442 C. LAPWORTH ON THE ROOKS OF ERIBOLL DISTRIOT.

Archrean, sedimentary, or intrusive materials respectively is in all probability an insoluble question. (4) Its gneisses may be either Archrean 01' (some) possibly formed by intrusion (injection of plutonic rocks) in later ages. (5) Its schists may be composed either of crushed A,·ch<.eans, crushed intrusives, or of a mixture of these with sedimentaries. (6) Its (so-called) slates may be (according to the locality, either normal slates or) crushed rocks not yet re-crystallized (and) of either Archrean, sedimentary, intrusive, or of mixed origin.

ON THE GEOLOGY OF SOUTH DEVON, WITH SPECIAL REFERENOE TO THE LONG EXOURSION.

By W. A. E. USSHER, F.G.S.

DEVONIAN ROOKS. PLYMOUTH TYPE. TORQUAY AND TOTNES TYPE. A. Picklecombe and Staddon Grits 7. Cockington Beds-purple and grey grits and slates. 6. Berry Park Beds-bluish and dark olive slaty shales. 5. Ramsleigh Limestone. 11. Green Slates of Rame Head .., Dartmouth Slates-greenish slates. C. Lilac and grey Slates, with calc­ spar and ash bands local... 4. Ashprington Series (Schalstein) dia, basic rocks, and tuffs, inter. stratified with slates. D. Calcareous Shales, Plymouth Limestone ...... 3. Stringocephalus Limestone - The Great Devon Limestone. E. Indian red and greenish Slates 2. Lower Slates-purplish and green­ ish slate. F. Looe Grits and Schists ... Ic, Warberry and Lincombe Hill-red grits. 1. Meadfoot grey and brownish grits and schists, To understand the Devonian Rocks of South Devon in a general way, you have to shut your eyes, as it were, to the great complexity of their relations, to ignore the many folds and flexures into which they have been thrown, and to pass over the particular difficulties which the position of this patch of limestone or that mass of shale present, unless you are prepared by slow and laborious investigation to take each complex bit of ground and un- W. A. E. USSHER ON THE GEOLOGY OF SOUTH DEVON. 443 ravel its structure, so that after years, it may be, this piecemeal geologizing enables you with some show of probability to put the disjointed fragments together, and build up a general structure and a succession of great divisions. As we cannot do so ourselves, we must accept the general conclusion arrived at by those who have studied the details, of whom my friend Mr. Champernowne has been the most assiduous. Before stating the general sequence he gives me, I may mention that the difference between the North and South Devon Devonian areas is in some respects very great. In North Devon we have a continuous succession-the beds are folded, it is true-but the folds do not affect the connection of divisions, and except in the case of the Lower Devonian, faults do not complicate their relation; the features also are persistent, characteristic, and well marked. In North Devon, the Upper Devonian consists of slates upon grits, perhaps from 2,000 to 3,000 feet thick; the Middle Devonian, of slates very like the beds near Rame Head and Cawsand, upon slates and shales, with Limestones, upon the Hangman Grits; the series being probably much thicker than the Upper Devonian. The Lower Devonian consists of slates, schists, and even bedded grits, the equivalents of the Lynton Beds-upon the Foreland Grits. Now we have in South Devon a constant recurrence of shales, slates and limestone, putting out of sight for a time the grits of Cockington Hill, Staddon Point and Picklecombe Fort. These beds cover a very large area, and exhibit every variety of complex relationship. Diabase tuffs, interbedded with slaty shales, form an important series of beds, for which, from a village in thc region where they are developed, Mr. Ohampernowne suggests the name Ashprington series, and correlates them with the Nassau Schal­ stein. These beds exhibit every kind of faulted relationship to shales and slates above and below the Great Devon Limestone. The oldest Devonian rocks known in the district are the red grits and schists of Warberry and Lincombe Hills in the Torquay promontory, and the grey and brownish grits and schistose beds of Meadfoot, near Torqnay, which owe their position to faults by which they have been thrust up. They are regarded as Lower Devonian, and Mr. Champernowne also thinks that part of the slates below the great Devon Limestone may be Lower Devonian. To ascertain the relations of a group of strata it is necessary either to discover in them bands sufficiently marked and persistent 444 w, A. E. trSB HE R ON THE GEO LOGY OF BOUTH DE VON. to serve as horizons, to ascertain the features peculiar to the different lithological varieties, to follow or in some degroe ascertain th e stratigraphical relations of the constituent divisions, or to have a very intimate acquaintance with th eir fossil contents, and an extensive knowledge of th e groups which arc equivalent to th em elsewhere. All th ese methods of research have been brought to bear upon a large par t of th e Devonian area between Ashburton, Torquay, and Plymouth by my friend Mr. Champernowne, and the reservation with which he is in many cases obliged to give his opinion respecting the position of the divisions and their cor­ relation, after a study extending over many years, proves th e extreme diffi culty of th e task. In North Devon, as I have said, the three great divisions of the Devonian have each a slate and a grit series, and the slates of all three are different lithologically and palseontologically, whilst the grits are also distinct and distingui shable, so that if in North Devon we had a quantity of dislocations, bringing in contact tile members of divisions of very different ages, we should still be able to unrav el th e structure as though no faults existed. I n South Devon, on the contrary, the Great Devon Lim estone, which may be regarded as the most, if not the only marked horizon, is, as its fossils show, more or less of th e natu re of a coral reef, and, there­ fore, in all probability, not only not persistent as a whole, but locally pr esenting abrupt natural terminations which would have th e appearance of faults. We will now glance at the Plymou th Sound District, from which I hope to effect a bett e!' starting point, in a little tract with which I am personally acquainted, than if 1 plung ed at once into my friend's excellent and erudite classification.

The Devonian Rocks of Plymouth. The main mass of the Plymouth Limestone terminates in th e north part of Mount Edgecumbe Park. It dips southwards under shales, partly calcareous, and associated with ash-beds. The shales near Barn Pool are intersected by dykes of igneous rock. Towards Pickleeombe Fort th e coast geology is confined to beach reefs, consisting of shales intercalated with grey grits, red grits, and slaty grits; and further on, lilac-brown grits with quartz veins. At half a mile from Kingsand the gr its are overlain by a small exposure of Triassic breccia, which dips under the Trap rock of Oaweand. W. A. E. USSHER ON THE GEOLOGY OF SOUTH DEVON. 445

The grits are probably cut off on the south by a pre-Triassic fault between Maker Barracks and Millbrook, and near Picklecombe Fort; and their dips being discordant, they are either unconform­ able to, or faulted against, the shales overlying the Plymouth Lime­ stone. These beds are evidently a continuation of the massive red grits, intersected by irregular joints, which form the cliffs above Staddon Pier, on the opposite side of the Sound. The Staddon grits seem to be faulted against the shales over­ lying the limestones of Mount Batten, Hooe, andOreston. South of the Cawsand Trap rock pale green quartz-veined slates are exposed on the coast forming Peulee Point. Rame Head is composed of grey slates, with beds of fine grey quartz-veined grit. Rounding Rame Head, and proceeding toward East Looe, we have a downward succession of lilac, grey, and greenish slates, with occasional gritty beds from the Rame Head, Peulee Point, and Cawsand slates, which exactly resemble those of Morthoe, viz., the upper member of the North Devon Middle Devonian. Near the Fort, south of Lower Tregantle these beds rest on about 100 feet of buff sandstones, succeeded by 300 feet of calcareous shales, with a mass of slaty limestone, upon about 200 feet of slates and sandstones. As these calcareous shales are on the strike of the Plymouth Limestones, the passage of the one into the other is a legitimate inference. Further on to Millelldreath, grey, lilac, greenish, and Indian-red slates, shales, and fine intercalated grits may be taken as the beds underlying the Plymouth Lime­ stone, exposed with more marked colouring in the railway cuttings between Plymouth and St. German's. Under these beds we have the greenish, reddish, and grey quartei­ ferous slaty and shaley beds and grits of Looe, with their ill-pre­ served fossils. The above observations give us the following series:- A. Picklecombe and Staddon Grits, probably unconformable to beds below. B. Green slates of Rame Head and Peulee Point, probably the upper part of the Middle Devonian. C. Lilac-greenish and grey slates, apparently associated with ash-beds and calcareous matter near Barnpool, where they overlie the Ply month Limestone, based by grits near Higher Tregantle. 446 w, A. E. USSHER ON THE GEOLOGY OF SOUTH DEVON.

D. Calcareous shales on the strike of, and therefore passing into, the great South Devon Limestone. E. Indian-red and greenish slates of St. German's, &c. F. Slaty grits and schistose beds of Looe, A. is Mr. Champernowne's No. 7=The Oockington Beds of Windmill Hill, Beacon Hill, South Down Cliff, &c.; equivalent in part to the Upper Devonian Pickwell Down Grit of North Devon, and to the Psammites de Condroz of the Belgians. It consists of "Purple and grey grits interstratified with slates of the same colours. Grey tints prevail near the passage into the under­ lying group." No.6. Berry Park, Upper Dartington, goo., Beds.-" Bluish and dark olive slaty shales, rather coarse; usually less evenly lami­ lated than those below the Great Limestone, but not invariably distinguishable." "Whenever these beds are sufficiently expanded, and not seen in narrow folds and strips, they pass up into the grits (No.7). At Higher Brixham they are very slightly represented." " These beds are sparingly fossiliferous, Streptorhynchus umbracu­ lum or crenistria being the prevalent Brachiopod." "In all proba­ bility" correlative with" Schistes de la Famenne." No.5. "Ramsleigh Limestone and other calcareous bands on or about the same horizon," containing" Acervularia, Ohonophyllum, &c." The Ramsleigh reef is a thick mass showing no bedding in the quarry, mostly red, yielding many species of Acervularia, Rhynchonella cuboides, Alveolites, and Paclojpora, and correlated with "Schistes et Calcaires de Frasnes." Nos. 5, 6, 7.-Mr. Champernowne brackets as Upper Devonian, the" Famennien" of continental geologists. " No beds," says Mr. Champernowne, " comparable with either the Baggy or Pil­ ton" (Upper Devonian Slates of North Devon) "series are known in South Devon, but they should overlie Group 7 if the series in South Devon went high enough. I presume it does not." Although No.7 is the same as A. in the Plymouth section, I do not see in it the equivalents of 5 and 6, which are probably missing through the unconformity of the Staddon and Picklecombe Grits. Dortmouth Slates, "not numbered, very perplexing."-" These have much the same characters as the Morte tllates. They may be bronght np in inverted folds from beneath the beds numbered 7­ intensely puckered on the small scale, with indications of much W. A. E. USS HE R ON THE GEO LOG Y OF SOUTH DE VON. 447 contortion on the large. They may be imagined as reaching a great development as they recede from the great reef areas." The above description by Mr. Champernowne, and the fact that they are in the same line of strike, seems to me to justify the cor­ relation of the Dartmouth with the Rame Head Slates (B) in the Plymouth section j and I think that our independent recognition of the resemblance th ese beds bear to the Morte Slates (upper part of North Devon Devonian) is some testimony to their correlation with those beds. " Nos. 4 and 5," says Mr. Champernowne, " should probably be classed as one group, but I have separated th em on lithol ogical g rounds, placing 4 lowest, as these masses are at many spots seen to rest directly on Middle Devonian Limestone." No.4. "Diabasic Rocks in great variety.- Diabase tuffs, com­ pact porphyritic and amygdaloidal diabase, highly peroxidated tuffs, iron ores, &c." These beds" might be called the Ashpring­ ton Series." They are " interstratified with slaty shales," and may be correlated with "Diabas gesteine del' mittleren und oberen gruppe " of Sandberger (" Th e Nassau Schalstein "). Tha t th e great development of t uffs should be local is not unlikely, and t hat this series, where th e shales and slates prevailed, should pass into th e underlying limestone in places is so probable that I do not hesitate to classify th em with Bed C. in the Plymouth section, which I take to represent the slaty part of the Ilfracombe Series, near the base of which, in North Devon, the Middle Devonian Limestones occur. Mr. Champernowne says : (, Bands of ferruginous limestone sometimes appear interstratifi ed with th e Schalsteins (4), but th ey may be on or about the horizon of ~ 5) Ramsleigh Limestone." No.3. "Stringocephalu8 L imestone "_I' Great Devon Lime­ stone," Plymouth, Torquay, Dartington, Ogwell, Chudleigh, Ash­ burton, &c."-This bed is, of course, D. in the Plymouth Section. It corresponds to th e Middle Devonian Limestone in North Devon and W est Somerset, but is more extensively developed. The lime­ stones of the same formation in th e Quantocks resemble it in many parti culars. It is correlated by Mr. Champernowne with th e "Eifel Dolomite, Paffrather Kalk, W estphalian Limestone" and the " Calcaire de Givet " of Belgium. No.2. Lower Slates (" I cannot lit present make up my mind on II better name "), " soft, iu the upper part especially," containing 448 w. A. E. USSHER ON THE GEOLOGY OF SOUTU DEVON.

the It zone of Calceola sandalina," and below it the "zone of Cyrtoceras bdellalitee " at Mudstone, near Brixham and Mead­ foot, near Torqnay-bracketed with Middle Devonian. The lower slates contain" many eruptive rocks, especially to­ wards their lower parts j also some contemporaneous volcanic bands (no grits)." Mr. Champernowne is inclined to regard the lower part of this series forming a "considerable belt of country north-west of Dartington and Ogwell and north of Ply­ mouth, &c. (slate quarries worked in purplish and greenish slates)" as Lower Devonian. It is, of course, the same as E. in the Ply­ mouth Section. They are correlated by Mr. Champernowne with H the Lenne Schiefer on the right bank of the Rhine, separated from Lower Devonian by German geologists, and with the su~. r­ incumbent limestone classed as Middle Devonian. This sedes would be homotaxeous with the Hangman Grits of North Devon. No. lA. Lower Devonian.-Red beds of Lincombe and Warberry Hill at Torquay, containing Homalonoti, Lamellibranchs, Pleuro­ dictyum, &c.; tough grits and sandy schistose beds. "These," says Mr. Champernowne, " are possibly equivalents to Hangman Sandstones." (No. 1.) " GI'eyand brownish Grits and Schistose Beds of Mead­ foot "-perhaps equivalent to the Lynton beds," (the Upper Part of the Lower Devonian in North Devon). The foreign equivalent to (Nos. 1 and la) are " Spiriferen Sand­ stein," "Coblentz Schichten," "Aeltere Rheinische Grauwacke and other synonyms." The above, which is Mr. Champernowne's prompt reply to my request, asking for the simplest possible classification of the South Devon rocks for a general and brief description, will show you the enormous difficulties in striving to arrive at any absolute or dog­ matic classification of the Devonian rocks of South Devon. Whereas in North Devon we have fine lithological breaks in each series, in South Devon we are confronted by great groups of slate and shale, which may not only have been accumulating during any periods or period when a marked change in the character and mode of sedimen­ tation in North Devon was taking place, but also, if we divide the Lower Slates (No.2) into Middle and Lower Devonian, may have gone on uninterruptedly whilst a drastic change from one group to another, differing from it both in sedimentation and in life­ forms, was being enacted, Also conversely lithological changes W• .1. E. USSElER ON THE GEOLOGY OF SOUTH DEVON . 449 may be markedin South Devon at horizons where none are apparent in North Devon rocks. The southern ar ea was also the theatre in which, at many re­ current periods, the eruptive forces burst into activity, eating their way through the sediments already thrown down, and showering th eir ashes and cinders and scorias upon those in process of deposi­ ti on j and if for a time coral reefs grew upward in th e tranquil waters, and the subterranean fires smould ered, it was but for a time, after which the Schal steins prove the renewal of their vigour to have been , if anything, greater than before. In addition to this, if we suppose the huge Dartmoor granite mass in after ag es, Pre-Triassic and Post-Carboniferous, to have been upheaved, what wonder is it that strata of such different dura­ bilities as the Great Devon Lim estone and the slates and tuffs above and below should be crinkled and folded, cracked, broken, and displaced. Devonian Notes. Near Fishcombe Point on the south side of Brixham Headland, rein s of hard bed sandstone occur in the Devonian Limestone. Are th ese produced by chemical agencies? On the west side of Silver Oove the limestone passes downward by intercalations of flaggy beds into reddish-brown slates. Two small block s of T riassic breccia-conglomerate cling to th e limestones on the west side of Galmpton Point. Paignton District. Old Gmvels.-Old riv er gravels are noticeable capping the low cliffs between Liv ermead and Preston Sands. A patch isolated from the main mass rests on a pinnacle of Triassic rock of light red sand , separat ed in one place on the beach from the dark red sand with brecciated bands by an uneven black line (?fault). Trace of Submerged F orest.-Peat, with traces of submerge d forest, associated with lead en-coloured clay, is exposed on Preston Sands. It slopes seaward from under the alluvium of Paignton Marsh. This will be pointed out by Mr. Pengelly. TI·iassic.-The Paignton Trias is joined to the main mass, ex­ tending to the north of Oockington and Tor Abbey, by a fringe of breccia and sand rock, forming th e promontory of Livermead and Oorbons Rock, where it is intersected by several faults. Oorbons Rock is composed of grey and yellowish-banded sands, ill part overlain by and faulted against breccio-conglomerate. 450 w. A. E. USSRER ON THE GEOLOGY OF SOUTH DEVON.

Livermead promontory is composed of beds of breecio-con­ glomerate, saud-rock and brecciated sandstones. The cliffs bordering Preston Sands consist of rock sand on brecciated rock sand, and further south of red rock sand, sometimes jointed in the upper beds. Roundham Head consists of breccio-conglomerate, with large grit pebbles, and a thick bed of sand, which is exposed on the cliff bordering Goodrington Sands, and thins seaward. The Paignton Trias consists of breccio-conglomerates, apparently dovetailing into sand in the manner of beach; and of breccia, which prevails locally inland. Outliers.-Breccio-conglomerate rests on Devonian slates in the middle of Goodrington Sands. South of Goodrington Sands a small outlier is shown, resting unconformably on a slate reef. Breccio­ conglomerate forms the cliff face for 10 chains on north of Saltern Cove, and small outlying patches are visible at the base of the cliffs in Saltern Cove. On north of Broad Sands there are two outliers probably faulted against the Devonian.

The Ooast from Babbacombe to Watcombe. Should you be so fortunate as to reach Petitor and Watcombe by way of Babbacombe on the day of your excursion to Torquay, you will be amply repaid. Middle Devonian.-The Middle Devonian Limestones of the Torquay promontory rest on, or are interbedded with, a thick mass of igneous rock in the cliff at Babbacombe, which seems to run along the strike. As you descend the cliff to the Carey Arms, or by the path to Oddicombe, you cannot fail to notice the broken character of its projecting lower portion, and in walking along the beach toward Oddicombe Sands, from the Carey Arms, you will perceive that the lower part of the cliff by the beach is principally composed of Devonian shales, in which a patch of limestone, pro­ bably faulted on both sides, occurs. The undercliff and the con­ tortion of the shales are accounted for by a fault not shown in sec­ tion, which throws the beds of the main cliff against the shales below, the latter having been weathered back so as to expose the harder limestoues upon which Babbacombe is situated. Lower Trias.-Going onward in the direction of Watcombe, at Oddicombe Sands, we find the Lower Trias conglomerates faulted against the Devonian slates, from which they dip at an angle of 20°. W. A. E, USSUER ON THE GEOLOGY OF SOUTH DEVON, 451

Further on, thick beds of sandstone are interbedded with the con­ glomerate, being cut off from the pure conglomerates by faults. The conglomerates are either faulted against Devonian (Middle) Limestone, or abut against it. Passing over the limestone to the Petitor Valley, we encounter chocolate-coloured shales, with a. nonpersistent mass of limestone, apparently faulted against lime­ stone on both sides. The P etitor limestone, which separates the shales from the Trias, is represented on the beach by a mass which lookslike Limestone Agglomerate, and from it the lowest beds of the Trias dip at a very high angle, from 40° to 50°. They consist of red shaly micaceous clays, intercalated with thin even beds of sand­ stone, and are cut off by fault against the Conglomerate, which forms the fine mural cliff of Petitor, and dips at 15°, The cliff from Petitor to Watc ombe is formed of the same conglomerate, with its large worn limestone fragments. At Watcombe the Conglo­ merate forms the cliffbounding the Cove on the south, it being a fault face, along which, when traced inland, you will find that th e lami, na.ted red Terra-cotta Clays are cut off. These clays may be seen at low-water under the boulders, tumbled from the breccio-con­ glomerate cliff. They are exposed in a pit at the head of th e combe. On the beach the clay assumes a marly structure in places ; it is red, with small green spots, and is slightly micaceous. The clay is overlain by about 50 feet of sandst one, some of th e beds being made up of grains of shale. The Sandstones exhibit annelid tracks on th eir surfaces, and they dip under Conglomerat e, beneath which they reappear, being brought up by fault just by their outcrop, and again under Watcombe Crags. The Conglomerate is intersected by seven faults, th e most northerly being the line which determined th e noble mural cliff called Watcombe Crags. Should you be able to go still farth er north to l\1incombe (M aidencombe) you would find th at the Conglomerates are over­ lain by th e great mass of rubbly breccia with large igneous boul­ ders, which forms the fiue cliffs at Labrador Inn, and between Teignmouth and the Clerk Rock, Succession of Watcombe and Petitor Lower T,.ias.-We have thus in a short distance got a distinct succession, for although th e whole of the Watcombe Clay series may not be visible through eliminating faults, th ere can be little doubt that th e clays with interbedded sandstones of Petitor are th e base of the clays of Watcombe, which, with their overlying sandstones, pass under the 34 452 w, A. E . USSHE R ON T HE GEO LOGY OF SOUT H DEVON.

Conglomerates, and those at Mincombe are succeeded by the rubbly breccias of th e Teignmouth type. There is no reason for thinking that the Lower Trias beds of the P aignton and Torquay district are as old as the W atcombe Clays; they are very probably locally modified representatives of part of the Conglomerat es. Scenery.-For scenery alone Babbacombe Bay, P etitor, and Watcombe, may compare with and outvie any other part of the South Devon coast, and I know of no place where the influence of geology upon scenery can be more advantageously studied. Pleistocene.-There is no necessity to allude to the Raised Beach of Hopes Nose, which will be pointe d out to yon by Mr. P engelly. It indicates a subsidence of 50 or 60 feet, and its elevation, coupled with the P aignton forest bed, prove that the land was subsequently lifted much above its present level.

EXCURSION TO RADLETT.

SATURD AY AFTERNOON, 1 2 TH J UL Y, 1884.

Director: JOHN HOPKI NSON, F.L .S., F.G.S., &c. (Report 011 the Direoior.) Rain had been falling the greater part of the day, and was still falling somewhat heavily when a very small contingent of the Association arrived at Radlett Station, meeting there the Director and a considerable number of members of the Hertfordshire Nat ural History Society, most of whom (including several ladies) had driven from W atford , while others had come by train from 8t. Albans. The road leading to Shenley was taken for a short distance, when, by permission of Mr. Thomas Bagnall, Newberries P ark was entered. After walkin g through the grounds adjoining the house, a meadow near th e park was crossed, and an opening in it, not easily found, revealed the only existing exposure of the Hertford­ shire conglomerate. This spot has not before been visited by the Association, and on this occasion th e conglomerate was examined under by no means favourable auspices. It was necessary to walk for a sufficient distance through wet grass to add materially to the discomfort of a walk in the rain, and moreover there was no one amongst the party well acquainted with the geology of th e neigh­ bourhood or with the strata of which th e conglomerate forms a part -the Woolwich and Reading Series. The rain, however, now