beds of
coal   5 «
6. Sandstone containing scattering frag
ments of coal  ;   30 "
At Challa (Kcasa claim) the group of coal beds about 12
feet in thickness are approximately one-third " bone " and the
thickest band of workable coal is probably less than two feet.
The section examined on the Taana claim shows at bottom
thin-bedded sandstones and shales followed upward by -
1. Carbonaceous shale, about half of which
is coal in wavy, impure lenses  4-6 feet
2. Shales and sandstone   20 "
3. White sandstone  60 "
4. Shales and sandstone with -J"-l" layers
of coal   20 "
5. White sandstone  ...   10 "
In quality the coal is not very satisfactory, pyrite is abundant,
and " high ash " is reported by the engineers of the Titicaca
steamers, but the tests made by the Bolivian Rubber Company
appear to have been fairly satisfactory. Mining on the island
will necessarily be expensive owing to high dip of strata, irreg
ular distribution of coal, the presence of water, and the distant
source of supplies. Stratigraphy.
Our knowledge of the stratigraphy of the Titicaca region
is based primarily on the work of D'Orbigiiy,* Forbes, f and
* Voyage dans L'Amerique Meridionale, tomo iii, pt. 3, Paris, 1842.
This volume, based on field studies during the years 1826-33, includes nine
large hand-colored maps and sections and twenty-two lithographic plates of
fossils. The government of Bolivia has made an important part of this rare
work accessible by the publication of » Spanish edition (Estudios sobre la
Geologica de Bolivia, translated and annotated by Victor E. Marchant La
Paz, 1907).
t Eeport on the Geology of South America by David Forbes, with notes on
fossils by Huxley, J. W. Salter, and T. Eupert Jones. Part 1, Bolivia and
southern Peru. Quar. Jour. Geol. Soc, vol. xviii, 1861. A Spanish trans
lation by Edmundo Sologuren was issued by the Sociedad Geographica de
La Paz, 1901. The Carboniferous as delineated by Forbes manifestly occu
pies too small an area.
Am. Jour. Sci. — Fourth Series, Vol. XXXVI, No. 213. — September, 1913.
14

204 H. E. Gregory — Geologic Sketch of
Agassiz.* Steinmann,-(- and especially Dereims,+ have by their
recent studies extended and somewhat modified the conclusions
reached by earlier explorers. The publication by the Bolivian
Ministerio de Justicia y Industria, La Paz, 1912, of a Mapa
Geologico de Bolivia by Leonardo Olmos, serves as a basis for
further field studies. §
This map so far as the Titicaca region is concerned is essen
tially a reproduction of D'Orbigny's Plate VIII, which exhibits
Paleozoic formations as bands with prevailing northwest-south
east extensions. The periods represented west of the Cor
dillera Real are in succession: Silurian, forming the base of the
range; Devonian, in a broad belt forming the eastern shore of
Lago Pequeno, as well as the peninsula of Taraco; Carboniferous,
forming the west shore and part of the south shore of Lago
Pequeno, the peninsulas of Achacachi and Copacabana, and all
the islands. ]No Cambrian has been reported from southern
Peru or northern Bolivia. The presence of Silurian rests on
ten species collected by D'Orbigny, none of which are accepted
by Salter as properly determined ; five Lower (?) Silurian and
fourteen Upper Silurian species, mostly from the Cordillera
Beal, collected by Forbes and described by Salter; Ordovician
graptolites described by Steinmann (1904); Steinmann's col
lection from southern Bolivia described by Ulrich,| and on a
collection of graptolites from Santa Domingo presented to the
writer by Mr. Collins, manager of the Inca Mining Co. Dereims
also reports Silurian at several localities south of Lake Titicaca.
The presence of Devonian in the Titicaca region was first demon
strated by the discovery of seven species by D'Orbigny, four of
which are accepted by Salter as characteristic of that era. These
species, including three additional ones collected by Forbes, are
unlike forms found elsewhere. Dereims found Devonian fos
sils in brown sandstone and shales near Lake Titicaca, a collection
which as yet has not been reported upon.
Carboniferous strata were encountered by D'Orbigny on
the shores and islands of Lago Pequeno, where brown sand
stone is underlain by compact bluish gray " mountain lime
stone." The fossils collected from Amasa and Quebaya islands
and from Yarbichambi comprise twenty-five species, all
specifically unlike European forms, but resembling, according
* Agassiz and Garman, Exploration of Lake Titicaca, Bull. Mus. Comp.
Zool., Harv. Coll., vol. iii, 1871-76, fossils described by Derby.
t A Sketch of the Geology of South America, Am. Naturalist, 1891, pp.
855-860. X Excursiories Cientificas 1901-04. Anexo de la Memoria de Gobierno y
Fomento. La Paz, 1906.
§ One of the cross sections accompanying this map is confusing, in that
the relations between Devonian and Carboniferous in the Copacabana
area are not in harmony with the surface geology.
| Paleozoische Versteinerungen aus Bolivia, Neues Jahrbuch, 1892.

Titicaca Island and Adjoining Areas.

205

to D'Orbigny, the fauna of Boulonais de Yise (Belgium).
Salter lists thirteen species from the Carboniferous of Copaca
bana, many of which are identical with known European
forms. The Carboniferous fossils from Yampupata collected
by Agassiz and described by Derby include nine species ; viz. :
Spirtfera camerata, Athyris subtilita, Chonetes glabra, Pro-
ductus costatus (?), Productus chanalessii, Productus cora,
.Fig. 8.
GEOLOGICAL, MAP OF
TITICACA ISLAND

Ch

uyu

\
•\\\ Sicuvxi _ *i.
\\\\ fr-

' £,Pallaya

"CiKoa

*~ Ken ata

LEGEND Lirnestorie
SFlclIgs &. Sctn.dstor\e Coal
Faults

Lauassani

m\ BatHymet

Dip &Strvlce
ric Contours

h^dsro Bay

Yumani
¦buntojn of the Jnca.
— Copacobana

Fig. 8. Geologic sketch map of Titicaca Island based on observations by
K. C. Heald and the writer. The base map is essentially that of Bandelier.
The magnetic declination is assumed to be 8°.

Euomphalus antiguus, Tropidoleptus carinatus and Vitulina
pustulosa ; all but one of which " are represented in the coal
measures of North America and Brazil by identical or closely
related species."* Dereims describes Carboniferous strata
from the Titicaca region including Copacabana. The fossils
*Bull. Mus. Comp. Zool., vol. iii, p. 282, 1871-76.

206 H. E. Gregory^ — Geologic Sketch of
from Titicaca Island collected by K. C. Heald and the writer
in 1912 are, according to Schuchert,* of characteristic Pennsyl-
vanian aspect.
The Permian, Triassic, Jurassic, Cretaceous, and Tertiary
from the Titicaca area have as yet not been satisfactorily dif
ferentiated. Forbes assigned certain strata to the Permian on
the ground of lithologic resemblance to the Russian Permian.
D'Orbigny mapped Triassic which Dereims considers Permo-
Carboniferons. The fossil Chemnitzia potosensis, relied upon
by both these writers, seems not to be of sufficiently diagnostic
Fig. 9.

LAKE LEVEL

Fig. 9. Approximate geologic section from Kea-Kollu to South Yumani
to illustrate section A, below.
value. The Puca sandstone at Cora-cora which extends north
ward into Peru,f and which is believed by Steinmann (1906)
to be Cretaceous, is assigned by Dereims to the Permian or
Permo-Carbouiferous. Fresh-water Tertiary may be present
in certain lake deposits of the Andean basin. Pleistocene
deposits of considerable thickness are represented, but the
glaciers appear not to have extended to the borders of the lake.
Through the courtesy of the Peruvian Corporation, the
writer was enabled to make a brief examination of the strati
graphy of Titicaca Island, and of the northern extremity of
Copacabana peninsula. The strata here are entirely sedi
mentary and of Carboniferous (Pennsylvanian) age. (See fi°\
8.) The following sections indicate the relations of the vari
ous beds. Sections A, C, and D were measured by the writer.
Sections B and E were compiled from data obtained by Mr.
K. C. Heald. All measures recorded are approximate, espe
cially for the thickest beds.
Section A.
Ahyjadero Bay (Tucara) to South Yumani. (Fig. 9.)
Distances determined by pacing, elevations estimated or meas
ured by hand level.
* This collection, now in the Yale University Museum, will be discussed by
Professor Schuchert at a later date.
f Adams, G. I., Ann. Report of the Smithsonian Institution for 1908
p. 404. '

Titicaca Island and Adjoining Areas. 207
Feet
1. Limestone ; dense, blue-gray, fossiliferous, in beds 2'-6'
thick ; numerous fractures with slight displacement.
Strike N. 60° W., dip S.W  340
2. Covered ; probable locus of north-south fault zone 
3. Limestone ; massive, blue -gray ; in beds 2-6' thick ; sep
arated by \"-W beds of calcareous sandstone ; weathers
like ornamental moulding ; abundantly fossiliferous.
Strike N. 60° W., dip S.W*Z20°   250
4. Like Number 3. Dip S.E. / 10°-20°  200
5. Sandstone ; brown with yellow and green tones ; calcar
eous ; in beds 6"-3'      100
6. Limestone ; blue and purple ; with flat pancakes and
cylindrical concretions of arenaceous material ; dip
E./20°  5o
7. Limestone and shaly sandstone, interbedded ; fossilifer
ous. DipE.Z40°      150
8. Limestone ; gray ; calcareous sandstone ; yellow-gray,
calcareous shales; in beds 3"-l' thick; forms wide
bench. DipE./50°    200
9. Sandstone, in beds 4'-10' ; medium- to fine-grained,
loosely cemented, quartz grains, some black grains, gray
with greenish and yellowish tones ; slightly cross- '
bedded ; one layer of dark red shale included  70
10, Shale ; dark red ; argillaceous and arenaceous ; includes
10" band of gray sandstone ; i-are fossils  25
11. Sandstone; coarse, cross-bedded; brown, gray, green;
with lenses of shale   _  4
12. Shale ; red, drab, green ; lenses and thin bands of fine
sandstone and 2' bed of coarse, cross-bedded sandstone. 30
13. Sandstone ; gray ; coarse, cross-bedded ; made up of
overlapping sandstone lenses (l"-3") with plant frag- '
ments    _  6
14. Shale ; argillaceous, arenaceous and carbonaceous ; and
yellow sandstone in thin beds including $"-2" beds and
lenses of coal   14
15. Shale ; argillaceous ; dark red and drab ; with lenses of
red-brown sandstone   .. 30
16. Sandstone ; brown, coarse, with red chert pebbles  5
17. Partly covered. Shales, shaly sandstone, and sandstone
in thin beds, becoming increasingly arenaceous with
depth. A few thin calcareous shale beds included.
DipE./55°     160
18. Sandstone; white, coarse, even-grained quartz; cross-
bedded ; massive and composed of overlapping lenses.
At base are two lenses of excessively fine-grained,
white, micaceous, paper-thin shales. Dip E. Z 50°  200
19. Sandstone ; white quartz, cross-bedded   10
20. Shale; arenaceous, paper-thin, white ; with plant impres
sions, and 3"-4" lenses of concretionary sandstone ;
with limonite  6

208 H. E. Gregory — Geologic Sketch of Feet
21. Shale ; arenaceous, argillaceous, aud carbonaceous ; with
abundant plant impressions and lenses of impure coal — 15
22. Sandstone ; white and arenaceous ; drab shale in beds
2"-l'     40
23. Sandstone ; white, cross-bedded, as No. 18  .... 40
24. Sandstone ; brown ; in beds 2 '-4', with thin brown and
drab shale partings    30
25. Sandstone ; brown and gray ; in beds 3-15', with argil
laceous, arenaceous, and carbonaceous shales, exhibiting
ripple marks, sun-cracks, and worm prints .  200
26. Sandstone ; in three beds (30', 10', 10') with white and
gray shale partings   50
27. Sandstone ; gray and yellow ; in thin beds with black
and drab shales, constituting about £ of the material  75
Section B.
Southeast end of Titicaca Island from summit of ridge
¦ to Kona Bay.
Measured by K. C. Heald. General strike N. 25° W. ,
Feet
1. Thin layer of ash (?).
2. Limestone ; blue-gray ; fossiliferous ; massive. Dip,
N. 20° E   515
3. Talus-covered, but mostly thin-bedded limestone ; fossil
iferous ; two bands of shale.     200
4. Limestone ; thin-bedded ; hard  ..,.. 75
5. Sandstone ; medium-grained ; pebbles, red and white ;
matrix, and general color, green; soft, thin-bedded, cross-
bedded in places; three bands of dove-colored limestone 35
6. Limestone; hard, blue-gray and soft yellow ; top bed
dove-colored ; beds 6"-l' ; fossiliferous    65
7. Sandstone; coarse, clear and white, well-rounded grains 40
8. Sandstone; medium-grained; gray to green; rounded,
clear, green and red grains ; massive; hard to medium.
Dip N.E.Z48°   40
9. Sandstone; soft; medium to coarse; purplish to gray, top
greenish; quartz grains, clear, red, green, and black, be
sides specks of lime. Bed of lime (4') in middle. Spar
ingly fossiliferous. At top sandstone is harder and "
includes zone of brecciation    150
10. Sandstone; massive; medium-grained quartz, clear, green,
red and black; also lime specks; all in green cement-
soft, but forms cliff face  1  _ 13
11. Shale; maroon, in part gray-green ; bed of soft sand
stone at 50'; some seams of limestone running across
strike  100
12. Shale, gray-green  lg

Titicaca Island and Adjoining Areas. 209
Feet
13. Sandstone; massive; medium-grained; quartz, lime and
limonite, and a green stone in purple cement; crumbles
on weathering; dip 34° in 30' (probably fault between
numbers 1 3 and 14)  _ _  g
14. Shale ; maroon and gray-green ; one 2' pinkish bed ;
lenses of coal  _' 45
15. Sandstone; or arenaceous limestone ; medium-grained;
beds l'-3'; hard, weathers in checks. Dip N. E. Z45° 13
16. Coal (bloom); clean; strike N. 25° W. ; dip N.E.Z47° ]|
17. Limestone, gray; thin-bedded; with drab shale  60,
18. Shale; gray-green; talus-covered    g
19. Limestone; impure; has plant fragments  _. 2
20. Shale; argillaceous; drab-gray; capped by 2' of arena
ceous shale filled with plant remains   . . 8
21. Sandstone; fine-grained; rounded quartz pebbles; calca
reous; general color gray-white; included beds and cap
of gray-green ; soft, thin, even beds; one belt of gray
shale; very few round, pea-sized limonite concretions.
• DipN.E.Z40°     .... 85
22. Sandstone; white; coarse to medium, with clear, suban-
gular quartz pebbles. Some bands almost a conglomer
ate. Soft, massive, weathers in rounded knobs. Hard to
tell from No. 13 at contact, but No. 13 is finer and has
lines of shale   100
23. Coal. Pour feet bone in middle ; weathered grav ; fair
quality. DipN.E.Z39°   "  8
24. Limestone; thin-bedded, grading into sandstone at top;
interbedded with shale ; much checked or broken ;
weathers gray or red-brown   : . . 30
25. Sandstone; fine grain ; clear quartz, well-rounded and
white flakes ; more lime near top than bottom. Color
white with some buff-yellow bands ; massive ; many
cracks across bedding. Like No. 33 except for absence
of specks of carbonaceous matter  70
26. Sandstone; fine-grained; clear quartz, rounded and white
flakes; weathers yellow-brown; fresh buff-gray. Even-
bedded l"-3'. One soft lens of buff -brown; at top is a
yellow band of limonite   35
27. Like No. 29, but limestone grades into a sandstone with
fine, rounded quartz grains at top; brownish gray; mica
on bedding planes     70
28. Gray shale; contains lenses of limestone like No. 32 from
3" to 1' thick ; has two seams of coal, one l£" about 11'
from bottom, the other 13"; very clean bloom at top 16
29. Limestone and shale; limestone like No. 30. Slate green
ish gray; very thin-bedded; mica on bedding planes  61
30. Sandy limestone; buff-gray; weathers mottled gray and
red-brown. Thin, regular bedding  30
31. Shale; gray; with 2' red-brown limestone 8' from bottom, 25

210 EC. E. Gregory — Geologic Sketch of Feet
32. Limestone; begins as limy sandstone and ends as lime
stone; first beds buff to gray; last beds blue-gray (fresh
fractured) ; beds even ; 2"-3'; heaviest beds near bot
tom ; much mica on bedding planes ; fracture uneveh
and often breaks in rounded forms ; between beds a
parting of gray shale. Top contains limonite concretions
like No. 33, and is weathered brown    50
33. Sandstone; fine-grained at top, medium at bottom; quartz
grains rounded, not colored ; a few tiny muscovite
flakes and occasional black specks of carbonaceous
matter. Much white lime or decomposed feldspar. Rare
pea-sized pebbles of quartz; gray-white on weathered sur
faces ; soft, weather-rounded ; bedding massive; cross-
bedding poorly developed ; contains seams of limonite-
stained rock; one little streak of quartz showing garnet;
round limonite concretions, size of pinhead to small pea;
at 130' bed of shale about 32' thick. Shale is gray-drab
to drab ; contains carbonaceous matter, clear quartz
grains, and occasional flakes of mica. Strike N. 24° W. ;
dipN.E.Z43°     ;.. 275
Section C.
Taana Bay.
Strike JST. 45° W; dip JV. E Z 50°. Feet
1. White, cross-bedded sandstone   10
2. Shale and thin sandstone ; a few very thin carbonaceous
layers     20
3. Sandstone; white, cross-bedded    60
4. Sandstone and sandy shales ; thin-bedded ; with plant
fragments irregularly distributed   40
5. Shale, carbonaceous ; coal in wavy lenses constitutes about
£ of the stratum ; the remainder consists of lignite inti
mately mixed with shale and sandstone ; coal appears to
be of good quality   __ 4
6. Drab shales <and sandstone like No. 8..   20
7. Carbonaceous bed, one-half shale; abundant pyrite.  4
8. Sandstone, gray, thin-bedded, £"-2"; shales, black and
drab ; wavy, cross-bedded ; concretionary ; with ripple-
marks arranged in overlapping patches a few inches in
diameter ; contains muscovite and a few plant impres
sions  200
The interleaving lense character of the coal is w.ell shown here ¦
500' distant, across a little bay, numbers 5 and 8 are scarcely rep
resented and shale occupies nearly the whole section.

Titicaca Island and Adjoining Areas. 211
Section D.
North end of Copacabana Peninsula, measured along
the lake shore. Strike JV. Jfi° W ; dip EZ.800. Feet
1. Shales and thin sandstones with three beds of carbona
ceous shale, 3', 4', 4' in thickness. Approximately one-
half of each bed consists of coal of commercial value  200
2. Sandstone ; gray- white ; cross-bedded   60
3. Shales, sandy ; alternating with very thin (i"-li") beds
of drab and gray sandstone ; rare streaks of carbonaceous
material     35
4. Shales, black ; alternating with gray-brown sandstone in
lenses, and cross-bedded shale, in part carbonaceous ;
with some thin (4"±) lenses of true coal. At top is l'±**
of impure coal    20
5. Shale ; black, lumpy, in part stained by limonite ; breaks
in flakes ; contains lenses of gray -brown sandstone  20
6. Sandstone; yellow-gray; in 6"-10" beds   9
7. Shale ; black to drab ; like No. 9  20
8. Sandstone ; yellow-gray      4
9. Shales ; drab ; thin-bedded (£") concretionary with wavy
surfaces    6
10. Sandstone ; yellow-brown ; thin bedded (l"-4") ; cross-
bedded, micaceous, lumpy, with mud concretions and
sun-cracks ; surface of sandstone wavy and beautifully
ripple-marked. Shales ; drab, sandy, lumpy, intricately
folded on minute scale  — 30
11. Sandstone ; yellow; in beds 4 "-10" thick; interbedded
with drab, arenaceous shales. Bedding very uneven and
surface of each stratum reveals overlapping flakes  15
12. Shales ; brown, yellow and drab ; with uneven, flaky
surfaces   -     25
13. Sandstone ; white to gray ; cross-bedded ; medium-fine
grain ; in beds 4'-6'    --   30
Section E.
Coal Mine at Yampupata, Copacabana Peninsula.
Measured by K. C. Heald. Feet
1. Sandstone ; medium-grained quartz, red and white ;
cement green ; general color green ; soft  —  10
2. Sandstone ; fine to medium ; rounded red and white
quartz ; cement a maroon color ; general color purplish ;
soft      100
3. Sandstone ; fine-grained ; rounded quartz ; slightly cross-
bedded ; beds about 1' thick    5
4. Shale ; gray  —    3
5. Sandstone.; medium-grained, brownish white ; soft ;
cross-bedded, massive  -   6

212 H. E. Gregory — Geologic Sketch of Feet
6. Shale ; purplish drab ; full of plant fragments ; two thin
beds of limestone included    20
7. Shale and thin-bedded limestone ; transverse seams stained
with limonite  -  -.--  1^5
8. Sandstone ; medium-grained quartz, clear, subangular
to rounded ; occasional large grains ; some lime ; gray-
white with limonite stains ; cross-bedded ; thin to heavy ;
some rare, spots of conglomerate   -   267
9. Sandstone ; fine-grained, rounded quartz ; much stained
by limonite ; even-bedded ; mica on bedding planes  50
10. Shale ; drab with lenses of yellowish limestone  4
11. Limestone ; gray, sandy     \
12. Coal, with 2" band of sandstone. Coal of fair quality
and with little "bone"  2
1 3. Shale ; gray to drab with purple streaks resembling
rootlets       8
14. Sandstone ; fine-grained, with clear, rounded, quartz peb
bles, white flakes and limonite ; even, heavy beds ;
toward top assumes greenish tone and contains much
mica and lime      20
1 5. Shale ; gray to purple   30
16. Sandstone ; fine, with well-rounded quartz grains, and
white specks ; some muscovite ; thin, even bedding  6
17. Shale ; gray, with thin beds of limestone  r.  40
18. Sandstone ; fine, with clear, well-rounded quartz grains
and white specks. Mica on bedding planes ; weathers
gray-white ; some raised veins of harder, dark rock ; bed
ding fairly even ; some Cross-bedding ; some twisted
beds ; calcareous at top  135
19. Limestone and shale ; the latter predominate ; shale is
drab ; limestone is gray, to a limonite yellow ; cross-
bedded and twisted ; has much mica on bedding planes. 55
20. Sandstone ; fine, with rounded, clear grains of quartz,
and numerous blotches of lime or other white mate
rial ; general weathered color gray-white with spots and
bands of yellow ; medium hard ; even-bedded ; massive ;
occasional small, rounded concretions of limonite. Strike
N 46° W ; dip N. E.Z 40°. 30
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