221

REPORT OF EXCURSION TO MERSTHAM ANDCOULSDON.

Saturday, April 14th, '923.

By A. G. DAVIS.

A party of nearly fifty assembled on the bridge at RockshawRoad, north of Merstham Station. Here the geology of theneighbourhood* was explained. From a good view-point theextensive Greystone Lime Works, exposing Lower and MiddleChalk could be seen , as well as th e cuttings on the SouthernRailway. now much overgrown , but still showing a section in theUpper Greensand. At a short dist ance was the new cuttingto widen the Brigh ton Road; thi s was the first secti on to beexamined.

An account of this secti on as observed in 1 9 21, t has beenpublished, but the cutting has since been extended up into theMiddle Chalk, and a pipe line sunk at the foot of the cuttinghas provided much additional inform ation.

Th e thickness of the two zones of the Lower Cha lk has beenascertained and a further series of fossils, including some newrecords, has been gat hered. The base of the Lower Chalk wasnot seen in the new cutt ing, but some trial holes mad e recentlyhave shown that only six feet of chalk is unexposed. Here theLower Chalk rests on a bed of slightly indurated sand (Glau­conitic Marl), green when fresh but ra pidly weatheri ng to a greycolour.

Every facility was afforded by Mr. W. P. Robinson, CountySurveyor to the Surrey County Council.

Description of the Merstham Road Cutting.The cutting, 6 00 yards long, was continuous on the western

side of the Bright on Road. The other side was not consideredexcept at parts of the southern end, as material excavated hereshowed evidence of disturbance, probably being chalk tippedfrom the adjacent railway cuttings.

Dips of 6° north were measured in the zone of Schloenbachiavarians and in the Plenus Marl. The exposure commencedat a point 120 yards N.E. of St. Katherine's chur ch , and endedin the zone of Rhynchonella cuvieri at 130 yards N.E. of theJolliffe Arms. The Plenus Marl was exposed opposite RailwayCottages; places shown on the 6" Ordnance Survey Sheet, Surrey26 N.E.

• A good account of the geology of Merstham is given by G. M. Davies, Geot. Excursions7'cxmd London , 1914 , rst ed. , p. 91 .

tAo G. Davis . Zone of Ammoni tes (Scbleenbachia) Varians. Contributions to the Geology .and Pal eont ology of the Croydon Regional Survey Area. Trans. Cmytkm, Nat. Hist, and Sc. SIX.vol. ix. , 1923. pt . iii., pp. 127- 8.

zzz A. G. DAVIS,

The detailed succession reading from south to north showed:Zone of Schloenbachia varians.

feet.Bed I Unexposed but ascertained by boring 6

Hard yellowish marly chalk . . 30" 2 Hard greyish chalk broken up into large blocks 22" 3 Grey marly chalk .. . . . . . . . . IS

{

Hard grey chalk . . . . • . . . 2

" 4 Marly yellow chalk . . . . . . . . IIFissured layer of hard yellowish chalk .. 2Alternations of chalk and marl, the chalk being

jointed 18Grey marly chalk,S feet.Buff-coloured hard chalk, I foot.

" 5 Yellowish marl, 5 feet.Hard yellow chalk, I foot.Grey marl, 5 feet.Yellow chalk, I foot.

" 6 Cream-coloured chalk broken up and disturbedby pipes and tree roots. Fossils frequent atthe base, Schloenbachia va,ians (Sow.) finallyoccurs at the top of this bed. .. 20

Zone of Holaster Subglobosus.Chalk similar to that of Bed 6 ., 30Whitish chalk, somewhat massive and passing

into cream coloured chalk with black joint-faces II

Seam of grey marl (Actinocamax plenus) 2Zone of Rhynchonella cutneri,

White, nodular chalk seen for 15

Total 184

In this section the approximate thickness of the Varianszone is 126 feet, and that of Subglobosus zone is 43 feet, thetotal thickness of the Lower Chalk being 169 feet. The sectionin the Subglobosus zone being shallower than that in the lowerzone, did not present so fine a section; in it unweathered chalkwas but little exposed.

LIST OF FOSSILS.

Zone of Schloenbachia varians.

A list of fossils has already been published.* The followingare additions :-

Mantelliceras mantelli (Sow.), Hamites sp., Aporrhais sp.,Gyrodes genti (Sow.), Pileopsis d. seeleyana Gard., Pleurotomaria

• A. G. Davis, op. Git., pp. 132-4.

EXCURSION TO MERSTHAM AND COULSDON. 223

sp., Fusus sp., Cyprimeria Sp., Terebratella d. pectita Sow.,Entalophora sp., Stomatopora sp., Enoploclytia suesexiensis (Mant.),Scalpellum trilineatus Darwin, Plocoscyphia sp., Porosphaira d.globularis Phill., Cornuspira cretacea Reuss, Webbina irregularis(d'Orb.).

All the above are of rare occurrence in this section, and werecollected from Beds I and 2.

Zone of Holaster Subglobosus,Exogyra conica (Sow.).

"Inoceramus pietus (Sow.)."Plicatula. inflata (Sow.).

" barroisi Peron.Lima (Plagiostoma) globosa, Sow.Pecten (JEquipecten) beaveri Sow.Holaster subglobosus, Leske.

" trecensis Leym."'Occur also in the Actinocamax Marl.

Zone of Rhynchonella cuvieri.Exogyra conica (Sow.).Inoceramus labiatus (Schlot.).Turnus ? amphisbcena (Goldf.).Rhynchonella cuvieri d'Orb,Cardiaster pygmceus, Forbes.Discoidea dixoni, Forbes.Echinoconus castanea Brong.

" subroiundus, Mant.Asteroidea (marginals).Serpula avita, Sow.

A brief inspection was made of the cutting for widening theBrighton Road at Star Lane, Hooley, where the chalk was seento be much eroded and covered by a thick deposit of drift. Thefossils indicated the Planus Zone and included Holaster planusMant., H. placenta Ag., Micraster pracursor, Rowe., Echinocorysscutatus, Leske, Isocrinus kloedeni (Hag.), Epiphaxum aulopo­rides, Lonsd., and Plocoscyphia spp. The Reussianum Subzoneis present a little below in the adjacent railway cutting (p. 213.)

A very fine section in the Planus zone, including the Reus­sianum Sub-zone, was next examined at Woodfield Hill.

Above the Reussianum Band the following forms occurred :­Inoceramus lamarki, Park., I. lamarki. var. cuvieri, Sow., I.inconstans, Woods. Crania egnabergensis, Retz., Rhynchonellaplicatilis, Sow., Echinocorys seutatus Leske. (common), Holasterplanus, Mant., H. placenta, Ag., Mieraster prceeursor, Rowe.,Prosotopora bicornis, Lang.

Below the Band fossils were rarer, and included :-Terebra­tulina lata, Eth., "<Terebraiula " semiglobosa, Sow., Discoidea

2 24 EXCURSION T O MERSTHAM AND COULSDO l\ .

di xoni , Forbes., Holaster pla nus, Mant., 1\1icraster pracursor,Rowe. (very rare), M leskei, Desm., and '< Te rebella " lewe­siensis Davies.

Tea was taken at Ashdown Park Hotel, oppo site th e WoodfieldHill section. Those of the party who remained visited Messrs;Halls' Lime and Cement Works in Marl Pit Lane, Couldson(Stoats Nest Pit, No. 95 of G. W. Young).

The Cortestudinarium and Coranguinum zones are extensivelyworked, and have been described by "V. Hill. *

In recent years the quarry has been extended northward.Many fossils were collected, and included the following:­Inoceramus involutus Sow., I . lamarki Park., Lima (Plag iostoma)cretacea Woods., Plicatula barrois i, Peron., Ancis tocrania paris i­ens is (Morris.), Herpetopora anglica Lang., Heierosiiuia obliquaBenett., and Plocoscyphia labyrinthica Mant., from the Cortestu­dinarium zone.

• In ]ukes--Browne, Cret, Rocks Britain, Jlem. Geol. S", v., vel, iii., 1904, P.177.