C. EVANS ON FORMS OF THE GENUS MICRASTER. 149

lC Proceedings of the Geologi cal and Polytechnic Society ofthe West Riding of Y orkshire," N ew Series, Part 3; fr om th eSociety.

The foll owing were elect ed Memb ers of the Association :-

Ernest Candelier, E sq.; Timothy Curley, E sq ., F.G.S.;Thomas J ones, E sq., F.G.S.

The following Papers were read :-

1. ON THE INSECT FAUNA OF THE TERTIARY PERIOD AND THEBRITISH AND FOREIGN STRATA IN WHICH INSEOT REMAINSHAVE BEEN DETE CTED.

By HERBERT Goss, Esq" F.L.S.

2. ON THE FORMS OF TIlE GENUS MICRASTER COMMON IN TIlECHALK OF \V EST K ENT AND EAST SURREY.

By CALEB EVANS, Esq., F.G.S.

The Chalk with bands of flint nodules is characteri sed in WestK ent and East Surrey by the great number of E chinoderm s be­longing to the genus Micrast er that it contains, and a bri ef noticeof the distinctive characters of the form s of that g enus;lf common inthe Chalk in the nei ghbourhood of London, and ofthe stratigraphi­cal positi on in which these form s are found may, th er efore, be of

some use.In Professor Morris's Catalogue, 2nd Edition, the following list

of form s of Mi craster, met with in the English Chalk, is given :-

M icraster acutus.

"""""

cor-anquinum," variety rosiratue," variety gibbus.

cor-bods.:Mantelli.

!! For a general description of the Echinoderms of the Chalk see Man.tell 's" Medals of Creation," and other work s.

150 C. EVANS ON FORMS OF THE GENUS MWRASTER.

A valuable description of Micraster cor-anouinum; the typicalspecies of the genus, was published by the late Professor EdwardForbes, in Docade V. of the " Memoirs of the Geological Survey,"and a complete Monogrsph of the genus is in course of pub­1ication by Dr. Wright, in the series of the PalreontographicalSociety.

The shell of this species is tolerably substantial, and is distinctlyheart-shaped, as the furrow on the anterior side is deep, and themonth is situated very near to the anterior margin of the underside. The lateral ambulacral areas are moderately depressed, andhave a longitudinal groove extending down the centre of each de­pression, and transverse grooves extend from the central one to themargins of the urubulacra, and in these transverse grooves the poresare situated, Tho shell of this form is somewhat variable in shape,but by one or other of these characters the species may be recognised.The variety rostraius is very common, and is composed of thosespecimens in which the edges of the posterior interambulacralplates are somewhat raised, and form a kind of keel from the apexto the posterior end of the shell. In the variety gibbus the poste­rior iuterambulacral plates are depressed, giving a more conicalshape to the shell. This form is less common than the typicalform or the variety rostratus,

With regard to JVficrastel' acuius, Professor Forbes observes*that it is difficult to understand how it is to be separated from11£. cor-anquinum, and that it is "a specimen of th e normal form inwhich the caudal extremity is slightly more produced than usual, avariety not uncommon."

Of M'icraster Montelli Professor Forbes observes that "thespecimens with this name attached do not differ in any respectfrom those recognised as the young of M, cor-anquinum, At thisage they are always very tumid, and the dorsal ambulacra arescarcely at all depressed."

A more distinct form is that described by Professor Forbes]under the name of M icrasier cor-boois, This form is not uncom­mon in the lower part of the Ohalk with flints. It equals andeven surpasses 11£. cor-onquinum in size, but it can be well distin­guished from the last-mentioned form by its more elongated shape,by the thinness of the shell, by the more delicate character of the

* "Memoirs of the Geological Survey," Decade V,t Dixon's "Fossils of Sussex," Plate xxiv, and Decade iii.

C. EVANS ON FORMS OF THE GENUS MICRASTER. 151

tubercles, and especially hy the ambulacral areas being withoutridges or furrows.

Among the various forms of kficraslcr, noticed by ProfessorForbes, is one which has been described by Goldfuss," and hasbeen recognised by Continental geologists under the name of l}I. C01'­

tcstudinacium, Of this form Professor Forbes remarks that it is" a very slight variety of the normal form" of M. cor-anquitnun," cons: meted out of specimens having the mouth slightly furtherback than usual, a feature not unfreqnently seen in depressed speci­mens." This form is further distinguished by the anterior furrowbeing shallower, and the lateral ambulacral areas deeper than inthe normal form.

The typical form of Microster cor-anquinum is common in theChalk of Gravesend, and also in that of Charlton. At both theselocalities an echinoderm of another genus, Galerites alho-qalerus[known to continental geologists as Echinoconus conicuej is verycommon, and is characteristic in West Kent and East Surrey of theChalk immediately below the Tertiary beds, being found in thatposition at Lewisham, Chiselhurst, Keston, and Croydon, but itappears to be rare or absent in the lower portion of the Chalk withflints.

In a paper read before tbe Geologists' Association, on 7thJanuary, 1870, I described some sections of the Chalk with flintsseen in the unfinished cuttings of the Surrey and Sussex Railwaynear Purley and Kenley, villages between Croydon and Caterham.The Chalk in the sections at Purley is probably lower in the seriesthan that of Gravesend and Charlton, since the Tertiary beds areonly seen on the highest part of the hills by Sanderstead, while thePnrley sections are more than 100 feet below the level of the junc­tion of the two formations. From the Railway sections in theneigh bourhood of Purley and Kenley I obtained a large number ofspecimens of Micmsier cor-onquinum, and, after comparing thesewith the figures and descriptions published hy Professor Forbes, Iconsidered them to belong totbe form lllicl'asiel', and. under that nameincluded them ill Illy list of fossils from those sections. About thetime that I was engaged in preparing that paper my attention wasdirected by tbe publication of Mr. Davidson's " Notes 011 Conti­nental Geology" t to the fact that foreign Geologists had recognised

* Goldfuss, "Petrefacten."t "Geological Magazine," p.162, Vol. vi.

152 C. EVANS ON F ORMS OF T HE GE NUS MICIlASTER.

in F rance and Germany two zones of Chalk, characteris ed respec­tively by Jl ir:raste}' cor-anquinum and M: cor-testutlinarium, but aftercomparing the specimens I had obta ined from Purloy with th osefrom K enley I failed to observe any distin ctive characters betweenthose of each ofthe t wo localiti es, Some time aft er my paper waspublished my friend, MI'. Meyer, informed me that M, cor- testud i­nm'ium was th e cha racte ristic fossil of th e Dover Chalk , and th at thetype-form of M. cor-anquinum occurred at Charlton, and on oncemore examining my specimens from the Puvl ey and K enley cut­t ings ( the Chalk of which I believed to be on about the samehorizon as the Dover Chal k) , I found that not a single specimenwas of the type of M, cor-anquinum , nearly the whole of th em beingof the form known as M, cor- testudinariu m, This fact is so striking ,and bas so important a bearing on th e correlation of tbe sub-divisionsof the English Cbalk with th ose established on the Continent, thatI am anxious, as early as possible, to correct the error that I madein th e description of th e Purl ey and Kenley railway sections, and inthe list of fossils contained in my formerpaper, and to sta te tha t inevery instance in which " M iaaster cor-anquinum' is there men­ti oned as being present in those sections, tbe name" Micraster cor­testudiuarium:" or " Micrasler cor-a tujuin um, vari ety cor-testudina­rium" should be substituted.

'With regard to Mic rastercor-boois, I have only found tb at formin the lowest part of the Chalk with flints, and I believe it islimited to t hat horizon, where it is associated with anotherechinoderm equally charac te rist ic, H olasier p lanus .

The correction of the name of th e characte rist ic fossil of theP urley and Kenley Chalk necessitates a modification of th e classifi­cation I proposed fO I" t he Chalk of the line of sections betweenCroydon and Oxtead.

Th e lowest, beds of tbe Chalk Marl were very imperfectlyseen in the spoil heaps around the shafts of the long tuunelnear Marden Park, but these beds are well exposed in the largepit in the escarpment of the North DOWllS, near Oxt ead, a littl eto the east of the line of railway. The highest beds of Chalkof the district were not seen in the Purley railway-cuttings,but are exposed in Ch alk-pit s at Combe Lane and Crohamhu rst,near Croydon.

Th e olassiflcation I am now disposed to adopt for th e Chalk of

C. EVANS ON r onsrs OF THE GE NUS MICR ASTER. 153

W est Kent and E ast Surrey is as follows, commencing at th e baseof t he Series :-

Zone of Holaster 'I< trecensie and Ammonites val'ians-Chalk Marland Grey Chalk-Chalk of Oxtcad.

Z one of B elemnitella plena-Yellowish concretionary Chalk, andhard White Chalk-Lower Chalk of Mard en Park.

Zone of I noceramus mytiloides (labiatus)-White Chalk with outflints-Upper Chalk of Mard en P arle

Zone of I noceramus Bronqniarti and Terebratulina gracilis­'White Chalk with few flints-Chalk of Whiteleaf.

Zone of Hola ster planus and lJi icraster cor-hovis-lowest beds ofChalk with bands of flint nodules-Lower Chalk of K enley.

Z one of Micraster cOI'-testudinarium- Chalk with bands offlint s-Chalk of Riddlesdown (or Upper Chalk of Kenley andChalk of Purley).

Zone of Micra ster cor-anquinuui and E chinoconus conicus (Gale­rites alho-gulerus) - Chalk with bands of flints-Chalk of Croydonand Cha rlton.

The Chalk of Gravesend is, perhaps, slightly higher ill th e seriesth an th e Charlto n and Croydon Chalk, as B elemnitella mucronatais common at Gravesend, the fauna ill that respect approaching toth at of th e Margate Chalk .

In the year 1876 a very valuabl e memoir Oil th e Chalk of En g­land and Ireland was published at Lill o by Dr. Ch arles Barrois, inwhich that gentleman described the Chalk of the Sonth Downs andth e H ampshi re Basin, and of most other parts of En gland, in socomplete and masterly a manner, that little more remains to bedone than the filling in of minor deta ils j and he has clearly shownth at it is possible to identi fy in the En glish Chalk the zones whichhe has already estab lished in th e Chalk of France.

Th e class ificat ion which D)'. Bar rois adopts is shown in th emiddl e column of th e following table. Th e left hand column showsth e manner in which he has corr elated his zones with those pro­posed by me in 1870 for the Surrey R ailway sections, and in th ecolumn on the right hand I hav e shown the classi fication I amnow disposed to adopt for the Chalk of East Su rr ey and We stK ent :-

" Holasi er su bqlobosus is usua lly adopted as the ty pe of this zone, bu t Ibave not as yet obta ined this fossil from Oxt ead.

o

151 C. EVANS ON FOR1I1S OF THE GENUS MICRASTER.

Gravesend Beds P

C. Evans (1877)East S"rrey and ]:Vest

Kent Class~fication.

C. Evans (1870) ISltrrey and EJ-i,sswlJ II C. HaTl'vis (1876)

GeneraL Classijication.Railway Classification'lI~---------I---------IAssise a Belemnitelles .. ,

Purley Beds 1Zone a Marsupites , ..

Zonea"M..cor-anguinum... Charlton and CroydonBeds,

Upper Kenley Beds... Zone a JIiI. eortestndina-rium Riddtesdcwn Beds.

Lower KeuleyBeds Zone a Holaster planus ... Kenley Beds.

Whitelea£ Beds Zone a Terebratulinagracilis Whitelea£ Beds.

Upper Marden ParkBeds Zone a Inoceramus labi-

atus UpperMardenParkBeds.

Lower Marden ParkBeds ..

Zone a BclemniteaplenusLower Marden Park Beds,

Zone a Holaster sub.globosus Oxtead Beds.

Chloritie Marl ..

Zone a Pecten naper......

Zone a Ammonites inflatus'

Dr. Barrois states in his memoir that he has not had time tostudy the Chalk of the Basin of the Thames with the exactnesswith which he has examined the Chalk of tIle Southern parts ofEngland, and he has relied to a great extent on the works publishedby previous writers on the subject, for the purpose of correlating thedivisions of the Chalk near London with those established else­where. Among the works cited he has included my paper on theCroydon and Oxtead Sections, and, trusting to the correct identifi­cation of MicrQster cor-anquinum as the characteristic fossil of thePurley Chalk, he has, I believe, placed that Chalk on too high ahorizon. I regret that the error I made in my list of fossilsshould have been the cause of thus misleading him, and I there­fore desire, as early as possible, to correct my mistake, and to con­firm his generalisation that the zones of life, which he has in soadmirable a manner established for the Chalk of the HampshireBasin, and in France, can be equally well recognised and studied inthe Chalk of the Basin of the Thames.

Miol' aster COl"_ t e s t u d rn a.r-i u.m Gold.fU.s s ,p,. 0 17'1- AN,. 7-0".

Mi Cl ' a s t e r- c ur -a n g u.i n u ln .(J~.

f'r.0 m- Ora.-e-s e-nd-.

P r oc Geo l. As soc Vol .Y. Pl I]

Mi c r- a s te r c or - b o vi e .Forbee .~(Tm,J.{eKller