?-62l rs J 87 i9ia 1^..^-*^- >^^r-^v ..<.-r^ ^vV/"-*^. ■ "-:.'-- >. ;_^>;^ y* » ^^ fV.T^ ?^^ r ^ ' . ^ TJ 'y rV'^ BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND THE GIFT OF HENRY W. SAGE 1891 Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004731463 lEMOIKS OF THE CxEOLOrTlCAL SUETEY ENGLAND AND WALES EXPLANATION OP SHEET 349. THE GEOLOGY OF THE COUNTRY AEOUND IVYBRIDGE AND MODBURY, BY W. A. E. USSHEE, F.G.S., WITH CHAPTER ON ALTERED ROCKS BY G. BARROW, F.G.S., PDBLISHED BY OEDER OF THE LORDS COMMISSIONERS OF HIS MAJESTY'S TEEASDET. LONDON : PKINTED FOR HIS MAJESTY'S STATIONERY OFFICE, By DARLING and SOX, Ltd., 34-40, Bacon Steeet, B. And to be purchased from . E. STANFORD, 12, 13, and 14, Long Acee, London j W. AND A. K. 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Sheet 357 with 360 (Isles of Scilly) 1906; Explanatory Memoir, price Is. (1906). Sheet 359 (Lizard) 1912 ; Explanatory Memoir, price 5g. (1912). P-, o CD Q 2226 J MEMOIRS OF THE GEOLOGICAL SUEYEY ENGLAND AND WALES EXPLANATION OF SHEET 349. THE GEOLOGY OF THE COUNTRY AROUND IVYBHIDGE AND MODBURY, BY W. A. E. USSHEE, F.G.S., WITH CHAPTER ON ALTERED ROCKS BY a. BAREOW, F.G.S., PUBLISHED BY ORDER OP THE LORDS COMMISSIONERS OF HIS MAJESTY'S TREASURY, LONDON : PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE, By darling and SOST, Ltd., 3i-10, Bacon Street, E. And to be purchased from B. STANFORD, 12, 13, and 14, Long Acre, London; W. AND A. K. JOHNSTON, Ltd., 2, St. Asdrew Square, Edinburgh; HOD&ES, FIGGIS, and Co., Grafton Street, Dublin ; From any Agent for the sale of Ordnance Survey Maps ; or through any Bookseller from T. FISHER UNWIN, 1, Adelphi Terrace, London, W.C, ■who is the Sole Wholesale Agent to the Trade outside the County of London. 1912. Price Three Shillings. \i (\.-^-]-z.S\ Ul PEE FACE. The original geological survey of this area, by Sir H. T. De la Beche, was published during the years 1834 and 1835 on Sheets 24 and 25 of the old series one-inch maps. In 1839 these sheets were partly revised, the ' Carbonaceous Series ' being separated from the ' Grauwacke Series.' Later (about 1846) the classification and colouring were modified and the term ' Devonian ' was introduced. The area included within the new series one-inch Sheet 349 was resurveyed on the six-inch scale by Mr. Ussher between 1892 and 1897, and was published in 1899 in a hand-coloured edition of the map. In that edition all the Devonian rocks except the limestones were coloured alike, and a considerable area near the southern margin of the Dartmoor granite was coloured as Car- boniferous. Advantage has been taken of the preparation of a colour- printed edition of this map to introduce certain additions and modifications necessitated by the increase of our knowledge of this and the neighbouring areas. The Devonian rocks have now been split up into five divisions and some of the area formerly taken to be Carboniferous has now been relegated to the Devonian. The Memoir has been written by Mr. Ussher, with the excep- tion of Chapter VIII. on the Aureole of Thermo-metamorphism, which has been contributed by Mr. Barrow. I have supplied the author with some petrological notes which he has, at my request, incorporated with his descriptions of the mode of occurrence of the rocks. Our thanks are due to Dr. Kayser and Dr. Henry Woodward for the determination of some Lower and Middle Devonian fossils ; also to Mr. R. H. Worth for information as to certain exposures which led to a modification of the granite-boundary in two localities. -T. J. H. TEALL, Director. Geological Survey Office, 28, Jermyn Street, London. 2nd July, 1912. (22265—17.) Wt. 27340—61. 500. 1/13. D & S, VI ILLUSTRATIONS. Page Fig. 1. — South of Langdon Farm. Irregular development of Grit in Dartmouth Slates ... ... ... ... •■. ••■ 21 2. — Great Mew Stone from Season Point 21 3. — Court Wood, by the River Yealm, opposite Glitters Wood. Inverted anticline in Dartmouth Slates, looking SW. ... 22 4. — Section for 300 yards northward from the fault on N. side of Andurn Point ... ... ... ... ■■• ■•■ 27 5. — ^Apparent structure at J mile S. of Bovisand Bay and section for 240 yards northwards ... 30 6. — Beach reef, Bovisand Bay, showing bedding and cleavage 31 7. — Bovisand Bay. Cleavage and bedding ... ... ... 31 8. — Coast for 120 yards north of Bovisand stream 32 9. — North of Leek Bed Bay. Contortions in Staddon Grits 34 10. — Wyatts Way, structure ... ... ... ... ... ... 34 11. — From Wyatts Way, looking toward Ramscliff Point, con- tortions in Staddon Grits ... ... ... ... ... 35 12. — Coast section for 220 yards north of Jenny Cliff ... ... 35 13. — Coast section for 90 yards, northward from a point about 420 yards N. of Jenny Cliff, showing axes of Lower Devonian grits in Middle Devonian slates ... ... ... 47 14. — Batten Bay. Quartz veins in slates ... ... ... ... 48 15. — Batten Bay. Coast section between 100 and 200 yards from Dunstone Point promontory ... ... 48 16. — Batten Bay. Junction of slate and sohalstein ... ... 49 17. — On south side of Laira Bridge. Limestone passing upward into slates through slaty limestone and calcareous slates with limestone bands ... ... 50 18. — Hazard Quarry. Junction of schalsteins and slaty lime- stone ... ... ... 53 19. — Cutting by the Kingsbridge Branch Railway at its junc- tion with the G. W. R. Calc flintas etc., in slates ... 54 20. — Opposite Laira Green on the north side of Saltram Point. Green banding in red Upper Devonian slates 65 21. — New road south of Compton. Anticline in grits (Wearde- Eif ord type) ... 73 22. — Hemerdou Ball Quarry. Schorl veins and dykes in granite 93 23. — Three sections through the Bickleigh river terraces. 34 furlongs N. of Bickleigh Station E. and W. ; 120 yards N. of Bickleigh Station E. and W. ; through Bickleigh Station E. 15° S. and W. 15° N .. 107 ,, 24. — Longitudinal section of mines on Hemerdon Ball, by D. A. MacAlister ... ... ... ... ... ... - jj^ Plate 1. — The Dewerstone, Shaugh ..Frontispiece 2. — Coast-section north of Andurn Point ... 3. — Bovisand Bay ... _ 1 4. — Cann Quarry . '" 1 at 5. — Coast west of Wembury ... ... ... fend. 6.— Whitehill China Clay Pit, Lee Moor ... ...' '".' '.''1 THE GEOLOGY OF THE COUNTRY AROUND lYYBHIDGE AND MODBURY. CHAPTER I. INTRODUCTION. The area comprised in Slieet 349 is 214 square miles. Its surroundings on the east, south, and west have been described in the Memoirs on the Torquay Map, Sheet 250 ; on the Kings- bridge Maps, Sheets 355 and 356; and on the Plymouth Map, Sheet 348, respectively. It includes the eastern suburbs of Plymouth, Compton, Lipson, and Prince Rock, Oreston and Turnchapel, and the small market towns of Plympton and Buck- fastleigh, besides Ivybridge in the centre of the map and Modbury and Yealmpton near the south-west margin. The coastline extends from the Cattewater to the mouth of the Yealm, but the promontories of Mount Batten and Staddon Point project into the adjacent map, Sheet 348. The highest land, from Ivybridge northward, between Buck- fastleigh on the east and Shaugh Prior on the west, forms the most southerly spurs of Dartmoor and rises to a height of nearly 1,600 feet above O.D. near Shavercombe Head, and to 1,575 feet at Petre's Cross. The surface beyond the limits of Dartmoor presents a very hilly contour with summits varying from 300 to 600 feet above O.D., the lesser summit levels being found between the coast line and Ivybridge in the south-western part of the map. The area is drained by the rivers Plym, Yealm, Erme, and Avon and their tributary brooks, and in the north-east corner by the Dart and its tributaries the Harbourne and Dean Water. The only catchment-basin completely included in the map is that of the Yealm which rises at Yealm Head, north of Cornwood, and reaches the coast near Newton Ferrers in a course of 12 miles. The Erme flows south through the centre of the map. The main streams, on emerging from Dartmoor, cross the strike of the rocks with which their tributaries often coincide, giving rise to features which mark the outcrops of the Lower Devonian grits, slates, and shales, and of the volcanic rocks. Tracts of flattish land border the Erme near Ivybridge and tributary brooks of the Avon and Dart. The scenery on the borders of Dartmoor and along the stream valleys descending from it is very attractive. The wooded valleys of the Yealm above Cornwood, known as ' Hawns and Dendles,' and of the Erme for a mile above Ivybridge, and below Ermington; Brent Hill and the Avon Valley above South Brent; the Plym Valley from the Dewerstone Rock to Ca»jii fi GEOLOGY OF IVYBEIDGE AND MODBTJRT. Wood, and the Laira below Marsh Mills; the Tealm Estuary and Tealiupton; the coastal district and Plympton Oastle may be specially mentioned. The area is mainly agricultural. The chief industries are China clay which is worked on Shaugh Moor, Crownhill Down and Lee Moor; lime manure works at Cattedown, Oreston, and Buckf astleigh ; paper at Ivybridge and Buckfastleigh ; tanning at Buckfastleigh and Modbury. The hand-coloured edition of the map was published in 1899, but since that date the ground has been partly re-examined. In the 1899 edition the Devonian slates, whether Upper, Middle, or Lower, were denoted by the same tint ; siij sequent researches however have led to the separation of the Lower Devonian slates from the rest, and to the indication of the Dartmouth slates as a separate division. There is still, however, so much uncertainty, through the scarcity of fossils, respecting the actual separation of the Middle and Upper Devonian slate-areas that their dis- tinction by colour must be regarded as purely arbitrary, and as having very little stratigraphical value ; for we have not been able to separate the cuboides or lower horizons of the Continental Upper Devonian areas from the Middle Devonian, and therefore beyond the termination of the limestone reefs we no doubt include slates and schalsteins in the Middle Devonian which would on the Continent be included in the Upper. In the eastern part of the map we are therefore more likely to have included too little than too much in the Upper Devonian when attempting to draw an arbitrary boundary. Table of Formations. In the following table of Deposits and Formations, cavern deposits and the old gravel relics on Cattedown are included, though they are not shown by colour on the map. f Bstuarine mud. Cattewater and Yealm Estuary. Recent ' Alluvium. and -' ^^^lley gravels and old alluvial tracts. Pleistocene. ' S'^T*®''!.'?:''® '}'^P,°''*l , Jlead on the old boach-plane, Wembury Coast, &c. L Cavern Deposits, Tektiaky? Eelics of old gravels on Cattedown. New Red i -□ . ^, j, ■-, „ . , Series ? / Isreccia on the north side of Andurn Point. Culm [Altered dark shales (chiastolite rocks), calcareous bands Measures 1 (calc-flmtas) and fine gritty beds, confined to the contact l^ aureole. Upper | C^reenish and grey slates and purple and green slates and Devonian ] 8£®y ^'^*®^ representing the Cypridinen Schiefer and L Frasmen. Wearde-Efford grits and volcanic rocks (local). Limestones of Cattedown, Turnohapel, Plymstock, Brixton, Middle „ Yealmpton Sequers Bridge and Buckfastleigh. Devonian. ^ Banded porcellanized rocks in the granite aureole. Slates and volcanic rocks replacing limestones. L Slates with impersistent local limestone-bands (Eifelian). Lower f ^ta^don Grits and slates. Devonian. Po^ks of the Meadfoot group. l_ Dartmouth slates. INTEODUCTION. 6 The igneous rocks are as follows : — contbmpokanbous . TTpper 1 px ( -^ndesitic basalt, pillow-lavas. Dorsmouth Hill. Middle \ Schalstein tufEs, amygdaloidal schalsteius, Calc-schalsteins, Devonian. J Diabases. LOWBK Devonian I ? TuQ! at Down Thomas and sheared lavas near Mothecombe. Basic. Intrusive. / Diabase and diabase-hornfels. \ Altered rock ? proterobase. Granophyre, Whympston House. Ann J ■'i'^yo'i*^, Shearlangstone. I Felsites ; Roborough Down. Fallapit. 1^ Granite. The district forms the connecting link between the Torquay area on the east (Sheet 350) and the Plymouth and Liskeard area on the west (Sheet 348), and presents besides, in the aureole of contact metamorphism round the southern projection of the Dartmoor Granite, types of selective metamorphism and of so- called pneumatolytic alteration. The Lower Devonian rocks form a continuous outcrop in the southern part of the map. In the Middle Devonian area on the north the outcrop of the volcanic series connects the Ashprington area in Sheet 350 with the limestones of Sequers Bridge, Yealmpton, and Plymouth, and the Buckfastleigh limestones and volcanic rocks are a repetition of the same general horizons which in an altered condition may be traced in the Granite aureole as far west as Cornwood and Hemerdon Ball. From the Plymouth limestones northward Upper Devonian slates occupy the western border of the area, but as they are followed eastward lithological distinctions cease to be recog- nisable, and it is very doubtful if Upper Devonian rocks are present east of the Tealm Valley until we approach Buckfastleigh. LiTEEATTJEE. In Lysons' ' Magna Britannia ' the slate quarries near Ivybridge and Cann quarry are referred to, as also the occurrence of lead and iron at Rattery, and the lodestones of South Brent are said to have been famous in the early part of the seventeenth century. In connection with this mention of magnets De la Beche's ' Report,' p. 618, tells us that " Magnetic iron-ore, of good quality, has been worked near South Brent," and in a footnote adds " Dr. Edward Cotton sent a piece of this ore, weighing 60 lbs., to the Royal Society in 1667, which moved a needle placed at a distance of nine feet. The classic work of Sedgwick and Murchison contains special references to this area. These authors discard the term ' gray- wacke,' under which deposits of distinct periods had been merged, retaining it for the mere purpose of mineral description, and add, " Though the term old red sandstone, when designating great groups of rocks like the Cornish killas and Devonian slates, should involve no error of classification, still it would, mineralogi- cally, be most inappropriate. We purpose therefore ... to 4 GEOLOGY OF IViBBIDGE AND MODBUEY. designate these groups collectively by the name Devonian system, as inYolYing no hypothesis, and being agreeable ^o analogy. " All the calcareous slates on the south-eastern side oi Cornwall are of the age of the lowest group of the South DeYon section, and therefore probably in the lower portion of t^i^ old red sand- stone The Petherwin and we think also the highly crystalline 'Tintagel slates appear to be of the ^p of the Barn- staple slates, and are therefore in the upper part of the old red ^^They^note granite-Yeins " above Ivy Bridge, injected among the oldest slates of Devonshire. "' . ^^ ,, On the north side of Ivybridge at a little distance, from the D-ranite they describe extensive tracts of hard porcellaneous rocks which " gradually pass into the common dark-coloured roohng- slate of this country," above this the slates are said to be cal- careous and to pass into the Ashburton limestone.^ The ascend- ing series is divided into four groups,^ viz. :— 1. The lowest, the slate-rocks partly altered, bordering the granite 2. A great group of more or less calcareous slates with the Ashburton lime- stone in the lower and " the great Plymouth and Tor Bay lime- stone " in the upper part, which also contains beds of red slate and sandstone under and replacing the limestones. Here the Lower Devonian rocks of the Paignton and iorquay anticlines appear to be confounded with the red volcanic rocks of the Ashprington Series, because the next, group 3— a great arenaceous group, containing many beds of red and variegated sandstone "—evidently applies to the mam outcrop ot the Staddon Grits. Their highest group 4, " with many courses ot sott, glossy g;[ate .... alternating with coarse quartzose bands " ; apparently unfossiliferous, would appear to include the Mead- foot group and Dartmouth slates. _ _ i , ,, Finally " a crystalline group of micaceous and chloritic slate " probably of metamorphic structure, and due to some obscure axis of elevation," describes the southern headlands of Ike Start, Prawle, and Bolt. On the west side of the map Sedgwick and Murchison mention the association of trap with the slates near EidgeAvay (Plympton), and of chloritic slate with a few felspar crystals passing into the ordinary dark-coloured slate, and conclude that this whole slate series is carried under the Plymouth limestone by a regular dip to the south.'' They state, that, "the upper beds of limestone are seen at Mount Batten, and are overlaid by a great, red, arenaceous group." From Mount Batten to the metamorphic rocks of Hope Cove the rocks are subdivided in an ascending series of 5 groups, which is a more detailed rendering of Nos. 3 and 4 in the general sequence quoted above, in the following ascending order: — 1. Mount Batten to Dunstan Point. Brown and yellow earthy slate 1 Tram. Geol. Soc, ser. 2, vol. v, 1837-9, p. 701. ' Ibid., pp. 698-699. ' Ibid., p. 686. * Ibid., p. 650. * Ibid., p. 661. « Ibid., p. 653. INTRODUCTION. 6 with beds of impure limestone. 2. Duustan Point to Withy Hedge. " Yellowish gray and bluish gray soft slate (shillot,) with some quartz veins and coarse arenaceous bands." 3. Withy Hedge to Bovisand Bay, "bright red, and some- times variegated sandstones, thick-bedded, and of coarse texture, but subdivided by bands of soft, glossy, red slate, and red mica- ceous flagstone. This division, in many parts, is exactly like the old red sandstone; and though thrown into violent contor- tions, it dips, on the whole, toward the south, and is of great thickness. It is overlaid by a reddish slate and flagstone, which gradually passes into the next superior division. 4. "On the south side of Bovisand Bay," earthy slates passing into shale with many small ironstone nodules; "sur- mounted by variously-coloured earthy slates, alternating with reddish arenaceous bands, as seen in the cliffs of Crownall Bay, near the southern end of which is a patch of new red con- gloTnerate, resting unconformably on the edges of the older strata." Crownall Bay here embraces the shore from the south horn of Bovisand Bay to the projecting coastline of Andurn Point. On the 6-inch map it is restricted to the cove on the south side of the south horn of Bovisand Bay. In a footnote, the occurrence of many fossils in the red cliffs of Crownhill Bay, of reddish limestone partly traversed by quartz-veins, and of transverse cleavage-planes near the cal- careous bands, are referred to. In the foregoing groups: — (1) corresponds to the Middle Devonian slates, volcanic rocks and limestone beds south of Mount Batten ; (2) to the Middle Devonian slates south of Dun- stone Point and their junction with the Staddou Grits; (3) to the Staddon Grits; (4) to the Meadfoot Group, including Lower Coblenzien and Taunusian (the fossiliferous red rocks and the limestone referred to in previous Memoirs as the ' Monticuli- poroid limestone '). Above this the authors place the rocks between Crownall Bay and the cliffs opposite the Mewstone {i.e., part of the Dartmouth Slates), in division 5, including "reddish slate and flagstone, and coarse red sandstone, occa- sionally contorted and penetrated by large quartz veins," and " reddish, grayish, and greenish gray chloritic slates, with hard quartzose bands and quartz veins."* From the cliffs opposite the Mewstone to Hope Cove the rocks are placed above group 5, and as these include the rocks of the Meadfoot group and the Dartmouth Slates described in the Memoir on Kingsbridge and Salcombe, no further identifications ore necessary. It will be seen from the above that the descending- sequence from the Start and Prawle rocks northward advocated by Sedgwick and Murchison required to be reconciled with their acceptance of the Upper Devonian age of the Petherwin beds, established by Phillips, and their correlation of the Tintagel slates with them. ' Trans. Oeol. Soc, ser. 2, vol. v, 1837-9, p. 657. 6 GEOLOGY OF IVYBRIDGE AND MODBTTEY. The map illustrating Sedgwick and Murchison's paper is prac- tically the same as De la Beche's index map, and, as is the case in that illustrating [Godwin-] Austen's ' Geology of South-east Devon,' gives no Devonian subdivisions, the limestone patches and only a few strips of igneous rocks being picked out. In De la Beche's ' Eeport,' p. 65, an ascending succession from the Plymouth limestone to the Staddon Grits is affirmed; the limestone-outcrops are traced eastward; and the dolomitic char- acter of the Yealmpton limestone is alluded to. On p. 66, the Buckfastleigh limestones are considered to be lower in the series than the limestone of Paytor [the patch ESE. of Eattery on the New Series Map, Sheet 349]. The small limestone-patches near Ugborough and North Huish and their association with slates and trappean rocks are mentioned as probably continuing the horizon of the Plymouth limestone to Dartington, but^the limestones of Yealmpton and Sequers Bridge were regarded " as somewhat higher in the series." In pp. 73 and 76-79, the arenaceous rocks and associated slates on the south of Modbury and Morleigh are treated, and the replacement of the sandstones by quartz-rock on Black Down east of Modbury and at Morleigh Down is pointed out. " A mass of argillaceous slates, generally fine-grained, and in many places red or claret-coloured [the Dartmouth Slates] rests on the arenaceous band [the Staddon Grits]." The quotation is from p. 77. On p. 78, he thus refers to the granophyres, rhyolites and felsites near Modbury described in this Memoir. " Near Erme Mouth [in Sheet 355] we find rocks [Dartmouth Slates], part of which are arenaceous, that range up, somewhat out of the general strike of the beds of the country, towards the grits and quartz-rock of Black Down, near Modbury. With them is a rock which we have ventured, though with some hesi- tation, to class as an elvau, as it is so extremely quartzose in part of its course, particularly near Torr and Sherlangston, where it more approaches the character of quartz rock, though near Modbury it is formed of a granitoid mixture of quartz and felspar." He then proceeds to consider the probability of these rocks being a continuation of the grits and quartz-rocks of Black Down and Morleigh Down, and these latter as a different series from the grits of Staddon Point, which are regarded as contemporaneous with the grits of Cockington. A comparison of the colour-printed edition of Sheet 349 with the previous hand-coloured edition will show how far the geological structure has been manifested by the tracing of the Dartmouth Slate boundary. The occurrence of schorl in the granite near Ugborough Beacon and near Blatchford, Cornwood, is specially mentioned (p. 158). The elvan-dykes of Roborough and Cann Quarry are described (p. 184), also the mapping of the rocks near Modbury running toward Erme Mouth "for convenience" as elvans. The calc-flintas bordering Dartmoor " in some places between South Brent and the Western Beacon" are described as " fels- pathic rock striped of different colours in the original structural lines of the slate " (p. 267). INTRODUCTION. I The tin and copper mine at Bottle Hill near Hemerdon Ball is referred to (pp. 285, 302), and its produce, &c. (on pp. 583, 609), also lodes on the south of Cann Slate Quarry and on Roborough Down (pp. 301, 302). The ossiferous fissures of Oreston and the section of deposits in the Tealm Bridge cavern, and the remains obtained in them, are described (pp. 412-416). In the ' Economic Geology ' Chapter, under the head of Build- ing stones, the [slate] rocks near Newnham Park north of Plympton, and the dolomitic limestones of Tealmpton are men- tioned (pp. 490, 491) and the Eoborough elvan (p. 495). Among the marbles the black limestone of Cattedown and the altered limestone in Kitley Park are referred to (pp. 498, 499). Under the head of Roofing Slates the following localities are given (p. 503) : — Tigley and Moor near [SE. and S. of] Rattery ; Roster Bridge [Roister] near Harbertonford ; Wood and Lud- brooke near TJgborough; Cann Quarry "to which a canal has been made up the Plym," and Leigham east of Egg Buckland. The local supply of lime from the Sequers Bridge and Tealmpton limestones is mentioned (p. 508). The southern granite of Dartmoor near Cornwood is given among the China Clay localities (p. 509). Plympton was made a stannary town in 1328 (p. 586). Finally, in the Appendix, we read " The last stream-work of which we can obtain information seems to have been that noticed by Vancouver as carried on near Plympton St. Mary's about the year 1808."^ Dr. Harvey B. HoU in 1868 communicated an important paper ' On the Older Rocks of South Devon and East Cornwall ' to the Geological Society,^ accompanied by a geological map of the area between Bodmin Moor and Torbay in which the Devonian rocks were for the first tiine actually subdivided. In accordance with the then prevalent view of a generally descending sequence from the south northward, he divided them into two groups, named the Upper South Devon group and the Lower South Devon group. The earlier Survey maps as maps (independent of the text) formed the foundation of all subsequent Devonian work, as, apart from the dips shown on them and the patches of limestone and trappean rocks, they suggest no structures. HoU's map, on the other hand, brings out the inconsistencies involved in an attempt to construct a map on the general structural principles then accepted. Thus we find the Lower Devonian rocks of the Torquay anticline included in the Lower group, whilst the Lower Devonian rocks of the Paignton anti- cline are included in the Upper group, in which the Middle Devonian volcanic series of Ashprington, subsequently discovered by Champernowne, are not differentiated. The Lower Devonian rocks of Looe, with the Petherwin Beds, and, in fact, all East Cornwall, except the promontory between Whitsand Bay and Plymouth Sound, are included in the Lower ' ' View of the Agriculture of Devon,' p. 67. 2 Quart. Journ. Geol, Soc, vol. xxiv, 1868, pp. 400-454, 8 GEOLOGY OF IVYKEIDGE AND MODBUEY. group. To justify this, HoU proceeded to show by fossil tables that the affinity of the Petherwin fauna to the Middle Devonian group of South Devon was stronger than to the "Upper Devonian of North Devon/ Jukes' work in 1867-8 (apart from his correlations) is of great stratigraphical value. In his assumption that the grits north of Bovisand Bay [the Staddon Grits], which he correlated with the Coomhola grits of Ireland, were above the red slates and grits [the Dartmouth Slates and, perhapSi the red beds of the Meadfoot group faulted against them at Andurn Point] on the south of Bovisand Bay , which he regarded as Old Red Sand- stone, in an inverted anticline,^ he supplied an entirely new and correct rendering of the stratigraphy of the coast-section south of Plymouth. His section of the anticlinal structure of the rocks of Dartmouth and Stoke Fleming,^ and his correlation of the grits of Black Down, Morleigh, etc., with the grits of Staddon agree with this.* Champernowne's detailed mapping of the Ashburton, Newton Abbot, Torquay, and Totnes district is memorable for placing the Middle Devonian rocks on a more satisfactory basis, by corre- lating the limestones of Ashburton with those of Newton Abbot and" Torquay, and by defining, in the Ashprington area, a Middle Devonian volcanic series equivalent to the Nassau Schalsteins. The contradictory field evidence revealed in the endeavour to obtain a clue to the general sequence induced him to turn with less diffidence than he usually displayed to the comparative simplicity of Jukes' reading of the South Devon section. Accord- ingly we find him in 1878 treating the outcrop of the Staddon Grits, south of Berry Head, as an anticline which, as he expressed it, " brings the Red Sandstones into direct and natural relation with those of Cockington, the Warberry, Lincombe, &c., at Torquay, which are beneath the limestones." A visit to North Devon and West Somerset in the latter part of 1878 with the writer, induced Champernowne to reconsider his attitude in regard to "the apparently simple version of the structure of North Devon put forward by the late lamented Prof. Jukes. "= Champernowne's actual survey of the old one-inch maps included the north-eastern part of our area from the granite- margin north of Wrangaton eastward ; but, beyond the indication of the outcrop of grits from Halwell westward to Blackdown Camp, it did not extend to the south of Wrangaton, Avon W^ick, and Roister Bridge. He had not begun the survey of the Lower Devonian rocks of the main outcrop so that he had nothing to guide him in ascer- taining the position of the Dartmoutli Slates. In his maps he had laid down the limestone-masses in detail, and had separated the volcanic rocks of the Ashprington series from the slates and grits with which they were confounded in all the earlier maps. ' Quart. Journ. Geol. Soc, vol. xxiv, 1868, pp. 444-453. ' Journ. Boy. Geol. Soc. of Ireland, New Ser. vol. ii, 1868, pp. 82, 83. ' Ihid., p. 76. « Ihid., p. 80. ' Quart. Journ. Geol, Soc, vol. xxxv, 1879, p. 532, INTRODUCTION. 9 Although always entertaining a doubt as to its correctness, Champernowne accepted HoU's view as to the grits of the Torquay promontory being a lower series, and those of Cockington an upper series and contemporaneous with the Staddon Grits of the main outcrop. In consequence of this, when he broke through the traditional interpretation of the age of the limestone-outcrops and correlated the Ashburton and Buckfastleigh masses with the limestones of Newton Abbot and Torquay, then known as the Great Devon limestone, he did so by assuming an anticlinal structure in the intervening slates from which the limestones had been removed by denudation.'- He singlied out the purple and green slates, which he had traced from Penrecca quarry (a mile and a quarter east of Buckfastleigh Church) to Knowle Hill, Newton Abbot, and had again recognised at Combe Cellars on the Teign, as "the crest of a denuded and overturned anticlinal line." This structure accorded with De la Beche's figure of Petitor, in which the limestones are shown arching over the intervening purple and green slates.^ In each case the Upper Devonian age of the purple and green slates was subsequently (1888) proved by the discovery of characteristic fossils.'' The synclinal structtire entailed by these discoveries would have demonstrated the infraposition of the Cockington grits, even if the Lower Devonian fossils obtained in them* had not been found. In 1884 a general classification of the Devonian rocks of the Plymouth district was published in a preliminary- notice to the long excursion of the Geologists' Association. This was based on a few coast-observations made by the writer of this Memoir in 1880. In this first essay (of 1880) entitled notes on " The Devonian Rocks between Plymouth and East Looe,"-'' the Looe beds at Looe (since shown to be the lower part of the Meadfoot group) were placed below the slates of the Seaton, Downderry, and Portwrinkle coast. These slates were then correlated with the Upper Devonian of St. Germans, biit are now known to be the Dartmouth Slates at the base of the Devonian. The Looe Beds in the Tregantle coast were regarded as the westerly continua- tion of the Plymouth limestone, in accordance with the views, of De la Beche, and placed above the Dartmouth Slates of Port- wrinkle, etc., and below the Dartmouth Slates of Whites^nd Bay, Rame Head, Penlee Point, and Cawsand, which were corre- lated with the Morte Slates of North Devon. The Maker and Mount Edgcumbe grits were regarded as unconformable to this series, and were correlated with the Staddon Grits and with Champernowne's Cockington Grits, as the top of the Devonian Series, whereas they have been since shewn to be the upper group of the Lower Devonian. ' Geol. Mag., 1881, pp. 410-416. ' 'Report on Cornwall, Devon, and West Somerset' {Geol. Snrv.), 1839, Fig. 27, p. 205. » See Quart. Journ. Geol. Soc, vol. xlvi, 1890, pp. 509, 512-515. * Ibid., p. 498. » Tram. Roy. O-eol. Soc. of Corn., vol. x, 1881, p. 70. 10 GEOLOGY OF IVYBRIDGE AND MODBUBY. Champernowne did not give a group-number to the Dartmoutt Slates in his classification, but simply placed them above the Ashprington volcanic series and the Stringocephalus limestone, and noted that they " have much the same characters as the Morte Slates." In the accounts of the excursion in 1884 will be found a map and section by Champernowne of the rocks of the Dartmgton district. These and his classification of the Devonian rocks, which is a record of his later views, are valuable, but the actual part which he takes in Devonian Geology is in the breaking up of the strata generalised by previous observers into definite groups. A comparison of the descriptions of the excursion of the Geo- logists' Association to Plymouth in 1884 with that of 1907^ shows the great change in classification and grouping which resulted from the detailed survey of South Devon and South-east Cornwall on the 6-inch map.^ Although Champernowne' s interpretation of the relations of these groups has since been altered, his mapping is substan- tially correct. As a palaeontologist his work has hardly received full recognition. He collected many specimens'' from the Middle Devonian slates of Bnglebourne slate quarry and else- where, which are now in the British Museum. Pengelly recorded the discovery of fossils at Black Hall on the Avon, and in E. N. Worth's lists fossils from Cattedown and other localities in this map are given." Dr. Busz in 1896* described a kersantite in the Avon Valley above South Brent, but not found in situ. In the same locality he described^ the alteration of the Devonian slates and of lime- stone bands in them, the occurrence of cassiterite in some of the andalusite bearing schists, and of crystals of corundum in fel- sitic porphyry in close contact with black hornfels. In a later and much more detailed communication" he des- cribed the mineralogical characters of the granite and contact- rocks of the Avon Valley above South Brent. He records in the garnetiferous altered limestone the occur- rence of augite, datolite, axinite, and quartz, and describes the differejit varieties of altered rock — Knotenschiefer, Chiastolith- schiefer, Andalusithornf els ; also the altered diabase and schal- stein, and the presence of typical adinole not found in situ. Amongst the papers contributed by R. N. Worth are many references to the igneous and altered sedimentary rocks of this area. ' The Rocks of Plymouth ' in 1886,' ' The Igneous and Altered Rocks of South-west Devon' published in 1887,^ and 1 Proc. Genl. Assoo., 1884, vol. viii, p. 442, and ihid., 1907, vol. xx, p. 78. ' Rep. Bril. Assoc, for 1889 (Newcastle-upon-Tyne), pp. 578-9 ; Quart, .rourn. Geol. Soc, vol. xlvi, 1890, pp. 487-517 ; ' The Country around Torquav ' ( Mem. Geol. Surv.), 1903. h j v ^ Trans. Devon. Assoc, vol. vi, 1874, p. 649, and Journ. Plymouth Inst., 1878. * Neu. Jahrb.f. Min., vol. i, pp. 74-78. ' Geol. Mag., 1896, p. 492. « Neu Jahrb.f. Min., BB. xiii, pp. 90-139. ' Trans. Plymouth Inst., vol. is, 1886, p. 21.^. * Trans. Devon. Assoc, vol. xix, 1887, pp. 467-497. INTBODUCTION. 11 ' Haterials for a Census of Devonian Granites and Felsites ' which appeared in 1892/ may be specially mentioned. The granite-area included in this map has been described by Worth in 1902 and 1903.^ In these communications the Geological Survey maps alluded to as erroneous as regards the granite- boundary are De la Beche's geological maps, not the hand- coloured edition of the geological re-survey of Sheet 349, New Series, issued in 1899, in which these errors had been rectified. In these papers Worth shows " that there exists on the border of the granite a rock, not continuously but at inter- vals, which carries its characteristics practically unaltered at its various exposures. Apparently merely a chilled granite, and contemporaneous with the intrusion of the mass, it points from its constancy of form, structure, and composition to an original unconformity of the magma from which the Dartmoor granite has consolidated."^ Worth described also the Tealmpton limestone ; * on old post- cretaceous deposit on Cattedown,'^ and the discovery of human remains in a cavern in Cattedown Quarry. ** In a paper on ' The Bone Caves of the Plymouth District ' he gives a table of the various discoveries in the Oreston Caves with respective dates. ^ Pengelly dealt with the ' Literature of the Caverns near Yealmpton.^ The survey of the Lower Devonian, or southern part of the area, was carried on in the years 1892 and 1893, that of the entire map having been completed between 1892 and 1897. As already stated, the results as regards the Lower Devonian sub-divisions and the altered rocks of the granite-aureole were defective through lack of evidence. The subsequent extension of the survey to Liskeard cast sufiicient light on the relations of the Dartmouth Slates to enable me to draw a boundary for that sub- division in 1902, which although very indefinite in the east part of the map, between Modbury and East AUington, is fairly well marked along the faulted outcrop, between Modbury and the coast near Down Thomas. The petrography of the rocks in the granite-aureole was prac- tically untouched during the progress of the survey. The sub- sequent mapping of the Peek Hill and Dousland district in Sheet 338' and of the Lostwithiel district in 1902, showed the necessity for a revision of the mapping on the granite-borders which was effected in 1906, when the writer showed the different types to Mr. Barrow, who had made a special study of similar types on the north of the St. Austell granite and on the west of Bodmin Moor, and who undertakes the petrological descrip- tion of this aureole. ' Trans. Devon. Assoc, vol. xxiv., pp. 183-213. » Ihid., vol. xxxiv, pp. 496-527, and vol. xxxv, pp. 759-767. ' Ibid., vol. xxxiv, p. 527. ^ Ibid., vol. vi, pp. 703-706. ' Trans. Roy. Geol. Soc. of Corn., vol. xi, 1888, pp. 151-162. « Ibid., pp. 105-112, 1887. ' Journ. Plymouth Inst, vol. vii, 1879, p. 87. 8 Trans. Devon. Assoc, vol. iv. pp. 81-105. ^ Ann. Eep. of the Geol. Surv., 1896 (^Mem. Geol. Stirv.), p. 52. 22265 12 GEOLOGY OF IVYBRIDGE AND MODBUBT, The evenly bedded calc-flintas and the dark argillaceous rocks with chiastolite had been included in the Cn m as no simdar chiasolite-rock had been met with m the altered undisturbed -DeYonian, and E. N. Worth had gone so far as to state that this special type of chiastolite-rock is restricted to the Luim. ^ Rocks of the calc-flinta type have, howeTer been met with .n the Lower Devonian within the aureole round the bt. Austeii granite; and similar materials occur at a higher horizon within the aureole of the Bodmin Moor granite. It thus appears that the occurrence of calc-flintas of itself affords no proof ot the presence of the Lower Culm beds. But the value of the special chiastolite-rock remains unimpaired. In the colour-printed edition of the map Culm measures are -still shown, where distinctive types of rock occur, such as cer- tain gritty bands near Nurston and the dark chiastolite-rocks near Gidley Bridge, Didworthy, Aish, Owley and Henlake Down (near Ivybridge). The mode of occurrence of these rocks will be discussed later on. General Structure. Lying along the strike of the rocks of the Plymouth and Lis- keard district on the west, and of those of the Torquay and Paignton district on the east, the structures exhibited on each side of our area, as might be expected, assimilate to those of the adjacent areas. Thus, on the east, we find a considerable superficial develop- ment of Middle Devonian slates with volcanic rocks, limestones occurring very occasionally. This is in accord vvdth the effect ot the dying out westward of the Paignton Lower Devonian anti- cline in the production of numerous small curves tending to lepeat the Middle Devonian rocks as already pointed out.^ When, on the other hand, we turn to the western border,^ whilst the Middle Devonian is restricted to an outcrop of a mile and a half in breadth, there is a great superficial development of Upper Devonian slates, apparently through constant repe- tition. The reconcilement of these two opposite extremes is involved in the structure of the area, and depends on the interpretation of the stratigraphy of the central part south of Dartmoor. The initial difiiculty consists in the extreme rarity of fossils and in the absence of definite lithological types which would afford a •clue to the fixing of even an approximate boundary between the Upper and Middle Devonian. The Plymouth limestone horizon is carried through the map by schalsteins forming an almost continuous outcrop, only broken for about three-quarters of a mile, betw^een Langford and Lin- combe west of Harberton, apparently through impersistence. ' 'The Country around Torquay' (Mem. Geol. Swv.), 1903, p. 11. ' ' The Country around Plymouth and Liskeard ' (Mem. Geol. Swv,), 1907, p. 12. INTEODTTCTION. 13 This outcrop connects the Plymouth limestone horizon with the Ashprington volcanic series. To the north of this the discovery of Calceola by Champernowne near Brooking- Cliurch (Tigley on the New Series one-inch map), south of the limestone-patch near Battery, suggests the occurrence there of lower beds in the Middle Devonian. The correlation of the Ashburton and Buckfastleigh limestones with those of Newton Abbott, etc., by Champernowne, and the discovery of Upper Devonian rocks in the interval in Sheet 339 by the writer proved the existence of a syncline, which on ap- proaching the granite is deflected southward. Upper Devonian slates have been recognised within the north- east border of the map at W. long. 3° 44' 40", but the manner in which they are troughed out in the termination of the syncline is not apparent. Although no fossils have been found to justify the idea that the igneous patches of Rattery and further north are representatives of the Upper Devonian pillow lavas of Sheet 348, this idea accords well with the occurrence of igneous rocks near Egg Buckland and at Dorsmouth Hill near Paignton, which are the continuation of this series westward from St. Budeaux and Mannamead. From Buckfastleigh westward to the granite the slate-rocks are of Upper Devonian aspect, and this is confirmed on tracing them northward toward Holne Bridge in the adjacent map. The Buckfastleigh limestones must therefore form part of an anti- cline, which is no doubt obscured and broken by thrust-faults. The continuation of the strike connects the Buckfastleigh limestones with the schalsteins of Dean which enter the granite aureole at Brent Hill. The associated calc-flintas of the aureole thus cannot be entirely dissociated from the series in which the volcanic rocks occur, and they are now considered as in part belonging to the slates which continue the horizon of the Buck- fastleigh limestones and in part to the Lower Culm. The terms Upper and Middle Devonian can obviously be only used in a relative sense in a country where no fossils distinctive of the lowest beds of the Upper Devonian have been found. With this qualification the boundary runs west, along the margin of the Plymouth limestone, entering the slates near East Sher- ford. It may then turn irregularly northward to Sparkwell, and thence to the granite-margin near Corn wood. If a specimen of dark slate containing a large Pleurodictyum labelled Cann Quarry, in the Plymouth Athenseum Museum, is correctly localised, there would appear to be an anticline of Middle Devonian slates there; although from the discovery of cyprids in the rocks of Elfordleigh, on the south-east of Cann Wood, there can be no question as to the occiirrence of Upper Devonian in that locality. Turning now to the north-east of the map, the Upper Devonian io confined to the tract between the Buckfastleigh limestone and the granite-margin on the north border of the map, and to the district east of the Buckfastleigh limestone where it may ter- minate near Lower Combe, or be prolonged southward toward 32265 B 2 14 GEOLOGY OF IVTBRIDGE AND MOBBTJRT. Brent so as to include the volcanic rocks of Battery. In any case it is improbable that the Upper Devonian extends nmcii further than the Harbourne Valley near Marley House, and there is no reason to think that its outcrop is continuous, even m a narrow band, to the south of the granite-mass. The distribution of the schalsteins and limestones, west of the Erme Valley and toward Harberton, shows their impersistent character, and their repetition by plication. The breadth of outcrop of the Middle Devonian slates south of Elburton and south-west of Harberton is due to the latter cause. The appear- ance of Lower Devonian grits in the Middle Devonian slates south of Diptford and North Huish, near Bickham Bridge and Coarsewell, is due to these plications. The broken lines on the map, between the patches of grit, indicate the possible exten- sion of the grits as bands in the slates. In the first edition of the new-series map, owing to the adoption of the same colour for all Devonian slates, there was nothing to distinguish the Middle from the Lower Devonian area, except the masses of Staddon Grit and the symbol letter near Wembury. The occurrence of the grits in a series of patches here and there separated by slates, between the Erme Valley and Halwell, taken in connection with the presence of schalsteins and limestones near Sequers Bridge and of schal- steins east of Modbury, suggested a series of anticlines of Lower Devonian grits of a very impersistent character in Middle Devonian slates. But without fossils, it was impossible to dis- tinguish Middle from Lower Devonian slates, sufficiently to draw a boundary between them. Between the continuous line on the map just south of Dun- stone and Flete, west of the Erme Valley, and the outcrop of the Staddon Grits of Holbeton, on the south, there is evidence, here and there, of the occurrence of thin grit beds in the slates, sufficient to differentiate them from the Middle Devonian slates on the north, but not sufficient to include them with the Staddon Grits on the south. The same indefinite character is exhibited in following this band of country eastward to Modbury and the abrupt eastern termination of the Holbeton grits at the Erme Valley is suggestive of the dying out of a strong series of grits into slates with occasional beds of grit. The Middle Devonian rocks of Sequers Bridge and the schal- steins of Modbury undoubtedly owe their position to faults and thrusts produced along the trend of a sharp synclinal plication, but, in the absence of any reliable data, I prefer to regard the slates, east of Modbury and south of the broken line of Staddon Grits, as Lower Devonian. From the Erme westward the line between Flete House and Dunstone may be taken as the northern boundary of a zone in which Middle and Lower Devonian junction beds are repeated by plication. From the Tealm Valley to the Staddon coast the Staddon Grits and shales are easily traced, although at Staddiscombe the line IS breached by slates which are apparently cut off by a fault against rocks of the Meadfoot group on the south. INTKODUCTION. 15 The coast-section proves the constant repetition of the rocks by plication and the presence of faults, or thrusts at the junc- tion of the grits, where strongly developed, with the more yielding Middle Devonian slates. One of the chief features of the Lower Devonian outcrop is the cutting out of parts of the Meadfoot group between Knighton and the coast (where the Taunusian or representatives of the Looe Beds are present), and the complete elimination of that group between Knighton and the Yealm, and south and south- west of Holbeton. On the east of the Erme the Meadfoot group is represented toward South Allington and Modbury, making a very indefinite junction with the Dartmouth Slates, which is nearly always the case where the relations of these groups are unfaulted. The southernmost deflection of the faulted boundary of the Dartmouth Slates, near Membland Hall, seems -to have some relation to the intrusion of the granite. If it could be proved that the granite was a laccolitic intru- sion^ its original contour would be inferable from its exposure at . the surface and from the occurrence of elvan-dykes subse- quently ejected from the molten reservoir. On these grounds the eastern and southernmost borders of the mass would appear to descend much more abruptly than in the western and south- western parts where the inliers of Hemerdon Ball and Crownhill Down occur, and where the elvans of Cann Quarry, Bickleigh, and Roborough Down reach the surface, so that the disruption and consequent deflection would be much greater on the east than on the west, whilst we might expect the evidences of com- pression and the consequent dislocation to be most intense to the south of the southernmost extension of the mass, south of Ivy- bridge and Hemerdon Ball. In other words the contour of the granite at, and, as far as can be inferred, below, the surface, according to its trend across, or in the direction of, the normal east and west strikes, has a direct relation to the structural phenomena displayed in the disposition of the surrounding rocks. The greatest deflection of strike, for instance, is along the granite from Ugborough to Buckfastleigh. West of Buckfast- leigh, where the granite border takes a north-westerly trend, the Upper Devonian slates occur, in a manner strongly sugges- tive of faulted junction with the schalsteins and limestones of Dean and Buckfastleigh. The deflection of strike decreases to- ward Harberton. On the south, besides the complex faulted relations of the Middle and Lower Devonian near Ermington, Sequers Bridge, and Modbury, there is the faulted boundary of the Dartmouth Slates with its most southerly deflection due south of Hemerdon Ball. ' That this was its character was supported by the writer in Trans. Devon. Assoc, vol. XX, (1888), pp. 141-157, but this view was abandoned, perhaps on insufficient grounds in Proc. Somerset. Arch, and Nat. Hist. Sac, vol. xxxviii, 1892, pp. 218-219. 16 GEOLOGY OF IVYBKIDGE AND MODBURT. To the west, the general strikes are maintained and the Upper Devonian slates are constantly repeated, being supported by the comparatively gentle subterranean slope of the granite. Gnarling and the small foldings with accompanying strain- slip cleavage had taken place in the Devonian strata prior to the granite intrusion, but to what extent the larger structural curves had been produced it is not easy to conjecture. There is, however, no reason to conclude that the north-and-south move- ments ceased on the intrusion of the granite. It is, in fact, more natural to attribute deflections of strike, extending far beyond the limits of the aureole, to movements obstructed, or influenced, by the consolidated, or consolidating, granite, than to attribute them entirely to the displacements occasioned by the intrusion of the mass itself. On the east, as has been already pointed out, the repetition and consequent superficial development of the Middle Devonian is due to the westerly termination of the Paignton Lower Devonian anticline in Sheet 350. The existence of the Lower Devonian anticlines of Paignton and Torquay, with their accom- panying faults, is equivalent to a deflection of the Lower Devonian boundary, after the consolidation of the strata, in a less degree than, but in a similar direction to, the deflection of the Middle Devonian outcrop round the east margin of the granite. When we consider that the minor folding produced so great a repetition as to have little effect in plicating the rocks in a large way, and that the larger folds are merely undulations produced in the further compression, or contraction, of strata already stiffened by innumerable folds, it does not appear unlikely that, after the intrusion of the granite had for a time relieved the stresses of the Armorican movement and produced a phase of temporary quiescence, the movements were resumed and the already folded strata were thrown into those undulations which constitute the main structural folds, the later stages of the move- ments being largely influenced by the extraneous masses which had solidified in the crust. A little map showing the strikes in relation to the granite- masses and to their assumed subterranean connection was pub- lished in 1892.^ Since then the geological map of Cornwall has been practically completed and the relation of the major geological structures to the granite-masses, if anything, has been more clearly established. The structural north-west and south-east faults in the area east ot Plymouth point to the angle between the Bodmin Moor and St. Austell granites. The termination of the Dartmouth Slate anticline m the vicinity of the eastern margin of the St. Austell granite, and the termination ojf the Watergate Bay Dart- mouth S ate anticline to the north-west of the same mass are also worthy of note. p.'lfr'' '-^'"""■''*- '*'■"'*• ""'' ^°'- ^'«'- Soc, vol. xxxviii, 1892, Map II facing INTRODUCTION. 17 If, on the other hand, the Arinorican moyements terminated with the intrusion of the granites, we are almost ohliged to assume that the later structural undulations were in process of formation and that their course was influenced hy the throes which immediately preceded and accompanied that intrusion. During the progress of the survey in 1893 the grits near Laira Green shown as Carhoniferous on the hand-coloured edition of Sheet 349, were first mapped. From their exposure in a quarry near a place called Efford on the 6-inch map, north of Laira Green, and from their development at Wearde Quay south of Saltash, in Sheet 348 (which has been already described),^ these beds were called the Wearde-Efford Grits. In his description of the Rocks of Plymouth^ and of South- west Devon,'' R. N. Worth mentions the occurrence of tuffs at Compton and Crabtree under which description he seems to have classed these grits. These rocks have been referred to by De la Beche in his men- tion of an " Abundant mixture of trappean rocks and greywacke (the latter occasionally arenaceous) in the vicinity of Saltash and, St. Stephen." He considered that the schistose trappean rocks were contemporaneous with the accompanying greywacke.* The different opinions entertained and expressed at different times as to the age and origin of these grits — at first regarded as tuffs, later as Culm grits, and now as of Upper Devonian age — and the reasons for these changes of opinion have been gone into at length in the Plymouth Memoir above referred to. As already stated, the volcanic rocks in the vicinity of the grits of Efford and Crabtree belong to the Upper Devonian spilite, or pillow-lava, group, and Dorsmouth Hill (near Plympton) is composed of similar rock. The first specimen of Styliola (identified by Prof. Rupert Jones) found in Devon, as far as I am aware, was obtained during the survey in grey slates apparently underlying the grits in a lane on the south of Compton. In 1907 Styliola was obtained in a slate-fragment in tuff at Wearde Quay, during the Easter Excursion of the Geologists' Association to Plymouth. The slates in which these tuffs occur are the same series as those at Compton. The indefinite nature of the boundary of the Dartmouth Slates between Modbury and East Allington already mentioned (p. 11), is due to the danger of placing too much reliance on colour-distinctions when unaccompanied by a definite change in lithological characters. Grey slates often occur in the area coloured as Dartmouth Slates, for instance in the vicinity of the masses of diabase south of Whympston House, between Modbury and Aveton Gifford, and these might denote synclines of the basement beds of the Meadfoot group. 1 ' The Country around Plymouth and Ijiskeard,' (Mem.. Geol. Surv.), 1907 pp. 15, 82-90. ' Trans. Plymouth Inst., vol. ix, 1886, p. 213. ' Trans. Devon. Assoc, vol. xix., 1887, pp. 485, 48G. ■■ ' Keport on the Geology of Cornwall, Devon, and West Somerset ' (Geol Surv.), 1839, p. 63. 18 GEOLOGY OF IVYBEIDGE AND MODBUHY. The Dartmouth Slates are often of a pale greenish hue gra- dating into hufE and grey; red tints being very rarely visible. This character renders the boundaries in the south-eastern part of the map so indefinite that they can only be regarded as the best general indications of a junction obtainable from the ex- posures. There can be little doubt that the fault bounding the Dart- mouth Slates, from Modbury westward, extends eastward, either in grey slates in which it cannot be traced, or in connection with the southern fault-boundary of the patches of schalstein which run south of east from Modbury. The junction between the Lower and Middle Devonian is visible on the coast about midway between Mount Batten coast- guard station and Bovisand Bay; but for some distance north of this the junction beds are repeated by faults and plications in the lower part of the cliffs. Wherever continuous observation of the cliffs is possible, contortions and faults are so numerous that they could not be adequately shown in a section drawn to the scale of even 25 inches to the mile. Moreover weathering, rainwash, and over- growth obscure the cliffs in places, and projections and indenta- tions in the coast line would make any general representation of it purely diagrammatic. The particulars will therefore be given in the Lower and Middle Devonian chapters. 19 CHAPTEE II. LOWER DEVONIAN. From what lias already been said as to the general structure and relations of the three divisions of the Lower Devonian, viz., Dartmouth Slates, rocks of the Meadfoot group and Staddon Grits, it will be seen that the lines, of demarcation between them are often uncertain, and this uncertainity may lead to the inclusion, under the Lead of each of the divisions, of strata without distinctive characters which may belong to the neigh- bouring groups. This is more especially the case in the area east of Modbury, where grey slates occur amongst masses of grit and where there is a strong probability that a fault, or faults, of which there 18 no surface-indication, may exist. In this case it is quite con- ceivable that Middle Devonian slates might be troughed, or faulted in, and, if so, would be undistinguishable from slates in the upper part of the Meadfoot group, or from slates locally developed in the Staddon beds through failure in supply of arenaceous materials. The occurrences of grit are similar in this area to those in this adjacent map (350) where the grey slates are considered as anticlines of the upper beds of the Meadfoot group. The possi- bilities of troughs of Middle Devonian slates may therefore be restricted to the strip of country between Modbury and Cra- badon Cross, crossing the Avon at Gara Bridge Station. On the map the slates of this tract are coloured with the same tint as that used for the Meadfoot Group, as no colour-distinc- tion can be made between Meadfoot beds and Staddon Grits where grits are developed in masses in the former and slates prevail in the latter. The colours simply denote Lower Devonian slates and Lower Devonian grits, ahove the Dartmouth Slate group, irrespective of geological horizon, in all such cases. The assimilation in colour exhibited by the lower beds of the Meadfoot group to the Dartmouth Slates, at their faulted junc- tion on the coast and in many places along its westerly pro- longation, often renders the exact position of the junction un- certain. In the absence of other distinctions this assimilation in colour would render the presence of synclines of the lower beds of the Meadfoot group in the Dartmouth Slates, or of anticlines of the latter in the former, undistinguishable. The local occurrence of dark grey slates in the variegated Dartmouth Slates and the frequency of grey tints in the varie- gation constitutes a much greater difficulty. As there is practically very little difference in the sediments where the apparently unfaulted junctions had to be drawn, in the district east of Modbury, the boundary-lines are merely general indications and must not be taken to represent the 20 GEOLOGY OF IVYBEIDGE AND MODBUKY. actual structure, which is much too detailed to follow in rocks similar in general characters and subject to these assimilations in colouring. In mapping the area in 1892, before the writer had any clue to the existence of the Dartmouth Slates as a distinct sub- division, he detected no mappable lithological type beyond the grits of the Staddon group in this part of the map. When, about nine or ten years later, he revisited this area, having in the interim established the position of the Dartmoiith Slates, a very general boundary was the only thing practicable in the short time at his disposal. The petrology of the basic igneous rocks in the Lower Devonian is incomplete, as many of the diabase patches shown on the map have not been examined microscopically. Dartmouth Slates. The Dartmouth Slates in this area present similar charac- teristics to those exhibited in the maps on the east, south, and west, and described in the Memoirs on Torquay, Kingsbridge, and Plymouth, respectively. Their characters are best dis- played in the coast section and Tealm estuary and in the Erme Valley, where the rocks are continuously exposed. These sections reveal occurrences of igneous rock which might otherwise escape detection, and in the coast from Andurn Point to Wembury Point, in the Yealm estuary, and in the Erme Valley, they cross the strike of the rocks. In the coast the Dartmouth Slates commence at a fault, on the north side of Andurn Point, which cuts them off against red grits and slates of the Taunusian, or lower part of the Mead- foot group. The assimilation in colour between the groups would at first sight suggest the same series, as the fault is obscured by head, talus, and overgrowth in the cliff, although marked by a breach in the coastal reefs. Just near the fault the rocks consist of red, buff and green spotted, and purple-mottled slates with irregular beds of hard, dense, lilac grit in contact with a mass of diabase. Beyond this the low cliff and beach-reefs consist of bright-red, purple, and greenish mottled slates with intercalations of the fine pale-greenish grit or siltstone and grit-shales. Beds of hard greyish or lilac quartz-veined grit are intercalated in the slates here and there, throughout the sections. These in places form masses interpenetrated by quartz veins and assume the character of quartzites, and quartz-rock. Such occurrences may be seen at Lentney Brake, about 300 yards south of Andurn Point, in Renney Rocks and in their continuation on the mainland on the north shore of Heybrook Bay in Orestone Brake, and on the north of Season Point and elsewhere. A good example of the local irregularity of the hard grits is furnished by an exposure near Langdon Court, south of Langdon Farm, where a mass of hard grit is overlain by lilac shales which also abut against it, and exhibit cleavage at a little distance from it (Fig. 1). The intercalated grit beds are sometimes sandy and micaceous, sometimes rough and haekly-fractured resembling the fish-grit beds of Portwrinkle coast, which are probably represented in the section by the new road leading westward from Newton Ferrers to the steamer landing-place, and near Langdon Court and Higher Ford, north of Wembury. DAKTMOUTII SLATES. 21 The slates vary in composition, being sometimes hard, glossy, and more or less silty, sometimes comparatively soft and argillaceous, and less glossy. The most persistent reddish tint is pale lilac. Fig. 1. — South of Langdon Farm. Irregular development of Grit in Dartmouth Slates. Small irregular patches and pellets of dark brown friable material occur in the coast section and in inland localities, chiefly in the slates. These are probably residues left by the decomposition of limestone of organic origin, as on the Tregantle coast, where Bellerophon has been found in pinkish limestone-nodules, and near Piskey's Cove, east of Revel- stoke, in Sheet 355, where remains of Pteraspis occur as irregular patches of pinkish limestone. On this coast the occurrence of these residues and hard nodules is best shown in the slates of Wembury Point and at three- quarters of a mile west of Wembury Church, where pellets and thin patches of reddish limestone are present as well as the decomposed residues. Owing to the variation in the materials and in the intercalations of the grits in the slates the structures are not always clear, but where the inter- bedded grits are prominent the rocks are thrown into numerous small folds tending to repeat the beds more or less horizontally. This is well shown at about a quarter of a mile south of Andurn Point where the slates rest on grits, the same beds being probably repeated at Heybrook Bay half a mile further south. The general strike of the bedding planes seems to be west-south-west, and east-north-east, that of the cleavage planes, though often coincident, more nearly appro:rimating to south-west and north-east. This strike is very clearly seen in the Great Mew Stone (Sheet 355), along the abrupt cliff forming the northern face of the island, where the alternating grits are slates crop out ; from this the dip-slope falls south-south-east, at an angle of about 25° (Fig. 2). Fig. 2. — Great Meio Stone from Season Point. «^ f<;. The east-north-east strike of the Great Mew Stone is continued on the mainland at about half way between Wembury and Season Point. Here the rocks consist mainly of grey silty slates and interbedded grits recalling the rocks between Rame Head and Penlee Point, but they cannot be traced as a distinguishable series in the Yealm section. Most of the coast-line from Wembury to Warren Point is practically inaccessible for detailed examination, the general appearance as seen from a coasting steamer suggests u repetition of the rocks by several folds with inverted south-east or east-south-east dip. 22 GEOLOGY OF IVYBRIDGE AND MODBUET. The Yealm estuary, proceeding southward along the western shore, from the quay east of South Wembury House, first exhibits red (or magenta), greenish or purplish slates with hard green grit-beds (recalling grit-beds of Aveton GifEord). The dip of the cleavage and, apparently of the bedding, is southerly, but at between 120 and 240 yards from the quay it is northward in one spot at 65°. A little further on the purple-mottled slates are of the same type as at Erme Mouth (in Sheet 355). From here to Glitters Wood (the small wood at the bend in the estuary, north of the Coast Guard Station), the cleavage- planes dip south-east at from 50° to 60° The bedding is seen to cross them in several places. At one spot, where a decomposed igneous rock occurs in the section, impersistent thin hard bands denote bedding dipping in the same direction as the cleavage planes at a lower angle. At Glitters Wood, proceeding southward, we encounter, successively, grey slates, with red (ologiste) splotches in places ; lilac, green, buff and yellow slates ; lilac and green slates with beds of grit. Soft rocks which may be of pyroclastic origin occur in two places. Opposite Glitters Wood, on the east side of the estuary, an inverted anticlinal axis is visible in lilac grits and slates, striking north-east. (Fig. 3.) Fjg. 3. — Court Wood by the B. Yealm, opposite Glitters Wood. Inverted anticline in Dartmouth Slates, looking SW. To the south of Glitters Wood shaly grits, hard grit beds, and massive quartzose grits are met with in the slates which often exhibit greyish as well as lilac tints. On the east shore, opposite the Coastguard Station, rough red and, occasionally, grey grits, resembling the iish grit of Portwrinkle occur at the old quay and Limekiln, where 15 feet of hard red jointed grit is exposed, and in the new road-cutting to Newton Ferrers. On the north shore of Newton Ferrers Creek, at first grey and dark grey slates are associated with the lilac and green slates and bedding is seen crossing the cleavage-planes. A fault is shown (apparently in a direction north by west, and south by east), near a mass of igneous rock at the Limekiln Quay (on the 6-inch map), and 3 furlongs further east thrusts intersect lilac slates with grit beds. A fault with an apparent north-west and south-east direction is also noticeable near the entrance to the creek on the south side. Further east toward Noss Mayo Greek the strike is east and west. Between Noss Mayo Greek and Bridgend signs of disturbances were noticed and, in places, gnarled or contorted bands denoting bedding are visible and cross the cleavage planes of the slates. DABTMOUTH SLATES. 23 The above localities are, with exception of the coastline north of Heybrook Bay, included in the 6-inch map 130 Devon, and the sections display the character of the Dartmouth Slates in the western part of our area. Their characters in the eastern part of the map as shown by the sections in the Erme and Avon valleys, and their tributaries (in the Devon 6-inch quarter sheets 131 NW., NE., and 132 NW., NE.), will now be mentioned. The Erme section commences on the south at the road to Mothecombe (in the 6-inch quarter sheet 131 SW.). The slates are here buif and drab and contain rough grits and arenaceous beds. On the east band an anti- cline of quartzite beds in buff rocks, perhaps partly of pyroclastic origin, is visible. The strike varies from west-south-west, and east-south-east, to south-west, and north-east throughout the Erme Valley sections, and need not be again referred to. At about 100 yards to the east of the Coastguard Station an inverted anticline is visible. For a quarter of a mile north of this igneous rocks are exposed here and there on both sides of the valley. The slates gradually lose the buff and grey tints, and lilac and green colours become prominent. Hard grits, sometimes compact and assuming the character of quartzite, are plentiful in this part of the section, and they seem to contain pegmatite veins on the south of the Fish Pond and on the opposite bank. Shaly grits and beds of a more arenaceous type also occur in the slates. Near the Keeper's Cottage (Skerril Coppice on the 6-inch map) an anticline is visible in the slates and grits. To the north of this red, purple, and greenish slates with grit-shales predominate, and no certain signs of igneous rock were met with, whereas on the east bank by Orcheton Wood, igneous rocks were encountered in three places. Orcheton Wood is the wood opposite Efford House. On the south side of Orcheton Wood there is an appearance of faulting near the confluence of the chief tributary of the Erme. In Oldaport Wood, on the east bank of this stream, above its confluence with minor streams near the Mill, an anticlinal axis is noticeable in green quartz-veined grits striking north-east. The rocks of the southern part of the Erme section, in which basic rocks are of frequent occurrence and buff, grey and brownish tints are common, continue eastward with the same general characteristics, and include the large masses of diabase shown on the map. The rather poor exposures and the surface stones show a sufiicient admixture of purple, green and lilac slates to prevent a separation of grey slates as a distinct series, and it is not therefore improbable that although grey tints occur in the Dart- mouth Slates, they may not also denote the presence of interfolded syn- clines of basement beds of the overlying series. Grey rocks are visible in situ on the east of Kingston, near South Langston, south and south-west of Tuffland, south of Challon's Combe, and north of Ashford. East of Wakeham and Ashford pronounced red and purple colours are very rarely seen, in the tract extending eastward beyond Woodleigh and coloured as Dartmouth Slates. Purple and grey slates were noted at about a quarter of a mile east of Chantry, in the north part of Silveridge Wood by the Avon, and at the bend in the lane from Grimpstonleigh to the Torr Brook the characteristic colours of the Dartmouth Slates are well shown. The lines drawn on the map would naturally suggest the nosing out east of Woodleigh of a continuous anticline of Dartmouth Slates and the trough- ing out westward of a syncline of the basement beds of the Meadfoot group west of Loddiswell. In a very general sense this may be the case, but the lines are merely arbitrary boundaries separating grit-shales and slates, with beds of grit in places, grey, silvery, and occasionally buff and lilac, taken as basement beds of the Meadfoot group, from somewhat similar sediments mostly lilac, buff and greenish but very often grey and sometimes silvery, which are coloured as Dartmouth Slates. There is very little doubt, making allowances for local assimilation in colour, that the real boundary, if we assume a particular horizon indepen- dent of variation to denote it, would be very intricate, the beds being so repeated by minor curves that anticlines of the older would occur in the newer series, and synclines of the latter in the former. 24 GEOLOGl OF IVYBEIDGE AJSTD MODBUUY. The continuity of the Dartmouth Slates between Chantry and Woodleigh is doubtful. In the Avon Valley the boundary has been drawn on the north of the purple and green slates in Silveridge Wood, before mentioned, but these may form a narrow anticline, as further soulh only grey grits and gnarled shales and slates are visible until we approach the assumed boundary, near which lilac slate and grit is exposed in a small quarry on the west side of the valley, and dark grey slates in the railway on the east bank of the river. Further south the assumed basement beds of the Meadfoot group, grey or dark grey slates and grit shales, are seen here and there on the east bank, in one place, near Loddiswell Station, containing 10 feet of hard grey grit. The grit-shales locally assume a reddish tint near Loddiswell Mill Bridge. The southern boundary of the assumed basement beds of the Meadfoot group west of Loddiswell Station is very uncertain. It is possible that the rocks on the north of Loddiswell Mill may belong in part to the Dartmouth Slates, as also some lilac slates and grits north- east of Weeke. East of Courtlands the evidence for the boundary is weak, through the scarcity of exposures. The slates and grit-shales are frequently greenish and lilac, although grey tints often prevail. In this, as in their extension from Ashford eastward by Woodleigh, the boundaries of the Dartmouth Slates are general and do not exclude the blending of basement beds of the Meadfoot group with then through plication. The basic rocks afEord no stratigraphical clues, as though carefully noted in the field the evidence is too obscure to show whether the harder diabase might be regarded in part as interbedded masses, or as fragmentary ex- posures of parts of an intrusive sill or sills, whilst the bands to which we are inclined to attribute a pyroclastic origin are, as a rule, too altered or decomposed for precise determination. Organic remains. When we turn to fossils these have only been detected in one place in the lower beds of the Meadfoot group, near South Allington, where besides moulds of spirifers, very much crushed, Pteraspis cornuhica was obtained. The manner in which the fossils occur between the com- pressed even laminae of shales in part of somewhat silty calcareous types in this quarry furnishes the explanation of their apparent scarcity in this district. The fossiliferous calcareous films have been decomposed to friable brown residues which have been so compressed that the preservation, even in outline, of organic structures is exceptional. We have already shown that brown residues are occasionally present in the Dartmouth Slates, so that, unless accompanied by braohiopods or crinoids, however obscure, evidences of occasional films of residue after calcareous material are in themselves quite valueless as a distinction be- tween the Dartmouth Slates and lower beds of the Meadfoot group. Its occurrence near South Allington above mentioned, at Long Sands in Sheet 350', at Ayrmer Cove in Sheet 355^ and in the lower beds of the Meadfoot group deprives Pteraspis of its value as a fossil distinctive of the Dartmouth Slates. This has been confirmed by Drevermann's discovery of Pteraspis in the Taunusian of Germany. Pish remains and Bellerophon' have hitherto been the only fossils recorded as occurring in the Dartmouth Slates; and, although Pteraspis and Bellerophon range upward, the in- coming of a comparatively abundant and varied marine fauna in the Taunusian, or lower part of the Meadfoot group, is the palwontological ground for a general separation between them. Organic remains were found in the Dartmouth Slates of the area in the following places. The coast would probably repay further search: At Wembury on the coast. Pteraspis fragment. By the lane from Wembury to Langdon Court reddish slate with greenish yellow patch with organic marking. PFish. At Langdon Court remains resembling honeycomb layers of Pteraspis, forming a fish-grit. > ' Summary of ProgreBs' for 1902 {Mevi. Geol. Su™.), 1903, p. 164; and ' The Countrv around Torquay ' (;Wem. Geoi.Sttre.), 1903, pp. 16-18. v^"uuuy 2 ' Summary of Process ' for 1902 (Ucm. Geol. Sun.), 1903, p. 161 ; and ' The Countrv around Kmgsbndge and Saloombe (Mem. Geol. Stirv.), 1904, p. 32. 3 ' The Country around Plymouth and Liskeard ' (Mem. Geol. Sum.), 1907, pp. 24 25 DAETMOUTH SLATES. 25 At Higher Ford, 3 furlongs east of Langdon Court, fish-grits also occur in purple and green slates, and remains, prohably pteraspidean, are discernible. Fish-grits seem, as already noticed, to occur in the new road west of Newton Ferrers, and at its termination at the Old Quay and Lime- kiln by the Yealm. In the lilac-red slates near Orcheton Corn Mill, about 260 yards north of Oldaport, markings were detected resembling dismembered patches of the honeycomb layers of Pteraspis. On the north side of Newton Ferrers Creek towards Bridgend, lilac slates contain occasionally somewhat similar patches to the last- mentioned. We will now trace the boundary of the Dartmouth Slates eastward. The apparent direction of the fault-boundary on the coast is west-north-west, but traced inland by surface stones and any other evidence procurable, it seems to run east-north-east, crossing the north part of the hamlet of Down Thomas. Near the Inn at Down Thomas a curious red-brown rock was exposed resembling a fine breccia of quartz or pellucid quartzite-granules in sheared shale or slate; this was at first taken for a tuff. The fault-boundary is shifted by a cross-fault, near Eaneleigh, for three quarters of a mile, to a little way beyond Langdon Court, whence it continues west by north for a mile. The position of the cross-fault is inferred from the distribution of the fossiliferous rocks of the Meadfoot group between West Wembury and Staddiscombe ; but south of Raneleigh red and pxirplish, green-mottled slates, with brown powdery ' lozenges,' occur on the east of the fault, and may be an anticline of Dartmouth Slate. The Dartmouth Slates contain grits between Langdon Farm and Langdon Court, and the beds undulate. The fault-junction, east of Langdon Court, separates Dartmouth Slates, purple, greenish, and buff, with arenaceous beds and grit, containing fish-remains at Higher Ford, from partly calcareous more or less fossiliferous rocks, often red, in the Meadfoot group, but, further east, south of Knighton, there are no exposures in the immediate vicinity of the fault. A little east of Knighton another deflection takes place, and the boundary is shifted by a cross-fault running E. 35° S., to the Yealm Valley. On crossing the Yealm Valley purple-mottled Dartmouth Slates, of the type seen on Mothecombe beach, are exposed ; but from this point till we cross Newton Ferrers Creek, north of Bridgend, the position of the fault-junction is xmcertain. It either continues in the E. 35° S. direction, or is deflected for nearly half a mile southward by the prolongation of a N. 20° W., and S. 20° E. fault, as shown on the map. The evidence in the - triangular tract between the version adopted and the undeflected continua- tion of the faxilt is entirely inconclusive. From Bridgend eastward the fault has been drawn as well as the very meagre evidence obtainable enabled me to judge, but its exact position cannot be relied upon. Fossiliferous rocks of the Meadfoot group (Taunusian) occur near Pool Mill (Mill on 1-inch map) and their prolongation eastward and the exposure of characteristic Dartmouth Slates near Alston, Whitemoor, etc., just south of our line, justify the position assigned to the fault, but as it follows the strike from the point of its southernmost deflection south of Membland Hall toward the Erme Valley, its exact position is doubtful. Near Pool a quarry on the southern margin of Pool Wood nearly three- quarters of a mile east of Membland Hall, exhibits greenish and purplish slates with cleavage planes dipping southward at 80° partly traversed by cracks which, if bedding, suggest an anticline. On the west bank of the Erme the boundary may be 100 yards north of its position on the map, as, in tliis distance, grey, buff and red slates (which might well belong to the Dartmouth Slates) are exposed, and just beyond grey, red (ologiste) splotched slates (which might well belong to the base of the Meadfoot group) are visible. As far as this evidence goes the boundary might well be a natural uufaulted junction. South of the boundary the purple and green slates seem to contain pegmatite veins, 26 GEOLOGY OF IVTBRIDGE AND MODBURY. Having regard to the termination of the Staddon Grits of Holbeton, at least as a distinct grit series, at the Erme; and in view of the fact that between the grey slates and the grit-shales often glossy and with compact grit beds, in places, which bound the Dartmouth Slates between the Erme Valley and Modbury, and grey slates with shaly grit bands which continue the strike of the Staddon Grits towards Modbury no separation can be made; it is probable that the Dartmouth Slate boundary-fault bifurcates. In this case the northern branch would probably have left the boundary- fault and have passed into the grey slates to the north of it south of Borough Farm, south-west of Holbeton, and may cross the Erme at the south boundary of the Holbeton grits, continuing thence to the schalstein boundary at the east end of Modbury. The fault-boundary probably continues to a point south of Modbury, whence the fault leaving the boundary is prolonged westward to the schalstein boundary. The Dartmouth Slate boundary can be easily traced from the Erme Valley by Butland toward Modbury except east of Great Orcheton, where it may be deflected eastward to include grey interlaminated beds which may be a syncline of the basement beds of the Meadfoot group. The Dartmouth Slates south of Modbury and east of Coldharbour consist of lilac, red and purple even slates or shales with pale-greenish and greyish grit-shales. Between Stoliford and Little Modbury and between Harraton and Fishleigh grey slates have been shown as synclines deflecting the boundary. Near Harraton fossiliferous rocks of the Meadfoot group are exposed. The evidence for a general line of separation between the Dartmouth Slates and lower beds of the Meadfoot group, however, is very unreliable about Whympston House and eastward, and grey rocks occur so often as to suggest that the real structure is an intricate association of both groups through repeating curves which could only be traced in rocks sharply differentiated from one another, and this, as regards the rocka under consideration, is very seldom, if ever, the case. This remark applies to the boundary near Loddiswell, Ashford, etc., already discussed, and is applicable to the northern boundary in which a deflection, between Aileron and Chantry, has been made so as to include grey slates and grit shales, exposed on the west side of the stream valley, as a syncline in the Mead- foot group. Meadfoot Geottp. The rocks of this group may be divided into two series — the lower corresponding to the Looe heds, and to the continental Taunusian — the upper being homotaxial with the Lower Cob- lenzian of the Continent. The organic remains are not sufficiently well preserved and the lithological types are too impersistent to allow of any clear line of demarcation between these subgroups, which will be here referred to as the lower and upper beds of the Meadfoot Group. In our area the lower beds are a variable association of shales, slates, and grits distinguishable by the calcareous bands which include monticuliporoid corals, and numerous organic remains for the most part crushed and indeterminable. The upper beds on the other hand consist mainly of slates with few fossils, occasionally calcareous, and with bands, and locally thick beds' of grit. ' Where the fossiliferous beds are cut out by fault imper- sistent, or otherwise irrecognisable, it is difficult to distinguish the basement-beds of the series from the upper beds From their faulted boundary on the north side of Andurn Point for about 300 yards northward the rocks undoubtedly belong to the lower, or Taunusian, part of the Meadfoot group. In OrownhiU Bay and thence northward to a little distance MBADFOOT GEOTJP. 27 J ^ S s e o o CO ^ 20 I north of the stream in Bovisand Bay we include the rocks in the upper, or Lower Coblenzian, part of the Meadfoot group. The accompanying' diagrammatic sec- tion (Fig. 4) shows the structure of the rocks for about 300 yards northward from the fault near Andurn Point. For the first 50 yards, the rocks consist of lilac or red grits, mostly compact, with impersistent bands of limestone resembling the monticuli- poroid limestone of East Looe beach and else- where, but often decomposed to brown or red- brown residues. The grits form three sharp anticlinals. The central anticline maybe faulted ; on either side of it calcareo-siliceous (decalcified) fossiliferous partly decomposed slates are seen overlying the grits ; their synclinal structure on the south side is clearly distinguishable. For some distance northward the structure is not at all clear. For about 30 yards the cliffs consist of decomposed red slaty (sihceo-calcareous) rocks, red limestone bands of the monticuliporoid type are visible in two places in the beach reefs ; hard lilac-brown grit is also present. Beyond this, for about 14 yards, blue slates are shown in the lower part of the cliff, becoming red upward 5 and affording no distinguishable dip. These rest ! on the calcareo-siliceous slaty rocks on the north ^ which dip under them at an angle of 15°, and > are evidently in an inverted syncline with I steeper limb on the south, possibly faulted. , Red and greyish calcareo-siliceous slates with ] thin bauds of limestone form the section for ] about 60 yards further ; their bedding is, for the most part, nearly horizontal and traverses the i highly inclined cleavage planes. These beds are ' in one place crossed by a small fault. On the north they terminate in a sharp southerly dip bringing in grey and buff slates with quartz veins, for about 14 yards or so, and again emerging with low dip gradually rise northward, to their termination south of Crown- hill Bay. In this part of the coast the rocks are most accessible, the slaty beds, especially near their termination, are very calcareous and con- tain bands of limestone. At their termination the bedding planes are seen to undulate verti- cally, the cleavage planes are well marked and dip south at about 40°. The section contains fossils in the siliceo-cal- careous slaty beds throughout, but owing to decomposition the rock is most often a slaty grit and the fossils top badly preserved for specific identification. The most fossiliferous beds prob- ably attain a thickness of 20 feet and the section above described may not represent more than 100 feet in rocks in vertical thickness. A very much greater thickness is exhibited by the corre- sponding beds on the Tregantle coast.' ' ' The Conntry aronnd Plymouth and Liskeard ' (Mem. Geol. Sm-v.), 1907, pp. 3G, 37. 22265 28 GEOLOGY OF IVYBEIDGE AND MODBUKT. The following list of fossils, obtained at nearly half a jnile south of the Staddon Coastguard station, is an ample indication, of their bad state of preservation. PPachypora cristata (Blumenh.) MonticuliporoidP •Zaphrentid Spirifer sp. Crinoidal columnals Philoxene? PenesteUid PteraspisP FistuHpora ? It is probable that a considerable part of the lower, or Taunusian, beds of the Meadfoot group is cut out by the Andurn Point fault, as below the fossiliferous beds dark slates and grits find grit-shales occur on the south-east coast of Cornwall and elsewhere, and these are probably represented along the boundary of the Dartmouth Slates east of the Erme, and near Loddiswell and East AUington. As it is, however, the fossiliferous beds which characterise, this part of the group, we will now mention instances of their occurrence as we proceed eastward. Their presence is attested by fossiliferous shale, slate and grit fragments (among which besides crinoidal columnals Spirifer sp., Bellerophon sp. and Pleurotomaria ? occur), here and there, on the surface for about three- quarters of a mile from the coast. The next evidence was furnished by surface stones about 200 yards north of Raneleigh at nearly half a mile south of Staddiscombe. These contained the following fossils : — Pleurodictyum problematicum Chonetes cf. saroinulata (Schloth.) Golclf. Tropidoleptus rhenanus Freeh Chonetes plebeia? Schnvr Ctenodonta maureri Beushausen The doubtful anticline of Dartmouth Slates at, and south of, Raneleigh is bounded on the south by grey slates with occasional grit beds which may be the basement beds of the Meadfoot group cut out by fault at Andurn Point. These have an outcrop of nearly a quarter of a mile in breadth and are bounded on the south by_ fossiliferous beds, largely decalcified, of the type described in the coast section north of Andurn Point. These beds aie exposed in Ford Wood (the wood east of Langdon Court) near Higher Ford, in quarries in the Rookery near the north end of Ford Wood, and in several small quarries and exposures west of Knighton, and north-west of West Wembury. They exhibit grey, lilac, red, greenish, and purplish colours. Limestone bands, as on the coast, are visible in the south part of Ford Wood. The planes of schistosity in the Rookery quarries dip south-south-east at 30°, but here and elsewhere it is diflftcult to distinguish bedding from cleavage when the exposures are partly overgrown or masked by talus. The following fossils were obtained in these quarries: — Cf. Pachypora cristata Davidsonia? {Blumenh.) POrthotetes umbrficulum (ScMoth.) Pleurodictyum sp. Spirifer sp. Crinoidal columnals Stropheodonta ? Bryozoon West of Knighton crinoidal columnals and Tropidoleptus rJienanus? Freeh, and north-west of Knighton, near Train (on 6-inch map), Spirifer sp., were found. The Meadfoot group is cut out by fault near Knighton, and the next evidence we obtain of the lower beds is near Membland Hall, in surface- stones at about a quarter of a mile' west of the Hall, and in a small quarry about 550 yards north-east of the Hall on the south side of the Mill (Pool Mill on the 6-inch map). In the quarry red slaty or shaly grit with decalcified, very fossiliferous, material gives a schistosity dip south by east of 42°. The following fossils were obtained: — Pachypora? Rensselaeria P Crinoidal columnals Spirifer sp. Hipparionyx ? Lamellibranch Orthis sp. MEADFOOT GROTTP. 29 The position of the faulted junction of these beds with the Dartmouth Slates on the south as previously mentioned, is vague; it might be at 150 yards south of the quarry but the general evidence seemed to be rather in favour of the position shown on the map. These beds seem to continue along the strike in an east-north-east direc- tion for about a mile and a half. At about a quarter of a mile east-north- east of Alston lilac and grey shales and grit-shales, with red splotches and dark-brown decalcified seams, are exposed. From a point south of Borough Farm the fossiliferous beds are no longer discernable and, as previously remarked, the fault may here bifurcate, a tributary fault continuing along the south margin of the Staddon grits of Holbeton and, on the east of the Erme bringing beds of the Meadfoot group against similar rocks belonging to the Staddon. The boundary-fault is continued to a point south of Modbury, and thence, leaving the boundary, across the slates westward to the schalstein fault-boundary in the valley between the schalstein patches, near the " Site of Battle " on the map. Some fossiliferous brown grit-stones containing brachiopods including Orthis sp. were found on the surface at about 3 furlongs north of Newton Ferrers Church. Small fossils resembling Chonetes were found in brownish slaty grit associated with grey slates, partly red-splotched, a short distance north-east of Great Orcheton. With these exceptions, which may belong to higher beds in the Meadfoot group, no fossils have been found in the rocks bound- ing the Dartmouth Slates until we arrive at Harraton, a mile and a quarter east-south-east of Modbury. At Harraton a grey brown-weathered grit contains crinoidal remains and obscure brachiopods. At a furlong east of Harraton grey brownish- weathered slate or shale contains small flakes of brown residues amongst which traces of brachiopods are recognizable. These fossiliferous beds are so close to our Dartmouth Slate boundary as to suggest, either that there is an intervening fault, or that the boundary is wrong and the purple and red slates south of Harraton may belong to the lower part of the Meadfoot group. The fault boundaries of the Modbury schalsteins are probably prolonged eastward, by Aileron, toward Ham, and between this assumed prolongation and the Dartmouth Slate boundary the rocks are assigned to the lower beds of the Meadfoot group. The surface-stones near the lane north of Ham seem to indicate lower beds, but no approximate distinction can be made east of Aileron between the lower and upper beds of the Meadfoot group. The lower beds are of the same type as those of the Kingsbridge and Ringmore district on the south of the Dartmouth Slate anticline. They consist of grit-shales often interlaminated, or interfilmed, with decalcified material, and of slates, generally grey but occasionally reddish, with occasional grit-bands. The only fossils found were obtained in grey slates or shales, of the type met with north of Instart and in many places along the southern margin of the Dartmouth slates.^ These are exposed near ToUditch Saw Mills, in a quarry on the north side of the road to East Allington, and yielded : — Bryozoon Tentaculites P Orthis .P Pteraspis cornubica (M'Coy) Spirifer sp. Interlaminated beds are exposed in places east of Aileron. ^Tiere the cohesion of the planes permits, these rocks have been quarried for building- stone in the following places: — al>out half way between Pitt Farm and Fallapit Farm ; by the high road north of Mounts opposite the turning to Fallapit Farm ; in two places south of Nutcombe. At half a mile west of Mounts Post Oflice a section shows grit-shales with impersistent dark-brown decalcified films with an appearance of distur- bance. Interlaminated beds aie also exposed at a quarter of a mile west of Torr Rock, near Loddiswell Mill Bridge, near Rake Rock, north of Weeke, and at the Mill south of Ashford. ' 'The Country around Kingsbridge and Salcombe' {Mem. Geo}. Stn-r.), 1904. p. 17. 22265 C 2 30 GEOLOGY OF IVYBEIDGE AND MODBURY. 'I Gnarling is often shown by the grit-shales in the neighbourhood of Loddiswell, both in those referred to the lower part of the Meadfoot group and to the Dartmouth Slates. In one exposure, by the high road near the Avon, the gnarled grit-shales dipping at from 30° to 40° southward were seen to rest on slates with cleavage-planes inclined in the same direction at 50°, separated by a crack, representing a bedding or thrust plane, from slates below with nearly vertical cleavage-planes. We must now return to the coast-sectiou to foUow the higher beds of the Meadfoot group, as they cannot be studied satisfactorily in any other part of the map. The decalcified f ossiliferous beds are succeeded at a quarter of a mile south of Bovisand Bay by tough dark slates or shales with which their junction is very obscure. This obscurity is due to uncertainty as to whether the undulating well-marked planes of the dark rocks represent bedding or cleavage in a stack of rocks on the beach just near the vertically-undulating termi- nation of the fossiliferous beds, as the main cliff is here too weathered and overgrown to afford reliable evidence. I believe the planes to indicate bedding and that the structure is here, as shown in the diagram (Fig. 5), complicated by a thrust intersecting a sharp synclinal plica- tion and cutting out the slates which imme- diately overlie the fossiliferous beds. Prom here to Bovisand Bay the section dis- plays these hard partly calcareous shales in, or 3 under, the grey slates with cleavage planes s dipping southward at angles of from 20° to 60°. -, If the undulating planes of the harder beds can * be relied on the whole series may not attain to II 200 feet in thickness. It is by no means certain 3 that these rocks should not be included in the 3 Taunusian or lower part of the Meadfoot group. -I They are not unfossiliferous, but relatively much s" less fossiliferous than the slaty beds with monti- Orj ')W\\ % culiporoid limestone seams with which they '^ are in junction on the south. Zaphrentids, crinoidal columnals, and other fossils (partly replaced by pyrites) are met .with, here and there, and dark grey and reddish nodules or concretions, apparently in part fossiliferous, also occur in them. The following fossils were obtained at the northern angle of Crownhill Bay in dark calcareous shales : — Pleurodiotyum sp. Zaphrentid. Crinoidal remains. Rhabdomeson? gracile (PhiU.). Orthis? Gasteropod (indet.). Orthoceras sp. Pish remains. Near this, on the south, the fossils are prob- ably distorted along cleavage-planes. There are indications of fault in three places, and a cleft on the north of the small promontory may also mark a fault. In the small promontoi'y the calcareous shales exhibit a tendency to gnarling which is also displayed by thin quartz veins in the slates. To the south of the pTomontory the dips of schistosity range from 20° to 45°, and the structure IS not clear MEADFOOT GEOUP. 31 Between downhill and Bovisand Bays the projecting coast-line is in- dented hy four small coves. Proceeding northward to the first of these the reefs are composed of hard undulating dark, partly calcareous, shales gnarled in places. There are appearances on the south margin of the reef which suggest nearly vertical bedding. Zaphrentids were found near the first cove, and between it and the second cove the same rocks occur. Between the second and third cove the same rocks form a pointed headland and dip sharply to the north-west and are intersected by cleavage-planes dipping in the contrary direction at 40°. These beds are faulted on the north and a band of pale-biift brown-weathered igneous rock occurs in the and in the next cove. From here to Bovisand Bay the section displays hard bands of partly calcareous siitstone, locally much gnarled, and slates with impersistent bedding planes. The section for about 60 yards, at the promontory forming the southern shore of Bovisand Bay shows dark grey slates with cleavage-planes dipping at 40°, crossed by undulating indications of bed- ding and mixed up with plicated bands of siitstone at a fault. From 5 to 10 feet of head overlies the slates. Finely cleaved dark slates may be seen between more or less gnarled pale grey siitstone bands in the beach reefs. The slates also, here and there, contain thicker bands of grit. Fig. 6. — Beach Reef, Bovisand Bay. Showing bedding and cleavage. In the bay these beds are faulted against siliceo-calcareous slates which are either a reappearance of the fossiliferous lower beds, or a separate occurrence in the Crownhill Bay series. In either case these beds must be faulted against those exposed in the cliffs just north of the Bovi.sand Valley. The bedding-planes undulate and are very distinct, on the whole dipping northward. As shown in the sketch (Fig. 6) the cleavage-panes dip in the contrary direction, at from 20° to 30° where the bedding is highly inclined, and from 60° to 80° where it is nearly flat. Fig. 7. — Bovisand Bay. Very pretty examples of the relation of bed- ding and cleavage luo to be seen in these beds. The accompanying sketch (Fig. 7) illustrates one of these — slates, with nodules tilted along the cleavage planes just above a band of soft gnarled shale, overlie a bed of hard brown siliceo-cal- careous rock. Although this bed seems to have protected the base of the overlying slates and produced fine puckering in them, for an inch or so, it exhibits a coarse cleavage. It is of course possible that the nodules may represent a dis- membered hard band which also to some extent Cleavage and bedding. protected the shale-band below. The rocks terminate on the south side of the Bovisand stream where they form conspicuous beach-reefs. Traces of fossils, possibly including Chonetes, were rarely noticed on the bed-surfaces in the beach-reefs. 32 GEOLOGY OF IVYBRIDGE AND MODBURT. The inland prolongation of the Crowuhill Bay series does not appear to extend much further east than Bovisand Lodge where it is cut off against the Staddon Grits on the north by a nearly east-and-west fault. Proceeding along the coast from the Bovisand stream flat toward Staddon Coastguard Station the upper beds of the Meadfoot group occupy the cliffs for about 100 yards. The section (Fig. 8) commences with a mass of bluish-grey brown-weathered grit, very irregularly broken by joints and cracks sometimes filled with quartz. Under this blue-grey shales with bands and beds of grey brown-weathered grit come on toward a fault, which cuts them off against dark grey shales with bands and interlamina- tions of hard grey grit, disturbed and gnarled near the fault. Between 20 Fig. 8. — Coast for 120 yards north of Bovisand stream. Scale, 1 inch = 40 feet. and 30 yards from the fault irregular masses of hard grey grit come on and, much contorted and disturbed, occur at intervals in the shales with thin grit bands, which at the axes of contortion become slaty. At about 70 yards from the fault these beds are in junction with hard lilac and red grits, very often shaly, which appear to be the basement beds of the Staddon Grits. The junction is marked by irregular zigzag contortions and, al- though probably faulted, there is no reason to think that there is a dis- location of any importance. The coast-section south of Brixham furnishes a parallel junction sequence, for there the Meadfoot shales and interlaminated beds contain masses and beds of hard grey brown-weathered grits of an impersistent character. The exposure of these rocks is confined to the coast, as they are faulted out between there and Bovisand Lodge. From the Yealm at Shortaflete Creek the upper beds of the Meadfoot group bound the Staddon Grits on the south as far as Borough Farm, south-west of Holbeton. In the dark slates and shales grits are occasionally exposed. North of Membland HaU grits and grit-shales are rather prevalent in the slates. The termination of the Staddon Grits at the Erme, east of Holbeton, renders the age of the slates with occasional grit beds which continue their strike from the Erme towards Modbury uncertain. As before mentioned, it is highly probable that a fault runs along the southern boundary of the grits and in its continuation towards Modbury cuts off slates and grits belonging to the Staddon series, on the north, from rocks' of the Meadfoot group undistin- guishable from them (owing to paucity of exposures, &c.), on the south. Between the Staddon Grit boundary near Edmeston and Modbury there is a triangular area evidently bounded by faults of which there is no evidence on the ground; its base is the Staddon grit boundary and its apex at the west end of Modbury. As evidenced by the high road the rocks here consist of dark grey buff-weathered slates with vertical and highly inclined planes of schistosity. In these interlaminated beds occur which show gnarling and, at about 300 yards west of Fancy (on the 6-inch map), purplish sheared grit, often thinly laminated and with sericitic films, is exposed by the high road. These grits are about 20 feet thick in all, and seem to be a sharp synclinal axis of basement beds of the Staddon Grits, somewhat similar to those exposed on the coast near their junction with the Meadfoot group. As regards the country east of Modbury, the Staddon Grits of Halwell, in part assuming the character of quartzites, are continuous past Morleigh over Blackdown Camp and Heathfield (near Coldharbour Cross) to Heath- field (near Babland), where they are in line of strike with the granophyre of Whympston House, and the Dartmouth Slates in which it occurs. As STADDO^" GKITS. '->-J already pointed out, this seeming continuity of strike led De la Beche to connect the rocks of Blackdown Camp with those of Erme Mouth, as a continuous series. The house not named on the 1-inch map, between Babland, Heathfield, and Harraton, is called Heathfield Down. At about 200 yards north of it the quartzite beds are exposed in a small quarry, and in the intervening distance they are cut off on the south by the easterly prolongation of the faults which bound the schalstein patches from here to Modbury. The prolongation of these faults is so hypothetical that, beyond a broken indication toward Ham, no line can be drawn on the map to justify the probability that the line of dislocation may continue eastward. The surface evidence throughout this part of the district is very un- satisfactory. The separation of the grits from the slates, owing to this and to the association of the slates with them, in variable and sometimes preponderating proportion, is not always reliable. Whilst we would refer tlie slates to the south of the Black- down Camp and Halwell quartzites and grits to the Meadfoot group, we cannot be sure that the grits south of Stanborough House, Moreleigh, and Preston Combe may not through assimi- lation in character be also represented amongst them. As, however, the colours for Lower Devonian grits and slates only denote the Staddon grits and the Meadfoot group, respectively, where the fo;rmer can be traced as a grit series and the latter mainly as a slate group, the partial assumption by either group of the characteristics of the other gives the colours used on the map merely a lithological vahie. The evidence on the ground does not enable one to ascertain definitely the extent of such changes in character, so that it would not be advisable to dis- tinguish them by letters or other signs on the map. Staddon Grits. Under this head we include — all the areas coloured as Lower Devonian grit, although these may include masses in the Mead- foot group' — slates where the junction-beds of the Middle and Lower Devonian appear to be repeated by plicatioii in such a way that no boundary can be dra^u, as between Puslinch south of Yealmpton and Modbury — slates which may be Middle Devonian, or belong to the Staddon series through replacement of the arenaceous beds as between Modbury and Halwell, which, although perhaps more Middle Devonian than Lower, are coloured as Lower Devonian slates, the same coloiir as that used for the Meadfoot group with which they must not be confounded. On the coast, the inverted lower beds of the Staddon series, commencing at their junction with the Meadfoot group, consist of lilac and deep red shaly grits, yellowish-gre}', red, and lilac, red-mottled and locally banded, shales with beds of compact red or lilac grit dipping southward. At 160 yards from their commencement the red and variegated grits and grit shales are contorted and faulted at a wall which here conceals a recession in the cliff face for a few yards. Beyond this for 44 yards on either side of a shoot pipe the variegated rocks are much contorted, and in part assume a grey tint. From here to Staddon Point the coast coincides more or less with the strike. The shales or mudstones and grits in the Staddon Point reefs are grey and pale greenish-grey. Hard, irregularly jointed, red-brown grits occiu- near the Point. There is a large quarry above Staddon Point Fort, by the path leading from thence to the summit, now enclosed in War Depart- ment land. In this quarry hard red grits and purple-brown grits, very 34 GEOLOGY OF IVYBEIDGE AND MODBTTEY. shaly in part and containing obscure plant remains, are associated with shales or mudstones of similar colours. There are several beds, of from 2 to 3 feet in thickness, of conglomeratic character, and apparently due to contemporaneous erosion.' These brecciated, or conglomeratic occurrences have been noticed elsewhere in the Lower Devonian grits of the Meadfoot and Staddon groups.^ The Staddon Grits are exposed in the ditches surrounding the Forts. On the coast they are everywhere violently contorted, and faults have been observed just south of Leek Bed Bay and at Eamsoliff. Tip to Ramscliff Point the strike is generally W. 15° S. to E. 15° N., but from Ramscliff Point northward the strike is nearly SW. and NE. ; at Wyatts Way it is W. 42° S. and E. 42° N. ; being therefore more or less coincident with the direction of the coast. Leek Bed Bay has been refei'red to in the Plymouth Memoir, certain patches of grey interlaminated rock, there seen in contact with an intrusive igneous rock, may possibly be connected with upper beds of the Meadfoot group displaced by the eruptive mass. Just north of Staddon Pier the contorted grits display a small thrust plane. The accompanying sketch (Fig. 9) shows the contortions in the foreshore reefs on the north side of Leek Bed Bay. Fig. 9.— North of Leek Bed Bay. Contortions in Staddon Grits. At Ramscliff dark grey cleaved mudstones are associated with red or lilac- grey compact grits. The fault determines the soiithern shore of the cove, and the rocks on either side are contorted in zig-zag minor curves. At Wyatts Way the rocks consist of irregular grey slaty micaceous grit, slaty mudstone, and fine-grained hard red grit. The cleavage is most Fig. 10. — Wyatts Way, structure. pronounced at the axis of the inverted fold shown in the sketch (Fig. 10). Interlamination is also well shown the dark grey mudstone : — Lingula ? Rensselaeria strigiceps? (F. Boem.) The following fossils were obtained in Spirifer hystericus (Schloth.) Bellerophon sp. Tentaculites sp. ' The Country around Plymouth and Liskeard' {Mem. Geol. Surv.), 1907, p. 41. ' The Country around Torquay' {Mem. Geol. Surv.), 1903, p. 16. STADDON GIUTS. 35 The contorted character of the rocks is best seen by looking along the coast in either direction from Wyatts Way (Fig. 11), although as the cliff seldom exceeds 50 feet in height and is partly concealed by \\ash and talus from the steep slope above, which is covered by grass and undergrowth, the contortions are only prominent here and there. Fig. 11. — From Wyatts Way, looking towards Ramscliff Point. Contortions in Staddon Grits. At about a quarter of a mile from Wyatts Way the Staddon Grits make afi inverted, and apparently thrusted and faulted, junction with the Middle Devonian slates. The bedding of the latter is shown by brown bands, nodules, and, occasionally, by calcareous bands and lenticles, and in part by interlaminated harder bands. When first noted in 1893 the very great resemblance of these Middle Devonian beds and of the igneous rocks of Toroross type which occur in them to the rocks in the Torcross and Tinsey Head coast, then recently mapped, led me for a time to regard them as contemporaneous. On the north of their junction with the Staddon Grits the Middle Devonian slates are repeated by numerous curves which bring up quartzose grits, in places, on the foreshore. At 360 and 400 yards north of the junction quartzose grits are seen in the cliff. The exposures are not suflBciently clear to enable one to trace the sharp anticlinal structure in them or to say to what extent their appearance may be due to faiUting. The main junction is too faulted and obscure for illustration. The section taken from Jenny Cliff northward (Fig. 12) represents a distance of about 230 yards. Fig. 12. — Coast section for 220 yards north of Jenny Cliff. Horizontal scale, 1 inch = 40 yards. At Jenny Cliff (A.) grey slates with cleavage planes dipping southward at 16° to 23° exhibit, by hard bands and nodules, generally brown-stained, more or less vertically-undulating or with zig-zag bedding, broken by small 36 GEOLOGY OF IVYBEIDGE AND MODBUHY. thrusts. In places silty and calcareous interlaminations show the bedding at the southern point of the headland. On the north of the headland beyond the outlet of a sewer, similar slates with contorted indications of bedding and calcareous films, sometimes crinoidal, continue the section. They are faulted at T. and F. Thin gnarled red bed-bands occur near the fault, the bedding being nearly vertical and the cleavage planes dipping southward at 19° to 26°. At B. masses of quartzite or quartzose grit occur at the end of a small promontory, apparently the continuation in strike of the exposure of Staddon Grits a little further on at C. At C. in the cliff above the grits horizontal beds of hard shale with lime- stone were noticed and, here and on the south side of the grits, cleavage and bedding appear to be more or less coincident. Between C. and D. the slates are occasionally visible with southerly- dipping cleavage planes, at 30° to 40°. Numerous hard brown bands denote bedding, but the section is mostly overgrown. At V. a slaty igneous rock is visible. At X. about 4 feet of hard grey grit is exposed with slates above and below. This is probably a very sharply folded axis of Staddon Grit which is exposed at D., where the beds of quartzite make a small promontory, probably along a faulted anticlinal axis. Beyond the grit (D.) the bedding in the Middle Devonian slates is shown by harder brown bands, occasionally not cleaved, dipping southward, at first at 70° and further on at 50°. The cleavage-dip is southerly at from 32° to 35°. Beyond this the section will be described in the Middle Devonian chapter. The junction of the Staddon Grits and Middle Devonian slates is gener- ally marked by a dominant feature made by the latter, but such repetitions as those displayed in the above section are no doubt the explanation of uncertainties as regards the actual boundary near the coast, between Staddiscombe, Spriddlestone, and the Yealm, and, more especially, between Wrescombe, south-west of Yealmpton, and Modbury. At over half a mile south of Turnchapel Station, 500 yards south of Lower Hooe on the 6-inch map, brown fossiliferous grit fragments con- taining Tentaculltes sp. were noticed among the surface stones. On the whole the Staddon Grits are well evidenced between the coast and Staddiscombe, but at Staddiscombe we encounter one of those breaches in their continuity which are so frequent in their outcrop east of the Erme. In this case the distribution of the fossiliferous beds of the Meadfoot group and Dartmouth Slates about llaneleigh and Knighton, already de- scribed, proves the apparent breach in "continuity to be due to faults. One of these bounds the Staddon Grits between the Yealm and Staddiscombe on the west and may continue, as their boundary with the Middle Devonian, beyond Staddiscombe, towards Hooe, or may unite with the other fault at half a mile south-west of Staddiscombe. The other fault is that running north west from Langdon Court. Between Raneleigh and Staddiscombe there is no exposure to guide one in forming an opinion as to the convergence or parallelism of these faults. At about half a mile east-south-east from Staddiscombe red, green, and mottled gi'its, with beds brecciated with fragments of shale, were seen in a quarry. Similar grits are evidenced towards Knighton, but north and east of Knighton there are very few exposures ; the grits seem to be mostly grey or dull coloured and often associated with grey slates. These are probably the upper beds of the Staddon Grits overlain on either side, between South Wembury House and Wheal Emily Antimony Mine, by Middle Devonian slates. In any case it is very probable that undetected faults affect the relations of the Staddon Grits on either side of the Yealm. Just north of Crawl Wood, opposite Steer Point, the strike of the Lower and Middle Devonian runs along the coast towards Puslinch. In West Wood, on the 6-inch map, there appears to be a passage, grey Middle Devonian slates with occasional limestone bands being succeeded by slates with grits and grit-shales, grey, lilac, red and buff. STADDON UHITS. . 37 On the Crawl Wood coast grey and dull greenish grits occur. South of Collaton there are quarries on either side of the valley, in lilac and purplish grit and irregularly-jointed slate or mudstone and in hard blue-grey, rather slaty, gi-it and slate. South of Gnaton Hall purple-brown irregularly- jointed grits and sandstones and arenaceous and argillaceous grey and greenish shaly and intei-Iaminated beds are exposed. South of Creacombe and half a mile east-south-east from Gnaton Hall there are obscxire traces of fossils in a quarry in purple, buff, red, and grey micaceous sandstones and irregular shale or mudstone dipping south at 30°. Here and south-west of Lusou there are beds brecciated with shale fragments. In Holbeton green, buff, red, and grey sandstones, arenaceous beds, grits, and shales are exposed. Between Creacombe and Holbeton the grits as a distinguishable mass give an outcrop three-quarters of a mile in breadth, but east of Holbeton it decreases to a quarter of a mile and there are fewer exposures. On the west bank of the Erme hard grey, red, and green grits and sandstones are evidenced, but on the east bank their south margin only seems to be prolonged, for half a mile by shaly arenaceous beds with some grit. At a quarter of a mile further along the strike grey shaly grits are again evidenced and seem to carry on this horizon to Modbury. To foUow the northern boujidary of the Staddon Grits as a mappable grit series we must now return to the Yealm. The grits and shales, or mudstones, mostly of lilac red, purple, and green colours, but occasionally grey, are evidenced from West Wood eastward to three-quarters of a mile beyond Wrescombe. A tongue of grey beds, which seem to be mostly slates or shales, here runs from Lolesbury westward, on the north of Gnaton Hall and Collaton, to Collaton Cross. The evidence is indefinite and of a similar character to that of the belt of country coloured as Lower Devonian slate on the north of the Staddon Grits, to which we will now refer. South of Puslinoh beds of grit, grey weathering brown and associated with slates, are exposed in the road, but beyond these the evidence does not admit of mapping grits on lithological grounds. From here to Modbury the surface evidence is suggestive of grey slates or shales with beds of grit and grit-shales. In a small quarry, half a mile south-east of Dunstone, 10 feet of very hard grey grit beds form an anticline overlain by grey slates, or shales, partly siliceous. Hackly grey grits and slates are exposed by the road near Dunstone. About Ford nothing but grey slates or shales nere noticed, and traces of grit were very seldom seen between the Ford Valley and the Staddon Grit boundary on the south; also in the prolongation of this horizon, on the strike, westward to Fursdon and Crebar, and from the Erme towards Modbury. On the north of the Ford Valley at Flete Mill Cottage there is a quarry in hard, irregular, blue-grey grit and slate, or shale apparently plicated. Grey grit-shales were seen about a hundred yards to the north. Similar evidence was noted at Hole. At about a quarter of a mile north and north-east of Hole there are evidences of the occurrence of red grits and shales. The patch of Lower Devonian near HoUowcombe was drawn from somewhat similar evidence. On the east of the Erme, in the higher part of Putt Wood, north-west of Little Oroheton, there are quarries in grey slates, or shales, with hard grey and pale buff grit beds. Similar grits, in part compact and shaly, occur by the road south of Goutsford Bridge. The boundary of the rocks we have been following is shown on the map ; it is a fault, or else there is an east and west fault bounding the schalsteins on the north of Flete and at Goutsford Bridge, and this fault uniting with one north of Sequers Bridge continues to Modbury school. West of Modbury school we have described a fault-bounded tract of rocks of the Meadfoot group with a sharp syncline of rocks referred to the 38 GEOLOGY OF JVYBEIDGSi AND MODBUEY. Staddon Grits between Fancy and Edmeston. If this opinion is correct the junction of these beds with the Staddon Grits at Edmeston is inverted. Near Edmeston red and purple grits, part shaly and shales are exposed in quarries, and Staddon Grits stones occur on the surface. The Staddon Grits are further evidenced by surface fragments between Sequers Bridge, the Fawns, and Edmeston ; but east of the Fawns towards Sheepham, between Strode Farm and Edmeston, their irregularly faulted relation to the Middle Devonian slates are not clearly distinguishable, and their connection with the mass between Sheepham Mill and Stockenbridge is doubtful. The evidences of characteristic Staddon Grits as we follow their northern outcrop are so irregular that purely lithological boundaries would give a series of patches between which slates very largely predominate, and grits are either interbanded or represented by impersistent beds, or arenaceous The red, buff, and purple grits north of Modbury seem to die out towards Stockenbridge. At half a mile further on they again become barely recognizable in a series of small patches, and at a mile from Stockenbridge buff, red, and green grits, grey brown-speckled grit-shales, etc., can be traced for a mile. Obscure traces of brachiopods were met with in brownish, irregular, probably lenticular, grit north-west of Brownston and east of Yarnicombe. About half a mile west of Brownston a quarry shows an anticline in grey mudstones, on the south of the line drawn to include the above evidences of grit. There is no evidence for continuing the grit north of Brownston Cross to the adjacent patch on the east which can be followed by surface stones to the Avon valley, but on the south seems to merge into grey slates or shales. Another recognizable patch of grits is evidenced by surface stones at, and west of, Crabadon Cross. To the south of this is a most indefinite tract where grey slates or shales, grit-shales, and occasional grit bands are evidenced. The Crabadon Cross grits may be litho logically continuous with those of Halwell. Some diabase stones at the bottom of an old quarry in red shaly grits, mostly overgrown, near Crabadon Cross on the north- west, suggest intrusive rock. The patches coloured as Staddon Grit near Coarsewell and by the Avon, to the east, are evidenced in the former case by a few surface stones, in the latter, on the west of the Avon, by irregular blue-grey, brown-weathered grits, and on the east by shales with irregular, broken, whitish grit and brown brittle grit, exposed under old river deposits in the railway cutting. The Staddon Grit outcrop is 5 furlongs in breadth north of Halwell and 7 furlongs north of Moreleigh. Hard grey, greenish, red, and lilac grits are exposed in quarries at Halwell Cross, Halwell, 3 furlongs north of Halwell, north and south of Boreston, nearly half a mile west of Boreston and at a quarter of, a mile further west. Only the southern part of this outcrop can be traced continuously west- ward, as a lithologically distinguishable series, on the south of Farleigh, across the Avon at Storridge Wood, and extending over Blackdown Camp to the fault between Babland, Heathfield, and Harraton. In this extension the grits are mainly quartzose, or quartzites. Fer- riferous particles and red-stained cracks, denoting a tendency to cleavage, often give the beds a pale lilac tint. The red staining also accompanies traces of brachiopods in them, which have been detected in the following places — at a little more than 3 furlongs south of Higher Storridge, east of Storridge Wood, where the markings resemble Bensselaeria and Rhynchonella — in the quarries near Hangman's Cross, 9 furlongs due west of Blackdown Camp, where whitish quartzose quartz-veined grits, associated with grey shales contain Bellerophon ? In Storridge Wood, by the Avon, the grits are often shaly, almost like quartz-schists in places; they occur as beds in the shales, but further south assume a more massive character and occaionally contain yellow-brown powder, suggestive of decomposed fossiliferous material although no trace rf fossils was found here. STADDON GEITS. 39 On the north of these quartzose grits grey slates, apparently devoid of grit bands, occur at Farleigh, and from thence very irregularly westward to Modbury. Whether these are a mass in the Staddon Grit series, irregu- larly developed between the quartzites on the south and the more fels- pathic grits on the north; basement beds of the Middle Devonian in syn- clinal plications; or upper beds of the Meadfoot group is not clear; but, from the irregularity the distribution of grit in the upper division of the Lower Devonian, we incline to the first view. On the south of the Halwell, Moreleigh, and Blackdown Camp grits and quartzites grey slates or shales again occur. They are best evidenced in the roads south of Halwell where they extend for half a mile southward, separating the Halwell grits from quartzose grits which as a lithologically mappable series are most irregular, the intervening slates being about 380 yards across at Moreleigh, only about 100 yards across at three-quarters of a mile further west, and 3 furlongs wide in the Avon Valley. Washes from the quartzites on the north frequently obscure the slates, especially north of Stanton. At the fork in the roads north-west of Wizaller a decomposed igneous rock occurs near the grit and quartzite boundary. The evidence for connecting the grit mass of Stanborough Camp with the Preston mass, by way of Moreleigh Hill Brake and Chilley, is not satisfactory. The same may be said as regards the dying out westward of the Preston grits, which may continue past Combe and Woolston, and as regards the patch of grit north of Wood Barton. It is difficult to regard these grits as a different series from those on the north, and they exhibit many of the varieties met with in the Staddon group in this and the adjacent map on the east (350). At between a quarter and three-eighths of a mile south-east from Stan- borough House fossiliferous quartzose grits of the Warberry type (but with orange-brown ferriferous interstitial matter) are scattered over the surface. Some of these proved to be very fossiliferous containing numerous examples of BcUerophon tiimidus 6. and F. Sandb. and fragments of Homalonotus sp., besides moulds and casts of brachiopods which resemble those found in Blackdown Camp grit and quartzite range south of Higher Storridge, already referred to, and those in the quartzose grits near Quarryhead Wood, Blackawton, in Sheet 350. In the New Cut, Lincombe Hill, Torquay, Champernowne discovered the Homalonotiis that bears his name in similar grits, and Bellerophon was obtained by the writer in the same beds. On the west side of Stanborough Camp there are quarries in cleaved lilac grits, which exhibit in one quarry anticlinal structure. At about half a mile west of ' Old Man ' Camp there was an exposure showing 20 feet of shaly lilac-red grit near the margin of the alluvium. In the Lowerdale Copse, near Morleigh Hill Brake on the south-west, there IS a quarry in massive hard grey grits and slaty mudstones. At, and near, Hendham, there are exposures — of grey slaty mudstone and grit dipping at 30° southward with cleavage in a similar direction at 55°, in a small quarry west of Lower Hendham — of grey, greenish, and yellow-brown arenaceous rocks at Higher Hendham, and of red mottled grits in an old quarry within a quarter of a mile to the west. Further east grey and brownish grit stones and hard grits, in Bedlime Wood, prove they cannot be traced, but they may be represented by buff arenaceous the extension of the Higher Hendham beds to the Avon. Beyond this rocks dipping south at 45° in » quarry between Woolsfx)n House and Wigford Cross and by similar materials west of Aveton and by hard quartz- veined brown grits in the grey slates or shales on the south of Woolston. Round Preston the grits and shales are mostly grey. Red grits, partly quartzose, in places of the Warberry type, are evidenced near Capton and Preston Cross, also near Lower Preston Cross. North of Preston a mass of diabase is shown on the map. A large diabase boulder was seen between Preston Cross and Capton in a field adjoining the latter place. Towards Wigford dull coloured grits and grey grits and grit-shales are evidenced and, south of Wigford, green and grey sandstones and quartzose grits. There is not sufficient evidence to trace these beds to Stanton and Cbillatoij. 40 GEOLOGY OF IVTBRIDGE AND MODBUEY. The patch of grit north of Wood Barton is evidenced by reddish and greenish grit fragments, and between the broken lines, denoting its probable eastward extension, grey and greenish grit stones are occasionally seen on the surface. Unless these grits are in the upper part of the Meadfoot group and not, as we suppose, the basement beds of the Staddon Grits, their proximity to the Dartmouth Slates (north-west of Grimpston- leigh) renders the intervention of an east and west fault cutting out part of the Meadfoot group very probable. Such a fault prolonged eastward might acount for the mass of grits in junction with the Dartmouth Slates at Dartmouth, but leaving their boundary and running from Woodbury Camp toward Blackawton, in Sheet 350. 41 CHAPTEE III. IGNEOUS EOCKS IN THE LOWEE DEVONIAN AEEA. The igneous rocks in the Lower Devonian comprise both acid and basic groups. Both betray evidence of shearing, but some of the harder and larger masses which, being associated with much softer clastic materials, have escaped with the doubtful exception of some very small patches of felsite hereafter to be specified. As in most cases the igneous rocks follow the strike of the slaty rocks in which they occur, the field evidence being incon- clusive we cannot with certainty distinguish interbedded con- temporaneous rocks from intrusive sills. Prom the vicinity of the Erme Valley eastward the acid and basic rocks can be easily distinguished, but west of this no acid rocks have been detected. In the western area even the larger patches, as at Warren Point and Season Point, are inconspicuous on the 1-inch map, whilst throughout the Lower Devonian area there are numerous patches of rock too small to be shown, and for the most part too decomposed, sheared, or otherwise indefinite in character to give any results to the petrographer, whilst they betray just sufficient difference from the known clastic rocks to enable the stratigrapher to detect signs of possible igneous origin. As few specimens of the basic igneous rocks of the Lower Devonian area were collected during the mapping of the area (during the years 1892, 3, 4), most of these with localities will be given in this notice. , We will first mention the acid rocks, then the basic rocks as far as petrologically examined. Owing to the paucity of names on the 1-inch map it will often be necessary to refer to the 6-inch maps. Acid Eocks. The most conspicuous rocks of the acid group occur in a belt of country stretching west-south-west from Whympston House and Stoliford, south-east of Modbury, to Tor Eock 5| furlongs north of King-ston Church, a distance of 2| miles. In this belt of country there are signs of several bands of felsitic rock, which we will now trace. The largest band is exposed in a large roadstone quarry near its eastern termination between Whympston House and Stoli- ford, where it is bounded on the south by buff slates. On crossing the valley a quarter of a mile south-west of the large quarry the rock is again exposed in an old quarry near its southern margin, at which lilac slates are seen dipping south- east at 85°. At 3 furlongs west of this banded felsite is ex- posed in a small quarry. Up to this point the mass can be easily traced, but among the surface fragments of this rock 42 GEOLOGY OF IVYBRIDGE AND MODBTTBY. at a furlong east-north-east of the small quarry there are some shaly fragments of a sheared rock of a type with which I am familiar in the Dartmouth Slates and consider to be prboably a highly sheared felspathic tuff, christened the Brookhill type from Brookhill near Kingswear, where it was iirst recognised. For about 7 furlongs from the small quarry there are no ex- posures, and the surface evidence when the ground was mapped was practically nil. At a point north-west and west of Shear- langstone the felsitic rocks are again exposed, also rocks of Brookhill type and slates on their northern border all dipping in the same direction between south-east and south-south-east and apparently conformable. The felsite is continued in Wastor Wood, a quarter of a mile west of Shearlangstone, and strikes west for a quarter of a mile where it ends. The rock from Whympston Wood (1828)* is a pinkish spherulitic felsite containing phenocrysts of quartz and alkali-felspar. The quartz crystals have been much corroded, but they not infrequently show marked traces of idiomorphism. The groundmass is mainly formed of spherulitic aggre- gates of quartz and alkali-felspar. Scattered aggregates of hematite give the rock its purplish colour. The specimens from a locality next to Wastor Wood (1821-1825) are grey or greenish-grey, banded or nodular felsites. Much fine sericitic mica has been developed at the expense of the felspar and in the nodular varieties (1824) the cores of the nodules consist of crystalline aggregates of quartz. These rocks probably represent rhyolites which have been more or less silicified. The next band is exposed in a quarry at 150 yards south of Shearlang- stone. The north-easterly prolongation of the rook for half a mile from the quarry was justified by surface fragments, but beyond this its extension is very doubtful. The prolongation of the rock from Shearlangstone west- ward to Tor Rock is evidenced by surface stones for about 3 furlongs from the quarry, beyond which no evidence on the line of strike was met with until we encounter the craggy mass of Tor Rock about a quarter of a mile further on. Following the line of strike westward at 3 J furlongs from Tor Rock there was some evidence of pegmatitic quarlz, but otherwise nothing to justify the prolongation of the rock was seen. The rock from the quarry south of Shearlangstone (182(5) is a purplish felsite composed of idiomorphic crystals of alkali-felspar embedded in a groundmass which is partly crypto-crystalline and partly spherulitic. Evidence of a third band similar in character to Tor Rock was obtained in a small quarry by the turning to Shearlangstone, at 150 yards south-east of Tor Rock; in a surface exposure at 150 yards south of the Shearlang- stone quarry and east of Wastor (a farm less than a quarter of a mile south-south-west of Shearlangstone). Midway between these exposures similar rook was seen by the road but it could not be proved in situ. There is a suggestion of pegmatite in the slates at 100 yards south of that previously noted as a possible indication of the prolongation of the Tor Rock band. Otherwise there was not evidence for connecting the exposures in a continuous band. A specimen from the locality east of Wastor is a compact rock mottled dark green and red. In composition this rook is similar to the one from Shearlangstone quarry, except that the pheno- crysts ot alkah felspar are absent. It is a brecciated felsite. The next group of felsitic rocks is met with near Bennick, 5J furlongs east of Whympston House. These consist of four isolated exposures beyond which they can only be traced far enough to determine that their directions are north or north bv east. * These numfeerB refer to microscopic slides in the Survey Collection. LOWER DEVONIAKT IGNEOUS KOCKS. 43 The most northerly of these is evidenced by the road between Bennick and Harraton at about 200 yards north of the former place. Its line of direction meets that of felsite striking north of a small quarry about 100 yards to the south of Bennick. There was no evidence for connecting the exposures or for ascertaining the strike of the slates in their vicinity. The next exposure is in a quarry at the west end of a wood at a furlong south-east of Bennick, the felsite here runs north by east, and the same direction is exhibited by the next exposure at 200 yards east in a quarry at the east end of the wood. Not far from the last exposure there is a quarry in greenish slates and quartzose grits dipping south-east; their strikes suggest that these rocks are of subsequent date to the folding. They form the dovibtful exceptions mentioned in the early part of this notice. The next exposures of felsite are of the same character as those included in the first group. Under the microscope they are seen to be traversed by films of sericitic mica and to possess other characters which prove that they were present when the adjacent sediments were folded and cleaved. The felsites of this group are, therefore, quite distinct in point of age from the well- known elvan-dykes which were intruded after the folding movements had ceased. They are met with in an outcrop in Putshill Copse at 3 furlongs east- north-east of Woodleigh Church and can be traced in a thin band running north-west for 200 yards. On the opposite side of the valley, about 200 yards west of this band, the surface stones gave indications of the presence of felsite. The only remaining exposure of felsite observed in the Lower Devonian is 7 furlongs to the east of the Putshill Wood band, in an overgrown quarry just between Fallapit House and Mounts Post Office. The felsite (1829) was exposed in a very small mass in the lower part of the pit. There is no evidence for extending it on the surface beyond the pit. In microscopic character the rock is identical with that of Whympston Wood. Basic Rocks. In the notes on the Middle Devonian coast section the resem- blance of some of the igneous rocks to those naet with in the Torcross Lower Devonian section has been referred to. This resemblance is accentuated by the examination of the harder diabases associated with the Middle Devonian schalstein tuffs and lavas as they are traced inland. On the coast section of the Lower Devonian, however, in this map the igneous rocks so conspicuous at Torcross cannot be shown. They are represented bj' three or four thin bands in the coves in the headland separ- ating Bovisand and Crownhill Bays, so sheared and decomposed that not a vestige of the original structure is left and even the secondary constituents cannot be made out. There is not the slightest doubt however as to their igneous origin. In colour and texture they form a marked contrast to the slates in which they occur and identical characters are displayed by weathered and decomposed igneous bands especially where thin, in the rocks of the Meadfoot group in the Torcross and Thurlestone coast sections. Amongst the rocks of this class too far gone for petrologioal investigation is the band shown for a quarter of a mile along an east and west strike at Idston north-east of Aveton Gifford. It is a pale greenish shaly rock with small flecks or patches of paler colour. It differs in colour and, markedly, in texture from the Dartmouth Slates in which it occurs, and resembles a decomposed altered highly sheared tuff. On the south side of Warren Point sheared diabase, vesicular diabase, and sheared yellowish decomposed rocks, perhaps tuffs, occur in plicated 22865 D 44 GEOLOGY OF IVYBKIDGE AND MODBTJBY. repetition in tlie Dartmouth Slates. The igneous rooks on the shores of Newton Ferrers Creek have been akeady referred to, also ^^^"^^ °''°\'i^2ur on the west bank of the Yealm. Season Point is formed ot a Higniy felspathic diabase (6747). This and a rock (3072) shown xn the foreshore reefs north of the Renney Rocks, composed of phenocrysts of alkali telspars and quartz aggregates in an andesitic matrix, belong to exceptional types. . . At Wembury Point a, decomposed porphyritic diabase is intrusive in the Dartmouth Slates, apparently along the strike for 100 yards. Just north of Andurn Point a much altered diabase (6746) is intruded among the Dartmouth Slates near their junction with the rocks of the Meadfoot group. It seems to occur at a line of fault and exhibits traces of shearing. In the Erme Valley the igneous rocks appear to be in part contemporaneous in part sheared diabase siUs. The former are mostly decomposed ; examples are met with on the west bank near the Coastguard Station, whence the band shown may extend west-south-west across the road between Mothe- combe and the estuary: at 3 furlongs above the Coastguard Station, this rock is the largest mass shown on the map, but its west-south-west ex- tension for three-quarters of a mile from the river was based on rather feeble surface evidence : at a. hundred yards to the north, and on the east bank opposite this in a small quarry in the wood west of Torr Down. Diabase occurs in three places on the east bank north of the last-men- tioned band and in two places on the west bank, in Skerill Copse at 3J and 4^ furlongs, respectively, from the Coastguard vStation. The last named was the only one examined microscopically. It is a good example of sheared ophitic diabase (1849). There are several bands of igneous rock too small to show on the map in the wood north of Torr Down and at the Ford opposite Efford House. The two bands on the map at Kingston are decomposed. The large mass of dia- base for 9 furlongs from Great Torr, where the rock seemed to be in situ, is, beyond a trace of probably decomposed igneous rock near Langston, purely hypothetical, the surface evidence of the nature of the subjacent rock being nil. Beyond this, however, the presence of diabase stones and a quarry and feature prove the extension of the rock which may be connected with the larger mass on the east, north of Cumery. The easterly termination of the large mass is extremely doubtful; it may be connected with the diabase bands south of Wakeham. There are diabase quarries at 3 furlongs east of Cumery, at a quartei of a mile south and 3 furlongs south-east-~t)f" Wakeham, and in the two patches near this. Near Stoliford diabase (1789) is exposed in a quarry, the rock is highly sheared in part with dark chloritic shear-planes. Under the microscope relics of the original ophitic augito are seen lying in a schistose matrix of chlorite and broken felspar. A schistose diabase or diabase tuff occurs at three-quarters of a mile west-south-west of Stoliford, near Little Modbury. East of Idston and south of Yanston there are several small patches of diabase. One of these at the turning to Yanston is doubtful, there is a quarry in the patch to the west of this and a spring is given out at the west end of the patch to the south of it. There are signs of decomposed bands of igneous origin just north of Yanston; 3^ furlongs north-north-west of Aveton Gifford Church; 3 furlongs west-north-west of Wakeham. Three hundred and fifty yards north of Loddiswell there is a mass of diabase evidenced by surface stones and one in situ exposure. It may be connected with the band which crosses the Avon east of Ham but no surface evidences of this was seen. The large mass of diabase east of Loddiswell Church was drawn from surface stones and features. South-east of this and opposite Loddiswell Station a mass of diabase is exposed in a quarry by the alluvium. At about 21 furlongs south of Loddiswell Church a small patch of diabase is exposed at the supposed junction of Dartmouth Slates and rocks of the Meadfoot group. At 350 yards from this, westward, and apparently on the same horizon, diabase is shown by surface stones. Such is also the evidence on which the mass to the south is based except at its east end where it ig exposed on the south face of a large quarry. LOWER DEVONIAN IGNEOITS ROCKS. 45 Rake Rock is a crag of ophitic diabase (1909) a quarter of a mile east of NewmiU Bridge, the rock is exposed in the neighbouring railway cutting in irregular vertical junction with the slates and also in a quarry by the road to Newmill Bridge, where it appears to have a dip of 75° to the north. There are several masses of diabase on the continuation of the east-north- east line of the Rake Rock viz. . five-eighths of a mile south-east of Loddis- well Church south of Wrinkley on the 6-inch map ; seven-eighths of a mile east-south-east of Loddiswell (in Longpark Wood, a quarter of a mile east of Wrinkley on the 6-inch map) ; at a little over a quarter of a mile east of the last patch, normal ophitic diabase (1878) is again met with. It is shown as two patches extending to Torr Rock (south-east of Woodleigh) biit these may be connected ; the rock is feebly evidenced within the broken lines connecting the Torr Rock with yellow decomposed material, probably of igneous origin seen at 160 yards south of Mount's Post Office. Buff material, probably volcanic, was seen near East Allington Inn at three- quarters of a mile east of the last-mentioned, and a small patch of igneous rock is exposed in n quarry north-east of this by the lane to Pool. A patch of fine grained diabase is exposed in a quarry at Fallapit Farm. A quarter of a mile north-east of this there is a quarry in sheared ophitic diabase (1850). The rock may extend farther than is shown on the map as the surface evidence is very unsatisfactory, and this was also the case where another but doubtful patch of diabase is shown at a quarter of a mile north-west of Fallapit House. A band of yellow-brown probably volcanic material runs through Grimpstonleigh, and for about 3 furlongs in a direction W. 20° N. Similar material was seen by the road a little north of Woodleigh. At 260 yards north-west of Woodleigh Church surface stones suggested the presence of a small patch of fine grained diabase. At 2^ furlongs east of Woodleigh Church diabase occurs apparently in irregular and partly plicated association with the slates. Near this on the south diabase is again exposed at about 360 yards soxith-east of Woodleigh Church by a road. On grossing an intervening stream sheared rock possibly diabase strikes east-north-east. Following the same line of direction west- ward from the road exposure for 3 furlongs we encounter a quarry in sheared diabase at a quarter of a mile south-south-west of Woodleigh Church. This rock (1867) may be regarded as a typical illustration of the effect of shearing on one of the normal ophitic diabases. Relics of the original ophitic augite lie in a foliated matrix of chlorite and zoisite. The original felspar has almost entirely disappeared and the rock is now an augite-chlorite-zoisite schist. The rocks above-mentioned occur in the Dartmouth Slates and Meadfoot groups, in which we recognise elsewhere contempor- aneous as well as intrusive materials. In the Staddon Grits there is a much weathered intrusive rock (diabase) at Leek Bed Bay, where the coast projects into the adjacent map 348. In this map a mass of diabase imperfectly exposed occurs on the north of Preston at 2 miles to the north of Woodleigh Church. At about 300 yards from this in a field on the east of Capton large diabase boulders were encountered in a field. The largest mass was 6 yards in length, although we have not shown the rock in the map, there cannot be much doubt that there is a diabase dyke under. The only remaining occurrence worthy of mention is that of a decomposed igneous rock at the road junction west- north-west of Wizaller, and seven-eighths of a mile south of Brownston Church. 22266 D 2 46 CHAPTEE IV. MIDDLE DEVONIAN. The Middle Devonian rocks of the area are almost continu- ously exposed in the coast section, where we will take up their description from the point at which Chapter II left off. This point is 26 yards north of the last and most northerly appearance of the grits, and is marked by a crack or fault. Throughout the section the cleavage has a southerly dip, and in every case where the angle of inclination is mentioned this direction must be understood, unless otherwise stated. For the first 26 yards we encounter grey slates with red interfilming in places, probably denoting coincident bedding planes. The cleavage planes dip at first at 40°, further on at 23°, then we encounter harder brown bands partaking of the cleavage, which dips at 32°, but crossing it with a low northerly inclination. These seem to indicate bedding and to be cut off by greenish and brown vesicular igneous rocks. The igneous rocks form a small promontory and occur irregularly along the planes of schistosity. For 30 yards further the slates exhibit cleavage dips of from 10° to 25°, crossed in places l3y cracks, resembling joints, with a southerly dip of 65°. In the next 20 yards blocks of greenish volcanic rock occur on the beach and have probably fallen from the cliff above. The grey slates beyond this, for 22 yards further, give cleavage dips of 15° to 17°, and are traversed by quartz veins near a fault. Beyond this, for 22 yards, up to another appearance of fault, the slates dip at 25° to 35° and contain hard, grey, lenticular, partially cleaved, bands and qviartz veins in the lower part of the cliff; above this there are dark grey slates with red films and higher up buff and grey-weathered slates with veins of quartz and carbonate. For the next 34 yards the slates contain occasional hard lenticles and red films which, in places, are distributed in a manner suggestive of gnarled, nearly horizontal, bedding, traversed by cleavage planes dipping at from 25° to 32°. Where these indications of bedding are sufficiently close to produce interlamination, the breaking up of the harder beds in the direction of the cleavage often gives the rock a brecciated or cross-hatched appearance, which has been noticed elsewhere where interlaminated beds occur, as for example on the Tinsey Head coast in Sheet 356. For the next 22 yards the section is partly overgrown and the dips of the cleavage planes, ranging from 35° to 70°, may be in slipped materials. For 22 yards further, although the section is mostly overgrown, masses of igneous rock of a pale brown or greenish colour, weathering red, are imperfectly exposed in slates dipping at 40°, the bedding being probably coincident. From here the section is represented diagrammatically (Fig. 13), as shown on next page. In the first 22 yards A. to B., we encounter successively, grey slates, cleavage at 35°, with cracks dipping southward at 48° across it, and a band of decomposed limestone coincident with it ; dark slates with irregular quartz veins ; slates with films of limestone and crinoids along the cleavage at 35° to 40° Volcanic rock, resembling the rocks in the Torcross section, veined with quartz and traces of epidote, probably interbedded; slates with another mass of igneous rock with quartz-filled amygdules striped with quartz gash-veins which also intersect the contact slates. This rock dips at 48° with the slaty cleavage. It is possible that the two occurrences of igneous rock may be due to a sharp anticline. From B. to C. we encounter successively grey slates, with signs of bedding dipping southward at 20° across cleavage planes dipping at 48° : hard pale-brown-weathered igneous rock recalling the Torcross types and cutting across the indications of bedding ; dark grey calcareous slates with fossils, individually tilted along the cleavage at 50°, but collectivelv form- ing lines across it denoting bedding which is probably contorted and folded. MIDDLE DEVONIAN. 47 There is an appearance of faulting in two places. One of these is at C, where the cleavage and bedding appear to be coincident at 40° ; lenticles of limestone occur and the rocks are fossilifersus. There may be igneous rook in the cliff above the fault. Between C. and D., in a distance of ^^ ^ 22 yards, we next encounter veins of car- bonate irregularly gnarled across the cleavage of the slates which contain impersistent calcareous films; then an irregular mass of igneous rock terminating upwards, probably faulted, resembling those already mentioned and containing veins of quartz and carbonate. In con- tact with this on the north the slates contain lenticular limestone films dipping >^ '^'^//^^^^/^^j/^lf^ at 40° with the cleavage, which further on dips at 50° Towards D., lenticular bands of lime- stone dip south at 25° to 30° across the cleavage, and higher up two irregular bands of pale grey and greenish igneous rook with veins of quartz and carbonate o > P .g o X ■^ From here to Dunstone Point tKe cliffs in Rum Bay (on 6-inch map) consist of dark slate, with veins of Quartz and carbonate in places and occasional lenticles of limestone in part very siliceous. The lenticles show bedding across the cleavage planes. These limestones contain numerous black patches besides remains of crinoids. Although no organic structures have been detected in these black patches they do not appear to be ordinary phosphatic nodules, and in view of the occur- rence of Pteras-pis in dark patches in Lower Devonian slates, they are deserving" of attention. A fault or thrust was noticed at Dunstone Point, and also beneath vertical beds of dark grey, irregu- larly slaty, limestone which form the north cliff of Dunstone Point at the Targets. Traces of fossils, such as Fenestella and crinoids, were seen on the bed surfaces of these limestones. Dark slates (apparently with hard calcareous bands) with a pale- weathered igneous rock, about a foot thick, are next encountered but their relations to the limestones are not clear, and where the coast resumes its normal trend the section is over- grown for 30 to 40 yards. 48 GEOtOG"? OF IVTBEIDGE AND MODBUE"?. e o o O o !>3 6 1^ 05 03 M An intei-esting section is shown in the low cliflfs between this and Mount Batten. Grey shales or slates with shaly limestone are first exposed. The slates, as shown in the sketch Fig. 14. — Batten Bay. Quartz veins in slate. (Fig. 14), are broken by small faults, or con- tortion-cracks, and contain gnarled quartz veins. Near this zaphrentids were noticed and an alternation, perhaps accompanied by plica- tions, takes place between dark fossiliferous shales, or slates, with dark grey limestone bands, partly decomposed to orange-coloured residues, and pale grey volcanic rocks with brown-mottled even surfaces and, in places, grey rock like a coarse calcareous tuff with veins of hard carbonate and a trace of copper carbonate. These alternations form a promontory for about 20 yards ; they are succeeded by grey slates with irregular brown-weathered lenticles and films with decomposed calcareous brown fossiliferous bands. At first cleavage and bedding seem to be more or less coincident at 35° to 40°- Then a corted fossil-band is visible and beyond this fossil-films dip at 50° southward. Further on the slates are interfilmed with quartz, and contain impersistent limestone bands, veined with quartz and partly replaced by quartz ; these bands are irregularly con- torted, being partly along, partly across, the cleavage. The beds are intersected by two small thrust planes and appear to be faulted as in the diagrammatic section. Fig. 15, which represents a distance of about 100 yards. The cliff in this distance is from 15 to 20 feet in height. The slates make an even junction plane dip- ping south at 45°) with pale grey and brownish, hard, slaty volcanic rocks which form the section for 18 yards. These rocks are in irregular junction, on the north, with dark grey slates with brown weathered siliceous limestone partly replaced by quartz. The irregular inosculation is traversed by the cleavage planes, so that specimens may be obtained showing the junction with the cleavage intersecting bom rocks alike. (See Fig. 16.) MIDDLE DEVONIAN. 49 The slates form a band about 5 yards wide, overlying on the north similar volcanic rocks to those on the south which are calcareous at the junction. These rocks are brown and pale greenish and occupy a distance of 18 yards, being then cut off by fault against Tfi.p -lo flftHfin ^°f* gi'ey slates with brown films, crinoidal ■ ■ remains, and lenticles of quartz, perhaps a ^o,y- replacement of siliceous limestone. These slates are shown for 15 yards and are faulted against soft grey slates with beds of yellow - brown fossiliferous material (crinoids, corals, &c.), and harder even beds of brown rock with straw-coloured films intercalated with irregular vesicular beds probably volcanic. To what extent these beds are an association of decomposed volcanic rocks and decomposed lime- stone it is impossible to say ; they are in plicated association with the soft grey slates, above and below; and are faulted on the north against buff, brown, and purple mottled volcanic rocks. The foreshore reefs consist of pale buff and J unction or slate greenish decomposed rocks with vesicular brown and schalstein. patches, possibly scoriaceous tuff or lava, apparently dipping south-east under the buff purple-mottled rocks which are probably sheared tuffs. These associations occupy about 30 yards. From this point for 180 yards the cliff is only from 8 to 10 feet in height and, where not overgrown, consists of a gravelly superficial deposit. The foreshore reefs, where accessible, consist of yellow, buff, and green volcanic rocks, irregularly mottled with red and purple patches, partly slaty and amygdaloidal and, in places, much decomposed. They are a continuation of the volcanic rocks noticed above. Between these rocks and blocks of compact pale grey limestone there are no exposures for 32 yards and the coastline enters the adjacent Map 348.' The limestone blocks are probably in situ and may denote the eastern termination of a synclinal fold of the Mount Batten limestones. Beyond this, yellow and buff decomposed, partly earthy, volcanic rocks are seen in the low cliff and on the foreshore, for 66 yards. They contain patches of irregular grey slate with occasional traces of limestone. The volcanic rocks appear to dip at 80° to the south at their junction with the grey, bedded limestones of Mount Batten which here form a tongue, whether an anticline or syncline it is impossible to say. The limestone seems to contain Cystiphyllum vesiculosum. The tongue tapei's out westward and about 20 feet (or 10 feet folded) of grey, brown- weathered, sheared volcanic breccia, or tuff, with limestone fragments is seen. The limestone is vertical, or nearly so, on either side of the volcanic rock which here wedges out eastward. As elsewhere stated in this junction under Mount Batten Coastguard Station " the lower part of the [Plymouth lime- stone] reef rests on, or dovetails into, volcanic rocks and slates and lime- stones, these materials having partly replaced the lower beds of the reef."'' The same idea is suggested by the termination of the limestone in Clovelly Bay (on the 6-inch map) in a quarry in this map (349) west of Turnchapel. Here the bedded grey limestones are apparently overlain on the south by red and yellow schalstein tuffs, a lenticular patch of limestone cropping out on the summit on the south, whilst at the west end of the quarry greenish volcanic rocks separate the main mass of the limestone from a patch which noses out westward in the schalsteins. Following the limestone east to Turnchapel, there is evidence of slate by the shore near the Infant School, the westerly continuation of a band which separates the limestone into two masses from Oreston westward. At Oreston volcanic rooks occur on the south of the slate band for about 100 yards. Volcanic rocks also bound the Turnchapel limestone on the ' ' See 'The Country around Plymouth and Liakeard' (Mem. Geol. Surv.), 1907, pp. 50 59, 69. 2 Hid, p. 69. 50 GEOLOGY OF IVYBRIDGE AND MODBTJEY. soutk, but on the west it is bounded by slates. Following tbe southern margin of the limestone, at Hooe it is bounded by slates and, perhaps, on the east of Plymstock where no reliable evidence is procurable, but else- where by volcanic rocks nearly as far eastward as West Sherford. A lenticular band of red crinoidal limestone can be seen in the volcanic rocks by the road between Radford and Plymstock (at Radford Hill on the 6-inch map). The slate band is probably an anticline. The Cattewater between Oreston and Laira Bridge runs across the strike of the limestone north of the slate band, and completes the coast section of the Middle Devonian. j. j xt. • The limestones have been well described by R. N. Worth' who noted their gradation into slate through calcareous shale on the north and south ; their crystalline character ; the regularity of their divisional planes ; the caverns running with the joints across the bedding, midway m the face of the cliffs at Cattedown and Oreston ; the shallow synclinal structure with undula- tions of the Cattedown limestone, and the otherwise prevalent southerly Compact dove-coloured, white-weathered, limestones are seen in Cattedown Quarry and dark limestones further north in Princerock and Pomphlett quarries. Between Princerock Quarry and Laira Bridge the dark limestones become slaty and are seen to pass into slate, in the cuttings of a mineral railway. Fig. 17. — On south side of Laira Bridge. Limestone passing upward into slates through slaty limestones and calcareous slate with limestone bands. In one place (Fig. 17) bedded limestones, dipping southward at 20°, become slaty and are overlain by slaty limestone in which thin bands of limestone occur and mark the bedding which crosses cleavage planes dipping south at 45°. In another place calcareous slates with cleavage planes dipping south at 50° to 60° are crossed by very thin bands of limestone dipping south at 30°, and these calcareous slates pass insensibly into ordinary slates. At the China-clay and granite quay thin-bedded limestones, becoming slaty, are plicated with grey slates. In Pomphlett Quarry the limestones are slaty in part and show signs of zig-zag bedding. The coast section, as we have seen, commences with grey slates with hard, occasional, limestone bands and other indica- tions of bedding, and as we proceed northward volcanic rocks, some probably intrusive, occur, and the limestone lenticles and films are found in the slates, in a manner suggestive of much plicated repetition. Still further north, at Dunstone Point, slaty limestones become conspicuous, although when traced inland they are distinctly impersistent. Beyond this the volcanic rocks become much thicker as we approach the limestone mass. ' ' The Geology of Plymouth,' Trans. Pit/mouth Intt., vol. v, 1875, p. 460. MIDDLE DEVONIAN. 51 The extremely irregular development of tlie volcanic rocks in relation to the limestones and to the slates is clearly shown on the map, and the impersistence of the limestone mass is as clearly evidenced. The sequence of the Middle Devonian rocks is therefore vari- able according to the presence or absence of the limestone, and its replacement by slate; and according to the development of volcanic rocks, on or below the horizon of the limestone masses. We have no reason to think that vulcanicity on a large scale commenced in the Middle Devonian, anywhere in this area, earlier than in the Ashprington district with which their vol- canic rocks are stratigraphically connected. From this it would follow that the volcanic rocks from Dun- stone Point northward, and perhaps those to the south of Dunstone Point where contemporaneous, with accompanying slates or limestone bands represent the lower horizons of the fully developed limestone masses of Newton Abbot and Tor- quay. In other words the base of the Middle Devonian invariably consists of slates, with occasional calcareous beds. The lime- stone masses are local and only contemporaneous in a general sense. The volcanic rocks are so irregularly developed that they suggest local centres of emission, from which the lavas and tuffs extended irregularly outward, becoming interbedded with slates and dying out in them, as seems to be the case between Elburton, East Sherford, and Brixton. Slates. The most fossiliferous slates in the Middle Devonian are those which occur on and below the horizons of the main masses of schalstein, where the Berry Park type (the corresponding slates near Berry Pomery in Sheet 350, named Berry Park slates by Champernowne) prevails. Limestones, locally developed in slates of this type, are shown on the map near Brixton Road Station, Spriddlestone, Combe, Goosewell, and Steer Point. These beds are well exposed by the railway between Brixton Road Station and Steer Point. Near Brixton Road Station a lenticular patch of limestone, 20 feet thick, passes into slate. Further south, limestones and calcareous slates pass into fossiliferous slates with soft yellowish films from the decom- position of limestone lenticles. Bands of igneous rock, as on the coast, too decomposed to be traced on the ground and too thin to be shown on the map, occur in places in the railway cuttings and by the adjacent creek, on the east shore of Cofflete Creek, about half a mile from Steer Point, and on the west shore about a quarter of a mUe higher up. Thin bands are visible in several places by thei Tealm shore above Steer Point. These creek sections show constant repetition. Fossils such as zaphrentids and traces of trilobites occur iii the slates. 52 GEOLOGY OF IVYBRIDGE AND MODBUEY. Prismatic jointing is often seen where undulating bedding is traversed by fine cleavage planes. At about a quarter of a mile north of Steer Point the slates and limestones are locally peroxidated. For about a mile from Steer Point, by the Yealm, and oppo- site the wood at Warren Point the slates pass irregularly into limestone and are in places nearly horizontal; the prevalent strike is north-easterly. Quartz-veined limestone bands, as in the coast section, are noticeable, in one place near the Lower Devonian boundary, on the north of West Wood (on the 6-inch map), south of Warren Point where the junction seems to be unfaulted. On the border of the wood, south-east of Puslinch, there is a small patch of limestone, probably a lenticular patch in the slates. There was no surface indication of the relation of the Yealmpton limestone mass to the Lower Devonian; if it is un- faulted then the basement slates are here very thin and this limestone occupies a lower position in the Middle Devonian than any other mass that I am acquainted with in South Devon and Cornwall. In view of the faulted character of the country round Modbury, we here assume the presence of a fault cutting out a considerable part of the lower beds of the Middle Devonian. Near Sheepham the slates are f ossilif erous ; their outcrop between the volcanic rocks and the Lower Devonian is only a quarter of a mile broad, increasing to two miles south of Har- berton. This irregularity in breadth is due to repetition by plication, which is shown by the presence of Lower Devonian rocks near Bickham Bridge, south of Diptford, and by the vol- canic bands at Witchcombe and near Shilston Barton; possibly to constricting faults near Sheepham ; and to the constant repe- tition of the slates by small folds toward Harberton in an area where the outflows from different foci of eruption were fining out. In this extension the slates here and there present the Berry Park type but, though occassionally calcareous, no recognisable limestone was discovered in them until we reach the vicinity of Harberton. Weathered bands of igneous rock, as on the coast, were occasionally detected. Fossilif erous calcareous tuff occurs near Poulston. The rocks are less fossiliferous on the whole and more evenly cleaved, as old slate quarries (on the 6-inch map) such as Combe Quarry near Witchcombe, Greyhills Quarry, Englebourne Quarry and Lincombe Quarry attest. Very locally the slates are peroxidated, or mottled with red. Near Harberton the slates become hard, siliceous, and irregularly cleaved, m places. This character is displayed in the Berrystone rock, a peroxi- dated roughly cleaved highly siliceous limestone. An old quarry just south of Langford is composed of hackly rock with well defined, irregular, cohesive, cleavage structure, and thin bed-bands of siliceous limestone. Somewhat similar slates are exposed between the volcanic rocks of Langford and Lincombe. A slate quarry east of West Leigh is said to have furnished the material of which Harberton Church is built. MIDDLE DEVONIAN SLATES. 63 In Hazard Quarry, north-east of Langford, 50 to 60 feet of more or less slaty, dark-grey, fine-crystalline and crinoidal limestone, dipping northward tit 15° to 20°, is overlain by 15 feet of cleaved volcanic rocks. The cleavage dips south-east at about 40°, and intersects both the rocks (Fig. 18). Cham- FiG. 18. — Hazard Quarry. ^ v\:^ A Junction of schalstein and slaty limestone. pernowne, in unpublished notes, thus refers to this quarry. " The top bed of the limestone which abounds in Alveolites vermicularis M. Edw. and H. appears to be intimately mixed with volcanic matter so as to be in Sand- berger's words either a ' Kalk schalstein ' or ' Schalstein Kalk.' " The extension of the limestone towards Hazard is doubtful. To the north of the schalstein, towards Hood and the volcanic rocks of Rattery, the grey slates are of an ordinary type. The limestone shown on the map is exposed in quarries near Brooking and Peloe, north of Tigley. Peloe is Paytoe on the old 1-inch map. At the west end of the mass, the limestones are rather thin-bedded and affected by zig-zag plications, recalling sections at Broadhampston ; near Peloe, towards the east end, they are partly even-bedded dark-grey limestones, veined with oalc spar and shaly near the surface. At the east end of the quarry they are contorted and overlain by buff and grey slates ; on the north side they appear to be nearly horizontal. In places the bedded limestones may be from 20 to 30 feet in thickness, but they pass into very dark calcareous slates and are so unstable that slates had to be included within their boundary. Further east there ai-e occasional traces of limestone in the slate between Peloe and Whiteley (on the 6-inch map). The slates in Hollet's Quarry (on the 6-inch map) north of the west end of the limestone are occasionally calcareous. The cleavage planes have prevalent south-east or south-south-east dips south of Hood. In the railway cutting on the north side of Riverford Bridge limestone, dipping north-west, occurs in the slates. Three patches of dark-grey limestone are shown on the map north of this. They are associated with calcareous slates passing into ordinary slates. In the northernmost patch the beds have a low dip to the north. East of the central patch, just within the adjacent map 350, the slates are fossiliferous and contain Pleurodictyum, Spirifer and Atrypa reticularis. No boundary can be drawn between these recognised Middle Devonian slates and the grey buff-weathered and, occasionally, purple and greenish slates, with vesicular igneous rocks and volcanic bands, which occur between them and the Buckfastleigh limestone. But, as red and greenish Upper Devonian slates occur in the quarry near Lower Combe on the north border of the map, it is very probable that these rocks may belong to the lower part of the Upper Devonian, and if so, the boundary would be a zig-zag irregular line, made by the troughing out of small east and west folds, somewhat similar to the hypothetical line shown on the map. E'rom Lisburne westward the slates call for little comment. Near Shorter Cross, on the north, they contain yellow seams apparently of volcanic origin. They have been quarried near Beneknowie and south-west of Wonton, at Bowcombe Wood, and Quarry Farm, near Ugborough. 54 GEOLOGY OF IVTBEIDGE AND MODBURT. The harder fine-grained siliceo-calcareous slates, which are not recognisable outside the granite aureole, seem to pass into hornstones or calc-flintas at Brent Mill and in the railway cut- tings north of Wrangaton. The association of calc-flintas with decomposed materials in the unaltered slates is to be seen in the railway cutting near South Brent Station (Fig. 19) . Fig. 19. — Cutting of the Kingsbridge Branch Railway at its junction with the G. W.R. Horizontal scale, 1 inch = 40 yards. Vertical scale, 1 inch := 60 feet. W. Cutting walled up. SI. Slate with quartz resulting from the decomposi- tion of calc flintas (or volcanic rocks ?). C. Hard calc-flinta. C. Hard calc- flinta in soft decomposed material for 20 yards. SI.* Slates. Assuming that the calc-flintas pass out from the granite aureole into Middle Devonian slates a line has been drawn on the map as a possible indication of the relative extension of the Upper and Middle Devonian. In the assumed anticline between Ivybridge and Plympton Station, there are grey slates which might be Upper Devonian from the Yealm Valley west- ward. The fossil evidence is extremely poor and, as we shall see, inconclusive. On the other hand if this structure is any guide, the anticline may extend further west, and the presence of folds of Middle Devonian appearing through Upper Devonian slates litho- logically undistinguishable from them in the slate area north of Plympton is not improbable. FOSSILS. We will now give the lists of fossils found in these slates from the coast westward and on the north of the schalsteins from east to west. R. N. Worth gives Staddiscombe as a locality for Actinocrinus tenuistri- atus, Orthis striaiula, Spirifer curvatus and Spirifer simplex.^ The f oUowing were obtained in a quarry in blue-grey slates in a wood at a quarter of a mile north of Staddiscombe : — Combophyllum ? Zaphrentid? Crinoidal columnals Fistuliporap PAthyris oonceutrica (von Bv^h) Atrypa reticularis (Linn.) Orthis (Dalmanella) circularis J. de C. Sow. Rhynchonellid Spirifer speciosus? (Schloth.) „ sp. Stropheodonta sp. ' Trans. Plymouth Inst., vol. vi, 1877, p. 207. MIDDLE DEVONIAN SLATES. 55 In an old quarry about 300 yards west of the above crinoid columnals, Fistulipora? Athyris? Orthotetes? and Spirifer specious? (Schloth.) were obtained. In the lane on the south-east side of Goosewell calcareous shales and lime- stone furnished the following : — Alveolites sp. Orthotetes? Crinoidal columnals Spirifer sp. Bryozoon? Stropheodonta cf. sedgwicki Orthis (Dalmanella) circularis? (de Vern.) J. de C. Sow. Edmondia? Orthis sp. R. N. Worth gives Goosewell as a locality for Pleurodictyum prohle- maiicum. A small Pleurodictyum was found in the slates in a wood south-south-west of Radford. On the south of the cross roads just south of Plymstock (near Beanhay on the 6-inch map) the slates in the road-cutting yielded the following : — Pleurodictyum sp. Stropheodonta cf. sedgwicki (de Petraia? Vern.) Crinoidal columnals ,, sp. [probably new] Orthis striatula (Schloth.) Cypricardinia ? ,, sp. Asteropyge sp. P Orthotetes umbraculum (Schloth.) Phacops latifrons? (B?-onn) Spirifer speciosus ? (Schloth.) Proetus? Stropheodonta interstrialis (Phill.) At Elburton, by the roadside on the north of the Inn, the slates contain : — Petraia sp. Orthis sp. Crinoidal columnals Spirifer speciosus? (Schloth.) Fenestellid ? Stropheodonta interstrialis (Phill.) Orbiculoidea nitidaP (Phill.) Phacops sp. Orthis arcuata? (Phill.) In a road-cutting about 600 yards south-east of Elburton and north of Halwell the slates yielded : — Alveolites sp. Spirifer speciosus? (Schloth.) Favosites? ,, sp. Zaphrentid? Stropheodonta gigas? (M'Coy) Crinoidal columnals MecynodusP Atrypa aspera (Schloth.) Modiomorpha? ,, desquamataP J. de C. Sov. Tentaoulites annulatusP (Schloth.) ,, reticularis (Linn..) Asteropyge punctata (Salt non Chonetes hardrensis? (Phill.) Stein.) ,, sp. Cyphaspis sp. [? new] Orthis (Dalmanella?) sp. Phacops sp. Orthotetes? Proetus? R. N. Worth' gives Elburton as a locality for Pleurodictyum problema- ticum, Petraia pluriradialis, Pleurotomaria aspera. East of Elburton no special search for fossils was made in the slates. In the collection of the late A. Champernowne there are several trays of fossils of dark slate from the following localities : — Englebourne, sometimes spelt Inglebourne, Slate Quarry; Great Englebourne; Roster Bridge Quarry ; Hanger's Quarry ; Railway cutting by Brooking Church, or near Brooking Church and Hanger's Quarry. These localities, with the exception, of Great Englebourne, are in- cluded in Sheet 349. Roster is spelt Roister on the new maps. On the 6-inch map (Sheet 126 NE.) the quarry near Roister Bridge is called Englebourne Quarry. This quarry is distingviished by the letters S. Q. on the old 1-inch map. There is, however, another quarry at about ■ Op.cit. 56 GEOLOGY OF IVYBEIDGE AND MODBUEY. the same distance from Great Engleboiirne in a south-south-east direction, within the border of jSheet 350, at Harbertonford where fossiliferous cal- careous slates have been quarried, which might possibly be Champernowne s Englebourne Quarry. There is an old quarry (small) in fossiliferous grey slates on the south border of the 6-inch quarter-sheet 120 SE., about 300 yards NNE. from Great Englebourne and within the border of Sheet 350. This last appears to be the quarry in the field adjoining the spot where Helianthaster filici- formis was found. Any doubt, therefore, which may attach to the exact position of Cham- pernowne's localities near Great Englebourne does not affect the strati- graphical position of the fossils, as the slates belong to the same series which underlies the Ashprington volcanic rocks, and the beds are evidently repeated by numerous folds. From Great Englebourne there are three specimens of starfish. One of these was figured and described by Dr. H. Woodward under the name of Helianthaster filiciformis.^ It was obtained in a small quarry, or road- side excavation, at Englebourne House [strictly speaking at about 380 yards E. 23° N. from Englebourne House in Sheet 350] " in coarse slates with one or two thin gritty layers " dipping about south-east at 15° The cleavage planes dip south at a much higher angle. Contrasting this south-easterly dip with an apparent northerly dip, crossing the dominant southerly dipping planes at Roster Bridge, Cham- pernowne considered the probability of a fault with downthrow to the north between the localities. He refers to " Roster Bridge where large Spirifers and other fossils are numerous " and this suggests the identity of Roster Bridge Quarry and Englebourne, or Inglebourne, Slate Quarry, or that the different names refer to parts of large quarries formerly worked just east of Roister Bridge, and called Englebourne Quarry on the 6-inoh map. The following fossils in the collection from Englebourne, or Inglebourne, Slate Quarries are given, as labelled. Some of the crinoid stems and pinnules are nearly a foot in length. Melocrinus deoadaotylus ? Spirifer cultrijugata F. Moem. ,, laevicosta Val. ,, speciosus (Schloth.) (3 specimens, 2 of which are pyritized). Actinodesma malleiforme? Sandb. Cypricardia Ptsrinea sp. Aoroculia (cast), Roster Bridge Quarry Goniatites ? Orthoceras [many specimens, up to 1 inch in diameter] Pteraspis [since identified as median dorsal plate of Coccosteus] Amongst the unlabelled specimens is one with a fern-like marking, several corals including Zaphrentid casts, three being sliced and suggestive of Favosites (jothlandicus Goldf., and several spirifers. There is also a specimen labelled " ? Crustacean wing or paddle." In 1881 Champernowne thus referred to this locality: "the slates of Englebourne Quarry near Harbertonford at once recall the Wissenbach slates with which to some extent the organic remains also correspond."^ From Ashridge railway cutting, south of the east end of the Peloe lime- stone, the following specimens, given as labelled, were obtained by Cham- pernowne : — Zaphrentis Rensellaeria ? ? Atrypa reticularis Linn. Spirifer sp., several specimens „ ooncentnca? „ laevicosta Val. Meristella soalprum Streptorhynchus umbraculum POrthis hipparionyx Phacops latifrons (Bronn) Pentamerus brevirostris Phill. I Geol. Mag., 1874, p. 6. ' Geol.iMag., 1881, p. 415. MIDDLE DEVONIAN SLATES. 57 The church on the map west of Ashridge is Brooking Church. In Champernowne's collection are several specimens of Calceola sandalina Lam. from Brooking railway cutting and near Brooking Church. In reference to his discovery of this fossil near Torquay Champernowne observed in 1874' " it may not be amiss to compare our section with another locality where I have had the good fortune to find it; viz., in the railway cutting close to Brooking Church. Stratigraphically, it appears to be near the base of the limestone at Paytoe and Tigley, which, as described by Dr. HoU, is brought down by a fault bounding it on the north; whilst a few Cal- ceolce and other fossils are found in the eastern part of the cutting, where are some thin limestones among shales, the western and lower part is entirely argillaceous." In his collection there are three specimens labelled : — Cyathophyllum helianthoides Railway cutting by Brooking Church. „ _ goldfussi? „ „ Phacops latifrons Brooking. Hanger's Quarry is about half a mile S. 34° from Brooking Church; the specimens from this quarry in Champernowne's collection are as follows : — Chonetes sp. Spirifer laevicosta Vol. Orthis hipparionyx? Tamix. „ macropterus Goldf. ,, striatula Linn. ,, speciosus, var. macropterus Spirifer curvatus Schloth. The following were collected from this quarry recently : — Zaphrentid? Chonetes hardrensis (Phill.) [?var.] Crinoidal columnals Megalanteris ? Fenestellid Orthotetes umbraculum? (Schloth.} ? Athyris concentrica (von Bvch) Spirifer sp. PAtrypa reticularis (Linn.) The railway cutting, at half a mile west of Hanger's Quarry yielded : — Petraia sp. Fenestellid Crinoidal remains Orthotetes umbraculum? (Schloth.) In a quarry at Moore Farm, about 3 furlongs south of the above railway cutting, the slates contain small zaphrentids and crinoidal remains. Near Avon Wick the slates in a quarry 300 yards north-east of Beneknowle yielded : — Crinoidal columnals Spirifer speciosus? (Schloth.) Fenestella sp. Stropheodonta ? [This is the impres- PAtrypa reticularis (Linm.) sion of a flattened valve with Leptaena? ribbing of same type as Stro- ef. Lingula subparallela Sandb. pheodonta gigas (M'Coy)]. Orthotetes unbraculum (Schloth.) At a field gate, 100 yards east of Black Hall, crinoidal columnals and Leptaena rhomboidalis (Wilck.) were obtained. In Holl's lists^ the follow- ing fossils from Black Hall are given; Phacops latifrons on Pengelly's authority, the rest from indentifications by Davidson of specimens in Pengelly's collection : — Chonetes hardrensis Phill. Strophomena rhomboidalis Wahl. Leptaena interstrialis Phill. Phacops latifrons Bronn Streptorhynchus crenistria Phill. In an exposure by the Alluvium, at about 500 yards west of Horsebrook, near Avonwick the slates contain fossils including brachiopods and Ten- taculites ? ' Trans. Devon. Ass ic, vol. vi, 1874, pp. 650-651. ^ Quart. Journ. Geol. Soc, 1868, vol. xxiv., pp. 432, 433, Sc^ also Pengelly, Trans. Devon, Assoc, 1874, vol. vi, p. 649, 58 GEOLOGY or IVYBRIDGE AND MODBUKY. Dark grey slates are exposed in Wood Quarry, west of TJgborough; some f ossilif erous material was met with among them which yielded : — Favosites fibrosus (Goldf.) Orthotetes umbraculum (Schloth.) Crinoidal columnals ? Spirif erina insculpta (Phill.) FenesteUid Stropheodonta ? PAtrypa reticularis (Linn.) Phaoops sp. POrthis striatula (Schloth.) Between Cadleigh House and Woodland, west of Ivybridge, at the cross roads there is a quarry in fossiliferous, weathered, slates, also exposed in the adjacent road-cutting leading north. Crinoidal remains, a fenestellid and Orthis? were obtained. In a quarry on the west side of the stream valley near Ford, at a mile and a-quarter west of Lee Mill Bridge, the slates contain Orihis? and Orthotetes? North-north-east of Lyneham, half a mile west of West Pitten, fos- siliferous grey slates on the north side of a strip of vesioiilar igneous rock yielded : — Petraia sp. Orthis? Crinoidal columnals Phacops sp. At a mile and a-half east-south-east of Plympton St. Maurice Church, slates, exposed under an uprooted tree in a wood 200 yards E. by S. of Tuxton, furnished : — Petraia sp. Fenestellid Pleurodictyum sp. Phacops? Fossiliferous slates by the road at 7J furlongs north of Kitley House contain the same fossils as those obtained at half a mile west of West Pitten. Limestones. Plymouth mass. — We have already pointed out the passage of the Plymouth limestone into slate between Princerock Quarry and Laira Bridge, a similar deterioration is observable in the low cliff by the estuary near the Lodge at the south-west corner of the Race Course north of Pomphlett Quarry. On their border the dark-grey limestones are associated with red shaly compact limestone, on the south of the Race Course and near their eastern termination. There are, however, tracts of flattish land where no evidence is procurable, such as that which for half a mile separates the eastern masses. In the general notes we have assumed the separation of the limestones into two masses by the eastern continuation of the slate band from Oreston, and for a mile and a quarter east of Oreston this is certain, then for a quarter of a mile there is no evidence of slate and a consequent possibility of the limestones joining, then for half a mile there is evidence of slate again, and then the flatfish tract mentioned above. North and north-west of West Sherford, through the absence of any indication of the nature of the subjacent rock, it is pos- sible that there may not be quite as much limestone as is shown on the map. At West Sherford a little limestone occurs in the schalsteins, and the latter continue as schalstein tul¥s in the slates west- south-west to the railway cutting, where they are full of carbon- ates and are both fine and coarse ; the latter presents the appear- ance of thin coarse whitish grit in the dark green-grey fine MIDDLE DEVONIAN LIMESTONE. 59 material. The evidence favours the view that the West Sher- ford volcanic rocks and limestone are repetitions of the volcanic rocks thinning out on the south of the limestone, and of the base of the limestone passed into slate. In Radford Quarry, about half u, mile east of Turnchapel, compact pale grey limestone exhibits markings resembling ' stromatactis ' in places. R. N. Worth^ gives Oreston and Prince Rock as localities for Stroma- topora pohjmorpha. The following fossils were obtained from Cattedown Quarry: — ■ Actinistroma sp. Cyathophyllum sp. cf. Stromatopora conoentrica Pavositeg goldf ussi E. & H. Ooldf. Pachypora cristata (Blumenl).) Alveolites suborbicularis Lam. R. N. Worth gives the following from Cattedown: — Stromatopora concentrica Favosites cervicornis „ placenta ,, fibrosa ,, ramosa Heliolites porosa Acervularia goldfussi Petraia ctltica ,, intercellosa Pleurodictyum problematicum „ pentagona Smithia hennahi Alveolites vermioularis Fenestella antiqua Cystiphylliim damnoniense ,, prisca „ vesioulosum Ptylopora flustriformis From Princerock Quarry the following were collected : — Aotinostroma sp. Pachypora reticulata (de Blainv.) Alveolites suborbicularis Lam. Crinoidal remains Cyathopyllum roemeri? E. & M. Bryozoon? Cyathophyllum sp. In the slates between Princerock Quarry and Laira Bridge Athyris? and Orthis interlineata?, J. de C. Sow. were obtained. The following were collected from Pomphlett Quarry : — Actinostroma cf. clathratum Endophyllum? Nich. ? Hallia pengellyi E. d- H. Alveolites suborbicularis Lam. ? Heliolites porosus (Goldf.) J, sp. Crinoidal cohimnals Cyathophyllum caespitosum ? Goldf. Briwton limestone. — On the north margin of the volcanic rocks of Brixton, south of WoUaton and south of Gorlofen, dark and pale grey crinoidal and coralline limestones are exposed in quarries ; the persistence of the limestone hand across the valley between the exposures is doubtful, and there is no evidence of its continuation east of Silverbridge Lake. The limestone is a mass of matted corals in places. The following fossils were obtained from an old quarry 440 yards NE. by E. of Brixton Church: — cf. Stromatopora concentrica Alveolites vermicularis M'Uoy Goldf. Pachypora cristata (Blumenh.) Acervularia? Spongophyllum sedgwicki E. & H. Alveolites suborbicularis Lam . In an old quarry at half a mile east of the above the limestone is veined with brown ferruginous streaks and contains : — Alveolites suborbicularis Lam. Favosites? sp. Spongophyllum sedgwicki E. & H. Emmonsia? TJncites? R. N. Worth gives Brixton as a locality for Stromatopora ramosa, Petraia celtica and Actinocrinus tenuistriatus. 1 Trans. Pit/mouth Inst. vol. vi, 1877, p. 207. 32265 60 GEOLOGY OF IVYBEIDGE AND MODBTJRT. There is nothing to prove that these limestones were connected with the Kitley Park limestones on the south, and there is no reliable evidence for the connection of the Kitley Park lime- stones with those of Yealmpton and Yealm Bridge If there was a connection it must have been through anticlinal struc- tures the limestone overarching the intervening schaJstems and slates and having subsequently been removed from off them m the processes of denudation. Kitley ZwTiesioTie.— North-east of Winston, on the north-west of Kitley, on the north borders of a mass of igneous rocks is a band of limestone and shale probably continuous, under inter- vening Head and talus, with a patch of limestone at the north end of Kitley Park, which is bounded elesewhere by volcanic TOO kS Between the last-mentioned limestone and that of Kitley House there is a small patch apparently surrounded by volcanic rocks. Near Kitley House, on the east, there is a quarry m dark grey rather coarsely crystalline limestone with yellowish veins. The limestone is exposed in a small quarry in the Plantation near the high road, at nearly half a mile east of Kitley House, close to its junction with a mass of diabase exhibiting spheroidal structure; it has been altered to a beautiful dark green and purple marble. E,. N. Worth^ noticed the alteration of slates, in contact with the diabase at Yealmpton, to red jasper for a few inches from contact and that at contact their laminae "were fused and scorified." Yealmpton limestone. — As regards the Yealmpton limestone, Worth says, " With one exception, the general characteristics of the Yealmpton limestone may be said to resemble those of the Plymouth. It is vari-coloured, fossiliferous — abundantly so in parts — highly crystalline. But the exception is an important one. Magnesia does occur in the Plymouth limestone; but in much of that of Yealmpton it is present in such large quantities as to convert immense masses into dolomite, highly crystalline layers of which are at times intercalated between the beds of common limestone, whilst at some points the rock is wholly com- posed thereof." He also points out the analogy to the Plymouth limestone in the elevation of the surface of the Yealmpton mass being less than the districts on the north and south of it. As in the case of the eastern part of the Plymouth limestone, the Yealmpton mass is broken by flat ground with detrital accumulations which may conceal slate. Yealmpton Station is situated in this tract; a similar expanse of doubtful ground traverses the limestone south of Yealmbridge. At Yealmbridge Mill the bluish limestone is in part slaty, it dips at 20° to the south, and cannot be traced westward, in which direction it probably is speedily replaced by slate, but the evidence on the west of the quarry is very defective. On the opposite side of the Yealm the probable continuation of this mass may trough out as a syncliue in slates. To the north of this, there is another patch of, apparently decomoosea. limestone bounded by slate and volcanic rooks at Orchard Farm ; it has no apparent connection with the small patch west of it (at Hall Torrs on the 6-inch map). ' Trans. Devon. 4?soc,, vol. xxii, 1890, p. 170, also ibid., vol. vi, 1874, p. 704, MIDDLE DEVONIAN LIMESTONE. 61 On the south of the Yealm pale pinkish and grey dolomitic, more or less massive, limestone is prevalent. Near the western termination of the mass (south of Western Torrs on the 6-inch map), on the nw-th side of the Yealm, dark grey ciystaUine crinoidal limestone with Pachypora cristata is exposed. As already remarked it is difficult to account for the position of the Yealmpton limestone without assuming a fault with a considerable downthrow to the north along, or near, its southern boundary. Between Dunstone and Yealmbridge I cannot say whether the limestone passes beneath the volcanic rocks or the reverse, but on the whole I am inclined to regard it as having been formed locally on, or against, volcanic materials. Such a theory accounts for the relative positions of the limestones on either side of Sequers Bridge, and admits of the possibility of a con- nection of the Sequers Bridge limestones with those of Yealmpton having been severed by the denudation of volcanic masses in the interval. On the other hand the Hazard limestone, to which we have before referred, underlies the schalsteins, and this also seems to be the case with regard to the small patches near Ugborough and North Huish, and some masses on the borders of the Ash- prington series in Sheet 350. It seems therefore impossible to discuss the stratigraphical relations of these rocks in the manner we should treat persistent stratigraphical horizons, and the remark as to the Mount Batten limestone probably dovetailing into slates and volcanic rocks, in the early part of this chapter, is the most generally accurate statement to apply to the relations of the limestone masses in this map. In R. N. Worth's lists the following fossils are given as occurring at Yealmpton : — Stromatopora polymorpha Smithia hennahi Cyathophyllum heliauthoides Fenestella antiqua Pleurodictyum problematicmn Phacops latifrons Petraia celtica It is probable that the Pleurodictyuin, Petraia, and perhaps also the Fenestella and Phacops were obtained from slates in the vicinity and not from the limestones, the same remark might also apply to the three first named, given in Worth's Cattedown list. Sequers Bridge. — The Sequers Bridge limestones are grey, or dark-grey, partly slaty. Those on the west of the Bridge (with the schalsteins, naturally, or invertedly, overlying them on the south) may be cut off on the west by a west-south-west fault. East of the bridge the schalsteins on the north of the limestone are faulted against Staddon Grits on the north. As we follow the limestone eastward the schalsteins on the south of it die out, or are concealed by alluvial deposits, and the limestone is in part cherty and in part shaly, nor can we be sure that it has not passed into slate before the horizon is cut off by the same fault which terminates the schalsteins on the north of it. On the south an east and west fault is almost certain from the 22265 E 2 62 GEOLOGY or IVTBEIDGE AND MODBTJKY. distribution of tlie Lower Devonian rocks toward Modbnry; but whether this fault is the actual boundary of the schalsteins. concealed by alluvium at Goutsford Bridge and north of Flete, or lies further south, there is nothing to show. Passing over the limestones already referred to in discussing the Middle Devonian slate area we next come to the Buckfast- leigh mass. Buckfastleigh limestones. — These limestones are a continua- tion of the horizons of the Ashburton limestone. Champernowne seems to have regarded their outcrop as an inverted syncline. The absence of the limestone along it being accounted for by fault wedges throwing out the inverted band. The reversal of the general structure however proves the lime- stone band to be either an outcrop, dipping beneath the rocks on the east and faulted on the west, or an inverted anticline. In either case the persistence of the limestone is extremely doubtful. On the north of Buckfastleigh thick-bedded grey limestones exposed in several quarries are bounded on the east and west and, in part, if not altogether, irregularly on the south by volcanic rocks. At a quarter of a mile south of Buck- fastleigh Station similar limestone is quarried, but it here forms a small patch bounded by volcanic rocks on the west and by slate on the south and, apparently also, on the east; it seems to be quite disconnected with the larger mass on the north. The alluvial deposits of the Dart conceal the relations of the lime- stone and volcanic rock on the west to those on the east of the river. The latter, near Ware, consist of dark limestones, con- cealed by superficial deposits on the south, but above Austin's Bridge evidently passing out by intercalation, or inter digation, into slates and volcanic rocks, as repetitions of slate and lime- stone and volcanic rock were seen for about 150 yards. We next encounter limestone, on the slope at half a mile south of the west end of Buckfastleigh, which can be traced for a quarter of a mile south, and is exposed in quarries giving dips to the west. Beyond this there was no reliable evidence for the con- tinuation of the limestone, which we have assumed as shown on the map. Mr. J. G. Hamling told me that a subsidence had taken place at a point in a hedge near the high road, between the road and Dean Court Orchard, and that a hole had appeared which it was hard to fill up. This suggests a swallet hole in subjacent limestone under alluvial deposits. Near the Smithy near Dean Court blocks of limestone which might point to limestone sub- jacent were noticed and umber is said to have been obtained at Dean, but otherwise there is no evidence for continuing the limestone westward under the alluvial deposits of Dean. The schalsteins which extend from Dean southward into the Granite aureole on Beara Common we consider to represent the schalsteins of Ugborough, etc.; that is to say we include them in the Middle Devonian. On their western border, north-east ot Deancombe, a small lenticular patch of limestone was noticed m the slates, and as we follow the boundary for half a mile MIDDLE DEVONIAN LIMESTONE. 63 southward occasional fragments were noticed on the slope approaching to the calc-flinta type. In the introductory chapter the value of the Upper and Middle Devonian boundary has teen briefly discussed. It is only by the discovery of distinctive fossils in the slates that we could hope to obtain a clue to a reliable boundary. Those recorded in this chapter from localities west of Ivybridge have no dis- tinctive value, and in the Buckfastleigh area, apart from the limestones, the rocks appear to be practically unfossiliferous. A reliance on the vesicular type of igneous rocks is falsified by the fact that vesicular igneous rocks bound the small patch of limestones south of Buckfastleigh Station on the west, so that a consistent line is difficult if not impossible to find. As the calc-flintas in the area are arbitrarily included in the Middle Devonian and this type of metmorphism is not visible between Buckfastleigh and the granite border to the north of Addislade, nor on the west of the granite north of Plympton, being in each case absent where practically unfossiliferous slates of a pale grey and greenish Upper Devonian type prevail, we have in each case assumed the existence of a boundary which in the Buckfastleigh area is probably a fault or thrust running irregularly from Deancombe to the granite border. CHAPTER V. UPPER DEVONIAN. At the end of tlie introductory chapter the nature of the arbi- trary boundary for the Middle and Upper Devonian has been pointed out. The Continental Upper Devonian groups of Fammenien and Frasnian in the absence of distinctive lithological and palseonto- logical evidence cannot be approximately divided, and the lower part of the Frasnian, or Zone of Rhynchonella (Wilsonia) cuboides, cannot be separated in ilio limestone areas of South Devon, where that fossils occurs, from the Middle Devonian. Consequently where the upper beds of the limestone pass into slate, or are represented by slates outside the limestone reefs, ■without characteristic fossils we are unable to distinguish the slates representing or equivalent to the continental Zone of Rhynchonella cuboides. In areas where indications of the higher Frasnian zone charac- terised by a goniatite and bactrite fauna with Buchiola (formerly Cardiola) retrostriata (or Cardium palmatum) are evidenced, they have been taken as indicative of the basement beds of the Upper Devonian, but in our present area with the doubtful ex- ception of one goniatite, not specifically determinable, obtained west of Saltram opposite Laira Green, signs of this fauna have not been detected. Other fossils such as Styliola and cyprids which acconipany the goniatite (or Biidesheim) fauna, but range above it, are extremely rare. As regards distinctive characters the Upper Devonian is broadly distinguishable from the Middle by texture and colour. The slates and mudstones have a cleaner aspect, they are less earthy and carbonaceous. In colour the Upper Devonian slates where dark grey weather to pale grey; steel grey and silvery tmts are common and the grey tint often gives place to, or blends with, greenish and pale greenish colours. Locally buff tints are prevalent. The most striking colour distinction is in the occur- rence m mass of Indian red, or purple, and green slates and mudstones, either colour -being locally prevalent; whilst red slates are of exceptional occurrence in the Middle Devonian. When ho-ivever we attempt to assign a definite stratigraphical value to the colouring the result is unsatisfactory. The Upper Devonian rocks on the west being separated from those on the east, we will commence with the former area. tl,?M^'lw f *f " *'°^'^T °lt^^ T"^ P'"?^^' «ag«nta, and green slates of the Mutley type are met with as far north as Plym Bridge. The colouring IS variously distributed and cannot be regarded as persistent. On thi coast on the north side of Saltram Point (on the 6-inch map) opposite Laira WHn°'tf Q^t '^^*^!' ""'^^ j=l?avage planes dipping in a south-easterly .lirection at 35°, are traversed by green bands in a manner siiggestive of XJPPEH DEVONIAN. 65 bedding (Fig. 20) ; but this may not be the case, as the green bands termi- nate on one side at a brown ferruginous band running along the cleavage, and on the other side horizontal green bands terminate before reaching Fig. 20. — Opposite Laira Green on the north side of Saltram. Point. Green banding in red Upper Devonian slates. G. Green bands, h. Brown ferruginous gnarled bands. another nearly vertical gnarled brown band. If the colour bands denote bedding they show a syncline ; if the ferruginous bands are any indication of bedding they show an anticline. On the north of Gattedown there are no exposures to show the nature of the boundary between the limestones passing into slate and the Upper Devonian rocks which appear to consist of grey, lilac, red, and green slates. On the south of Ghelston Meadows the Pomphlett Quarry limestones are bounded by slaty limestone partly compact and reddish, somewhat sug- gestive of the Goniatite-limestones of the Torquay area ; but, as this is a type often met with in veins in the Plymouth limestone, the suggestion cannot be maintained. The slates associated are grey, greenish, and some- times red. Pale brown bands, probably decalciiied shale, full of traces of bryozoa and with thoracic plates of a trilobite ( fFliacops), are also met with. Traces of bryozoa were also noticed in grey slates near Choakford nearly 5 miles east of the above. At Hay Farm grey and red-lilac, or purple, slates bound the lime- stone on the north. At three-quarters of a mile south of Plympton Castle, and 7 furlongs east of Hay P'arm (Traverse b), I thought I could recognise Entomis serratostriata (Sandb.) in red slates in the road cutting, and at the time I made a note at this locality of ?Posidonomya venusta. On the assumption that fossiliferous grey slates near Butlass on the east, near Tuxton, and west of West Pitten are Middle Devonian, or represent the limestone border passed into slate, the boundary has been drawn towards Choakford so as to include purple and green slates evidences about half a mile west of Choakford. At a quarter of a mile south of Ford, near CoUaford, on the 6-inch map, there are small lenticles of limestone in the grey slates, and at 3 furlongs south-east of Ford traces of small fossils. As we have already said the slates between Lee Mill Bridge and Plympton Station which we have included in the Middle, might well belong to the Upper Devonian. The spilites of Dorsmouth Hill and the mass east of Hardwick are included in the Upper Devonian. Grey slates occur north and west of Hardwick ; they are bounded on the north by purple and green slates between Merafleld and Saltram Point (on the 6-inch map). In the latter crinoidal columnals and Phacops sp. were found, near the spot where the doubtful goniatite was obtained. West of Laira Green Inn the purple and green gives place northward to grey and dark grey slates which are associated with the Wearde-Efford grite. 66 GEOLOGY OF IVYBRIDGE AND MODBUEY. By the narrow lane south of Compton, grej buff-weathered slates are exposed on the north border of the grits. Styliola sp. was obtained in them and was identified by Prof. Rupert Jones. Near the Mill, half a rdile north-east of Egg Buckland, a small lenticular patch of limestone (apparently striking north-west) was observed in grey slates which appear bo contain Styliola. This might suggest the Upper Devonian age of the slates with limestone lenticles near Collaford, south of Ford, but without further proof such occurrences cannot be taken as distinctive of Upper rather than of Middle Devonian. Purple tints were not observed in the slates north of a line connecting Fursdon, Elfordleigh, and the northern vicinity of Newnham Park House, nor were they met with west of Newnham Park House outside the granite aureole, although red tints are common in the altered slates within the granite aureole. ThA VERSES. The nature of the evidence in the western part of the area is best shown by the following north and south traverses : — (a) From the limestone border at Wixenford north through Plym Bridge; (b) from the limestone border at a mile and a furlong farther east- — three-quarters of a mile east of Hay Farm ; (c) from the Brixton limestone band northward by Hareston, Tuxton, and Hemerdon. In these traverses it must be borne in mind that the exposures are far from continuous and often few and far between. (a) From Wixenford northward we encounter successively : — Red and greenish slates for about 3 furlongs Grey slates for half a mile. Red and green slates for nearly a quarter of a mile. Vesicular igneous rock mixed with grey slates for about 80 yards; then grey slates with a band of ? tuffs, and a terrace deposit for 140 yards to the Plym alhivial flat. These igneous rocks and slates are probably a repetition or continuation of those on the north border of the Dorsmouth Hill spilite. On the north of the Alluvium, for 3 furlongs, grey, occasionally buff and brown, slates are exposed on either side of the line of traverse, at Marsh Mills, and at the farm 3 furlongs east (Woodford Farm on the 6-inch map) where they seem to contain obscure crushed brachiopods and are penetrated by diabase. Slate and volcanic bands for 60 yards. Grey slate, apparently, for 60 yards. Grey schalsteins for 150 yards. Grey slates, apparently, for 3 furlongs. Purple and green, with occasional grey, slates for 2i furlongs to Plym Bridge. At Plym Bridge for 22 yards we cross diabase; this rock is in- trusive in the purple and green slates, and Worth" points out the presence of spilosite, desmoisite, and a modified type of adinole in its vicinity. This recalls the spilositic alteration of the purple and green Upper Devonian slates penetrated by intrusive diabases at Newton Abbot, and Black Head Torquay. ' For half a mile northward to the Cann Quarry grey, occasionally greenish, slates succeed the green and purple and green slates near the diabase. These slates are grey in Cann Quarry, where they are intersected by an aplite (see Pla-te IV.). They yielded Cardiomorpha? Fcf. Gardio- morpha? artecostata (Maur)] and Posidonomya venusta (Miinst) Worth', however, gives Gyathophyllum helianthoides as occurrin Ibid., p. 478. IGNEOUS aOCK.S. TQ at three-quai'ters of a mile west of Harbertoii Churcli ; near Yeo Bridge ; south and north-east of Belsford ; and in Earner Beacon Quarry where there is a granitoid diabase in which the dominant felspar is probably albite (1084). The Kitley Park limestone is bounded on the north by a mass of diabase exhibiting spheroidal structure. There is a possibility of, but no evidence for, the connection of this mass and the limestone with the Yealmpton limestone and the diabase on its northern border, which Worth describes' as ophitic diabase of the same character as that of Rock and Estover which is quarried on the north side of Plym Bridge for road metal under the name of ' green granite.' He gives Prof. Bonney's description of the composition of the latter rock: " much decomposed plagioclase felspar, augite in fair preservation, grains of iron peroxide resembling ilmenite, and a group of greenish minerals all probably resulting from the alteration of a magnesia- iron silicate, but consisting of more than one species — viridite, chlorite, serpentine. A few unchanged granules of the original silicate resemble olivine but others suggest enstatite, and both minerals have been present." The rock at, and east of, Estover House and east of Fursdon is a slaty diabase sill. There are three patches of diabase by the high road east of Plympton. A quarry in one of them at half a mile south-west of Chaddlewood is worked in a coarse diabase with alkali felspar similar to the rock of Yarner Beacon (6828). There are large masses of diabase on either side of Hareston prolonged, north of Lyneham, towards Furzehill on the east. The large mass of diabase south of Lee Mill Bridge is bounded on the west of the Yealm, by schalstein on the north, it is a sub-ophitic diabase (2151). The diabase between Wood and Fillham, near its western extremity, is exposed at Combe Cross (5369), and at its eastern end (5370), in a quarry near Higher Broadaford. It exhibits spilitic characters. In the slates by the high road to Ivybridge east of the quarry mudstones and yellow friable bands suggest the presence of tuffs. No specimens were collected from the diabase masses and patches near Elfordleigh and Newnham Park, outside the granite aureole. A large mass occurs near Yondertown, south-west of Cornwood, within the aureole, and shows the usual type of alteration. Sheared tuffs were seen at 3 furlongs south of Cornwood, at Tucker's Mill Head (on 6-inoh map 119 SW.). ' Trans. Devon. Asioc. vol. xix,-iS87, -p. in. 80 CHAPTER VII. CARBONIFEROUS. The rocks regarded as Carboniferous are confined to the metamorphic aureole or its borders. They evidently owe their position to an overthrust or to a series of faults and thrusts. In their unaltered condition they appear to have been dark carbonaceous shales and siliceous or siliceo-calcareous beds belonging to the Lower Culm Measures, and fine grits and dark shales suggestive of the presence of the overlying shale and grit series (the Middle Culm). The surface evidence is unfortunately very defective, so that the outcrops of the different types are not ascertainable, just where evidence is most needed, especially in the country north of South Brent and west of Ivybridge. Consequently it is im- possible to show the structure with an approximation to accuracy. The dark dense chiastolite rocks, considered peculiar to the Culm, are very feebly evidenced south of Gidley Bridge, but near Didworthy and on the border of Henlake Down, north of Ivybridge, they are exposed in quarries and display identical characters. In both these exposures and ■ between Owley and Corringdon Ball the chiastolite rocks are in close proximity to the granite, but these rocks are also evidenced between masses of calc-fiinta east of Aish and on Henlake Down. Proceeding southward from Wallaford Down the calc-flintas first appear in a connected outcrop near Bloody Pool and can be traced to Aish, near ^Ahicli place chiastolite rocks separate them from another mass which extends to Owley. The thrust boundary running south-west from Nurston must either form the eastern or western boundary of the calc-flintas between Bloody Pool and Aish. In the former case they would be included in tlie Culm and from Aish to Owley the altered igneous rocks would be bounded by the thrust. In the latter case it would be most reasonable to include the Owley calc-flintas in the Devonian, and the thrust would form their boundary cutting them off from the small patch of chiastolite rock in contact with the granite near Corringdon Ball. On either of these hypotheses the thrust if prolonged would run along the granite boundary to the Wrangaton Valley, becaiise there is a large mass of calc-flintas at Wrangaton and Bittaford ]3ridge which cannot be dissociated from the Devonian. The problem then arises as to which group of rocks we are to refer the calc-flinta outcrops shown on the map on either side of Stowford House. If these are included in the Culm the thrust will have to be drawn from the most southerly part of Ihe granite boundary so as to include them; if on the contrary these calc-flintas are treated as Devonian, the thrust will leave CAXIBON IFEllOU S . 8 1 the granite just east of the Ernie Valley, trend south west to the southern margin of the Henlake Down eale-flinta mass, and thence westward so as to include the Fardel calc-flintas, but beyond this the evidence is so defective that the line originally drawn may be taken with slight modification to represent the boundary between Culm and Devonian. 82 CHAPTER VIII. AUREOLE OF THERMO-METAMORPHISM.* Of the Aureole round tlie Granite 20 miles are included in this map. The rocks present consist mainly of more or less altered fine- grained sediments, some of which are calcareous. Associated with these altered sediments is a considerable variety of altered igneous rocks more or less basic, of these some undoubtedly were ' sills ' originally. But in many cases these rocks have been so altered previous to the granitic intrusion that their further alteration (by the granite) has completely obliterated all traces of original structure. The more common type of altered fine sediments occurs, almost to the exclusion of all other types, throughout the western and in the extreme north-eastern portions of the aureole. In these areas the more ordinary types met with are practically identical with those in the aureoles encircling the other granite masses in the south-west of England. Commencing with the outer margin of the aureole, at first a faint spotting is i)er- ceptible, becoming more distinct and the spots generally larger as the granite is approached ; and these spots can now, in most cases, be proved to be andalusite. This mineral, however, is rarely pure, but contains included particles of some of the other components of the rock, the most common being a dark dust, or small black grains, mostly iron ore, and less commonly car- bonaceous material. The spotted rocks first encountered at rather more than half a mile from the granite north of Bickleigh Station are occasionally associated with specimens containing well formed crystals of chiastolite, easily visible to the naked eye, though their form can be better recognised by the aid of a hand lens. The matrix in which they are set is an extremely fine-grained micaceous phyllite. Larger crystals of chiastolite occur in similar phyllites of a reddish tinge, 200 yards south-east of Coleland Bridge, south of Lee Moor clay works, at about three furlongs from the granite. Slightly nearer the granite, north of Bickleigh Station, the structural arrangement of the slate has been largely preserved, although the rock has been entirely recrystallised. The rock is mainly composed of white and brown mica; the latter, usually forming the larger crystals, which are specially well developed along and parallel to the plane of strain-cleavage originally existing in the slate ; the strain still persisting in the slate when the rocks were raised to a higher temperature determined the direction of maximum elongation of the biotite. Between the planes the crystals forming the ground mass of the rock are not arranged in the same direction, but often at right angles to it, and are on the whole much smaller. In many cases these smaller crystals follow the minute puckering of the original bedding. Erom this it follows that all the interstitial movements * By Gr. Barrow. METAMORPHIC AUREOLE. 83 within these sediments took place anterior to the intrusion of the granite, and further that reconstruction takes place most readily along the planes of movement and strain; the latter being the dominant cause of the parallel arrangement of the large crystals. A specimen taken about 240 yards from the granite shows a more or less lenticular structure, the lenticles being separated by more or less continuous films of finely granular quartz. The material between these quartz films is largely composed of minute crystals of white and brown micas arranged criss-cross fashion ; a true hornfels structure, the parallel structure of a schist being but locally developed. Close to the granite, in Shaugh Tunnel, a specimen was obtained specially rich in white mica. In this crystals of this mica have been developed having their basal plane almost at right angles to the plane of foliation. They are considerably larger than the micas of the groundmass, and on the cross-fractured face of the rock appear as easily visible glistening specks. The rock thus belongs to the type known as ' spangled mica schist.' A further point of interest is that no brown mica is present ; the material capable of forming it has been used up in the formation of blue and brown tourmaline, which occurs in fair-sized aggregates of small grains scattered through the rock, which has thus been partly tourmalinised. This tourmalinisatiou seems to be re- stricted, in the area about Shaugh Tunnel, almost to the imme- diate margin of the granite; localtourmaliuisation, however, is met with at the margins of the veins by which the killas is traversed. The southern and south-tu^tevn portion of the Aureole (between. Cornwood and Dean, near Buckfastleigh). This portion of the aureole is of special interest not only on account of the variety in the original composition of the rocks affected, but also owing to the fact that these rocks have been altered by two separate and distinct metamorphosing agencies, which may be described as normal thermo-metamorphism and pneumatolytic action, or alteration by special gases along fissures and cracks. As stated previously there are present in this part of the area basic igneous rocks, the common type of fine-grained sediment, and also a group of more or less calcareous beds which show specially well the development of certain special minerals by the second metamorphosing agency. An account of these rocks in the Avon valley near Brent has been published by Dr. Busz, as stated in the introduction, but though he has described the minerals due to pneumatolytic action, he does not ascribe to them a distinct origin, or note that they were developed at a slightly later date than those produced by the normal thermo-metamorphism ; to make this clear it seems advisable to describe the two types of rocks separately as far as possible. Normal thermo-metamorphism. — The ordinary fine-grained sediments are altered on exactly similar lines to those already described, and it will be sufficient here to give a brief reference to localities where specially good examples can be found. 84 GEOLOGY or IVYBRIDGE AJSTD MODBUBY. Above Ivybridge there is an almost continuous exposure of the rocks on the margin of the granite in the bed and by the side of the River Erme. The granite, owing to its uneven surface, is seen in a small mass in the bed of the river some distance before its main outer margin is reached, and the clastic rocks are well crystallised throughout. Owing to repetition by folding, however, only a small portion of the sequence is observed, and there is not much variation in the type of rock produced. The dominant rock was probably a gritty shale originally (now a flinty siliceous biotite-hornfels) associated with small infolds of the chiastolite-bearing rock. Where the former type is in direct contact with the main margin of the granite it is coarsely crystalline and apparently saturated with granitic material, having all the appearance of a rather coarse gneiss. To the west of this point on the summit of the gorge is the well- known quarry from which (as noted by Worth) specially good specimens were obtained. The chiastolite seems to be equally well developed in dark and pale coloured rocks in this quarry. A similar phenomenon occurs in a small quarry by the wood (Overbrent Wood, on the 6-inch map) above the Avon valley at about a quarter of a mile south-east of Didworthy. Chiastolite- bearing rocks also occur at Corringdon, and are observable here and there for a mile or more north of the quarry by Overbrent Wood. Xo more need be said about the chiastolite rocks as this type has been fully described by Dr. Busz. The flinty biotite-hornfels, however, is interesting as the stages of its metamorphism have been fully traced, and as it has been found at fully a mile from the margin of the granite, the lime- bearing rocks being altered at a greater distance. The original material of the flinty biotite-hornfels was a fine gritty shale — composed of finely-divided clastic chlorite, minute quartz grains, and a small but variable amount of felspar. The water of hydration in the clastic chlorite seems to be set free at a distinctly lower temperature than that of the mica in ordinary shales, ond readily acts upon and digests the finer quartz grains. This results iu the production of a rock composed of fine, somewhat elongated, crystals of biotite set in a matrix of very fine quartz grains, which is in most cases intensely hard and somewhat brittle, and has a distinctly brownish colour due to the brown mica. When, as in this area, the original material has been subjected to great strain anterior to heating, the micas are arranged rigidly parallel and the rock can be split open parallel to the original strain plane, and the splitting face in fresh specimens has a marked bronzy lustre. It is a marked charac- teristic of these rocks that, as the margin of the granite is approached, the texture, as seen in the microscopic sections, increases very slowly in coarseness, their fine compact structure being retained almost to within a few yards of the granite margin. This feature of the homfels is well shown by a specimen (5417) obtained in a quarry situated a little north of the one in chiastolite schist referred to above. Thus although it is more readily altered than a normal shale it does not usually participate in the increased coarse crystallisation CALC-FLINTAS. 85 shown by the latter. Though this material occurs for the most part in thin bands it has a very widespread distribution and forms abundant small partings in the altered calcareous rocks to be described next. Altered Calcareous Rocks (Calc-fiintas). The calcareous sediments which form so important a feature in this portion of the aureole have a natural outcrop in the bed of the Erme beneath and to the south of the viaduct. They occiir next to the altered sediments already described but furtlier from the granite so that their highest phases of thermo-meta- morphism cannot be studied here. The chief interest of the section lies in the clearness of the order of succession, whether ascending or descending. Throughout most of this part of the aureole the altered calcareous sediments have pale greenish and dove-grey hues, a very fine-grained matrix, a somewhat flinty cross-fracture, and are intensely hard; a combination of characters which causes them to form a valuable road metal. Numerous quarries have been opened in these rocks, and per- fectly fresh material can be obtained for microscopic examina- tion which is rarely possible in the natural exposures. This alteration of the calcareous sediments to a hard flinty rock in which practically all the original component grains have been reconstructed extends fo^; more than a mile from the granite margin. As the margin of the granite is approached, however, the increase in coarseness of texture of the rock is extremely gradual, and the matrix retains its flinty aspect until within a few yards of the granite, when the rock rapidly becomes much coarser, so much so that the component grains can be occasionally recognised by the unaided eye. Owing to this retention of their extremely fine grain and accompanying fiinty aspect, the term calc-fiintas has been applied to these rocks. Under the microscope in a typical specimen from Wrangaton quarry, a quarter of a mile from the granite (5423), the. fine matrix is composed of a great number of vividly depolarising grains of a calc-silicate associated with a smaller number of minute grains of quartz and at times some of felspar. The calc- silicate is either pyroxene or epidote ; the pyroxene may be either white or very pale green, while the epidote is frequently asso- ciated with zoisite. The occurrence of zoisite is important; as the grains are so small that it is often difficult to say if pyroxene or epidote is present, but if the zoisite be abundant, the accom- panying vividly depolarising calc-silicate is generally epidote. The same type of matrix occurs in a specimen taken from a quarry at the mill west of Fardel, a mile from the granite border. In this specimen the texture is somewhat finer but the structure is the same. At this distance, however, the calc-silicate seems to be entirely epidote or zoisite, though owing to the minuteness of the grains the point is difficult to prove. In many cases larger isolated ciystals of pj-roxene or epidote are embedded in this fine matrix, and when these become numerous the compactness of the rock is somewhat lost, and it becomes less valuable as a road stone. 86 GEOLOGY OF IVYBBIDGE AND MODBURY. In some cases the original calcareous sediments were distinctly of a more muddy cliaracter, and then a considerable amount of actinolite may be developed, which tends to form larger crystals than the other calc-silicates, and the rock is darker in colour. When quite close to the granite the increased coarseness of the rock renders it valueless as road metal, and as no quarries have been opened in it, we have to rely upon natural outcrops which are very rare. Good specimens, however, were obtained in the immediate vicinity of the granite west of Owley, and in some of these the quartz grains of the ground-mass could be distinguished by the unaided eye. Pneumatolytic Action. — These calc-flintas show better than any other material the efiects of ' pneumatolytic action ' or of gases that have invaded the rocks along fissures or cracks or other planes of easy yielding. As a result of this action a series of special minerals have been developed, of which a full account is given by Dr. Busz. These include axinite, green prismatic pyroxene (hedenbergite), markedly anomalous garnets, datolite and quartz. Of these minerals by far the most widespread is axinite, which ■ occurs in cracks and films in almost every quarry in the district, but there is a great variation in the amount of it present. Though this mineral has been met with at a mile from the granite (5406) it may be, and often is, entirely absent from specimens taken close to the granite margin ; thus there is no direct connection between the invasion of these gases and the granite itself. But as the phenomenon is restricted to the neighbourhood of the great granite masses, it seems clear that both proceed from the same deep seated source. That this pneumatolytic action is slightly more recent than the granite intrusion can be proved by microscopic examination of a typical specimen of a normal contact altered calc-fliuta within which axinite has been developed. Thus in a specimen from AYrangaton road-stone quarry, the axinite has been de- veloped in a crack crossing the original bedding of the rock, and here the junction of the contact structure with the materials in the crack is clean and sharp so that it is at once seen that the axinite is not only later than the granite, but also later than its contact metamorphism. The axinite can be traced from the crack into the body of the rock approximately following the original planes of bedding. In this case the margin of the area affected is not so sharply defined, and scattered small particles of axinite have been developed round the margin of the continuous patch of this mineral. It may be here noted that schorl is never developed in this manner in the calc-flintas, and in the few cases in which this mineral has been met with, microscopic sections show that it really occurs in a thin film of originally muddy material within the calcareous rock, too thin to be identified in the hand specimen. It is thus clear that the difference in the minerals produced is essentially dependent on the difference in the original com- position of the rock. METAMOHPHIC AUREOLE. 87 This type of alteration differs fundamentally from that nor- mally produced round the granite mass. In the latter case the new minerals in the contact roclfs except quite close to the granite margin are wholly endogenous, that is, have originated exclusively from materials already present in the rock. The minerals, however, developed by pneumatolytic action have a douhle origin, being formed from the endogenous material with the addition of a foreign or exogenous constituent. In other words the veins and patches composed of these special minerals are partly of intrusive origin. The other special minerals have been developed in a similar manner to the above. The anomalous garnets, which are often beautiful objects under the microscope, have been met with in many other areas^ ; but datolite and the prismatic green pyroxene have a much more restricted range. The datolite in particular has rarely been identified in similar specimens in other localities^ ; moreover in the large series of slides examined, from this area, Mr. Dick has succeeded in finding it in only one section. Clearly Dr. Busz has had the good fortune to find a specimen excep- tionally rich in this mineral. The bright green prismatic pyroxene, so far as is known at present, is developed in greater abundance in the South Brent district, near Aish, than in any other part of the south-west of England. It is fairly common on the north and north-west of the St. Austell granite, and was un- doubtedly found many years ago in West Cornwall, but was generally taken for actinolite, which it resembles, but its true nature was pointed out by Dr. Flett. A striking feature of these special minerals is the great size of the crystals in which they occair as compared with the component grains in the calc- flintas. These special minerals may be quite, as large nearly a mile from the granite as they are close to its margin. IGNEOTTS ROCKS. In the eastern and southern part of the aureole rocks rich in actinolite are abundant, and often form large coherent masses, as on Beara Common, the hill which forms the most prominent feature on the north of South Brent. Brown mica in crystals of variable size is also present in many of these rocks, sometimes in considerable quantity. Though many of these rocks have undergone great mechanical deformation, it does not follow that the two minerals above mentioned are of dynamic origin, for they do not occur outside the granite aureole of thermo-metamorphism. It should, however, be noted that these crushed igneous rocks show heat alteration to a considerably greater distance from the margin of the intrusion than ordinary sandstones and shales. That the actinolite is really of thermal origin is further shown ' G. Barrow and H. H. Thomas, ' Metamorphic minerals in Calcareous Bocks in the Bodmin and Camelford Areas, Cornwall.' Min. Mag., vol. xv, 1908, p. 113. * W. F. P. McLintock, ' Datolite from the Lizard District, Cornwall.' Min. Mag., vol. xv, 1910, p. 407. 88 GEOLOGY OF IVYBHIDGE AND MODBURY. by the fact that the crystals steadily increase in size as the granite is approached. In many cases these rocks also contain vividly depolarizing granules of sphene which again are usually larger when the rock is nearer the granite. Toward the outer margin of the aureole these grains are so small that where matted together it is often difficult to decide whether we are dealing with leucoxene or sphene; both, however, result from the alteration of ilmenite in the original rocks. This double metamorphism, firstly mechanical and secondly thermal, often makes it difficult to decide the original character of the rocks, whether sills, lavas, or tuffs. Thus, taking first the case of a very fine-grained rock, such as that forming the summit of the hill north of South Brent, microscopic sections show no dragged out oval bodies (infilled cavities) such as one would expect had the rock been a lava. Fui-ther the examination of the sections shows that this rock agrees in every detail with similar rocks in a similar position (on the outer margin of the aureole) which have been proved by field evidence to be fine- grained moderately basic intrusive diabase sills. The present extremely fine structure is partly due to the position in which it occurs ; had it been nearer the granite the texture would have been considerably coarser. As a contrast to the above, we may take a rock (5376) east of Dinnaton which is shown by a single microscopic section to be undoubtedly intrusive, for remnants of its original ophitic struc- ture are still clearly visible although the rock has undergone considerable thermo-metamorphism. But it has largely escaped dynamic metamorphism, and the original method of piecing together of the mineral is partly left. The thermal action has thus produced paramorphic alteration, the original pyroxene being altered to actinolite. In this case the large size of the actinolite crystals is mainly dependent on the original size of the pyroxene crystals, which being an original component and older than the granite can have no connection with the latter. Specimens (5380, 5381) taken close to the granite at the head of Wrangaton Bottom, still show moderately coarse ophitic struc- ture. An example of a fine-grained rock of which the origin ifc somewhat doubtful may be seen in the lower crags of Brent Hill or Beara Common facing north-west. This also is a very fine- grained, dark, actinolite-bearing rock ; but that it was probably a tuff originally is suggested solely by the field evidence. Brown mica hearing varieties. — Brown mica is abundantly developed in two specimens, one 5390 (at Binnamore near Aish) close to the granite, the second 5391 (east of Didworthy) being somewhat further off. In the former occasional good sized sheets of brown mica are met with, in which the original felspar laths are ophitically embedded exactly as in the pyroxene of a dolerite. The second specimen was clearly the same rock originally, tho felspar laths are the same size, but the mica crystals are con- siderably smaller owing to the fact that they have been developed by heating at a greater distance from the granite. It will thus be seen that the brown mica plays the role of the actinolite in the rocks previously described. It is a point whether this h^d METAMOEPHIC AtJEEOLE. 89 anything to do with original difference in composition. It seems more likely to be due to decomposition before metamorphism accompanied by a loss of lime, so that in the altered rock a silicate as rich in lime as actinolite could not form, and its place is taken by brown mica which contains much less. It has been clearly proved in other aureoles of metamorphism both in England and Scotland that the amount of contact mica developed in inter- mediate and moderately basic rocks is largely dependent upou the extent to which they had been previously decomposed. In the area here dealt with a third specimen 5392 contains only a small proportion of this red-brown mica, hornblende being abun- dant. As there is good reason to think all three intrusive rocks were of the same original composition, the much greater amount of hornblende present in the last is easily explicable if we suppose it to have been less decomposed, and in consequence much less lime to have been leached out. 90 CHAPTEE IX. GEANITE. In the north central part of the map the granite occupies on area of about 40 square miles in which are included the china clay districts of Lee Moor, Cadover Bridge, and Heddon Down. In the Introductory Chapter the irregular boundary of tlie granite, and its influence on the strikes of the surrounding rocks has been pointed out, an influence which extends far beyond its immediate surroundings. The irregularity of the granite surface, as exhibited around Cornwood and Eingmoor Down, produces considerable extensions of altered rocks in the embayments of the granite, so to speak; whilst at the steeper headlands as along its southern projection on either side of Ivybridge, at the south end of Hemerdon Ball, and near CoUard Tor and Shaugli "Bridge, the aureole is com- paratively narrow. On the south of Hemerdon Ball it is less than a quarter .of a mile wide and in the other instances about half a mile, whilst on Wallaford Down, at Beara Hill north of South Brent at Goodameavy, Hoo Meavy, and Callisham Down it is a mile or more in breadth. The late E. K". Worth^ made a special study of the Dartmoor Granite, of all the varieties of altered granite and elvans found not only in situ but in the gravels of streams descending from Dartmoor, and of the contact rocks, especially of those within this map. In his paper on ' Contact Metamorphism in Devon- shire ' he says, " I am inclined to attribute the exchange of anda- lusite for chiastolite, or the reverse, to variations in the com- position of the metamorphosed rock " and adds " Casual crystals of chiastolite occur indeed elsewhere, as at Cornwood ; but our only well-marked example of chiastolite-slate is a massive blackish slate at Ivybridge. And I am strongly disposed to the belief that while our andalusite-slates are of Devonian origin, this is Carboniferous . ' ' Stibsequently when mapping this part of the area I came to the same conclusion as Worth respecting the chiastolite slates. Subsequent mapping in Cornwall proved the representation oE lower horizons in the Upper Devonian by dark slates which might well yield this type of alteration. Worth described the types of alteration near Shaugh, the advance of metamorphism from talcose slate to andahisite slate. He points to the development of mica in the andalusite spots as the next stage in alteration, imtil the rock near contact with the granite becomes a mica schist. ' ' The Rocks of South-West Devon,' Trans. Devon. Assoc, vol. xix, 1887, pp. 489, 490, 494. 497 ; 'Contact Metamorphism in Devonshire.' Ibid., vol. xxii, 1890, pp. 169-184 ; ' Materials for a Census of Devonian Granites and Felsites,' Ibid., vol. xxiv, 1892, pp. 189-192, 194-203 205-207 GEAJS'ITE. 91 Worth in 1900 mentioned {op. cit., p. 178) the tourmalinized rocks of Shaugh Tunnel/ alluded to in the previous chapter, as veinstones consisting of altered slates traversed hy veins of peg- matite alongside of one of a more distinctly granitic character. Contact exposures were observed by the stream near Shaver- combe Tor^ ; in a small quarry at the north-western spur of Hemerdon Ball ; in the Erme Valley, and in the quarry on the moor above it on the west. The granite is of the usual porphy- ritic type varying in coarseness and in colour from grey and buff to pinkish and red. Great Trowlesworthy Tor affords a good example of the red granite, the rock here consists of " microperthite, quartz, oligo- clase, white mica, and tourmaline, no biotite visible." There is a pillar of this rock in the Museum of Practical Geology. Red and grey muscovite granite with tourmaline, with pseudo- bedding planes dipping south at 20°, was worked by the Great Western Railway Company in a quarry close to the margin of the mass, 1 mile east of Ivybridge Station. The quarry at 3 furlongs north of Ivybridge Station exhibits grey granite, of quartz, orthoclase, twinned and crossed, tourma- line and biotite, flesh coloured at its extreme margin. By the River Avon west of Dockwell Ridge a quarry yields rather large blocks of pale grey granite, determined by well defined horizontal floors crossed by clean joints. The character of the Tors is determined by the intersection of the pseudo- bedding floors by vertical or inclined joints. The Dewerstone (Plate 1), Legis Tor, Hen Tor, Tristis Rock, and Tor Rocks near Harford, are split into more or less cubical masses. Gutter Tor, Black Tor, and TJgborough Beacon exhibit cake-like forms. In some places, as on Brent Fore Hill and in the Erme west of Sharp Tor, through the evenness and definition of the fioors the granite forms tabular masses. The pseudo-bedding joints, or floors, conform more or less to the general slope of the surface, as at Western Beacon, being often horizontal on the summits, as at TJgborough Beacon and Eangershell Rock. On Burford Down these planes dip eastward near the Erme ; in a quarry at a quarter of a mile south-east of Lukesland they dip to the west, here the granite is much disin- tegrated. The granite is frequently disintegrated to a considerable depth from the surface, and in this disintegrated material or growan which commonly forms the soil or subsoil and lines the peaty hollows on the surface of the moor, gravel or sand-pits have been opened for metalling contiguous farm roads and paths north and east of Corringdon Ball, west of Downstow, and west of Skerra- ton, at and near the granite margin. On Hanger Down near Donore on the west there is a pit in pink and pale-grey disin- tegrated granite partly yellow through ferruginous staining, penetrated by irregular veins of red schorlaceous granite and ' See also Proc. Somerset. Arch, and Nat. Hist. Soc, vol. xxxviii, 1892, pp. 210-213. • Shavercombff junction rock. See Worth, Trans. Devon. Assoc, vol. xxiv, 1892, p. 208. 22265 G 92 GEOLOGY Of IVYBEIDGE AND MODBURY. overlain by 5 feet of growan. Owing to the impossibility in distinguishing growan soil washed or slipped from the disin- tegrated rock in situ the granite boundary is very uncertain near Donors and west of Harford; on the east of Wotter, on the northern extremity of the Crownhill Down granite (which may not extend as far as shown on the map by 300 yards) ; and between Wrangaton and Owley. The granite between Crownhill and Heddon Downs is mostly kaolinized. As seen in the clay-pit north-west of Smallhanger it is a decomposed schorlaceous porphyritic rock, intersected by schorl and quartz-schorl veinstones seen in the east side of the pit and mostly dipping north. Between the kaolinized granite and the altered killas there appears to be a granular felsitic rock or aplite. Fear Tory Brook Head a China Clay Pit at 3J furlongs north of Cholwich Town exhibits greisen and schorl veins apparently dipping north-west at 30° to 40° in the kaolinized granite. The large pits south of Lee Moor House show dyke-like masses of harder greenish granite and occasional quartz-schorl veins in the kaolinized rock. The deeper pit will be referred to in the Economic Chapter. West of this and north of Wotter there is a China Clay pit in which thin quartz-schorl veins seem to dip north-west. Mr. J.. H. Collins^ expressed the opinion that the China Clay rock seldom extends more than a few fathoms on either side of the schorlaceous veins in which kaolinization seems always to have originated, but may accompany them to a depth of 100 fathoms or more from the surface. The old pits and ponds, as well as those worked, at Shaugh Lake Works, half a mile south-east of Cadover Bridge, and in the tract coloured as Head on the east of Wigford Down suggest a more or less continuous area of kaolinization. Further east the clay had been proved in a few places and worked to a small extent, as is shown on the six-inch maps in Petre's Pit north of Knatta Barrow, at Left Lake, and at Brent- moor Works by the Avon Valley north of Zeal, near Shipley Bridge. Additional localities will be described in the Economic Chapter. At 290 yards south of Smallhanger there is a small patch of decomposed granite. A small band of granite is shown on the somewhat doubtful evidence of surface stones between Lynch Common and Brisworthy north-east of Wigford Down. Another band of granite is shown on the map on the north of Olderwood plantation. This and the larger mass at Callisham Down may be connected; they, including the previous instance if in situ, are exposures of the subjacent granite, not el vans. Mr. R. H. Worth showed me a fragment of apparently un- altered Devonian lava of spilite type which he had picked up on the surface north-east of Brisworthy, but I have never seen any signs of basic igneous rocks rocks in situ in the locality. The irregularity of the granite surface is further evidenced by the small mass above Shaugh Tunnel south of Goodameavy ' Journ. Mill. Soc, vol. vii, 1 882, p. 205. GRANITE. 93 and by the irregular mass of Hemerdon Ball. The latter is exposed in a quarry in the central part, in which it is seen to be a granular micro-granite intersected by numerous schorl veins and dykes which dip north (Fig. 22) ; the granite also exhibits Fig. 22. — Hemerdon Ball Quarry. Schorl veins and dykes in granite. highly inclined joints, more or less parallel with the veins and dykes, and has a more or less pronounced horizontal flaky struc- ture, or close cross jointing. In the contact quarry at the north-eastern end of the mass a fine micaceous quartz-schorl rock forms the granite border, it contains nests of mica flakes. The banding in the altered slates is cut off by the granite, but the quartz veins and major joint lines are more or less parallel to the line of contact. On the south margin of the granite of Hanger Down, north- east of Dinnaton, schorl forms the contact rock for a quarter of a mile. West of Skerraton the granite is very schorlaceous and for 3 furlongs from its margin in an east-south-east direction the surface, south and west of Skerraton, is studded with boulders of quartz-schorl rock. To what extent these may have gravi- tated down the slope it is impossible to say, the line on the map merely denotes their extension and the limits within which an apophysis of this type occurs. R. N. Worth, in his paper on the ' Igneous and Altered Rocks of south-west Devon, '^ describes the following: — A dark grey contact rock at Shaugh, compact, partly foliated, largely felsitic with quartz, mica, tourmaline, and, apparently, a little plagio- clase. A contact specimen from near Cornwood showing a micro- granite, with orthoclase, quartz, brown mica and garnets and a micaceous schist. From Shaugh — a schorlite — or fine grained dark grey mixture of schorl and porphyritic quartz. From Lee Moor a white luxulyanite — " Felspar partly kaoli- nized, grey, and some yellow and blue, tourmaline and a little quartz. From Wigford Down a form a luxulyanite, white orthoclase in schorl matrix; also a specimen of greisen with " a <'rystal of staurolite? " From Trowles worthy^ a surface block pronounced by Prof. Bonney to be an altered granite. This rock, named trowles- worthite, contains red felspar, velvety tourmaline, and purple ' Trans. Devon. Assoc, vol. xix, 1887, pp. 49B, 494. ' See also ' The Rocks of Plymouth,' Trans. Plymouth Insl., 1886. 22265 G 2 94 GEOLOGY OF IVTBEIDGE AND MODBURY. tluor, " The mica having been replaced by brownish tourmaline some portions of the felspar by greenish-black tourmaline and quartz, and the original quartz by fluor-spar." In Worth's ' Materials for a Census of Devonian Granites and Felsites'^ many specimens from this area, of varieties of granite, pegmatite, and felsite, are included, — 8 from Hen Tor, 7 from Harford and its vicinity, 7 from Trowlesworthy, 6 from TJgborough Beacon, etc., the descriptions are in alphabetical order. In his ' Petrography of Dartmoor and its borders' R. H. Worth describes a felsite " immediately associated with the Dartmoor granite," and found at intervals as a sheet on the outer surface of the granite separating it from the surrounding rocks, or occurring on the irregular surface from which the overlying sediments had been denuded. He describes specimens of this (red) felsite at length from Legis Tor where the red granite passes into it on the east, and other places. " Immediately above Shavercombe Waterfall the red felsite is to be found in situ."^ The next in situ exposures mentioned are at the granite border in junction with the altered slates, by the confluent of Broadall Lake west of Dendles Wood — in the Ludbrook Valley west of Wrangaton. Long. 3° 52' 55", lat. 50° 24' 23". Several cases are mentioned as north of Pithill (north of Ivy- bridge) Brockhill Mire Leat Ford (west of Buckfastleigh) where the surface stones are sufijciently abundant to be taken as evidence of the felsite, in situ, and many where its presence in the vicinity may be inferred from stones in walls and hedges. During the progress of the survey an elvan was observed on the east bank of the Plym at the northern border of the map. West of the Dewerstone Rock, at about 340 yards north-east of Shaugh Bridge, a section of the granite is exposed by the road at the entrance to a quarry. The rock is a two-mica medium- grained granite, with rather small orthoclase crystals often twinned, tourmaline locally scarce. It here shows very distinct pseudo-bedding with a sharp northerly or north-westerly dip. In one place between the pseudo-bedding planes a reddish aplite, sprinkled with tourmaline, about 4 feet thick, was noticed. Oligoclase and quartz are specially abundant in it. About 5 feet of the aplite is visible in the adjacent quarry where its smooth surfaces suggest folding. In the plantation near Hall blocks of felsitic rock were noticed. Near Ball Gate, in the vicinity of Corringdon Ball, occasional fragments of greenish granitoid rock have been found on the surface (also by Mr. R. H. Worth). A granitic dyke or vein was noticed in the altered slates in Broadall Lake, at about a quarter of a mile above its confluence with the Tealm. In the bed of the Erme, at 260 and 300 yards above the railway viaduct, granite veins or dykes traverse the altered sediments. One of these is probably an aplite. At about 50 yards higher up 1 Trans. Devon. Assoc, vol. xxiv, 1892, pp 1«.3-21.=?. ' Trans. Devon. Assoc, vol. xxxiv 1902, pp. 511-557 ; and vol xxxv, 1902-3, pp. 759-767. ELVANS. 95 a patch, of granite forms the river bed, the floors, or pseudo- bedding joints, dip under the altered sediments at a low angle, whilst the planes of the latter m.ostly dip toward, and are cut off by, the granite. An elvan — a cream coloured fine grained quartz porphyry with specks of schorl — was noticed in a granite quarry 200 yards north- west of the Plymouth Asylum (Blacket on the old 1-inch map) . In a quarry on the west side of the valley, north of Bittaford Bridge, at about 380 yards from the granite boundary, biotite- hornfels is cut through by three elvans, or granite apophyses, which appear to strike north-east and south-west in parallelism with the granite boundary. One of these splits into branches and it is doubtful whether any of them reach the surface. It consists of medium-grained muscovite granite with tourmaline, making a very sharply defined junction with the biotite-hornfels. In Worth's list four varieties of granite and felsite are given under the locality ' Blackett.'^ Amongst these is a felsite, "with small porphyritic granules of quartz and needles of schorl," varying in texture, and in part weathering chalky. By the river Avon, at 300 yards east of Binnamore and nearly 5 furlongs north-west of Lydia Bridge an aplite dyke containing brown and blue tourmaline was noticed. The rock is by no means easy to find. Another instance of elvan dykes in the altered rocks on the granite margin was furnished by the trench on Skerraton Down, before mentioned, in which elvan dykes were observed at 260 and 340 yards from the granite boundary. In the cases cited above of elvans outside the granite margin- but less than a quarter of a mile from it, as far as can be judged from the exposures, the dykes strike in more or less conformity to the trend of the granite boundary. ELVANS BEYOND THE GRANITE PERIPHEET. These have already been localised in the Upper Devonian Chapter, viz., two on Roborough Down; one south-west of Shaugh and half-a-mile east of Bickleigh Station; two in the vicinity of Bickleigh and Roborough ; one at the Ford (Riverf ord Viaduct on the 6-inch map), which splits eastward in Great Shaugh Wood; one between the streams on the north side of Cann Wood; the Cann Quarry (see Plate IV) elvan which runs westward on the south of Colwill and Derriford. These are evidenced by natural or artificial exposures. Some blocks and sur- face stones suggest the occurrence of an elvan north of the Riverford Viaduct. These elvans approximate to an east and west direction. The largest mass on Roborough Down, is the most persistent and has been traced at intervals for a distance of 4 miles into the adjacent naap, Sheet 348, as far as the South Western Railway south of Beer Alston. The general distribution of the elvans in Sheet 348 and 349 suggests a westerly trend of the steeper slope of the concealed ' Trans. Devon. Assoc, vol. xxiv, 1892, p. 189. 96 GEOLOGY OF IVYBRIDGE AND MODBUEY. granite mass, from Hemerdon Ball as far as the western border, of this map, and a north-westerly deflection across the north- eastern corner of Sheet 348, which a little further north resumes the westerly trend on the south of Kitt Hill and Kingston Down and on to the south margin of the Bodmin Moor Granite. The lioborough Down elvan is described by E. N. Worth as " Greenish-grey; compact sub-vitreous base, with small pyramidal quartz crystals, and cavities from which they have disappeared, the latter occasionally lined with a greenish yellow crust. Weathers earthy and ferruginous."^ " Under polarized light, shows a very fine granular mosaic, with little nests of ferrite. The ground mass is composed of quartz and a fine micaceous mineral, which is probably a result of the alteration of the felspar."^ Jump, on the old 1-inch map, corresponds to Eoborough on the new. Worth describes the Jump, or Eoborough, elvan as " green grey weathering brown; a granular quartzose micaceous elvan, cut in road in laying water pipes." ^ Worth described the elvan in Cann Quarry as an aplite ; at GJ^olwill he gives its width as about 30 feet, its direction W. 5° S. and its dip south at 65°.* Its character " Brownish-grey; finely- granular felsite with occasional small bleb of quartz or fleck of white mica; interpenetrated by dendritic markings from some of the joint faces.'" The Cann Quarry elvan is shown in Plate IV. It has been figured and minutely described by E. H. Worth, ° who enters at length into the relations of the buff or cream coloured rock which forms the main mass of the dyke, and the green rock which forms its chilled margin and occurs as veins in it. The one he regards as "a true micro- granite, the only deviation from the type being the ragged ends of the felspar"; the other he considers to be "a quartz-ortho- clase mica-felsite, with indiscriminate ground mass." I obtained a specimen containing fluor spar from this dyke. The slide was described by Dr. Teall (The British Culm Measures — Proc. Somerset. Arch, and Nat. Hist. Soc, vol. xxxviii., p. 213} as " white fine grained massive rock composed of a micro- crystalline aggregate of quartz and felspar (unstriated) with scales of white mica." ' Trans. Devon. Assoc, vol. xxiv, 1892, p. 202. > Ibid., vol. xix, 1887, p. 495. ' Ibid., vol xxiv, p. 196. * ' The Rocks of Plymouth,' Trans. Plymouth Inst., 1886, p. 23. ' Trans. Devon. Assoc, vol. xxxiv, 1902, pp. 503-511. CHAPTER X. NEW EED SANDSTONE. Tlie only reference to the occurrence of New Eed Eocks in this map will be found in Sedgwick and Murchison's paper (1837) already referred to in the Introductory Chapter. The passage is as follows: — "(4). On the south side of Bovisand Bay, the slates become so earthy as to pass into the form of shale with many small nodules of ironstone; and these are surmounted by variously coloured earthy slates alternating with reddish arena- ceous bands, as seen in the cliffs of Crownall Bay, near the southern end df which is a patch of new red conglomerate resting unconformably on the 'edge of the older strata. '"^ Now the section is overgrown and masked by rainwash and talus but there is no mistaking the locality — at a fault marked by the abrupt termination of the beach-reefs and taken as the boundary between the Dartmouth Slates and the rocks of the Meadfoot Group. At the bottom of the cliff red, partly-consolidated, loam with local fragments is visible, and higher up Head of similar composition but paler colour. No doubt when visited by Sedg- wick and Murchison the section presented a different aspect. There is no antecedent improbability of the occurrence of New Eed here, in view of its presence on the beach north of Cawsand, but beyond this we have no remarks to make on the above passage. E. H. Worth, commenting on the result of dredgings made under the auspices of the Director of the Marine Biological Laboratory, Plymouth, says " In the vicinity of the Eddystone and the Hand Deeps Triassic rocks are found in situ, and form the general sea bed (wherever rock is exposed), through which protrude the reefs. The variety of these rocks is considerable, including conglomerates, coarse red micaceous sandstones, fine red jaspideous sandstone, mottled sandstone, and salmon-drab sand- stone, as well as a red felsite and a variegated felspathic Trap." " Gravels and sands of unknown depth intervene between the Eddystone and Bolt with no known rocky patches, but in none of these sands does the Trias fail to constitute the great mass of the rock fragments." . . . " Northward the known shore- limits are Cawsand Bay and Bovisand Bay. There is no informa- tion as to whether there is a continuous series between the Eddy- stone and these points."^ ' ' On the Physical structure of Devonshire, and on the sub-divisions and Geological Relations of its older stratified Deposits, &c.,' Trans. Geol. Soc, ser. ii., vol. V, 1837-9, p. 657. ' ' The Bottom-Deposits of the English Channel from the Eddystone to Start Point, near the Thirty Fathom line,' Trans. Devon. Assoc, vol. xxxi, 1899, pp. 365, 366. 98 CHAPTER XI. TEETIAEY EELICS. Messrs. R. N. Worth, N. Whitley, and J. H. Collins mentioned the occurrence of deposits on the limestone-plateaux of the Hoe and Cattedown disconnected with the Hoe Raised Beach. These deposits were found, so far as regards the area included in Sheet 349, in a fissure, or pocket, at least 60 feet in depth in the lime- stone of Headman's Bay, which was filled with white clay and pehbles of the same character as on the Hoe.^ In contradistinction to those now to be noticed, Worth^ briefly described them as " beds of sand, clay, and pebbles, lying in hollows, or filling pockets, in the limestone plateaux." . . . ' ' The fine sands are quartzose ; the larger pebbles almost wholly either of quartz or schorl-rock, with an occasional example of grey grit; the smaller pebbles include also quartz and felspar gravel, hornblende-schist, iron-ore vein stuff, and brown pumiceous rock ; the coarser sand is substantially a schorlaceous-granitic debris. All the recognizable rocks have their prototypes on the western flank of Dartmoor between Meavy and Brent Tor ; that is they are those of the watershed of the Tavy rather than of the Plym." A fragment of light wood, " probably birch," is the only organic material mentioned as occurring in them. Mr. Collins also con- sidered " the rocks are mainly of Dartmoor origin." They were regarded as of glacial derivation by Whitley. The following is cited as quite distinct from the above. A deposit of " well-rounded pebbles and subangular stones scattered through undisturbed clayey subsoil, immediately overlying the limestone, on the northern slope of Cattedown, 60 to 70 feet above datum, and at a depth ranging from three to five feet. The pebbles run from 3i lbs. in weight down to a c^uarter-ounce or less ; and that some, if not all, of them have been redeposited from fissures .... is evident from their stalagmitic incrus- tation." Flint pebbles, mostly well-rolled, up to 2 lbs. in weight, form 40 per cent, of the whole, chalk flints predominating. Sub- angular fragments of Schorl -Rock, compact to crystalline, form the next highest percentage — 13. Of the remaining 47 per cent, more than half consist of lime- stones, grits, and quartz-veinstones. The limestone-pebbles form 10 per cent., and are mostly of local origin, but " a large pebble of Lias limestone," " a pebble of drab, cherty, possibly Carboni- ferous limestone;" a pebble of Cretaceous freestone, closely allied to that of Beer," were found amongst them. Grits and quartzites, together form 10 per cent., the grits being to the quartzites as two to one. Quartz-pebbles froin veins forin ' ' The Country around Plymouth and Liskeard ' (Mem. Ge'ol. Suf^.) 1907, p. 119. ' ' Some Detrital Deposits associated with the Plymouth limestone,' Trans. Roy. Geol. Soe. of Com., vol. xi, 1888, pp. 151-162. TERTIARY. 99 nine per cent. The remaining 18 per cent, include hard slate, culm chert, lydian-stone, quartz-schist or schistose quartzite, and hornblende-schist, which constitute five per cent, and " rocks of direct igneous origin or association " which form 13 per cent. The last-named are described at length. They include small pebbles of : — Elvans of aplitic and quartz-porphyry types, schorl- aceous-pegmatite, granitoid rock with black mica and porphyritic quartz, and schorlaceous granite, but no typical granite. The following are next described : — Devonian volcanic rocks " compact lavas of the ordinary type." Diabase similar to that of Rock and Estover (Plym Bridge), gabbro or epidiorite of the Coxtor type and like a rock at Houndall (near the western (>,nd of the large diabase-mass south of fondertown). A pebble like the New Red trap of Cawsand, orthoclase-porphyry, or orthophyre. In addition to the above the description of a series of rocks by Professor Bonney is given. Two pebbles are of a grey rock, determined as hypersthene-andesite, one of a blackish brown colour, from structure and general aspect he inclined to regard rather as an augite-andesite than a basalt. One pebble of red-brown volcanic grit or conglomerate, with particles up to a tenth of an inch in diameter, suggest a Culm conglomerate, or a felspathic greywacke of the Wearde-Efiord type, that I give his remarks in extenso. " The rock is composed of more or less rounded fragments, cemented by a little ' paste,' which is probably quartz, sometimes clear and chalcedonic, some- times crowded with dust-like particles. Some of the fragments are felspar, fairly irregular in outline, in part at least plagioclase. One or two may be quartz ; one or two are a kind of viridite, probably replacing a pyroxenic mineral ; and one small grain resembles epidote. The rock fragments are all, so far as I can see, of igneous origin. Some are fairly clear, some a rich-brown colour, some almost black with opacite ; some are homogeneous, except for a little opacite and some belonites or trichites of a dark- grey colour, which often are grouped in more or less dendritic forms or bundles like rootlets. A few of these grains are still isotropic, but most of those which are transparent exhibit devi- trification structure. Small- -spherulites, showing the black cross with the two nicols, are rather common ; one fragment seems part of a large spherulite. Other fragments show flow structure ; one is perlitic. Clearly several varieties of rock are present, but I think the majority may be referred to Andesites, some of which may not be far removed from basalt ; others may have a tolerably high percentage of silica. I think the materials have undergone attrition and have been deposited by water, but believe they have been obtained by the denudation of volcanic cones." Several hard-worn green siliceous pebbles which appear to be " of clastic origin, and composed of volcanic materials," were also obtained. A dark-grey rock, a fine volcanic breccia, probably of Devonian age, is the rock last mentioned. At 300 yards to the east of the locality where the above specimens were obtained, and higher up on the hill, pebbles were found of smaller size and few above three ounces in weight. loo GEOLOGY OF IVYBEIDGE AND MODBUEY. Here the percentage of flints is 67, that of quartz-vein pebbles 15, of schorl-rock 9, of limestone 4, and of quartzite 2, of mis- cellaneous rocks 3. The miscellaneous rocks include grit, fine- grained elvan, hard slate, Devonian lava, diabase and doubtful rocks. From the nature of these pebbles Worth concluded that the drift of materials was from the north and east and that the deposits are " the relics of a very early stage of Dartmoor denudation, when there still remained a large quantity of covering rocks to be removed from the granite of the southern and western flanks of the Moor." The distinction drawn between the Hoe and Deadman's Bay deposit and those we have been considering does not invalidate the idea that both may be remains of the deposits of the same epoch, when conditions similar to those depicted by Worth in the above passage prevailed. The former seem to be the result of more local operation than the latter, which furnish a strong analogy to the gravels bordering the Bovey Basin, on Haldon, and north of Kingsteignton, described by Mr. Reid in 1898. "^ ' Quart. Journ. Genl. Soc, vol. liv, 1898, pp. 234-236. 101 CHAPTEE XII. POST TERTIAEY. Of the earlier Post-Tertiary changes we have no evidence independent of that just noticed. That evidence, however, pos- tulates the removal of detritus extending over a considerable area, and the obliteration of the surface contours that then existed. Generally speaking the deposits date from the formation of the raised beaches, and as far as the evidence obtained by Mr. Tiddeman in South Wales and by Messrs. MufE and Wright in South Ireland enables us to judge they must therefore be re- garded as including deposits contem.poraneous with those of the Glacial period as well as subsequent. Thanks to the labours of J. C. Bellamy and others, more especially of E. N. Worth, the caves of the district have received considerable attention. Caveen Deposits. " In 1816 an Ossiferous fissure was discovered at Oreston, and this was the first bone cave in England which was made the object of scientific enquiry."^ The find was due to a request made by Sir Joseph Banks to Mr. Whidbey, appointed superintendent of the Breakwater Quarries in 1812, to examine any caverns encountered and to- have their fossil contents preserved. The cavern discovered in November, 1816, " was 160 feet in the hill from the original edge of the cliff, and was reached after blasting away 60 feet of the rock horizontally (100 feet having been previously removed). The face of the rock was 74 feet perpendicular above high -water mark. The bones were found at a depth from the surface of TO feet, and 3 above the bottom of the cavern, which was wholly filled with clay." The cavern was 15 feet wide, 45 long, and 12 deep. The bones con- sisted of portions of the skeletons of rhinoceros well preserved and belonging to 3 distinct animals. In 1820 another bone-cave, 1 foot high, 18 wide, and 20 long, was found, containing remains of rhinoceros, bear, &c. This- cave was reached by working about 120 yards inwards from the other. " It was about 8 feet above high-water mark, 55 feet below the surface." In 1822 in further working "at 180 yards in a western direc- tion from the cave of 1816, the first of five other caves or chambers, was discovered, communicating by passages and associated with galleries. The top of the cliff here was 93 feet above high-water springs, and while the bottom of the lower cave was about 30 feet above high-water, the roof of the upper- ' ' The Bone Caves of the Plymouth district,' Trans. Plymouth Inst., vol. vii,, 1879, p. 87. 102 GEOLOGY OF IVYBRIDGE AND MODBURY. most of the series was only 17 feet below the surface. Of the five chambers the lowest was the largest, and here the bulk of the bones were found." The bones belonged to ox, deer, horse, hysena, wolf and fox. The next find took place in 1858, when the quarry-face had been worked back to 1,090 feet from the river margin. It was investigated by Pengelly.^ The face of the quarry was about 60 feet high. The cavern commenced about 8 feet below the top of the cliff and extended to its base, where the bottom was not reached. It increased from 2 feet in width at the top to 10 feet at the bottom. Its length from north-north-east to south- south-west was 90 feet. The deposits occurred in descending order from the surface thus : — Feet. Angular limestone debris mixed with some sand ... 8 Similar materials with rather more sand and a considerable quantity of tough dark unctuous clay ... ... ... ... ... ... 32 Dark very tough unctuous clay. The bones were found in a nearly vertical brecciated stalac- titic dyke about 2 feet in thickness, and in the uncemented por- tions of the bed. The roof was formed of cemented limiestone breccia stopping the orifice through which the cave was supposed to have been filled from the surface. The bones belonged to mammoth, rhinoceros (leptorhine), cave-lion, cave-bear,, wolf, horse, ox, deer and hog. Pomphlett Cave. — In 1878 bones were found by Worth in Pomphlett Quarry at the extreme end of the Oreston quarries, in a fissure about 20 feet from the surface and 70 feet above the bottom of the quarry, 25 feet in length and 4 to 6 in height. The bones were embedded in " very dense tough red clay." " The remains were chiefly those of the aurochs." Ox, red deer, canine tooth of bear, and bones of birds were also found. Cattedown. — In the autumn of 1886 in re-working an old quarry at Cattedown opposite the Oreston quarries, Messrs. Burnard, Lack, and Alger discovered a fissure-cavern which is described by Worth as " a gallery running north and south, on the line of the natural jointing, to a total length of 54 feet. The gallery itself averaged about 4 to 5 feet in width, but at each end expanded into a chamber. The southern chamber was 20 feet in length, about 5 feet wide, and 9 feet deep below the recent quarry level." The northern chamber was 20 feet long, 8 feet at widest, and " excavated to a depth of 13 feet below the quarry level, when the tide found its way in from the Cattewater, about 150 yards to the south. The northern chamber partially sloped with the dip of the strata." The connecting gallery does not descend more than 2 feet below the quarry-level so that the lower parts of the two chambers were separated by nearly 20 feet of rock. Bones were found in the chambers and gallery. ■ 1 See Geologut,^%h^, pp. 434-444." ~~ 2 ' On the discovery of Human remains in a Devonshire Bone Cave,' Trans Geol. Soc. of Corn., vol. xi, 1887, pp. 105-112. CAVEEJS" DEPOSITS. 103 The uppermost deposit in the northern chamber undisturbed by- spoil from previous workings was a floor of stalagmite from an inch to a foot thick upon a mass of worn stones mixed with a little earth and clay with cavities containing numerous bones. Traced northward this thickened and became infiltrated with stalagmite until it formed a stalagmitic breccia that had to be removed by blastings. Beneath this the cave earth for 2 feet was so compact as to resemble concrete. The cave earth continued down to the lowest point excavated. In the sketch accompanying the description granular stalag- mite coats the wall of the fissure, intervening between it and the cave earth, but thinning out downward. The total depth exca- vated in the northern chamber was 27 feet, and of this 20 feet was more or less ossiferous. The remains in the stalagmitic breccia differed from those in the cave earth in representing "more or less perfectly, complete skeletons. The bones found here were chiefly those of deer (pre- dominating), man, hyeena, and wolf." Worth took from the harder part of the stalagmitic breccia, after a blast, portions of a human skull, and molar tooth with " fragment of jaw attached, and other portions of the skull were subsequently recovered. And at the very lowest point of the breccia, 7 feet below the stalag- mitic floor fragments of a human upper and lower jaw were found in relationship." In the concreted upper part of the cave earth the remains of hog were specially abundant "but the most important finds in the earth proper were humeri and teeth of cave lion, and a radius and and vertebra of rhinoceros, again associated with teeth and bones of man. The remains in the cave earth, however, were neither so plentiful nor so complete as in the breccia, and were evidently the result of more gradual accumulation," gnawed bones and fragment of charcoal were found, also ' ' a roughly chipped flint nodule." The human remains represented 15 or 16 persons, both sexes from childhood to old age. " The tibiae are distinctly platy- cnemic." A photograph of two facially perfect skulls is given. The cavern yielded remains of man, rhinoceros, lion, hyaena, wolf, fox, badger, polecat, weasel, bison, urus, red deer, roe deer, hog, goat, hedgehog, common bat, horseshoe bat, mole, shrew, water-vole, field-vole, bank-vole, rat, and various birds. Yealmpton. — De la Beche says^ " Lieutenant Colonel Mudge in describing the Tealm Bridge cavern states that large quantities of the bones contained in it had been for some time burned in the limekiln, until Mr. Bellamy, of Yealmpton, discovered their importance. It appears that this cave contained the following five, distinct, deposits commencing with the highest: — Feet. (a.) Loam, containing bones and stones ... 3| (b.) Stiff whitish clay (c.) Sand (d.) Red clay (e.) Argillaceous sand 2i 6 3^ 6 to 18 ■ 'Report on Geology of Cornwall, Devon and West Somerset' (Geol: Supv.), 1839. 104 GEOLOGY OF IVYBRIDGE AND MODBURY. The upper bed only contained the animal remains, which con- sisted according to Mr. Clift and Mr. Owen of the bones or teeth ■of the elephant, rhinoceros, horse, ox, sheep, hysena, dog, wolf, fox, bear, hare, water-rat, and a bird of considerable size . . .' " Many of the bones were chipped, gnawed, and splintered, the fsecal remains of hysenas were detected in the same bed with the bones, and in one part, where the roof of the cavern was lower than usual the limestone is beautifully polished, as if by the friction of the animals which inhabited the cave ' all evidences of the residence of hyjenas in this place." " The pebbles found in the bed with the bones are stated to be apparently derived from the confines of Dartmoor, and to differ from those in the bed of the Tealm, while in another and more spacious cavern, in which there were no animal remains, the pebbles corresponded with those now in that river." In 1871 Pengelly entered fully into the literature of the Tealmpton caverns^ and quotes Bellamy's references to them in extenso from his ' Natural History of South Devon ' in which he mentions the occurrence of caves at Tealmpton, in one of which hones of hysena and deer were found, and the discovery of an hyaena's tooth and other remains in Kitley Cave which he believed to have been washed in. He describes the Yealm Bridge Cavern, and in footnotes passages from articles by Bellamy in the Edinburgh Joum. Nat. Hist, are quoted. In one of these quotations the pebbles in the uppermost stratum are said to be granite ; in another he questions Colonel Mudge's account of the succession of the strata found in the cavern thus — " The red clay was unquestionably the lowermost stratum, not the argilla- ceous sand. From want of specimens, I presume he has also omitted to insert the names of the deer, pig, glutton and field mouse." Head on the Coast. The seaward slope of the old beach-plane, modified by subse- quent denudation, is well shown on the southern coast from Wembury westward {see Plate V). It is bounded by low cliffs of Head which rises on a gentle slope inland to considerably above the 50 feet contour, making a conspicuous terrace-feature from which the ground rises steeply in the north. The cliff at about 370 yards west of Wembury Church consists of Head with rather large fragments of the local rocks for 8 or 10 feet, below this it is of a reddish-yellow colour and contains smaller fragments for 5 feet. It rests on 2 to 3 feet of boulder- beach, apparently belonging to the raised-beach period. The old beach-reefs, with bounding strips and shelves of Head, are more or less persistent to Andurn Point. Beyond Andurn Point the Head forms a marked feature on the headland between Bovisa^d and Crownhill Bays. It is well shown in the cliffs between Bovisand Bay and Staddon Coastguard Station, and is here associated with sand disclosed in excavations connected ' ' The Literature of the Caverns near Yealmpton,' Trans. Devon. Assoc, 1870 vol. iv, pp. 81-105. ' HEAD. 105 with the construction of the Forts. Spence Bate described the section.-' The Head is of red colour and has been mainly derived from the Staddon Grits. ISTear Andurn Point the red stony Head in the upper part of the cliff gives place downwards to pale-red and orang-e-brown sandy loam. At 300 yards north of Staddon Point a pinnacle of Head, elsewhere denuded from the upper part of the old beach-plane, is noticeable. About 70 yards further north the Head still rests on the inner angle of the old plane, preserved on either side of Leek Bed Bay. On the border of the map, south of the Catte- water and west of Tnrnchapel, an isthmus of lowland connects the Mount Batten limestone tnoU on the north (in sheet 348) with the higher ground on the south and east, toward Dunstone Point and Clovelly Bay quarry on the 6-inch map. The surface to a depth of from 8 to 10 feet is covered by earthy sand and fine gravel, the base of which near Mount Batten is little above high- water mark but rises southward to from 15 to 20 feet higher, being capped by Head up to the 50 feet contour. This isthmus was primarily no doubt planed during the raised-beach period; but it is not improbable that the lower part near Mount Batten may have been subsequently eroded and may have formed a stream-outlet during the earlier stages of the elevation of the old beaches. Relics of the raised beach — such as more sandy condition and the presence of worn stones sometimes observable toward the base of the Head — justify the belief that were the sections less slipped and overgrown more definite traces would be discovered. River Deposits above High-Watee-Maek and Inland Head. It is not possible to classify the various deposits and accumu- lations in the different drainage areas in chronological order, owing to the di£B.culty in distinguishing accumulations of Head or material mainly or entirely due to atmospheric waste of different ages, in correlating such materials near the sources with hond fide river gravels along the courses of the stream, and in ascertaining how far such materials may have been subsequently redistributed by fluviatile agencies. There is no reason however to conclude that any of the super- ficial deposits under consideration were much older than the raised beaches although some, such as the terrace-gravels of the Plym near Bickleigh, of the Avon at South Brent and south-east of Loddiswell; of the Dart between Hood and Buckfastleigh, may be of earlier date. The same remark may be applied to the tracts of ancient talus and rainwash at or near the heads of lines of drainage such as those on the south of Trowlesworthy Warren, at Tory Brook Head and Newpark' Waste, and near Shipley Tor in the granite- area, and at Babland, Stanton, Wigford, Place Moor and Stan- borough Brake in the Lower Devonian area. Some of these tracts around stream-heads as at Coyton and Tod Moor to the west of Ermington afford no evidence of Head ' Trans. Devon. Assoc, vol. i, 1862, p. 42. 106 GEOLOGY or IVYBKIDGE AND MODBUEY. beyond contour. The extension of Head or of old river-deposits affords in most cases little indication of their importance, as most of the patches shown on the map are inferred from features at the heads, or along the lines, of drainage, and a thin or irregular covering of detritus often covers a larger area than a thick deposit. For example the gravel tract on the north of Cadover Bridge, west of Brisworthy, consists mainly of an overburden of more or less worn granite-debris seen to overlie the kaolinized granite of the Wigford Down China clay works to a depth of from 5 to 10 feet; but on the south-east side of this tract there is well-defined terrace of worn granitic material on the border of the Alluvium, or old bed of the Plym, in which its present course is cut. The deposit between Trowlesworthy Warren and Lee Moor House is partly a flat of granite- gravel studded with worn boulders, but its thickness is unknown and its extent somewhat doubtful. The Head at Lee Moor China clay works is probably thin and rendered indefinite by debris from the pits. One cannot say how far the granitic detritus of Tory Brook Head and Newpark Waste has been deposited. On the north margin of the China Clay Pit north of Cholwich Town, the detritus is 15 feet thick. Newpark Waste below the 500 feet contour seems to be a broad terrace of granitic detritus with boulders. At, and east of, Harford the deposits are river-terraces bordering the old stream-bed. East of Shipley Tor and north of Talland there were no deposits shown in the flat tract coloured on the map. The tract is defined by feature except at the northern end where a strip of low ground connects the drainage of the Tealm with that of the Harbourne, a tributary of the Dart. The drainage-areas of the Erme and Tealm are connected by a belt of lower ground west of Ivybridge, shown on the map as apparently covered by Head and stream-detritus. From the watershed south of Cadleigh, 230 feet above O.D., the ground slopes gently both to the east and to the west. This feature at first sight suggests the former deflection of the drainage of the Erme into the Tealm Valley, but of this there is no proof, and it is more probably due to the erosion of the Tealm tributary, rising near Cadleigh House, and of tributaries of the Erme, rising at about half a mile south-east of the Inn flowing north, and near Dinnaton flowing south, the barrier between the catch- ments being gradually lowered by atmospheric degradation. At about a mile east of Ivybridge Church the ground slopes evenly southward from the 500 to 300 feet contours. Its surface is masked by a brown loamy soil with granite and altered rock debris, this has been mapped as Head, and appears to be a mere surface soil, gradually spread out and washed down the slope. The feature, however, may be the relic of an old plane of the Pliocene or an earlier period. We will now briefly mention the river-terraces, not already described, in the different river-basins, beginning on the east. The Plym unites with the Meavy at Shaugh Bridge in a boulder-studded gravel-flat about a quarter of a mile broad. Through this the river has put its channel for a quarter of a EIVEH DEPOSITS. 107 mile below Shaugh Bridge. Here the more modern stream-bed or aUuvium commences at a slightly lower level. This is of similar composition to the older bed which now forms a terrace on its western border. The old river gravel was exposed at Shaugh Bridge to a depth of 10 feet and consists of worn stones of quartz, altered slates, granite and schorl rock in a matrix of fine gravel and coarse earthy sand showing strong current bedding in places, and containing large granite boulders here and there. From its commencement to Bickleigh Bridge, a distance of one mile, the alluvium varies in breadth from 60 to 220 yards, and the river has cut its course through it in the same way as through the older bed. As we follow the older bed or terrace southward past the tributary valley on the north of Bickleigh Station, ii becomes differentiated into a higher and lower terrace separated by a bank of slate. East of Bickleigh Station the alluvial tract crosses the lower terrace which is now found on its eastern margin; on its western margin the bank of slate increases in height to between 20 and 30 feet between the alluvium and the higher terrace. The accompanying sections show the relations Fig. 23. — Three sections through the Bickleigh river terraces. Section 3i furlongs N. of Bickleigh Station. W. E. Railway R.Plym Section 130 Yards North of Bickleigh Station. W. /? Plyn Section through Bickleigh Station. Bicltisigh Station R.Ply.T, of these terraces (Fig. 23). The oldest terrace may date to the raised beach period, during subsequent elevation it was partly denuded and cut through in the formation of the lower terrace during the succeeding elevation, and the lower terrace was cut through in the production of the alluvial flat which in its turn is eroded by the present stream-channel. Below Bickleigh Bridge the stream has cut so narrow a channel that all traces of th-? 22265 H 108 GEOLOGY OF IVYBEIDGE AND MODBUEY. older terraces have been swept away, and the alluvium forms a narrow strip which broadens below Plym Bridge. In the Yealm Catchment, apart from Newpark Waste which may owe its extent to the planing of an earlier denudation, parts of the lower terrace, if features are to be relied on, bound the alluvium of the Piall tributary, near Lutton, and the main river, near Wisdome and Woodburn ; below this a patch seems to have been spared as an inlier in the alluvial flat south-east of Lee Mill Bridge, and the deposits between the Erme and Avon valleys west of Ivybridge, already mentioned, are probably of the same date. The lower terrace feature is conspicuous at Puslinch and a strip is exposed in the railway-cutting north of that place, the deposits occupying broad valleys in the lime- stone south of Tealmbridge and Tealmpton may belong to the same period. The Erme below Ivybridge Station has cut through the boulder-studded gravel and sand of its old bed, on which the school-house is built, and has deeply grooved its channel in the rocks beneath it. A little further down the alluvium com- mences and the old bed broadens out in an extensive terrace on its eastern margin ; this tract may include remnants of an older terrace as well as stream wash and Head toward its western borders. The southern part, between Caton and Penquit, may belong to the older terrace. With the older terrace-deposits may also be included an apparently redeposited irregular patch on the north-east side of Modbury. With the lowest terrace we would include the comparatively broad gravelly boulder-studded tract which occupies the valley descending from the golf links at Wrangaton. This is truncated by the narrow strip of alluvium bordering the brook on the south. The superficial deposits shown by the tributaries of the Erme at and near Strode Farm, and about Shilston Bridge are tracts in which there are no exposures but which from the shape of the ground and surface soil are probably covered by Head and rain- wash, perhaps masking low terraces on the borders of their respective alluvia. A good example of the older terrace is shown on the east bank of the alluvium of the Erme south of the Eawns. The deposit rests on a low slate-clifi, the edge of the terrace being about 20 feet above the alluvium. Owing to the small scale of the map this intervening rock-exposure cannot be shown. The terrace rises eastward and may be masked by Head beyond the boundary drawn on the map. Where the Avon emerges from the harder rocks of the granite- aureole its alhivial flat broadens out, rising imperceptibly on the west in a tract which seems to represent the lower terrace ; this is terminated on the west by a steep slope over 20 feet in height, above which part of an old river-terrace of brown gravelly loam with boulders is exposed in the Great Western Railway cutting. This terrace may be of greater extent than is shown on the map. On the east of the river the alluvium is boimded by a cliff, above which the old gravel-terrace makes a conspicuous feature, from the vicinity of Lydia Bridge for half a mile southward. The gravelly loam is exposed near South Brent Station and at it^ margin near the church. BIVER TERRACES. 109 In this locality there is a gentle gradient between the 500 and 400 feet contours on either side of the Avon Valley. This is suggestive of early surface-planing, possibly of Pliocene data, as east of Ivybridge, and possibly at Newpark Waste. West of Horsebrook the older terrace-feature is shown. At Avon Wick the low terrace is conspicuous on the border of the alluvium. A patch of old terrace-deposit is exposed in the Kingsbridge Branch Eailway-cutting south of Bickham Bridge, at about a mile south of Diptford. Here it consists of brown loam with fragments of slate and quartz, and worn stones of granite and schorl-rock upon pale-buff and yellow-banded loam, and is exposed to a depth of over six feet. South of Storridge Wood the alluvium is apparently bounded by the lower terrace on the west, making a yellow clay stony soil with quartzite- boulders. It also makes a narrow feature south of Topsham Bridge. The older terrace was exposed by the Branch Railway near Loddiswell Station, under five feet of brown stony loam. It con- sists of brown loam and loamy clay, with small fragments and occasional worn stones, including granite, and of red, grey, and brown-banded gravelly loam. West of Loddiswell Station and south of the mill (Loddiswell Mill Bridge on the 6-inch map), a patch of older gravel is exposed in the railway-cutting, here more than 50 feet above the alhivium. The section in descending order is as follows : — Soil Drab and purple loam with slate fragments ... Red-brown sand Gravel with worn boulders of quartzose grit (with a blackish seam at the top) on an irregular surface of lilac and grey slate on which it is overlapped by the deposits above 4 It is sometimes impossible to separate the alluvial flat from the lower terrace deposits of tributary brooks on the 1-inch map. The streams above Aileron, north-west of Loddiswell, furnish a good instance of this. The large drainage-catchment, or ' cirque,' below the Lower Devonian grit outcrop, includes Head, rain-wash, and stream detritus. The brooklets in this tract converge and unite on the south near Stanton, where the above-mentioned materials merge into the detritus of the lower terrace or old stream-flat (the boun- dary on the map being arbitrary), in which at some 300 yards lower down the alluvium commences in a narrow thread that cannot be shown on the 1-inch map — separate from the terraces on either side of it for three and a half furlongs southward, where the latter disappear. Traces of the lower terrace are encoimtered along the Har- bourne, near Whiteoxen, west of Forks Cross, and inside the bend in the river west of Harberton. A large tract of lower terrace gravel is shown on the map at Dean ; it has been inferred from the flat nature of the ground, but no further evidence was procurable. On the east of the allu- vium a patch has also been coloured, which may be Head or Wash, 22265 H 2 ft. in. 2 8 2 110 GEOLOGY OF IVYBRIDGE AND MODBUET. no evidence of the nature of the snhjacent rock being visible. From here to Buckfastleigh, and in most of the eastern part of that town, the low terrace is evident by contour on the west of the alluvium. Buckfastleigh Station is on a low terrace of the Dart, the up- ward slopes of which may be masked by Head. Below Austin's Bridge, on the east side of the Dart, an old terrace commences at about 30 feet above the alluvium, its upward rise westward toward the 200 feet contour is probably masked by Head, and its con- tinuity near Caddaford is doubtful, being probably breached and removed in the hollow of a small drainage-depression, but on crossing this it can be readily traced for three furlongs, in pajrt of which distance it is separated by a slope of slates from a lower terrace which commences at half a mile below Austin's Bridge and continues southward for half a mile. Here the upper terrace reappears, and with a breadth of 300 yards or more continues for three-quarters of a mile round the bend in the river. The allu- viiim wa,s seen to a depth of three to five feet, consisting of gravel and loam and resting on slate, in which the river-channel has been cut. The higher terrace declines at its eastern extremity at Stretchford, where it receives tributary drainage material, pro- bably of later date, this is cut ofE by a belt of slates on the slope from a continuation of the liigher terrace, which forms a narrow band, broadening near its termination, at five furlongs further east, near Riverford Bridge. On the opposite side of the river, near Hood, the higher terrace is well developed between the 50 and 100 feet contours. It is separated from the alluviam by a low cliff of slate. West of the Riverford Bridge road the lower terrace borders the alluvium, rising nearly to the 100 foot contour, here the higher and lower terraces are evidently present without an intei'vening cliff of slate. At three-quarters of a mile west of Hood Ball a fragment of the higher terrace is visible, 30 feet or more above the alltivium, and below it, on the north, the lower terrace forms a narrow strip on the western border of the alluvium for three furlongs. Rock Valleys and Deposits below High-Watee Maek. The river-gravels and alluvia above described clearly prove the gradual erosion of successive river-beds planed during periods of terrestrial stability in the final stages of the excavation of the lines of drainage. Besides this they manifest a decrease in rainfall and consequent transporting power. The latter is evident from the absence of earlier terraces or signs of deposits on a contour which has been not only swept clean of eroded materials, but has had the salient features attending all but the latest processes of denudation obliterated. We have now to consider the estuaries of the area. In the case of the Laira, or estuary of the Plym, R. H. Worth^ has shown that it is a true submerged rock-valley cut in Devonian limestone in which the iron cylinders for the railway bridge ' Trans. Devmi. Assoc, vol. xxx, 1898, pp. 384, 390 and Plate II, flg. 1, see also Trans. Plymouth Imt., vol. xi, 1888, p. 66. EOCK VAILETS. Ill were sunk at 106 feet apart. The sinkings proved the centre of the channel to be a practically level floor 87 feet below low water for a breadth of 212 feet. This valley " is filled up to low-water level with sand, much of it of a coarse grain. Two layers of oyster-shells of considerable thickness were met with, one at about 30 feet, the other at between GO and 70 feet below the level of low water." Worth and Mr. Codrington^ attri- bute the excavation of these valleys to glacial erosion, and regard the stony clay, found in some cases on the rock sides or floor, as boulder clay. " The valleys from which the boulder clay had been almost entirely removed," says the former observer, " are now full of alluvial deposits. Periods of rest occurred during this last subsidence, as evidenced by successive layers of sand and oyster beds in the channel of the Laira." Worth^ notes that " Eecent borings in the silt of Catte- water Harbour confirm the result obtained at Laira Bridge. The depths reached are as great or greater, and the channel imiaa- diately below the bridge is very much wider than at the bridge itself contracting again at Turnchapel Rock, and again expanding in the lower reaches of the harbour." Mr. Codrington regarded the estuaries of the Tealm, Erme, and Avon as true rock-valleys. Of their rock-beds, however, no sections are available. R. N. Worth mentioned a sinking of 40 feet without reaching rock by the Tealm at Puslinch.^ As bearing on the former force and volume of the rivers I quote the following from R. H. Worth": "For instance, at the mouth of our estuaries granitic pebbles are of constant occurrence, and in the case of the Yealm we have a river incapable of bringing down any granite boulders or pebbles to its estuary ; yet on the beaches outside the estuary a notable proportion of granitic material is found — a remnant, as the author suggests, of great quantities of material originally transported by the glacier which occupied the Yealm Valley." The question which presents itself regarding these valleys is the date of their excavation relative to the raised beaC-hes and the agency to which the planing of their beds may be referred. If the latter is due to glacial action it would have taken place during the elevation that succeeded the formation of tlie raised beaches, unless it can be shown that the raised beaches are interglacial in this part of England. The view here taken is that the planing is due to marine agency during a protracted period of stability. Such a period of quiescence may have taken place either during the elevation of the beaches or during the succeeding depression. The writer would suggest the former, and the removal of the estuarine deposits and infilling of the valleys by river-detritus, possibly assisted by some form of glacial agency, the removal of these deposits during the ensuing subsidence and the filling iip of the ' T. Codrington, Quan-t. Jourii. Geol. Soc, 1898, vol. lir, pp. 264, 2G.5, and 272-276. ' Op. cit, p. 384. » The Geology of Plymouth,' Tram. Plymouth Insl., 1875. * Op. cit., p. 388. 112 GEOLOGY OF IVYBBIDGE AND MODBTJEY. estuaries by sand, silt, and mud. To suppose that these rock- valleys were in existence before the formation of the raised beaches would entail the free access of the sea at that period and the consequent cutting of shelves or terraces on their borders where we should expect to, but do not, find them. Submerged Forests and Peat. At the mouth of the valley in Bovisand Bay patches of vegetable matter with decayed wood were noticed on the fore- shore in 1893. They represent the seaward extension of a peat bed underlying the alluvium of the stream valley, and probably belong to the final stages of forest growth. In the granite area the disintegrated granite is often covered by a peaty soil varying from a surface-film mixed with growan to a layer four feet or more in thickness. Unfortunately the surface does not enable one to distinguish the thicker peat soils, and in only one case has a peat bog been mapped, viz., in the Head tract just south of Trowlesworthy Warren House where the peat contains roots and stems of birch and forms a patch half- a-mile long and nearly a quarter of a mile broad. Peaty soil containing bog wood covers the growan north-east of Tory Brook Head. Peaty ground is met with near the head of Broadall Lake which is in marshy ground for a quarter of a mile from its source ; also around Shavercombe Head, whence a marsh, shown on the map, extends to Langcombe Head. At the Kistvaen, near the latter, three feet of peat was seen on growan. Peat soil is met with round the source of the stream on Quickbeam Hill and around Petre's Cross. The source of Red Lake is in a peaty marsh shown on the ordnance map. Between this and the Avon on the east there is a variable thickness of peaty soil ; in one place, below a feature running along the slope just north of Abbot's Way, four feet of peat was seen. Three to four feet of peat was exposed by ponds in decomposed granite at a quarter of a mile north-west of Knatta Barrow. There are occasional small patches of surface peat in many of the valley bottoms on the moor. Coast Erosion. The comparative hardness of the rocks and reefs protects the coast from rapid waste, and where reefs are absent and gravel beaches are formed, reefs in the vicinity tend to retain the shingle as by natural groynes. Amongst the pebbles in the beach on the north side of Andurn Point a good number of well-worn and sub- angular fragments of the Kingsand felsite are present. 113 CHAPTEE XIII. ECONOMICS. Water Supply. There are no available records of the numerous wells sunk in this well-watered district for the supply of farms and hamlets, and none of these are deep. The numerous springs from which the tributary streamlets rise, on Dartmoor and in the Devonian area below, offer facilities :l^or impounding, or piping, small supplies not utilized to their full extent. The old leats which conveyed the Plymouth and Devonport water supplies from Dartmoor traverse the north- western corner of the map. One of the reservoirs for distributing the present supply from Burrator (described in the Plymouth and Liskeard Memoir) is situated near Eoborough, on the north. The following parishes in, or partly in, this map, with popula- tion from census of 1901, are within the area of control of Plymouth : —Heavy, 261; Bickleigh, 296; Buckland Moua- chorum, 1,717; Egg Buckland, 1,285. The total quantity of water drawn per annum from the Dart- moor drainage areas is, from an estimate in 1901, 2,225,000,000 gallons. The average annual rainfall over the drainage area for ten years is 5148. The total available supply per annum from the Dartmoor area is estimated at 4,015,000,000 gallons. The storage capacity of the Burrator reservoir is 657 million gallons; that of the Eoborough service reservoir is one million gallons. ■^ In connection with the Plymouth water supply Mr. W. Whitaker called my attention to the omission in the Plymouth Memoir of reference to an account of the Anchor Brewery well published by him in 1881.^ The boring- made by Messrs. Isler and Co. at or near the same spot is given in detail on page 133 of the Memoir, in which the upper part for 112 feet is given as pit in made ground 3 feet, boring 109 feet. Mr. Whitaker's account supplies the details for 57 feet from the surface in a well which was sunk previously by Messrs. Legrand and Sutcliff. " The water level is 7^ feet below the surface of the ground, and the yield is 12 gallons a minute." The details are as follows : — [Surface deposits / Stony clay 13^ feet] I Black pebbles ... Bock Shaly stone Hard black stone Hard shaly stone Grey stone Shaly rock Feet. lOJ 2i i 7 3 4 2+ ' ' Waterworks Directory and Statistics,' 1903, p. 92. * Trans. Devon. Assoc, 1881, vol. xiii, p. 298. Il4 GEOLOGY OF IVYBEIDGE AND MODBUBY. Feet. Hard blue shale stone ... ... 5i Clay • >■ Blue shaly stone ... Hard blue stone ... H Clay ... i Hard blue stone ... 5 Clay i Plympton is supplied from an adit of the Bottle Hill disused tin mine driven in slate in the valley north west of Hemerdon Ball at the 400-feet contour, from which it is piped to the town. The following are from notes on the water supply of the area kindly supplied by Mr. R. H. Worth at my request: — " Plymstock and Elburton are supplied with water by an extension of the Plympton main from Bottle Hill. Works to increase the supply at Bottle Hill have failed to be of any use, and now an additional supply from Lee Moor is in contemplation. A futile attempt was made, by order of the Local Governm.ent Board, to obtain a supply from the local slates at Plymstock by means of wells." The Ivybridge supply is obtained from the reservoir on Henlake Down, and from the river Brme through the reservoir about a quarter of a mile above the railway viaduct. South Brent is supplied from springs in the tributary valley which joins the Avon at Lutton. One of these rises above Gingaford about a quarter of a mile east of Downstow, at the 800-feet contour, the other rises near Overbrent, about a quarter of a mile to the south of Downstow. " The valley from Brent past Lutton to Gingaford is full of springs." ' ' TJgborough takes water from a spring under the road near Whitehouse (on the 6-inch map, near Ugborough, on the north). This yields less than a gallon per minute. I now have in hand a supply for Ugborough from springs which rise at the foot of (Jgborough Beacon near Wraugaton Moor Gate ; these springs rise close to the junction of the granite and the calc schist, and ai'e ample in quantity. " Bittaford is supplied from a spring about a quarter of a mile north. This valley of the Ludbrook presents frequent springs, especially just within the border of the granite. " Dean is supplied from a spring rising south of the village and east of the main road, a little over a quarter of a mile away. " Yealmpton has a comparatively new supply, I believe from springs at Hall Tors. Near Yealmpton, west of the village, and at the point where the railway crosses the river between Puslinch and Yealmpton, there is on the south bank of the river a fissure in the limestone which is partly filled with pebbles of Dartmoor origin, and from which issues a spring of some quarter million gallons a day at oi'dinary times ; perhaps it may fall at extremes to about half this quantity." " Modbury is supplied with water from a spring known as ■' Silver Well,' rising on a slope to the north of the town, and within two or three hundred yards of the main body of the buildings; on the Train Estate. The water is led into a small Mines. 116 reservoir at the top of Brownston Street, and thence distributed to standpipes. The supply is ample with proper precautions as to leakage. Mines and Minerals. Mining enterprise has been for many years extinct in the area, and when most flourishing but few mines were worked to any considei'able extent. Except in two or three cases where mining plans are procurable, the information regarding the ores worked and positions of the workings is from miscellaneous sources and of a very indefinite character. Tin, copper, iron, lead, silver- lead, and antimony mines have been worked, manganese and umber have also been extracted. Additional lodes were laid down on the old geological map. Sheet 25, by the late Sir [then Mr.] W. W. Smyth in 1866. Within the area included in Sheet 349, eight lodes are shown on the old geological map, viz. : — A tin lode, from a point at about 170 yards north of Yeoland, running three-quarters of a mile east to the words Yeoland Consols Mine on the 6-inch map (112 SW.). A tin lode, 24 chains (528 yards) south of the above, running for a mile and a half to the granite at a quarter of a mile north-east of Hoo Meavy, belongs to Yeoland Mine, apparently. These are no doubt the nearly east and west lodes " on Roborough Down " referred to by De la Beche.^ A copper lode running west for three furlongs from a point in the road half a mile north-west of Bickleigh Church. No signs of mining are shown here on the 6-inch map 118 NW. A tin and lead lode at 100 yards south of Plym Bridge and a little over half a mile south of Cann Quarry. This runs for half a mile east from the Plym through Boringdon Park Mine (silver and lead disused) to a shaft at half a mile north by west of Boringdon on the 6-inch map, sheet 118 SW. This does not appear to be the lode aUuded by De la Beche " on the south of Cann Slate Quarries," as run- ning " a few degrees more to the north and south " than the Bottle Hill lodes. ^ At Bottle Hill a copper and tin lode is shown running for about a mUe, a few degrees north of west and south of east. At about 300 yards to the south a tin lode is shown running east and west for 5 fiirlongs. At a quarter of a mile north of the Bottle Hill lode and a quarter of a mile south of Wheal Florence (name on the 6-inch map 118 SE.), a tin lode for 3 furlongs from a few degrees south of west to north of east is shown. Near FuUaford House, Buokfastleigh, a copper lode is indicated by a broken line running for nearly a mile from a few degrees south of west eastward. The direction indicated by dumps on either side of the old shaft on the 6-inch map 114 SW. is west-south-west to east-north-east, and iron seems to have been extracted. The following mines are indicated by name and symbol for ore on the old 1-inch geological map : Huel Virgin, copper, at 7 furlongs north of Bickleigh Church; Huel Lopez, copper, at nearly '5 furlongs north of Bick- leigh Church. This mine is shown on the 6-inch map sheet 118 NW. in the vaUey west of the symbol on the old map. In the valley there are 6 old shafts on the east margin of the alluvium and 3 in the wood on the west. These occur at intervals for nearly a quarter of a mile from north to south. From the relations of the shafts, ' 'Report on Geology of Cornwall, Devon, and West Somerset' {Geol. Sure.), 1839, p. 301. » IhiJ., p. 302. Il6 GEOLOGY OF IVYBIUDGE AND MODBUEY. on the east and west, the direction of the lodes appears to be a little north of west to south of east, but without knowing the hade it is impossible to tell the number and outcrop of the lodes. The position of the Wheal Virgin symbol is not far from a dyke of quartz-veinstone which runs for about half a mile east-north-east, towards the northern end of Shaugh Tunnel. The following are indicated on the old geological map by symbols only : — Iron, 4^ furlongs south-west from Shaugh Prior Church, and 5 furlongs east from Bickleigh Station. Manganese, about 200 yards north of Tordean, near Dean Prior. The nature of the subjacent rock is not clear around Tordean. The soil is red-brown with siliceous ferruginous boulders. The following mines are mentioned only on the new maps : — Wheal Sidney. — Tin. On 6-inch map 118 SE., and on 1-inch, sheet 349, at a mile and a half east of Cann Quarry. Wheal Florence. — Tin. On 6-inch map 118 SE. only, at 9 furlongs east of Wheal Sidney ( ? easterly continuation of the same lode) . Wheal Mary Hutchiugs. — Tin. 3 fui-longs east of Newnham Park. On 6-inch map 118 SE. An open shaft was observed at 120 yards south-east of Lobb Farm, probably connected with this mine. Huntingdon Tin Mine, in granite, on the north border of 6-inch map, 113, SE. by the West Walla Brook, a tributary of the Avon, east of Warren House, and in the adjacent 1-inch map 337. Iron mine in 6-inch map 118 NW. in Square's Wood, 3 furlongs south of Shaugh Bridge, probably Shaugh Iron Mine referred to in Mr. Mac- Alister's Notes. Bulkamore Iron Mine at junction of slate and volcanic rock between Luscombe Wood and Chohvell in 6-inch sheet 120 NB. Fillham Silver-lead Mine (disused). On 6-inch sheet 125 NE., near the border of an old alluvial flat, at 9 furlongs south-east from ■ Ivybridge Church. Wheal Emily Mine. — Antimony. Is shown at the boundary of 6-inch maps 130 NW. and NB., near the west bank of tlie Yealm, east of Knighton, probably at, or near, a faulted junction between the Middle Devonian slates and Staddon grits. Umber Works (disused), in open pits in calc-fliutas on either side of the road by Torrs Wood (east of the Plymouth Asylum), in 6-inch map 119 SE. On the 6-inch map 114 SW. two shafts are shown on the north margin of the wood near Bowerdon, at about a mile and a half west of Buckfast- leigh. Mineral not mentioned. Mr. Tozer, of Higher Ludbrook, between Ermington and Ilgborough, informed me that a lode carrying 75 per cent, of haematite runs through his farm, near the house. The following notes of the mines of the district are by Mr. MacAlister : — Mining. The mines have been neither numerous uor very productive, and have long since been abandoned, the last -norked — Teoland Consols — having ceased to sell ore in 1888. As will be seen by the statistical table the ores obtained from time to time comprise those of tin, copper, argentiferous lead, sulphides of iron and arsenic, zinc, and oxide of iron. Although occasional references to the minerals are to be found in works dealing with the district, the small economic importance of the mines has attracted but scant attention from writers, and practically the only information obtainable is that of the outputs of the mines published in Government reports or from direct enquiry in the district. The mines are situated for the most part in the western portion of the district, near the margin of the granite. The richest tin mines are those of Bottle Hill, Wheal MINES. 117 Mary Hutchings, Wheal Sidney, and Teoland Consols, the last being located in the north-west comer of the district and the other three on or near the small granite intrusion of Hemerdon Ball. Bottle Hill, Wheal Sidney, and Yeoland Consols have probably yielded much more tin ore than is stated in the table, but with the exception of the production of Bottle Hill in 1837, 1838, and 1839, the figures prior to 1852 are unobtainable. In the case of Bottle Hill it should be noted that most of the copper was produced in 1823 and 1835, the details for other periods prior to 1856 being unrecorded. De la Beche, however, states that ores of tin and copper were raised in fair quantity from Bottle Hill Mine. Similar observations apply to the other minerals raised, the information of their total amount being equally in- complete, except for the specific periods mentioned. The iron ores were mainly limonite or brown hsematite, those from the Shaugh iron mines varying in price from 10s. to 15.s. a ton, and from the Bulkamore Mine from 15s. to 18s. at the mine. The latter is probably the mine at Rattery, where, according to Mr. R. N. Worth,' iion ores were raised in quantity. The iron ores have a wide distribution in the district, but with the ex- ception of the mines already noted their importance is small compared to those of the adjacent districts. The occurrence of specular iron ore near Buckfastleigh in association with limonite has been noted by T. M. Hall.' Subjoined is a longitudinal section of Hemerdon Consols and Wheal Mary Hutchings (Fig. 24). Fig. 24. — Longitudinal section of mines on Hemerdon Ball (by D. A. MacAlister). Hemerdon Consols. IMary Hutchings Tin Mine. ^^^"""^"f^'imv ^^'"'"--^ - IT^'^mF'''''^:.^ w SoFrns. 3o ""---^ SC/^LS Aciil: Uvel ' ' The Economic Geology of Devon.' Trans. Devon. Assoc, vol. viii, 1875. p. 235. ' Catalogue of Devonshire Minerals. Trans. Devon. Assoc, vol. ii, 1867-1868, p. 336. 118 1^ "=! ■p^ d -^ S "o s § „ " ra CO iJ — 'Da -S « e s ■Si §< e « ^ ft? ■w' eg p , §^ fw CO .5 I-H '^ S Ed's O B fc! »H CD 3 ^ o'a 9<-!3 cS a o O to Produced between 1852 and 1857. Pyrites arsenical. Between 1852 and 1855. 1,800 tons of copper ore raised in 1823 and 1835 ; the rest between 1856 and 1875. 281 tons of the black tin raised between 1837 and 1839 ; the rest between 1852 and 1882. In 1873. Brown Hsematite in 1874 and 1875. Between 1855 and 1861. In 1852. In 1858. In 1855. In 1825. Between 1866 and 1880. Py- rites arsenical. Between 1870 and 1874. Between 1854 and 1864. In 1854. From 1852 to 1857 ; 1883 to 1888. a o5 15 Tons. 680 4,400 4,670 g •3| - o : : : : Crude and Refined Arsenic. Tons. "is 230 •41 CM Iron Pyrites and Arsenical Pyrites. coo O a lO * CC ; • o ,-1 : : : : : : : : "M : : : : :(M :':■': T— ( Silver from Lead. _L O * O o : : CTJ : : : O (M y-t co~ Lead from Ore. Tons. 205 150 _<» -# : 1 = : OO CO CO 1| Tons 400 360 : CO CO : • : .1—1 ... i : : : 05 Copper from Ore. a >» O 00 CO : : ; : : : : : CO 00 1—1 M Tons. 2,000 1,230 26 : : : : CO >Q eo' §a i« O tH S : :■* : O . . CO CO CO . - . ■ -^ Ol o o I-cf ^ T-l Name of Mine. 3 o Borringdon Consols Borringdon Park Bottle Hill and "Ok Bottle Hill." Bottle Hill East Bulkamore Devon Wheal Buller .. East Borringdon Florence, Wheal Hemerdon Consols Lopes, Wheal Mary Hutchings, Wheal.. Shaugh Iron Mine Sidney, Wheal South Yeoland Yeoland Consols MINES. 119 LIST OF MINES GSOUPED ACCOEDING TO THE PARISHES IN WHICH THEY ABE SITUATED. The following index gives the positions of the mines on this Sheet. The Roman numerals indicate the numhers of the 6-inch and 25-inch maps issued by the Ordnance Survey. The letters indicate the quarter sheets of the 6-inch maps, while the figures represent the numbers by which the 25-inch maps are designated. Thus, Teoland Mine, CXII., SW., 9, means that Teoland Mine is situated on the 6-ineh Ordnance Map CXII. in the SW. quarter sheet; while on the 25-inch map it is situated on Sheet CXII. in Map No. 9. BuoKLAND MoNACHOETJM, Parish of. Bottle Hill Mine CXVIII., SE. 16. South Wheal Yeoland, see Yeoland Florence, Wheal CXVIII., SE. 12. Mine. Hemerdon Consols Tin Mine Yeoland Mine CXII., SW. 9. CXVIII., SE. 16. BiCKLEiGH, Parish of. Mary Hutchings, Wheal CXVIII., Lopes, Wheal CXVIII., NW. 1. SE. 16. Meavt, Parish of. Sidney, Wheal CXVIII., SE. 11. Yeoland Consols Mine CXII., SW. 10. Rattbry, Parish of. Plympton St. Mary, Parish of. Bulkamore Iron Mine CXX., NE. 8. Borringdon Park Mines CXVIII., Shaugh Prior, Parish of. SW. 14. Shaugh Iron Mine CXVIII., NW.2. D. A. MacAlister. Most of the valleys in the granite area and descending from it have been streamed for tin ; but beyond the disturbed nature of the granite detritus in their bottoms, there are no indications of these operations or of old men's workings, although, as men- tioned by De la Beche, Vancouver noticed stream works being carried on near Plympton St. Mary as recently as the year 1808 or thereabout. In the description of the visit of the Geologists' Association to the Lee Moor clay works in 1884^ the following account of the driving of the adit necessitated by the deepening of the pit is given : — " This adit, although worked on continuously night and day by three gangs (locally ' cores ') of men took nine years to execute. For a considerable distance it followed the line of a ' flookan ' or cross-course, which extends from end to end of the pit. In the course of driving the level several interesting minerals were found. [A series of these were exhibited by Mr. W. L. Martin.] They included beautiful specimens of opal and jasper, an example of torbernite, and magnificent crystals and stones of tin found at the intersections of some lodes and the cross-coiirse. Although there are several lodes in the sett, the quantity of tin they contain is so small that Mr. Martin was perfectly astonished at the amount of work the old tinner's must have done on that very spot, for what must have been very meagre results. The various lodes were clearly seen traversing the faces of the huge excavation, with the course of the flookan, and its effect in heaving the lodes. One lode had been carried some distance along with the flookan before it started on its own course again." ' Proc. Geol. Assoc, 1884, vol. viii, p. 474. 120 GEOLOGY OF IVYBRIDGE AND MODBUET. Mr. J. A. Howe tells me that in a new adit now being driven Lelow that mentioned in the above passage, foi' the further deepening of the pit, torbernite was also met with. Wheal BuUer, given in Mr. Mac Alister's notes, is in Sheet 338, but so near its southern border that it should be noticed like Huntingdon tin mine. It is shown on the 6-inch map. Sheet 112, SW. ; the north border of which overlaps the junction of the 1-inch map. China Clay. In 1834 the China Clay industry " was started at Lee Moor in the parish of Shaugh by the late Mr. John Phillips, who vras the first to open up China Clay working combined with tin. Some few years after, the first fire-bricks were made at the Lee Moor Works, and subsequently salt glaze sanitary pipes. "^ In 1884^ the Lee Moor Pit was " a huge excavation, over 120 feet in depth, scarring the face of the hill for a considerable distance. Originally this pit was worked very shallow, and the water carrying the clay washed down from its sides to the depositing pits had to be pumped up. By driving an ' adit ' level from a lower point in the face of the hill, a distance of about half a mile, the depth to which the pit can be worked " has been greatly increased. Since the survey of this district in 1894 the China Clay works have been considerably extended. I am indebted to Mr. J. A. Howe, who has recently visited the district, for the following information. The pits now worked m^ay be divided into foiir groups — as regards ownership. Messrs. Martin's group includes Lee Moor, White Hill, and Cholwich Town. The works on the granite mass north of Hemerdon Ball belong to one company and include the Heddon, Hemerdon, and Smallhanger Pits. Wigford Down and Shaugh Moor Works belong to another set of owners, and Wotter Pit to another. The Lee Moor Works now include large pits worked at White Hill on the south-east (see Plate VI.) and at ' Klondyke Works ' with settling pits, tanks, and drys on the south-west. A new low- level adit is being driven beneath the old one with a view to deepen the Old Lee Moor Pit. In the Lee Moor, White Hill, Wigford, and Shaugh Moor Works the clay water with the sand is conveyed directly from the bottom of the pits to the sand pits, drags, micas, settling pits, etc., at a lower level. The other pits are worked on the principle in vogue in most of the Cornish China Clay pits, the clay water being pumped to the surface and thence conveyed by gravitation through the various processes of refinement. The sand and mica clay at Lee Moor is still xised in the manufacture of fire-bricks for the drys, etc. The clay from White Hill and Lee Moor is similar in character and of the highest quality, suitable for paper sizing, etc. The other clay pits afford clay of ordinary quality, or potting clay. 1 ' A Perambulation of Dartmoor,' by S. Rowe. Third edition, edited by ^- Brooking Rowe, 1896, p. 271. ' ' Proc. Geol. Assoc, 1884, vol. viii, pp. 474, 475. CHINA CLAY. 121 Mr. R. H. Worth has kindly contributed the following notes on the extension of the clay in other parts of the granite area east of the Lee Moor Works. " The whole area between the rivers Erme and Avon shows sporadic indications of clay. The southernmost important bed, recently discovered, lies a little north and east of Black Pool between the summits of Western Beacon and Butterdon Hill. The centre of the bed is situate approximately long. 3° 53' 32", lat. 50° 24' 28". Pits have been sunk to a depth of 50 feet. The clay is of strong potting qiiality, but not suitable for bleaching purposes. " The next known deposit of importance is at Left Lake. There some years ago a commencement was made at working on the western border of the clay, but matters got very little beyond the prospecting stage. Apparently the true body of clay was overlooked or missed. It lies above the old work on the course of the brook and has been proved to a depth of 40 feet. It is a good potting clay. " Proceeding northward we come to an old clay-pit north-west of Knatta Barrow, lying long. 3° 53' 39", lat. 50° 27' 50". From this pit pipes were laid to a point adjacent to the South Devon Railway, east of Glaze Viaduct. The attempt was made to send both sand and clay through this pipe, but the sand soon cut out the invert of the stoneware pi]>e. I cannot say why the pit was abandoned. Further north is Petre's Pit, so called on the Ordnance, but I think mistakenly. This is another abandoned olay pit, it lies long. S° 53' 15", lat. 50° 28'. The clay was piped to Shipley Bridge. The pit yielded a very fair potting clay, and is not worked out although abandoned. " The most recent discoveries are at Redlake, in the area between the Redlake, the Abbot's Way, and the Old Tramway, and also at the source of the Redlake. The southern area lies long. 3° 54' 20", lat. 50° 28' 42", the northern lies long. 3° 54' 36", lat. 50° 29' 10". The northern area has been the more thoroughly examined. It is intersected to some extent with gullies made by the old tin streamers, none of these gullies, although deep, are shown on the Ordnance Map. The clay has been proved to a depth of 50 feet, and a length in one straight line of 2,000 feet. Its width is variable and not fully ascer- tained, but perhaps 600 feet would be a fair measurement for the largest body so far discovered, with branches extending further. The clay amounts in some samples to 47 per cent, of the whole material, and runs over 33 per cent, on an average. It is a high grade potting clay, suitable also for bleaching." R. Hansford Woeth. The waste water from the Lee Moor Company's works is con- ducted to a large pond or lake not far from the ' Klondyke ' pit. This prevents the pollution of the neighbouring streams, and makes a very noticeable feature in the landscape. China Stone has not been found in the area, " but," says R. N. Worth, ^ " there is a decided approach to it in a rock of The Rocks of Plymouth,' IVans. Plymouth Inst, vol. ix, 1886, p. 239, 122 GEOLOGY OP IVYBRIDGE AND MODBTTEY. the Plym Valley, which contains crystals of gilbertite, the micaceous constituent of the St. Stephens rock." Building Stones. De la Beche^ singles out the Tealmpton dolomitic limestone as " well fitted both on account of durability and specific gravity for sea-walls and piers for harbours " and owing to the facilities for transport afforded by the Yealm Estuary. The granite has been quarried by the Great "Western Railway Company, near the border of the Moor east of Ivybridge, for the construction of the railway viaducts spanning the Erme Valley and the valleys on either side of Corn wood Station. The lime- stones are largely quarried for building purposes. Some varieties of the vesicular igneous rocks make a rough but durable building stone, frequently associated with other local materials in church architecture and other old buildings. The slates in the Upper Devonian area, where suitable, have been quarried for common building stone. De la Beche^ refers to Newnham Park on the north of Plympton as affording the better beds for this purpose. The Middle Devonian slates, where their planes of cleavage or bedding, as the case may be, are sufficiently cohesive, furnish building materials. A slate quarry between East and West Leigh is said to have supplied the materials of which Harberton Church is built. In the Lower Devonian area the grits are used as local building materials and the interlaminated beds of the Meadfoot Group, where cohesive laminae and joints are favourable, as on the north of Mounts and WNW. of Fallapit. De la Beche^ in alluding to the harder elvans as furnishing the best building materials, mentions the Hoborough stone, the elvan which crosses Roborough Down, as celebrated in the neigh- bourhood for its appearance and durability. Worth'*' says that this rock was " largely used for building in the Middle Ages," this no doubt accounts for the numerous overgrown pits on its outcrop. It is a free working material of great durability. Granite is used as a building stone on Dartmoor and its borders. The calc-flintas, quartzites, and harder diabases are too refrac- tory to work for building purposes. Ornamental Stones. De la Beche, pp. 498-499, observes, " The marbles of Ply- mouth are not very dissimilar from those obtained at Petit Tor, with the exception of the black, a good variety of which is found at Cat Down." " A beautiful green marble is found in Kitley Park, and the rose-coloured dolomite in the vicinity of the same place affords a ' ' Report on Geology of Corawall, Devon and West Somerset ' (Geol. Surv ) 1839, p. 491. ' Ibid., p. 490. ' Ibid., p. 495. * Trans. Devon. Assoc, 1892, vol. xxiv, p. 203, and ' The Rocks of Plymouth ' Trans. Plymqufh Inst., 1886, p. 23. ' ROAD STONIE. 123 very handsome though hitherto neglected material." Some of the granites, such as the red variety from Trowles worthy Tor, yield suitable material for polished columns entablatures and rough or polished monumental work. Road Stone. The calc-ilintas and diabase-hornfels, more particularly the former, the harder diabases, the felsites, the Lower Devonian quartzites, and the limestones are quarried for road metal. The calc-flinta quarries of Wrangaton, Bittaford Bridge, Ivy- bridge Siding, in the band east of Stowford House, supply materials for the main roads ; those of Ivybridge opposite the church, Dinnaton, Fardel Mill, are used on the roads in their vicinity. In the diabase-hornfels of Bottle Hill and on Beam Common quarries have been opened for road metal. Amongst the principal roadstone quarries in the Devonian diabases are : — Waterloo Quarry, by the Erme Valley, 2^ fur- longs from Ermington Church, where some of the joints are lined with asbestos ; Dunhill Quarry, in porphyritic diabase, near Diptford, 2| furlongs east of the church ; quarries on either side of the Avon about half a mile south of Loddiswell Church ; quarries at 3 furlongs north-west and half a mile east of Cumery, south of Modbury. Amongst the felsites the granophyre, near Whympston House and the Cann Quarry elvan are worked for road metal. The Lower Devonian grits and quartzites, near Halwell, Stan- borough Camp, Moreleigh, and Coldharbour Cross have been quarried for local road metal, and stones collected from the sur- face of the fields are also used. In Plymstock Parish the roads were metalled lately with volcanic rock from Notter, in Sheet 348. In the granite area the harder varieties of granite and vein- stones are used for ordinary road metal. The calc-flintas furnish the most durable material and their development on the south border of the moor renders it prac- tically inexhaustible. Roofing Slates. De la Beche (p. 503) says, " There is much roofing slate in the grauwacke ranging round the southern part of Dartmoor." Amongst the quarries he enumerates the following are in this map: — " Near Wash, on the east of Buckfastleigh "; south-east of Rattery [HoUet's Quarry]; at Wood, west of TJgborough; north of Ludbrook ; " at Cann Quarry, near Boringdon Park (to which a canal has been made up the Plym, and extensive works have been carried on) ; at Leigham, on the east of Egg Buck- land " ; at Roister Bridge. Roofing slate is no longer quarried in the district. One of the principal quarries not mentioned in the above list is Lincombe Quarry, shown on the one-inch map, east of Harberton. In the same district nvimerous old slate quarries are shown on the six- inch maps. 22266 I 124 reology of ivybhidge and modbury. Lime. De la Beche, p. 508, mentions the lime industry of the area in his day in the following passages : — ' ' Plymouth limestones being imported into the Kingsbridge estuary, a large portion of the land near it is supplied at moderate cost. The like happens up the tidal portions of the Avon and Erme, at the heads of the creeks in which lime-kilns will be generally found. The lime- stones of Sequers Bridge and Yealmpton plentifully supply the country near them. The extent to which the Plymouth limestones are worked is very considerable ; not only are they sent to the east- ward as above noticed, but they are also plentifully exported to the westward, where there are no limestones to compete with them, except those from Soutli Wales. A great quantity of the former limestone is also carried iip the navigable parts of the Tamar, Tavy, and Lynher; so that we are less surprised at the vast excavations near Plymouth than we might otherwise be, more particularly when we recollect the great number of tons which have been used at the Breakwater in the Sound. From the great distance to which the Tamar is navigable, a large por- tion of country in which lime would otherwise be an expensive article, is supplied at moderate cost." Very little lime is burnt in the district now, but the numerous disused lime-kilns amply bear out the statements in the above quotation. Messrs. Burnard, Lack, and Alger's chemical manure works are supplied from the Cattedown Quarries. Peat. Peat could no doubt be dug for fuel in places — south of Trowles- worthy Warren House; between Shavercombe Head, Langcombe Head, and Yealm Head; on Quickbeam Hill, north-west of Knatta Barrow, where it was proved to a depth of 3 or 4 feet in ponds; about Red Lake and between it and the Avon on the east, where 4 feet of peat was noticed. The general absence of exposures prevents our distinguishing -norkable peat from peaty soils, and the extent of the former could only be ascertained by numerous trial holes. Ageicultuee. ^ The volcanic and intrusive basic rocks make the most naturally productive soils for grazing or tillage. They form an almost continuous belt of country from the Plymouth limestones on the west to Harberton on the east and from Buckfastleigh to the granite border west of South Brent. Patches and bands of volcanic rock also occur in the district east and south of Buckfastleigh, around Plympton, Cornwood, and Newnham Park. Numerous patches of basic igneous rock also occur in the Lower Devonian area between the Erme Valley and East AUington. The volcanic rocks are often very calcareous, and the presence of limestone or calcareous beds in the Middle Devonian slates is seen in the coast section and west of Brixton. The slate soils AGRICULTURE. 135 vary from a moderately stiff to a loamy clay, the occasional presence of pliospliatic nodules and of volcanic and calcareous bands tends to improve their character. The soils of the greenisli and variegated Upper Devonian slates are often thin, and this is locally the case in the Dartmonth Slate districts in the Lower Devonian. North of South Brent, at the foot of the crags of Beara Com- mon, a rich red-brown soil affords fine grazing land, but whether it is a natural soil of subjacent igneous rock faulted down on the west or rain wash there was no means of ascertaining. The granite area, owing to the absence of lime, is more suitable for pasture than tillage. ," The man who has his land fairly dry and uses a little cake and corn in the grazing season will be able to send good cattle and sheep off the moor in the autumn and at the same time improve his pasture." " Wherever a sheltered valley can be got for the home enclosures a practical farmer can always do well."'^ ' Rowe'H ' Perambulation of Dartmoor.' Third edition, 1896, p. 257. 22265 I 2 126' APPENDIX. List of Peincipal Works on the Geology op the Distbict. 1808. Vancouver, C. General View of the Agriculture of the County of Devon. 8vo. London. 1811. Bergbr, Dr. J. F. Observations on the Physical Structure of Devonshire and Cornwall. Trans. Geol. Soc, vol. i, pp. 102-105, and 117-120. 1817. Hbnnah, Rev. R. Observations respecting the Limestone of Ply- mouth. Trans. Oeol. Soc, vol. iv, p. 410. Home, Sir E. An Account of some Fossil Remains of the Rhino- ceros, discovered by Mr. [Whidbfey] Whitby in a cavern enclosed in the limestone rock from which he is forming the Breakwater at Plymouth. Phil. Trans., vol. cvii, p. 176. 1821. Hennah, Rev. R. An Account of the Limestone of Plymouth. Trans. Geol. Soc, vol. v, p. 619. Whidbey, Jos. A further Account of Fossil Bones discovered in Caverns enclosed in the Limestone Rocks at Plymouth. Phil. Trans., vol. cxi, p. 133. 1822. Hennah, Rev. R. A Succinct Account of the Lime Rocks of Ply- mouth. 8vo. Plymouth and London. Lysons, Rev. D., and S. Magna Britannia (Devon). 1827. Hennah, Rev. R. Additional Remarks on the Nature and Character of the Limestone and Slate principally composing the Rocks and Hills round Plymouth. Proc. Geol. Soc., vol. i, p. 1. 1830. . On the Animal Remains found in the Transition Limestone of Plymouth. Proc. Geol. Soc, vol. i, p. 169. Pbideaux, J. Geological Survey of some parts of the Country near Plymouth. Trans. Plymouth Inst. 1837 and 1839. Sedswice, Rev. Prof. A., and [Sir] R. I. Murchison. On the Physical Structure of Devonshire and on the Subdivisions and Geological Relations of its older Stratified Deposits. Trans. Geol. Soc, ser. ii, vol. v, parts i and ii, pp. 633-687 and 688-703. (See also JRep. Brit. Assoc, for 1836. Tr. of Sections, p. 95.) 1839. Bellamy, J. C. The Natural History of South Devon. Chaps, ii, iii, and iv. Geological. 8vo. Plymouth. De la Beche, [Sir] H. T. Report on the Geology of Cornwall, Devon, and West Somerset. [Geol. Surv.) 8vo. London. 1841. Phillips, Prof. J. Figures and Descriptions of the Palaeozoic Fossils of Cornwall, Devon, and West Somerset. (Geol. Surv.) 8vo. London. 1842. Williams, Rev. D. On the Stratified and Unstratified Volcanic Products of the West of England. Pep. Brit. Assoc, for 1841, Tr. of Sections, p. 61. 1843. . On the Killas Group of Cornwall and South Devon. Trans Roy. Geol. Soc Corn., vol. vi, p. 122. 1846. Moore, Dr. E. On the Fossils of Crownall Bav. Ihid.. p. 285. 1852-1881. " Mineral Statistics." Mem. Geol. Surv. 1853. Milne-Edwards, H., and Jules Hai:iie. A Monograph of the British Fossil Corals. Fourth part. Pnl. Soc, pp. 211-244. 1855. Pengelly, W. Observations on the Geology of the South-Western Coast of Devonshire. Trans. Boy. Geol. Soc Corn., vol. vii, p. 291. 1857. Phillips, J. A., and J. Darlington. Records of Mining and Metal- lurgy. 1859. Pengelly, W. On the Ossiferous Fissures at Oreston, near Plv- mouth. Geolor/ist, vol. ii, p. 434. 1862. Bate, Spence. Bovisand Sand-Beds. Trans. Devon. Assoc, vol i • p. 42. Davidson, T. A Monograph of the British Devonian Brachiopoda Pnl. Soc, vol. xvi, part vi, no. 1. 1863. . Ibid., vol. xvii, no. 2. BIBLIOGRAPHY. 127 1868. Hall, Townshend, M. On the Mineral Localities of Devon. Trans. Vevon. Assoc, vol. ii, p. 332. HoLL, Dr. Habvby B. On the Older Rocks of South Devon and East Cornwall. Quart. .Journ. Geol. Sue, vol. xxiv, p. 400. Jukes, Prof. J. B. Notes on parts of South Devon and Cornwall, with Remarks on the True Relations of the Old Red Sandstone to the Devonian Formation. Jouni. Boy. Geol. Soc. Ireland, vol ii, p. 67. 1870. Pengelly, W. The Literature of the Caverns near Yealmpton. Trans. Devon,. Assoc, vol. iv, p. 81. 1871. Worth, R. N. The Ornamental Rocks of Devon and Cornwall. Western Chronicle of Science, no. 7, p. 99. . Building Stones of Devon and Cornwall. Ibid., no. 8, p. 120. 1872. Pengelly, W The Literature of the Oreston Caverns near Ply- mouth. Trans. Devon. Assoc, vol. v, p. 249. WoHTH, R. N. Notes on the Rocks in the Neighbourhood of Ply- mouth. Ibid., p. 62. 1873. Champebnownb, A. On the Discovery of a Species of Starfish in Devonian Beds of South Devon. Rep. Brit. Assoc, xliii, p. 77. Pengelly, W.' On the Literature of Caverns at Buckfastleigh. Trans. Devon. Assoc, vol. vi, p. 70. 1874. Champernowne, A. On the Discovery of a Species of Starfish in the Devonian Beds of South Devon. Geol. Mag., p. 5. . On a contortion of the Limestone of Torquay. Trans. Devon. Assoc, vol. vi, p. 548. Pengelly, W. Notes on Recent Notices of the Geology and Palseon- tology of Devonshire. Ibid., p. 649. Woodward, Dr. H. Description of a New Species of Starfish from the Devonian of Great luglebourne, Harberton, South Devon. Geol. Mag., p. 6. Worth, R. N. Notes on the Limestone of Yealmpton and its Associated Rocks. Trans. Devon. Assoc, vol. vi, p. 703. 1875. . Alluvial Deposits on .Plymouth Hoe. Ibid., vol. vii, p. 150. . The Economic Geology of Devon. Ibid., p. 209. . The Geology of Plymouth. Trans. Plymouth Inst., vol. v, p. 450. 1878. Champernowne, A. Notes on the Devonian and Old Red Sandstone of North and South Devon. Geol. Mag., p. 193. Worth, R. N. On the Origin of the Ossiferous Deposits of Oreston Caves. Trans. Devon. Assoc, vol. x, p. 404. . The Palseontology of Plymouth. Trans. Plymouth Inst., vol. v, p. 204. 1879. Champernowne, A., and W. A. E. Usshbr. Notes on the Structure of the Palaeozoic Districts of West Somerset. Quart. Journ. Geol. Soc, vol. XXXV, p. 532. Worth, R. N. The Bone Caves of the Plymouth District. Trans. Plymouth Inst., vol. vii, p. 87. 1881. Champernowne, A. The Ashburton Limestone; its Age and Rela- tions. Geol. Mag., p. 410. Ussheb, W. A. E. The Devonian Hooks between Plymouth and East Looe. Trans. Boy. Geol. Soc. Corn., vol. x, p. 70. Whitaker, W. Well-section at Stonehouse. Trans. Devon. Assoc, vol. xiii., p. 298. 1882-1907. Mines and Quarries. General Report and Statistics (Home Office), part iii, Output. Collins, J. H. On the Nature and Origin of Clays ; the composition of Kaolinite. Journ. Min. Soc, vol. vii, p. 205. 1883. Worth, R. N. The Rocks in the Neighbourhood of Plymouth. Trans. Devon, .issoc, vol. xv, p. 396. . Plymouth Stratigraphy. Ibid., p. 398. , On Trowlesworthite, and certain Granitoid Rocks near Plymouth. Trans. Boy. Geol. Soc. Corn., vol. x, p. 177. 1884, Champernowne, A., W. A. E. Usshbr, R. N. Worth. Excursion to South Devon. Proc Geol. Assoc, vol. viii, pp. 442-449, 458-472, 473-480. j'38 UEOLOGY OF IVYBKIDGE AND MODBUEY. 1884. Worth, R. N. Trowlesworthite. Trans. Devon. Assoc, vol. xvi, p. 72. 1886. . The Rocks of Plymouth. Trans. Plymouth Inst., vol. ix, p. 213. 1887. . On the Occurrence of Human Remains in a Bone Cave at Cattedown. Trans. Devon. Assoc, vol. xix, p. 419. . The Igneous and altered Rocks of South-west Devon. Ibid., p. 467. . On the Discovery of Human Remains in a Devonshire Bone Cave. Trans. Boy. Geol. Soc. Corn., vol. xi, p. 105. 1888. UssHBB, "W. A. E. The Granite of Dartmoor. Trans. Devon. Assoc, vol. XX, p. 141. Worth, R. N. The Limestones of the Plymouth District. Ihid., p. 410. . The Cattedown Bone Cave. Trans. Plymouth Inst., vol. x, p. 146. . The Dartmoor Volcano. Trans. Plymouth Inst., vol. x, p. 146. . Some Detrital Deposits associated with the Plymouth Lime- stones. Trans. Boy. Oeol. Soc. Corn., vol. xi, p. 151. 1 389 Champernownb, A. On the Ashprington Volcanic Series. Quart. Journ. Oeol. Soc, vol. xlv, p. 369. Worth, R. H. A Detrital Deposit at Cattedown. Trans. Devon. Assoc, vol. xxi, p. 77. 1890. Tkall [Dr.] J. J. H. Metamorphism in the Harz and West of England. Trans. Boy. Geol. Soc. Corn., vol. xi, p. 221. ITssHER, W. A. E. The Devonian Rocks of South Devon. Quart. Journ. Geol. Soc, vol. xlvi, p. 487. . The Devonian Rocks of Great Britain. Bep. Brit. Assoc, for 1889. Tr. of Sections, pp. 578, 579. Worth, R. N. Contact Metamorphism in Devonshire. Trans. Devon. Assoc, vol. xxii, p. 169. 1891. . Occurrence of layers of Carbonized Wood in a Limestone Fissure at Pomphlett. Ibid., vol. xxiii, p. 112. 1892. UssHER, W. A. B. The British Culm Measures. Proc. Somerset. Arch, and Nat. Hist. Soc, vol. xxxviii, pp. 136, 210-213, 218, 219, and Maps. Worth, R. N. — Materials for a Census of Devonian Granites and Felsites. Trans. Devon. Assoc, vol. xxiv, p. 188. . The Succession of the Plymouth Devonian. Trans. Boy. Geol. Soc. Corn., vol. xi, p. 381. 1893. . The Age and History of the Granites of Devon and Cornwall. Ibid., p. 480. 1896. Busz, Dr. K. On the Occurrence of Corundum produced by Contact Metamorphism on Dartmoor. Geol. Mag., p. 492. . Ueber einige Eruptivgesteine aus Devonshire in England. Neu. Jahrb. f. Min., part i, p. 57 (p. 74). Director-General of the Geological Survey. Annual Report, p. 52, Rows, Samuel. A Perambulation of the Antient and Royal Forest of Dartmoor. Third Edition, Revised and Corrected by J. Brooking Rowe. 8vo. Exeter and London. 1898. CoDRiNGTON, T. On some submerged Rock-valleys in South Wales, Devon, and Cornawll. Quart. Journ. Geol. Soc, vol. liv, p. 251. Worth, R Hansford. Evidences of Glaciation in Devonshire. Trans. Devon. Assoc, vol. xxx, p. 378. 1899. Btjsz, Dr. K. Mittheilungen uber den Granit des Dartmoor Forest in Devonshire, England, und einige seiner Contactgesteine. Neu. Jahrb. f. Min., BB. xiii, p. 90. Worth, R. Hansford. The Bottom-deposits of the English Channel from the Eddystone to Start Point, near the thirty-fathom line. Trans. Devon. Assoc, vol. xxxi, p. 356. 1900. TJssHBE, W. A. E. The Devonian, Carboniferous and New Red Rocks of West Somerset, Devon, and Cornwall. Proc. Somerset .irch. and Nat. Hist. Soc, vol. xlvi, p. 1. 1901. . Excursion to the Start, Prawle, and Bolt Districts. Proc Geol. Assoc, vol. xvii, p. 119. Map, p. 121. BIBLIOGRAPHT. 129 1902. Worth, R. Hansford. The Petrography of Dartmoor and its Borders. Part i. Trans. Devon. Assoc, vol. xxxiv, p. 496. 1903. UssHBR, W. A. E. The Geology of the Country around Torquay. (Mem. Geol. Surv.) . Remarks on the Devonian and Carboniferous Rocks in South Devon and Cornwall. Summary of Progress for 1902 (Mem. Oeol. iSurv.), p. 164. Water Works Directory and Statistics, London. Worth, R. Hansford. Petrography of Dartmoor and its Borders. Part ii. Trans. Devon. Assoc, vol. xxxv, p. 759. 1904. TJssHBR, W. A. E. The Geology of the Country around Kingsbridge and Salcombe. (Mem. Geol. Surv.). 1907 . Excursion to Plymouth. Proc Geol. Assoc, vol. xx, p. 78. . The Geology of the Country around Plymouth and Liskeard. (Mem,. Geol. Surv.). 130 INDEX. Abbot's Way, 112, 121. Acid rocks, 41-43, 90-96. Actinolite, 87, 88. Addislade, 63. Adinole, 10. Agriculture, 124, 125. Aish, 12, 80, 87, 88. Alaskite, 77 Aileron, 26, 29, 109. Alston, 25j 29. Anchor Brewery, 113. Andalusite, 10, 82, 90 Andesite, 99. Andurn Point, 2, 5, 8, 20, 21, 26-28, 44, 104, 105, 112, PI. n. Antimony, 36, 115, 116. Aplite, 66, 92, 94-96. Area described, 1. Armorican movement, 16, 17. Arsenic, 116, 118 Asbestos, 78, 123. Ashburton, 4, 8, 9, 13, 62, 71, 127. Ashford, 23, 24, 26, 29. Ashprington volcanic series, 4, 7, 8, 10, 13, 56, 61, 75-77, 128. Asliridge, 56, 57. Augite, 10. Aureole, 11-13, 67-69, 76, 80-89. Austin's Bridge, 62, 70, 110. Aveton Gifford, 17, 22, 39, 43, 44. Avon, 1, 10, 19, 23, 24, 30, 38, 39, 44, 83, 91, 92, 95, 105, 108, 109, 111, 112, 114, 116, 124. Wick, 8, 57, 75, 109. Axinite, 10, 86. Ayrmer Cove, 24. Babland, 32, 33, 38, 105. Ball Gate, 94. Banks, Sir J., 101. Barkington, 70. Barnstaple, slates of, 4. BarroTv, G., 11, 12, 76, 82-89. Basic rocks, 43-45. Bate, Spence, 105, 126. Batten Bay, 48, 49, 77, Battisford, 68. Beam Common, 123. Beanha}-, 55. Bear, 101, 102. Beara Common, 62, 69, 87, 88, 125. Hill, 90. Bedlime Wood, 39. Beer Alston, 95. Stone, 98. Bellamv, J. C, 66, 101, 103, 104, 126, ' Belsford, 79, Beneknowle, 53, 6i Bennick, 43. Berger, Or. J. F., 126 Berry Head, 8. Park, 51, 52. Pomeroy, 51. Berrystone, 52. Bibliography, 126-129 Bickham, 67. Bridge, 14, 52, 109. Biokleigh, 15, 67, 82, 95, 105, 107, 113, 115, 116, 119. Bigadon House, 70. Binnamore, 88, 95. Biotite-hornfels, 83, 84, 95. Birch, 98, 112. Bison, 103. Bittaford, 114. Bridge, 80, 95, 123. Blackawton, 39, 40, Black Down, 6, 8. Blackdown Camp, 8, 32, 33, 38, 39. Blacket, 95. Black HaU, 10, 57, Head, 66, 75. Pool, 121, Tor, 91, Blatchford, 6, Bloody Pool, 80. Bodmin, 87. Moor, 11, 12, 16, 96- Bolt Head, 4, 97. Bone Caves, 11, 127. Bonney, Prof. T. G., 78, 79, 93, 99. Boreston, 38. Boringdon, 68. Consols, 118. Park Mine, 115, 118, 119. Borough Farm, 26, 29, 32. Bottle Hill, 7, 76, 114H19, 123, Bovey Basin, 100. Bovisand Bav, 5, 8, 18, 27, 30, 31, 43, 97, 104," 112, PI. III. Bowcombe Wood, 53. Bowerdon, 116. Brent, 14, 83, 114. Fore Hill, 91. Hill, 1, 13, 69, 71, 88. MiU, 64. Brentmoor Works, 92. Brent Tor, 98. Bridgend, 22, 26. Brisworthy, 92, British Museum, 10, Brixton, 51, 59, 60, 66, 68, 78, 124, Barton, 68. Boad, 76. Broadall Lake, 94, 112. INDKX. 131 Broadhampstou, 53. Brockhill Mire Leat Ford, 94. brookhill, 42. Brooking, 13, 53, 55, 57. Browuston, 38, 45. Buchiola retrostriata, 64. Buckfastleigh, 2, 3, 6, 9, 13, 15, 53, 62, 63, 69-71, 78, 83, 94, 105, 110, 115-117, 123, 124, 127. Buckland Monachorum, 113, 119. Budesheim fauna, 64. Building-stones, 122, 123. ' Bulkamore, 70, 71. Mine, 116^119. BuUer, Wheal, 120. Bumpston Cross, 69. Burford Down, 91. Burnad, Lack, & Alger, Messrs.. 102, 124. Burrator, 113. Busz, Dr. K., 10, 83, 86, 87, 128. Butland, 26. Butlass, 65. Butterdon Hill, 121. Caddaford, 70, 110. Cadleigh, 106. House, 58, 106. Cadover Bridge, 90, 92, 106. Oalceola, 13, 57. Calc-flintas, 12, 13, 54, 03, 69, 71, 76, 80, 81, 85-87, 123. Callisham Down, 90, 92. Camelford, 87. Oann Quarry, 6, 7, 13, 15, 66, 67, 95. 115, 116, 123, PI. IV. Wood, 1. Capton, 39, 45. Carboniferous, 17, 80, 81, 90. Gardiola restrostriata, 64. Gardiuni palmatum, 64. Cassiterite, 10, 115-118. Cattedown, 2, 7, 10, 11, 50, 59, 61, 65, 98, 102, 122, 124, 128. Cattewater, 1, 2, 50, 102, 105, 111. Caton, 108. Caverns, 11, 101-104, 126, 128. Cawsand, 9, 97, 99. Chaddlewood, 79. Chalk-flints, 98-100. Challon's Combe, 23. Champernowne, A., 7-10, 13, 39, 51, 53, 55-57, 62, 127, 128. Chantry, 23, 24, 26. Chelston Meadows, 65. Chiastolite, 10, 12. 80, 82, 84, 90. Chillaton, 39. Chilley, 89. China clav, 2, 7, 120-122, PI. V. Choakford, 65, 68, Cholwell, 116. Cholwich Town, 92, 106, 120. Cleavage, 31. Clenemeads, 77. Clift, Mr., 104. Clitters Wood, 22. Clovelly Bay, 49, 77, iUo CoarseweU, 14, 38. Coast Erosion, 112. Coblenzian, 5, 26, 27. Cockington Grits, 6, 8, 9. Codrington, T., Ill, 128. Cofflete Creek, 51, 77. Coldharbour, 26. Cross, 32, 123. Colebrook, 68, 77. Coleland Bridge, 82. Collaford, 65, 66, 69. Collard Tor, 90. CoUaton, 37. Collins, J. H., 92, 98, 127. Colours of slates, 19, 20, 64. Colston, 70. Colwill, 95, 96. Combe, 39, 51. CeUars, 9. Cross, 79. Quarry, 52. Compton, 17, 66, 71-74, 78. Conglomerate, Devonian, 34. Contortions, 16. Coomhola Grits, 8. Copper, 115, 116, 118. Cornwood, 6, 7, 13, 69, 79, 83, 90, 93, 122, 124. Corringdon, 84. Ball, 80, 91, 94. Corundum, 10. Cotton, Dr. E., 3. Courtlands, 24. Court Wood, 22. Coyton, 68, 77, 105. Crabadon Cross, 19, 38. Crabtree, 17, 71, 72. Crawl Wood, 36, 37. Creaoombe, 37. Crebar, 37. Cretaceous, 98. Crownall Bay, xce Crownhill Bay. Crownhill Bar, 5, 26, 27, 30-32, 43, 97, 104. ■ Down, 2, 15, 92. Cuboides-heds, 75, 76. Culm, 12, 13, 17, 80, 81. Cumery, 44, 123. Darlington, J., 126. Darnicombe, 77. Dart, 1, 62, 70, 105, 100, 110. Dartington, 6, 10. Dartmoor, 1, 7, 11, 12, 90-95, 98, 100, 104, 113, 114, 120, 122, 128, 129. Dartmouth Slates, iv, 2, 4-6, 8-11, 15-26, 28-30, 32, 40, 43, 44, 97, 125. Datolite. 10, 86, 87. Davidson, T., 57, 126. Deadman's Bay. 98, 100. 132 INUJiX. Dean, 13, 71, 83, 109, 114. Deanoombe, 62^ 63, 71. Dean Court Orchard, 62. Cross, 78. Prior, 70, 71, 116. Quarry, 70, 71. Water, 1. De la Beche, Sir, H. T., iii, 3, 6, 9, 11, 17, 33, 103, 115, 117-119, 122- 124, 126. Derriford, 67, 95. Devonian, introduction of the term, iii, 3, 4. DevonDort, 113. Devon' Wheal BuUer, 118. Dewerstone, 1, 91, 94, PI. I. Diabase, 43-45, 78, 79, 99, 123. -hornfels, 123. Dick, A., 87. Didworthy, 12, 80, 84, 88. Dinnaton, 88, 93, 106, 123. Diptford, 14, 52, 76, 78, 109, 123. Dockwell Ridge, 91. Dolomite, 6, 60, 122. Donore, 91, 92. Dorsmouth Hill, 3, 13, 17, 65-67, 74, 78. Dousland, 11. Downderry, 9. Downstow, 91, 114. Down Thomas, 3, 11, 25. Drevermann, Dr. F., 24. Dunhill Quarry, 78, 123. Dunstan (Dunstone) Point, 4, 5, 47, 50, 51, 105. Dunstone, 14, 37, 61. Dunwell, 77. East AUington, 11, 17, 28, 29, 46, 124. Borringdon Mine, 118. Leigh, 122. Looe, 9, 27. Pitten, 69. Sherford, 13, 51, 68, 75. Eddystone, 97. Edmeston, 32, 38. Eflford, 17, 68, 72, 73, 77, 78. House, 23, 44. Lane, 73. Egg Buckland, 7, 13, 66, 71, 78, 113, 123 Elburton, 14, 51, 55, 76, 114. Elephant, 102, 104. Elfordleigh, 13, 66, 68, 76, 79. Elvans, 6, 15, 43, 67, 73, 94-96, 122, 123, PI. IV. Emily, Wheal, 36, 116. Englebourne, 10, 52, 55, 66. Entomis .lerraiostriata, 65, 68. Epidiorite, 99. Epidote, 85. Erme, 1, 14, 15, 20, 23, 26, 26, 29, 32, 36, 37, 41, 44, 72, 76, 81, 85, 91, 94, 106, 108, 111, 114, 122, 124. Erme Mouth, 6, 22, 23. Ermington, 1, 15, 78, 105, 116, 123. Estover, 79, 99. Eallapit, 3, 43, i22. I'arm, 29, 45. Fancy, 32, 38. Fardel, 81, 85. Mill, 123. Farleigh, 38, 39. Faults, 19, 20, 25, 26. Faunstone, 68. Fawns, 38, 108. Felsite, 41, 43, 94, 96, 97, 123. Fillham, 79. Silver-lead Mine, 116. Fire-bricks, 120. Fish-grits, 20, 26. Fishleigh, 26. Flammenien, 64. Flete, 14, 37. House, 14. MiU, 37. Flett, Dr. J. S., 73, 77, 87. Flint-implements in caves, 103. Florence, Wheal, 115, 116, 118, 119. Fluor-spar, 96. Folding, 16. Ford, 37, 68, 65, 66, 68, 69, 95. Wood, 28. Forks Cross, 109. Fowlescombe, 77, 78. Frasinian, 64. FuUaford House, 115. Fui-sdon, 37, 66, 79. Furzehill, 79. Gabbro, 99. Gara Bridge, 19. Garnet, 10, 86, 87. Geologists' Association excursion, 9, 10, 17, 119. Gidley Bridge, 12, 80. Gilbertite, 122. Gingaford, 114. Glacial erosion, 111, 128. period, 101. Glaze Viaduct, 121. Glutton, 104. Gnarling, 16, 30 32. Gnaton Hall, 37. Gneiss, 84. Godwin-Austen, R. A. C, 6. Goniatite-beds, 64, 65, 75. Goodameavy, 90, 92. Goosewell, 51, 65. Gorlofen, 59. Goutsford Bridge, 37, 62. Granite, 16, 16, 90-96, PI. I. ■ quarries, 122, 123. , soil of the, 126. Granophyre, 6, 32, 73, 123. INDEX. 133 Giaywacke, 3. Great Englebourne, 55, 56. Mew Stone, 21. Orcheton, 26, 29. Shaugh Wood, 67, 95. Torr, 44. Trowlesworthy Tor, 91. Green granite, 79. GreyhilJB Quarry, 52. Grimpstonleigh, 23, 40, 45. Growan, 91, 92, 112. Gutter Tor, 91. Haematite, 116-118. Haime, J., 126. Haldon, 100. Hall, 94. Hall, T. M., 117, 127. Hall Torrs, 60, 114. Halwell, 8, 14, 32, 33, 38, 39, 55, 123. Ham, 29, 33, 44. Hamling, J. 6., 62. Hand Deeps, 97. Hanger Down, 91, 93. HangersheU Rock, 91. Hanger's Quarry, 55, 57. Hangman's Cross, 38. Harberton, 12, 14, 15, 52, 76, 79. 109, 122-124. Harbertonford, 7, 56. Harbourne, 1, 14, 106, 109. Harbourneford, 77, 78. Hardwick, 65, 67. Hareston, 66, 68, 71, 79. Harford, 91, 92, 94, 106. Harraton; 26, 29, 33, 38, 43. Hawns & Dendles, 1. Hay Farm, 65-68. Hazard Quarry, 53, 61, 76. Head, 60, 92, 97, 104-106, 108-110. Heathfield, 32, 33, 38. Heddon Down, 90, 92, 120. Hedenbergite, 86. Heights, 1. HeUanthaster filiciformis, 56. Hellyer's Cleave, 78. Hemerdon Ball, 7, 15, 66, 69, 90, 91, 93, 96, 114, 117, 120. Consols, 117-119. Hendham, 39. Henlake Down, 12, 80, 81, 114. Hennah, Rev. R., 126. Hen Tor, 91, 94. Heybrook Bay, 20, 21, 23. Higher Beara, 69, 77. Broadeford, 79. Ford, 20, 25, 28. Hendham, 39. Ludbrook, 116. Storridge, 38, 39. Wells Farm, 77. Kingston Down, 96. Hoe, The, 98, 100. Holbeton, 14, 15, 26, 29, 32, 37, 72 Hole, 37, 70. HoU, Dr. H. B., 7-9, 127. HoUet's Quarry, 53. Hollowcombe, 37. Holne Bridge, 13. Homalonotus, 39. Home, Sir E., 126. Hood, 53, 105, 110. Hooe, 36, 50. Hoc Meavy, 90, 115. Hope Cove, 4, 5. Hornblende, 89. Hornfels, 83, 84. Horsebrook, 57, 109. Howe, J. A., 120. Houndle, 69, 99. Huntingdon Tin Jline, 116. Hyaena, 102, 103, 104. Idston, 43, 44. Ilmenite, 88. Ingleboume, 55, 56. Iron-ore, 115-118. Isler & Co., Messrs., 113. Ivybridge, 1^, 12, 15, 54, 58, 63, 77, 79, 80, 90, 91, 94, 106, 108, 109, 114, 116, L22, 123. Jasper, 60, 119. Jenny Cliff, 35, 36, 46, 47. Jones, Prof. T. R., 17, 66. Jukes, Prof. J. B., 8, 127. Jump, 96. Kaolin, 92, 127. Kayser, Dr. E., iii. Keaton Bridge, 68, 76, 77. Kersantite, 10. Killas, 3. Kingsand, 112. Kingston, 23, 41, 44. Kingsteignton, 100. Kingswear, 42. Kistvaen, 112. Kitley, 7, 58, 60, 68, 79, 122. Kitt Hill, 96. Klondvke Works, 120, 121. Knatta Barrow, 92, 112, 121, 124. Knighton, 15, 25, 28, 36, 116. Knotenschiefer, 10. Knowle Hill, 9. Lacc-olite, granite, 15. Ladydown Quarry. 78. Laira, 2, 110, 111. Bridge, 50, 58, 59. Green, 17, 64, 65. 134 INDEX. Landscove, 69. Langcombe Head, 112, 124. Langdon Court, 20, 21, 24, 25, 28, 36. Langford, 12, 52, 53. Barton, 78. Langston, 44. Lava, 75, 76, 88. Lead, 115, 116, 118. Leek Bed Bay, 34, 45, 105. Lee Mill Bridge, 58, 65, 108. Moor, 2, 82, 90, 92, 93, 106, 114, 120. China - clay Works, 119, 120, 121, PL VI. Left Lake, 92, 121. Legis Tor, 91, 94. Legrand & Sutcliffe, Messrs., 113. Leigham, 7, 123. Lentney Brake, 20. Leucoxene, 88. Lime, 124. Limestones, 49-01, 53, 122-124. Limonite, 117, 118. Lincombe, 8, 12. Hill, 39. Quarry, 52, 123. Lion, cave, 102, 103, Lisburne, 53. Liskeard, 11, 12. Little Efford, 72. Modbury, 26, 44. Oroheton, 37. Lizard, 87. Lobb Farm, 116. Loddiswell, 23, 24, 26, 28-30, 44, 45, 105, 109, 123. Lodes, 115-117. Lodestones, 3. Lolesbury, 37. Long Park Wood, 45. Looe Beds, 7, 9, 15, 26. Lopes, Wheal, 115, 118, 119. Lower Coblenzian, 26, 27. Combe, 13, 53, 69. Lowerdale Copse, 39. Lower Hendham, 39. Hooe, 36. Preston Cross, 39. Ludbrook, 94, 114, 123. Lukesland, 91. Lusoombe Wood, 70, 116. Lutton, 108, 114. Luxulyanite, 93. Lydia Bridge, 95, 108. Lynch Common, 92. Lyneham, 58, 68, 72, 78, 79. Lvnher, 124. Lysons, Rev. D. & S., 3, 126 Manganese, 115, 116. Man in cave deposits, 103. Mannamead, 13. Maps, dates of geological, iv, 2, 6, 8, 10, 11, 16. Marble, 122, 123. Marley House, 14, 70, 71. Marsh Mills, 2, (6, 78. Martin, W. L., 119. Mary Hutohings, Wheal, 116-119. Meadfoot Group, 4, 5, 8, 9, 14, 15, 17, 19, 20, 23-33, 97, Pis. II, III. Meavy, 98, 106, 113, 119. Membland Hall, 15, 25, 28, 32. Merafield, 65. Metamorphism, 80-89. Mewstone, 5. Mica schist, 90. Milne-Edwards, H., 126. Minerals, 115-121. Mines, 115-120. Modbury, 1, 2, 6, 11, 14, 15, 17-19, 26, 29, 32, 33, 36, 37, 39, 41, 52, 62, 108, 114, 123. Monticutipora, 5, 26, 27. Moore, Dr. E., 126. Moore Farm, 57. Morleigh, 6, 8, 32, 33, 38, 39. 123. ■ Hill Brake, 39. Morte Slates, 9, 10. Mothecombe, 3, 23, 25, 44. Mount Batten, 4, 5, 18, 48, 49, 61, 76, 105. Edgcumbe, 9. Mounts, 29, 43, 45, 122. Mudge, Lt.-Col., 103, 104. Muff (Maufe), H. B., 101. Murchison, Sir R. I., 3-6, 97, 126. Mutley, 64. Nassau, schalstein of, 8, New Cut, 39. Newmill Bridge, 45. Newnham Park, 7, 66, 76, 79, 116, 122, 124. Newpark Waste, 105, 106, 108, 109. New Red Sandstone, 97, 99. trap, 99. Newton Abbot, 8, 9, 13, 51, 66, 75. Ferrers, 20, 22, 25, 29. Crpfiir 44 NichoU's Farm, 68. North Huish, 6, 14, 61, 77, 78. Noss Mayo Creek, 22. Notter, 123. Nurston, 12, 80. Nutcomhe, 29. MrtcAlister. D. A., iv, 116-120. McLintock, W. F. P., 87. Maker, 9. Mammoth, 102, 104. Oldaport, 23, 25. Older wood. 67, 92. Old Man Camp, 39. Red Sandstone, 4, 8. INDEX. 135 Ologiste mottling, 25. Opal, 119. Orchard Farm, 60. Orcheton, 23, 25. Oreston, 2, 7, 11, 49, 50, 58, 59, 101, 102, 127. Orestone Brake, 20. Overbrent, 84, 114. Owen, Sir R., 104. Owley, 12, 80, 86, 92. Paignton, 4, 7, 12, 13, 16. Paytoe, 53, 57. Paytor, 6. Peat, 112, 124. Peek HiU, 11. Pegmatite, 25, 42, 91. Peloe, 53, 56. PengeUy, W., 10, 11, 57, 102, 104, 126, 127. Penlee Point, 9, 21. Penquit, 108. Pen Recca Quarry, 9, 69. Petherwin Beds, 4, 6, 7, 8. Petitor, 9, 122. Petre's Cross, 1, 92, 112, 121. Phillips, Prof. J., 5, 126. Mr. J., 120. J. A., 126. Piall, 108. Pillow-lava, 13, 17. Piskey's Cove, 21. PithiU, 94. Pitt Farm, 29. Place Moor, 105. Pleurodictyum, 13, 28, 55, 66. Pliocene, 106, 109. Plym, 1, 66, 94, 98, 105-108, 110, 111, 123. Bridge, 65, 66, 68, 76, 79, 99, 115. Plymouth, 4, 8-13, 16, 17, 60, 68, 75, 77, 113, 122, 126. Asylum, 95, 116. Athenaeum, 13, 66. Limestone, 9, 13, 49, 58, 59, 60, 76, 124. ■ Race Course, 58. Sound, 7. Plvmpton, 4, 7, 17, 54, 63, 67, 68, 76-79. 114, 122, 124. Castle, 65. Lodge, 68. St. Mary, 7, 119. St. Maurice, 58. Station, 65. Plymstock, 50, 55, 114, 123. Pneumatolvsis, 83, 86, 87. Pomphlett, 50, 58, 59, 65, 102. Pool, 45. Mill, 25, 28. Portwrinkle, 9, 20. Posidonomya venustaj 65, 66, 68, 69. Post Tertiary, 101. Poulston, 52. Prawle, 4. Preston, 39, 45, 78. Combe, 33. Prideaux, J., 126. Princerock Quarry, 50, 58, 59. Puslinoh, 33, 36, 37, 52, 108, 111, 114. PutshiU Copse, 43. Putt Wood, 37. Pterasjns, 21, 24, 25, 29, 47. Puckering, 82. Pyrites mined, 118. Pyroxene, 85-88. Quarry Farm, 53. Quarryhead Wood, 39. Quartzite, 77, 123. Quartz-porphry, 67. Quickbeam Hill, 112, 124. Radford, 50, 65, 59. Raised Beach, 98, 104, 105, PI. V. Rake Rock, 29, 45. Rame Head, 9, 21. Ramscliff, 34, 35. Raneleigh, 25, 28, 36. Rattery, 3, 6, 7, 13, 14, 53, 70, 71, 78, 117, 119, 123. Rectory Cross, 77. Red Lake, 112, 121, 124. Reefs as natural groynes, 112. Renney Rocks, 20, 44. Revelstoke, 21. Rhinoceros, 101-104. B'hynchonell-a cuhwles, 64, 71, 76. Rhyolite, 6, 42. Ridgeway, 4, 76. Rill, 71. Ringmoor Down, 90. River Deposits, 105-110. Riverford, 67. Bridge, 53, 110. Viaduct, 95. Road-stone, 123. Roborough, 6, 7, 67, 95, 96, 113. Down, 3, 15, 115. stone, 122. Rock, green granite of, 79. Rock-valleys, 110-112. Roister Bridge, 7, 8. 55, 56, 123. Roofing-slates, 123. Rookery, 28. Roster Bridge, 17, 55, .56. Rowe, J. B., 120. S., 125, 128. Rum Bav, 47, 77. St. Austell, 11, 16, 87. Budeaux, 13. Germans, 9, — ' Stephen, 17. 136 INDKX. Saltash, 17, 72. Saltram Point, 64, 65. Sandberger, Dr. F., 53. Schalstein, 12-14, 26, 29, 51, 58-63, 68-71, 75-79. Schorl, 83, 86, 91, 93, 94. Season Point, 20, 21, 41, 44. Seaton, 9. Sedgwick, Rev. A., 3-6, 97, 126. Sequers Bridge, 6. 7, 14, 15, 37, 38, 61, 62, 124. Sharp Tor, 91. Shaugh, 90, 95, PI. I. Bridge, 90, 94, 106, 107 Iron Mine, 116-119. Lake Works, 92. Lane^ 68. Moor Works, 2, 120. Prior, 116. Tunnel, 67, 83, 91-93, 116. Shavercombe Head, 1, 112, 124. Tor, 91. Waterfall, 94. Shearlangstone, 3, 6, 42. Sheepham, 38, 52. Shilston Barton, 52, 77. Bridge, 103. Shipley Bridge, 92, 121. Tor, 105, 106. Shortaflete Creek, 32. Shorter Cross, 53. Sidney, Wheal, 116-119. Silverbridge Lake, 59, 77. Silverbrook Lake, 72. Silveridge Wood, 23, 24. Silver-lead, 115, 116, 118. Silver WeU, 114. Skerraton, 91, 93, 95. Skerril Coppice, 23. Slade Hall, 69. Slate quarries, 3, 7, 123. Smallhanger, 92, 120. Smyth, Sir, W. W., 115. South Allington, 15, 24. Brent, 1, 3, 6, 10, 54, 80, 87, 88, 90, 105, 108, 114, 124, 125. Langston, 23. Wembury House, 22, 36. Yeoland Mine, 118, 119. Spangled mica-schist, 83. Sparkwell, 13, 69. Sphene, 88. Spilite, 3', 5, 6, 13, 17, 49, 51, 53, 58, 59, 66, 67, 71, 73, 77. 78, 92. Spilosite, 66. Spotting in altered rocks, 82. Spriddlestone, 36, 51. Square's Wood, 116. Staddiscombe, 14, 25, 28, 36, 64. Staddon Coastguard Station. 28, 32, 104, 105. Grits, 4^6, 8, 9, 14, 19. 26, 29, 32-40, 61, 105, PI. n. Stanborough Brake, 105. Camp, 39, 123. House, 33, 39. Stanton, 39. 105, 109. Starfish, 56, 127. Start Point, 4, 97. Staurolite, 93. Steer Point, 36, 51, 52. Stockenbridge, 38. Stoke Fleming, 8. Stoliford, 26, 41, 44. Storridge Wood, 38, 109. Stowford House, 80, 123. Strain-cleavage, 16, 82. Stream-tin, 7, 119. Stretchford, 110. Sfringocephalus, 10. ' Stromatactis,' 59. Strode Farm, 38, 108. Structure, geological, 12-18. Styliolu, 17, 64, 66, 73. Submerged forests, 112. Surveys, date of, iv, 2, 6, 8. SwaUet-hole, 62. Table of formations, 2. Tamar, 124. Taunusian, 5, 16, 20, 24-26, 28, 30. Tavy, 98, 124. Teall, Dr. J. J. H., iii, 96, 128. Teign, 9. Tertiary, 98-100. Thomas, H. H., 87. Thurlestone, 43. Tiddeman, R. H., 101. Tidwell, 69. Tigley, 13, 63, 57. Tin, 115-118. Tinsey Head, 35, 46. Tintagel, slates of, 4, 5. Tod Moor, 105. ToUditoh Saw Mills, 29. Topsham Bridge, 109. Torbernite, 119, 120. Torcross, 35, 43, 46. Tordeau, 116. Torquay, 4, 7, 8, 9, 12, 16, 39, 61, 57, 65, 66, 75. Torr, 6. Brook, 23. Down, 44. Rock, 41, 42, 45, 91. Torrs Wood, 116. Tory Brook Head, 92, 105, 106, 112. Tourmaline, 83, 86, 91, 93, 94. Totnes, 8, 75. Tozer, Mr., IIB. Train, 28. Trebv, 68. Tregantle, 9, 21, 27. Trias, 97. Tristis Rock, 91. Trowlesworthite, 127, 128. Trowlesworthy, 93, 94, 106. Tor, 123. Warren, 106, 112, 124. Tucker's Mill Head, 79. INDEX. 137 Tufis, 17, 72, 74, 75, 88. Tuffland, 23. Tvirnchapel, 36, 49, 77, lOo. 111. Tiixton, 58, 65, 66, 68. Ugborough, 6, 7, 16, 53, 58, 61, 62, 69, 76-78, 114, 116, 123. Beacon, 6, 91, 94. Umber, 62, 71, 115, 116. Urus, 103. Vancouver, C, 7, 119, 126. Virgin, Huel, 115, 116. Volcanic rocks, 3, 5, 6, 13, 17, 70, 71, 74-78, 88. Wakeham, 23, 44. Wallaford Down, 80, 90. Warberry, 8, 39. Ware, 62. Warren Point, 21, 41, 43, 52. Wood, 78. Wash, 70, 123. Wastor Wood, 42. Watergate Bay, 16. Waterloo Quarry, 78, 123. Water supply, 113-115. Watts, Prof. W. W., 72. Wearde, 72, 73. EflPord Grits, 2, 17, 65, 71-74, 78, 99. Quay, 17. Weeke 24 Wembury,'2, 14, 20, 21, 24, 44, PI. V. Western Beacon, 6, 91, 121. Torrs, 61. AVest Leigh, 52, 122. Pitten, 58, 65, 68, 78. Sherford, 50, 58, 59, 76, 77. WaUa Brook, 116. Wembury, 25, 28. Wood, 36, 37, 52. Whetoombe Cross, 78. Whidbey, J., 101, 126. Whitaker, W., 113, 127. White Hill, 120, PI. VI. Whitehouse, 114. Whiteley, 53. Whitemoor, 25. Whiteoxen, 70, 109. Whitesand Bay, 7, 9. Whitley, N., 98. Whympston House, 3, 17, 26, 32, 41, 42, 123. Wood, 42, 43. Widov, 78. Wigford, 39, 105. Down, 92, 93, 106, 120. Williams, Rev. D., 126. W'dsoniii, ciihri'i O %^. 'm PL, FQ rt O SB o C6 O < o M H O 3 PUBLICATIONS RELATING TO THE SURVEY OF CORNWALL AND, DEVONSHIRE— cowifcZ. Of the before-mentioned One-inch sheets, Nos: 311, 326 with 340, 335, 336, 337, 338, 346, 347, 348, 349, 352, 353 with 354, 357 with 360, and 359 are issued coloar-printed, price 1». 6d. each. Sheet 351 with 358 is also issued colour- printed, price 2s. 6d. , The fpllowing sheets are, at present, issued in hand-coloured form, only at the prices stated : — Sheet 325, 12*. M. ; Sheet 339, 9s. 9d. ; Sheet 350, lis. Sd. ; Sheet 355, 5s. 3d. ; Sheet 356, 3s. SIX-INCH MAPS ON THE SCALE OF 6 INCHES=1 MILE (1 to 10560). i The following Six-inch maps are published, and can be bought uncoloured, price Is. 6d. each quarter-sheet, or hand-colouted at the cost of colouring : — .Cornwall — 63 NW, 63 NB, 63 SW, 63 SE ; 67 SW ; 69 NW, 69 NE, 69 SW, 69 SE ; 73NW; 75NW, 75NE. 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