190 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. l~Iaidstone .function of the South-Eastern Railway), seem to be identical with the marine clays found at Hythe and at Atherfield in the . He adds, " There is also a bed of stone, not a continuous bed, but in concretionary masses, just above the junction, from which I obtained fossils, and which, I consider, re- presents the Atherfield rocks. This bed is also similar to the blocks taken from the cutting in the vicinity of Red Hill, near Reigate." He adds, that the same junction can be traced from the Teston Cutting in the direction of Maidstone, to near the Farley Cutting through the Kentish Rag. The junction of the Wealden and greensand clays is at the bottom of the valley, near the banks of the river Medway.

4. On the Section between BLACK-GANG- and ArHER- FIELD POINT. By CAPT. L. L. B. IBBETSON, and PROF. EDW. FORBES, F.R.S. THE accompanying Table exhibits the succession of strata pre- sented in ascending order from the Wealden to the top of the Upper Green Sand in the Isle of Wight between Atherfield Point and St. Catherine's Down. The measurements of the upper portion were ascertained by trigonometrical survey, by Capt. Ibbetson, during the years 1833---38, those of the lower portion during the winter of 1842-3. The following observations refer to that portion of the section which includes the Lower Green Sand strata, visited by Capt. Ibbetson and Prof. Forbes in March~ 1844. Between the Gault, as seen near Black-Gang-Chine, and the Wealden at Atherfield Point, there are sixty-three distinct strata, the total thickness of which is 843 feet. § 1. Description of the Strata. The lowest of these is a brown clay 3 feet thick, the base of which, at the junction with the Wealden, abounds in remains of fish. Through this clay are scattered many fossils, none of which are peculiar to this lowest bed, but mostly such as run on through the fossiliferous clays of the Lower Green Sand. This is suc- ceeded by a harder bed or rock of a sandy texture, 2 feet thick, characterised by the presence of numerous fossils, among which the most remarkable is the Perna Mulleti, peculiar to this bed. The clays which succeed are fossiliferous at the lower part, but very slightly so in the middle, where they contain numerous crys- tals of sulphate of lime. The uppermost of these clay strata, called the Lower Lobster-bed, is an impure fullers' earth, abounding with fossils, the most characteristic of which are numerous remains of .4stacus scattered here and there, and found in so perfect a state that no time could have elapsed between the death of the animal and its entombment in the strata, sufficient to permit decomposi- tion to take place. These clays present a thickness of 99 feet. The hard noduliferous bed which succeeds, termed the Lower IBBETSON AND FORBES ON THE LOWER GREEN SAND. 191 Craehers, is full of Gervillia avieuloides and other fossils, and a similar stratum immediately above (the Upper Craehers) abounds in fossils peculiar to itself; indeed it is in this bed that most of such of the species as are limited in their distribution, occur. The Crackers occupy a thickness of 18 feet. A clay bed, 20 feet thick, having the properties of fullers' earth, and similar in appearance to that preceding the Crackers, succeeds : it is very fossiliferous, and, like the other, abounds in Crustacea, mostly of species identical with those in the Lower Lobster Bed. This is termed in the section the Upper Lobster Bed. Am- monites and several bivalves accompany these crustacea. A dark sandy clay succeeds, and is very fossiliferous ; the cha- racters of the fossils do not for the most part differ from those in the lowest clays. It is 20 feet thick. This is capped by a band of Terebratulze (mostly T. Gibbsii) imbedded in the stratum of dark sand, 22 feet thick. The Tere- bratulte are in immense abundance and accompanied by Serpul~e. A series of beds containing zones of Gryph~ea sinuata imbedded in dark sand succeed. The Gryph~ea zones mostly alternate with rows of large nodules containing Crioeeras and Seaphites. This assemblage of Gryph~ea zones is interrupted in the centre by a bed of sandy clay, 34 feet thick, very fossiliferous, and in which a great many of the fossils of the lower clays reappear. These Grypheea and Crioceras beds, with the included clays, have a thickness of 155 feet. Thirty feet of dark sand, containing prolific zones of Terebratula 4 chiefly T. biplicata, succeed, and form the base of a newsuccession of Gryph~ea bands imbedded in dark sand; but the Crioceras nodules are absent. Twenty-four feet is the extent of this upper- most series of Grypheea zones. Above this the beds become ferruginous, and are occasionally, though rarely, mixed with dark blue clay. Fossils in some parts are abundant, but mostly in the state of casts, and no new forms appear. A lignite bed occurs in the lower part of these ferrugi- nous beds, the lignites being arranged in zones. There are also here and there rows of calcareous concretions, usually of an oblong shape, and mostly having a direction towards the S.E., like the lines of oblique bedding occasionally presented in this part of the series. At the top of Black-Gang-Chine waterfall, a series of indurated ferruginous sand rocks alternating with dark sandy clays appear. The sand rocks are composed of quartz grains, and exhibit lines of oblique bedding. They contain no fossils. At the uppermost part of the Lower Green Sand is a series of thin beds, alternately ferruginous and sand, lying immediately below the gault. Casts of a Solarium (species unknown), and of an Ammonite, were found in these bands. § 2. Grouping of the Strata. The 63 strata enumerated may be grouped under three divisions, from their general mineral character. ][92 PROCEEDINGS OF TtIE GEOLOGICAL SOCIETY.

A. The lower asscmblage of clays, mostly fullers' earth, abound- ing in fossils, and in which the Perna sand-rock and the Cracker nodules are exceptional strata indicating temporary conditions. B. The region of Gryphcea sinuata sands in which the Tere- l~ratula bands and upper clays are exceptional strata. This region may be subdivided into three portions, the two lower containing Crioceras nodules separated by the clay, and the upper containing no nodules. The noduliferous part of the series, and that which is free from the nodules, have each a zone of Terebratulee for a base. C. The region of ferruginous sands, which may itself be divided into two or three sections, the lowest of which is fossiliferous. § 3. Chemical Peculiarities of the Beds. A chemical analysis of the composition of thc several strata was next given ; the principal results of which, affecting the distri- bution of the organic remains, are the following : The beds which are most fossiliferous are those containing most carbonate of lime. In the ferruginous beds, whether upper or lower, there are no traces of lime ; but large quantities of peroxide of iron. This is true as well of the fossiliferous as the non-fos- siliferous parts. The gault which caps the iron bands at Black- Gang-Chine contains but few fossils, and those occur rarely. On analysis it was found to exhibit no trace of carbonate of lime, but a little gypsum ; whereas the fossiliferous gault of Folkstone and other places abounds in carbonate of lime.

§ 4. IndicationsofConditions underwhich these Beds were deposited. At the close of the deposition of the Wealden, there appears to have been a sudden depression of the bed of the great freshwater estuary, and an influx of the sea. The first effect of such an influx would be the destruction of the animals in the estuary not adapted for living in salt water; hence we find a total destruction of the Wealden animals, the remains of which accumulate towards the point of the junction of that formation with the Lower Green Sand ; a fact which indicates the nature of the change. Even the Cerithium, although belonging to a genus many species of which are capable of living in the depths of the sea, was destroyed- not- withstanding that its appearance, only in the uppermost beds of the Wealden, indicates that its presence there was due to the com- mencement of the very state of things which eventually destroyed it. That the depression was of some extent, though not, perhaps, of very many fathoms, is indicated by the nature of the animals which lived in the first-formed sea-bed, and which, when they died, were often imbedded in the fine and, probably, fast depositing mud, in the vertical position which it is the habit of the animals of such genera as Pinna and Panop~ea to assume when alive. After this, a tem- porary change followed, when an influx of sand, mingling with the calcareous mud, caused a state of sea-bottom peculiarly fa- vourable to the presence of animal life. In this way were called IBBETSON AND FORBES ON THE LOWER GRV-EN SA~D. 193 into existence a multitude of species which were added to those which had appeared before them. This was, in fact, such a state of sea-bottom as is now presented by great shell banks ; but it does not seem to have lasted long, and new depositions of mud appear to have extinguished some forms, whilst others suffered by the change only in the diminution of their numbers. In the midst of this muddy epoch, a temporary and peculiar condition of sea- bottom, forming what are now called the Crackers, called forth the presence of numerous mollusca, at first of various species of the genus Gervillia, and afterwards of Auricula, Cerithium, Dentalium, and other univalves, which appear to have enjoyed but a brief existence (as species) in this locality, since similar conditions were never afterwards repeated. The greater number of the Gastero- podous mollusca of the English Lower Green Sand are found within this very limited range. At the close of the deposition of this great mass of clay there was for a time a great multiplication of the individuals of certain Brachiopoda which had commenced their existence in the lowest beds. Thus Terebratula Gibsi suddenly appears in immense abundance, covering the bottom of the sea, and predominating over the animals among which it had previously been but thinly scattered. This lowest zone of Terebratul~e marks the commencement of a new state of sea-bottom where sands predominated over the clays, each interval of deposition being usually marked by the presence of a layer of Gryphwa sinuata, the period of rest being almost always sufficient to enable the Gryphwa to attain its full growth. Other bivalves are found with it, but in comparatively small num- bers, and not such as are of gregarious habits. During the whole of this period enormous Cephalopoda including species of Crioceras and Scaphites frequented these seas, and when dead formed the nuclei round which calcareous and sandy matter collected and formed nodules. The death of these animals seems to have been con- nected with the periodical charging of the sea with sediment; hence we find them usually alternating with the zones of Grypheea, and forming irregular bands in the intervening sedimentary deposits. In the midst of this epoch of Gryphcza, there is a sudden re- appearance of the muddy deposits, during the predominance of which those animals adapted for such a sea-bottom, and which had survived the cessation of the deposition of the fullers' earth, again multiplied, but the species which had become extinguished were not replaced by representative forms. This, however, did not last long, the sand again predominating with its zones of Gryphwa and lines of Crioceras nodules. .k temporary multiplication of Terebratula seUa suddenly marks a change in the zoological conditions- for the Cephalopoda dis- appear, although the zones of Gryphwa, which animal does not appear to have been affected by the change, (probably a change in the depth of the sea.,) go on as before, there being, however, no alternating lines of nodules. It would seem that the sea began to VOL, I. 0 194 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. shallow, probably from elevation of the sea-bottom, until at last the Gryphaea itself disappears, the bands exhibit traces of the in- fluence of currents, and become more gravelly ; lignites, indicating a shallow sea, become common, form belts in the ferruginous sand, and in one place a bed in the wavy blue sand, at a time when much iron was deposited. The deposition of the peroxide of iron appears to have been connected with the disappearance of the majority of mollusca, though Trigonia, Thetis, and Venus occasionally occur in considerable numbers. In the uppermost strata scarcely any animal remains are found, and every thing appears to indicate a shallow and barren sea, previous to a new state of things, when a fresh series of clays (forming the Gault) being deposited, the majority of the animal forms which characterise the clays of the Lower Green Sand disappear, and are replaced by distinct species, representative in time.

§ Bearing of these Observations on the Jgeoeomian Question. These statements regarding the distribution of organic remains and indications of mineral conditions, presented by the Atherfield section, lead to a few considerations which bear importantly on the question which has been agitated respecting the separation of the lower part of the Lower Green Sand as a separate bed under the name of "2~Teocomien.'' 1st. It would appear that there is but one system of organic re- mains throughout the series of beds, entitled Lower Green Sand, in this locality, and that whenever similar conditions are repeated, the same species reappear. 2d. Throughout the series of beds examined, we find that when a species is extinguished by a change of mineral conditions, it is not replaced by a representative species. 3d. That the influences which determine the distribution of species throughout are mineral and local, and that these mineral in a great measure, chemical- conditions enable us to divide the strata into groups, which groups, being from their very nature local, cannot be regarded as other than artificial, and have no claim to be numbered as subdivisions in time of the great series of cretaceous deposits. A change of mineral conditions may determine the absence of certain species; but, unless when, under a repetition of similar mineral conditions, such species are replaced by representative species, or the general assemblage of species is replaced by repre- sentative and distinct forms, the change cannot be considered as indicating a great sectional division. It appears to us, therefore, that the evidence of the Atherfield Section maintains the unity of the Lower Green Sand;and that the accumulation of clays at its base can be regarded only as a local phenomenon. IBBETSON AND FORBES ON THE LOWER GREEN SAND. 195

Thichness and Description of Strata. [GAuLT, WITH FOSSILS.]

Thickness No. in feet. 64. Iron band, fragments of fossils - I 63. Dark sand .... 2 62. Iron band - 1 61. Dark sand - - - 2 60. Iron band .... 1 59. Dark sand ..... 2 58. Iron band ...... 1 57. Iron clay and sand ..... 12 56. At the top, white sand ; at the bottom, black sand and clay 11 55. Iron at the top, and sand ..... 3 54. Iron at the top, and dark yellow sand - 4 53. Yellow sand and clay - - - 6 52. Blue clay - - - 2 51. Yellow and white sand, very quartzose ..... 15 50. Above, white sand, tolerably solid at the top, clay and sand in the middle, and white sand at the bottom - - - 19 49. Black clay (perhaps lignite) with brown sand in thin laminae, tolera- bly even, but in some parts wavv .... 17 48. Yellow sand and blue clay, thinly laminated in some parts, wavy at the bottom, the sand white - - - 31 47. A second white sand, tolerably solid - - - 13 (No. 31. crops out on the shore, a little to the west of Chine. ) 46. Blue sand and some clay ..... 32 45. A line of nodules at the top, and blue sand and some clay below - 33 44. Third white sand, with tolerably solid yellow at the bottom. This stratum runs up from Rocken End - - - 22 43. Three sorts of black clay and sand - - - 40 42. Iron, fossiliferous, top of Blackgang-Chine Waterfall 1 (No. 24, (the Terebratula zone) crops out on the shore.) 41. Sand and clay varying from brown to black - 4 40. Iron, fossiliferous .... 1 39. White sand, tolerably solid, yellow on the surface ; near the top there are laminae of pebbles ; the bottom of it is in thin laminae, divided by blue sand and clay .... l 1 :38. Iron, fossiliferous - - 1 37. White sand ..... 10 36. Blue clay and sand, the blue very conspicuous 1 35. Iron at the top, with fossils ; dark sand below - - - 26 (Nos. 22. and 23. nodules crop out on the shore.) 34. Iron at the top, fossillferous, and dark sand below - - - 18 33. Iron, fossiliferous, and grey sand below, much used for mhking mor- tar. Bottom of Blackgang .... 28 (No. 21. nodules crop out on the shore.) 32. Iron, fossiliferous, and white sand below .... 9 S l. Thin very wavy laminae of black clay (or lignite) full of pyrites, with a layer of spongiform nodules near the bottom - 25 (No. 20. nodules crop out on the shore.) .q0. Iron at the top, fossiliferous, with dark sand - 2 02 196 PROCEEDINGS OF THE GEOLOGICAL SOCIETY.

Thichness and Description of Strata. Thickness NO. in feet. 29. Iron, fossiliferous, with dark sand. Above the boat-houses, Ladder Chine - ~ - .~ (No. 19a crops out on the shore.) 28. Gryphaece at the top, with dark sand - - 8 2'7. Gr!lphcece at the top, with dark sand .... 3 .'26. Grb,ph~ee at the top, with clark sand containing Terebratul~e, Echini, &c. &c. &e. - .... 4 25. Gryph~e~e at the top, with dark sand - - 9 (Nos. 15, 16, 17, 18, 19. Grypho~a and Crloeeras nodules crop out on the shore. ) 24. Terebratul~e at the top, with dark sand - - - 30 25. Nodules containing Crioceratites, a layer of Gryphcea under them, with dark sand .... 7 (No. 14. or Scaphite nodules croF out on the shore.) 22. Crioceras nodules ; a zone of Gr.~lph~ea, with dark sand - - 1.~ 21. Crioceras nodules, a zone of Gryph~a, with dark sand containing Gryph~a irregularly placed - - 3 20. Crioceras nodules with Ammonites - - - 26 19 a At the top black sand and clay, a zone of Gryph~a in the centre, with clay under, very fossiliferous - - 34

19"18. t 17. Crioceras nodules with zones of Gryph~v, dark sand between them $8 16. 15. (Nos. 13. 12. 1 l. 10. crop out on the shore below these zones.) 14. Nodules containing Scaphites; Grypkcea zone under ; Oslrea cari- nata, &c. at tbe top of dark sand ; at the bottom layers of Serpuke, ferebratukv, &c. &c ..... 16 (No. 8 crops out on the shore below. ) 13. Zone of Gryph~ea ; below red sand and clay, full of Gryph~e~e, Ostre~, Terebratul~, Peetens, Serpul¢, &c. &c. &c. very fossiliferous, and in some places divided into four zones of Gryphcece 22 (No. 7. crops out on the shore.) 12. Layer of Terebratul~e, dark sand at the top, and a layer of small no- dules and yellow sand at the bottom - - - 22 1 i. Dark clay, red at the top, and very fossiliferous - 20 (No. 6. crops out on the shore.) 10. Upper lobster bed, dark sand at the top, fullers' earth in the middle, and sand at the bottom, very fossiliferous - - 45 9. Upper Crackers ; nodules at the top, clay and sand, very fossiliferous 6 8. Lower Crackers ; nodules at the top, full of Gervilli~e, &e. &c., with brown sand and clay, fossiliferous - - - 12 (No. 4., or Perna MuUeti bed, crops out on the shore.) 7. Lower lobster bed, fullers' earth, very fossiliferous - - - 29 6. The best fullers' earth with clay at the bottom, some fossils, but not very plentiful, and in some parts full of large crystals of sulphate of lime ...... 64 5. Layer of small nodules, clay at the bottom containing fossils - 6 EGERTON ON THE MOUTH OF HYBODU$. 197

Thichness and Description of Strata. Thickness No. in feet. 4. Perna Malleti bed, with numerous Gryphon, Ostre~, &c. &c. very fossiliferous ..... 3 3. Clay, very fossiliferous, containing layers of fish-bones, teeth~ &c. but regular ..... 3 (WE~LD~S.)

In the accompanying Table are given the ranges of such of the fossils of the above strata¢ as were collected and noted by the au- thors on the spot.

5. Description of the Mouth of a HYBODUS found by Mr. BOS- CAWEN IBBETSO51" in the ISLE OF WIGHT. By Sir PHILIP MALl)AS DE GREY EGERTON, Bart. M.P.F.R.S.F.G.S. THE present memoir is the result of the examination of an Ich- thyolite discovered by Mr. Boscawen Ibbetson in the Isle of Wight, near the junction of the Lower Green Sand with the Wealden, and sent to me in the hopes that it might tend to show to which of the two formations this bed should be assigned. The evidence it affords on this question is neither direct nor conclusive, inasmuch as it is an undescribed species, and consequently any deductions beyond those based upon general affinities would be unwarrantable. In another point of view, however, this specimen is of high scientific value, as it sets at rest the long-mooted ques- tions of the relative characters of the upper and lower teeth, and their general contour in the individuals composing the genus Hy- bodus so extensively occurring in the secondary strata. Mr. Ibbet- son has had the rare fortune to bring to light the entire mouth of a fish of this genus. The left side is slightly crushed, but the other retains its natural form, and the greater portion of the teeth in both the upper and thelowerjaw. The former measures 10inches, and appears to have carried twenty-four teeth in the front series; the latter measures 7~ inches, and has nineteen teeth in series, one on the symphysis and nine on either side. Two rows of succession teeth are traceable behind the front series. The mouth is slightly open, and when seen in profile is more arcuate than in the recent sharks. The upper jaw has a broad notch for the reception of the thickened symphysis of the lower mandible. The teeth have a central cusp, rather hooked, and two secondary cusps on either side; the enamel is strongly plicated; the teeth only recently brought into use have the plica~ extending to the apex. The bases are wide, and have the rugose character so generally found in this genus. The lateral teeth present the same characters as the more central ones, but are rather smaller near the angle of the jaw.. 03 To face page 157. TABLE

SHOWING THE DISTRIBUTION OF LOWER GREEN SAND FOSSILS (AS NOTED ON THE SPOT) IN THE ISLE OF WIGHT.

BY CAPTAIN BOSCAWEN IBBETSON AIWD PROFESSOR E. FORBES.

The object of this table is to show that the majority of species composing the Lower Green Sand Fauna, as observed in the Isle of Wight, commence their range in the lower beds of that formation~ and that the species assembled in the lowest beds include many common to the Lower Green Sand and other divisions of the Cretaceous Series.

NOTE. -- The Figures refer to the Beds as numbered in the Table of Strata ; the Roman Letters in the second columns to Formations above or below the Lower Green Sand. Names of Species within brackets have been applied since the Paper was read.

In the beds above 19a no species were observed to commence their range.

3. lO--ll. 12--13. 14. 15--16. 19a. 6 --7. Range. 8--9. Lowest Clay. Band. Range. Lower Lobster Clay. Crackers. Range. Upper Lobster Clay. Range. Lower Gryphma Range, Middle Clay. Range. Middle Gryphma Range Upper Clay. Range, Sands. Sands, J Panop~ea mandibula - artoni 4--9 Corbula st ,6--10 Cardium Ibbetsoni - 8--9 Astacus. No. 2. - 10--11 Modiola eequalis 12 Cypricardia un- I 14 Crioceras Bower- 15--29 Cardium ? 19a dulata. J bankii. imbricato- Panop~ea plicata oeomiensis) 4--14. Gervillia lingu- 6--10 Venus Orbignyana - 8--9 Pholadomya 10--20 Gryph~ea conica 12 rium. loides. Martini. Nucula spatulata 14 Scaphites gigan- 15--2[ Hemicardium Austeni- ,ata - 4 Nucula obtusa - 8--U.G.S Terebratula ob- 12 teus. Anomia ra- 19a Ammonites Des- 6--10 Cardium pere- 10--11 longa. Gervillia solen- 14--56 diata. Venus? parva - o-costata - 4--19a hayesii. Tellina vectiana 8--9 grinosum. oides. l Nautilus radiatus 15--1f Ammonites Mar- 12--29 Area seeuris 19a Venus ? fenestrata tgata 4 Astacus. ,~o. 1. - 16--10 Gryphma harpa - 8--14 Serpula Sp. 10--20 tini. Lima elongata - 14--Glt. t Belemnites Area Raulini ulata 4--9 Dentalium cylindri-8--U.G.S. Serpula Sp. 10--15 Crinoidal stems 12 Spatangus re- 14~29 Sp. 19a QUirt. tusus. :Nueula (seapha) 'nuelianum) 4--14 Rostellaria glabra - 8~19 Trigonia caudata r o t--U.G.S. Rostellaria Fittoni - 8--9 Perna Mulleti (oblongus) 4 i Tornatel!a marginata 8--9 Gervillia aviculoides formis - I--U.G S. i I Tornatella albensts - ! 8--9 [alma 14.... U G S Ostrea carinata - Cerithium (Lallieri- 8--9 uata - 4--29 ! Peeten 5-costatus anum.) 1 I ,eymerii - 4 Cerithium Phillipsii 8--9 l Pecten obliquus - - aerii 4 Cerithium turricu- 8--9 Pecten orbicularis latum. ..cun~ea 4 Rostellaria Parkinsoni Ceritllium (Neocomi- 8--9 Sella 4--41 ense.) Rostellaria bicarinata. Gibsii 4--41 Solarium sp. - 8 I Lingula truncata - 4 Natica (Cornueliana) 8--9 Natica rotundata 4--9 Ammonites Hambrovii 8--9 Cidaris Sp. o - 4--19 Astraea Sp. - - 4