Aug. 26, 1875J 



NA TURE 



355 



long well known to geologists, and was in former days described 

 by Bright, Gilby, Buckland, and others. 



Rhivtic. — Between the uppermost beds of the grey marls of the 

 Keuper and the lowest beds of the Lias there lies a remarkable 

 assemblage of strata, which I formerly described,^ as the 

 ^^ Azicula contorta beds," from that shell forming the leading 

 fossil therein. The name Rhoetic has since been given to the series, 

 from a supposition that the beds are identical with some that 

 occur in the Rha'tian Alps, which is, however, more than doubt- 

 ful. Typical sections of the Avicula contorta series are exposed 

 at Garden Cliff, Aust Cliff, Penarth, and Watchet on the Severn, 

 and at Weston, Keynsham, Willsbridge, and Saltford near Bath, 

 and Puriton, Uphill, and Wells in Somersetshire, as well as 

 at many other localities. Two of the most classical of the 

 series are Garden Cliff and Aust Cliff ; the latter has been long 

 known to continental geologists as the Bristol Bone-bed. In the 

 upper part of the section are dark grey shales, intersected by 

 hands of limestone ; Avicula contorta, Card'mm, RJuttictim, 

 Pecten Valottiensis, Axirius, &c. are found in these. The Bone- 

 bed consists of a hard dark-grey siliceous grit full of the bones, 

 spines, scales, and teeth of fishes belonging to the genera Nema- 

 canthus, Acrodus, Sargodon, Hybodus, Ceratodus, &c. Beneath 

 this thin Bone-bed, with its ichthyic debris is a bed of shale 

 which rests upon the grey marls of the Keuper. A similar suc- 

 cession of strata is repeated in most of the other typical sec- 

 tions. I have named especially those of Garden Cliff, Penarth, 

 Uphill, and Watchet. 



Aust has been long famous for its Ceratodus teeth, and is, I 

 believe, the only locality where they are collected. You will 

 find a fine series of them in the Bristol Museum. This wonder- 

 ful collection is quite unique and will well repay an attentive 

 examination. 



The only living representative of the genus Ceratodus now 

 lives in the rivers of Queensland ; and a fine specimen was lately 

 ])urchased for and presented to the Museum by W. W. Stoddart, 

 Esq., F.G.S., for the purpose of showing the comparative size 

 of the recent and fossil teeth. 



5. UuNDRY District. 



The Oolitic Fonitations. — The Oolitic formations will long 

 remain classical ground to English geologists, as it was whilst 

 studying these rocks in Wilts and Somerset that Dr. William 

 Smith first acquired that knowledge which enabled him to 

 "identify strata by organic remains," and establish a true 

 natural system of stratigraphical geology. 



The Oolitic period admits of a subdivision into three groups 

 — the Lower, Middle, and Upper ; each group is based on a 

 great argillaceous formation, on which rest minor beds of sands 

 and cream-coloured Oolitic and Pisolitic limestones. The 

 argillaceous formations form broad valleys, extending diago- 

 nally across England in a direction north-east by south-west. 

 The limestones constitute low ranges of hills, with escarpments 

 facing the south-west, and overlooking the valleys. The Lower 

 Oolites rest on tlie Lias, the Middle Oolites on the Oxford 

 Clay, and the Portland and Upper Oolites on the Kimmeridg 

 Clays. 



The Lias Formation is well developed around Bristol ; and 

 many interesting and instructive sections of the Lower beds may 

 be studied at Horfield, Keynsham, Saltford, and Weston, 

 whilst the Middle and Upper divisions are exposed in other 

 localities. It has been often repeated of late years that the 

 geological record is imperfect, and that many of the leaves, and 

 even whole chapters of the Rock-book on which the hieroglyphics 

 of its history were written, are wanting ; yet "Time, which an- 

 tiquates antiquities, and hath an art to make dust of all things, 

 hath yet spared these minor monuments ; " for it is certainly 

 true that the Jurassic formations contain a marvellously complete 

 record of the succession of life in time during their deposition 

 from the dawn of the Lias until the close of the Coral Sea, 

 amid whose islands fossil Cycadea luxuriantly flourished, and 

 whose remains are buried in their native Dirt-beds in the Port- 

 land Oolites. 



I have shown elsewhere that the three divisions of the Great 

 Lias formations admit of several subdivisions or zones of life, 

 each characterised by a group of species which individualise it. 

 A careful examination of these subdivisions has further proved 

 that there is no confusion in the rocks when carefully examined 

 — that Nature is always true to herself, although all geologists 

 are not true to Nature. The fossils of the Lower Lias are quite 

 ' Quart Joum. Ceol. Soc. vol. xvi, p. 374. 



distinct from those of the Middle Lias, and both specifically 

 different from those of the Upper. 



The Ammonites are important leading Liassic shells, that 

 appear to have had a limited life in time, but a wide extension 

 in space ; and they have greatly aided us in determining periods 

 and making out the history of the Liassic sea. The great 

 Sauroptkrygia, represented by the Plesiosaurus, and the 

 ICHTHYOI'TERYGIA by the Ichthyosaurus, are remarkable forms 

 of Reptilia, adapted to the waters of that epoch, whilst the 

 DiNOSAURiA, represented by Scelidosaurus, the Pterosauria 

 by the Ptcrodactyltts, lived in this area during the Lias age ; 

 magnificent specimens of these different forms of reptiles adorn 

 the walls of the Bristol Museum. 



The Jurassic Age. — Dundry Hill, 700 feet in altitude, is the 

 most westerly outlier of the Oolitic range, from which it is nine 

 miles distant. It is a locality of great interest to the local 

 naturalist, as it affords capital lessons of stratigraphical geology, 

 admirable examples of surface-rock sculpture by denudation, 

 and a commanding point of view for surveying the same, and 

 showing the grand panorama in the midst of which it stands. 

 The greater portion of the hill is composed of Lower Lias 

 strata, which are well exposed at Bedminster Down, Whitchurch, 

 Keynsham, Queen Charlton, Norton, Malreward, Winford, and 

 Barrow. The beds consist of alternations of limestones and 

 shales, having a total thickness of 550 feet. The Middle Lias 

 and Marlstone are feebly developed, and the Upper Lias repre- 

 sented by some thin clays, with dwarfed specimens of ^/;/wc7«//« 

 bifrons and A.communis ; and the Upper Lias sands, from one to 

 two feet thick, are not fossiliferous. On these rest beds of Inferior 

 Oolite rock which have long yielded a very fine series of organic 

 remains, some of the best of which are now preserved in the 

 Museum collection. The Inferior Oolite of the south of Eng- 

 land admits of a subdivision into three zones of life : the Lower 

 resting upon the Lias sands has the Ammonites Murchisotta: as 

 its leading fossil ; the Middle contains a large assemblage of 

 Mollusca, and especially of ^w;«<?«?to, among which Ammonites 

 Ilumphriesiamis, Sowerbyi, concavus, and Blagdeni are con- 

 spicuously characteristic ; the Upper contains Ammonites Par- 

 kiiisoni, Martinsii, and subradiatus, with many Echinoderms 

 and a large series of reef-building chorals. These three sub- 

 divisions are rarely all developed in the same section ; but the 

 order of their sequence in nature is as stated in Dundry. The 

 lower beds are feebly represented ; and there is an immense 

 development of the middle and upper divisions. 



In the iron shot shelly beds there is a fine assemblage of 

 Lamellibranchs ; and the stratum which covers them is very rich 

 in Ammonites, many with their shells preserved, and having 

 their oral lobes and other appendages in situ. 



These are succeeded by other conchiferous strata ; and the 

 whole is covered by Ragstone and Building-stone, forming the 

 upper zone, with Ammonites Parkinsoni, Echinidie, and Corals. 

 The stratigraphical, lithological, and palseontological conditions 

 seen in the Oolitic capping of Dundry Hill, are repeated in 

 other localities in Gloucestershire, Somersetshire, and Dorset- 

 shire ; and a full development of all the zones in actual super- 

 position may be examined in certain sections in the Cotteswold 

 Hills, as at Leckhampton and Cleeve. 



The Fuller's earth must be studied at North Stoke and 

 Lansdown, and the Great Oolite at Coombedown, Lansdown, 

 and other localities around Bath ; the typical Bradford Clay, 

 with Apiocrinital heads and stems, and beautiful Brachiopoda 

 near Bradford ; the Forest Marble and Combrash at Faulkland, 

 Chickwell, Marston Bagot, and Cloford. The Middle Jurassic 

 rocks are admirably exposed near Calne, and the Upper Jurassic 

 near Swindon, Wilts. 



The great importance of the Bristol district as a source of 

 mineral wealth, added to the complicated structure of this region, 

 led my old friend Mr. William Sanders, F.R.S., to construct 

 an elaborate geological map of the Gloucestershire and Somer- 

 setshire Coal-fields and adjacent country, on the scale of four 

 inches to a mile. The topographical portion of this undertaking 

 was reduced to one scale from the Tithe-Commission Maps ; 

 and Mr. Sanders traced out all the geological boundary lines in, 

 the field, and laid them down in MS. copies of the Tithe Maps, 

 making copious notes of the strata as he proceeded with his 

 work. The whole was finally reduced to one scale four times 

 the size of the Ordnance-Survey Maps, and reproduced with the 

 most scrupulous care by Mr. Stratton, who for many years 

 assisted Mr. Sanders with the work which he had made the 

 chief object and occupation of hii> later life ; and it is but simple 



