8. V. Wood, Jun. — Reply to Mr. James OeiMe. 171 



VL— Eeplt to Mr. Ja3ies Geikie's Correlation of the Scotch 



AND English Glacial Beds. 



By S. V. Wood, jun., F.G.S. 



IN his fourth paper Mr. Geikie sweeps the entire Glacial series of 

 the Eastern side of England into correlation, not only with the 

 Scotch Till, but with the Boulder-clay, both Upper and Lower, of 

 the North-west of England. This he does, so far as I follow him, 

 without any other grounds than that there are beds of "gravel, 

 sand, mud and clay " in the Scotch Till. It is impossible, within 

 the compass of these remarks, adequately to contest Mr. Geikie's 

 views ; but if the evidence of organic remains is to be regarded as 

 worth anything, such a correlation cannot, I contend, be maintained. 



1 did, indeed, regard the Scotch Till as probably coeval with the 

 " Great chalky clay ; " but I am now disposed to think that even 

 this clay is older than the Till, and to question whether the latter can 

 b« correlated with anything older in Yorkshire, Lincolnshire, or East 

 Anglia, than the purple clay of the two first-named counties. 



Geologists are aware that there is a Crag fauna in Britain, and 

 that it is not identical with any recent assemblage of moUusca ; and 

 if the fauna of one set of Glacial beds shows a close approach to 

 this Crag assemblage, and the fauna of another set shows no such 

 approach, most geologists will, I think, agree that the former set is 

 the older of the two. Now from the Lower Glacial sands of Norfolk 

 there have been obtained 32 forms of mollusca, all of which, with 

 one exception (Tellina Balthica), are Norwich Crag shells ; and of this 

 number three (or 9 per cent.) are not known living, viz., Tellina 

 prcetenuis, Tellina ohliqua, and Nucula Cobholdice.^ The Middle 

 Glacial sands of Norfolk and Suffolk have yielded 81 forms of 

 mollusca ; all of which, with four, or perhaps five, exceptions, occur 

 in some part of the Crag ; and of these 81 there are 10 (or 12^ per 

 cent.) not yet known as living, viz., TropJwn mediglacialis, Troplwn 

 Billochbiensis, Nassa pidchella, Fleurotoma assimilis, CeritMum tricinc- 

 tum, Nuctda Cohboldics, Astarte Burtinii, A. Omalii, Erycinella ovalis, 

 and Tellina ohliqua? From the Bridlington bed, which occurs in the 

 Purple Clay of Yorkshire (a clay that rests upon the great chalky 

 clay along the Holderness coast), 59 forms of mollusca have been 

 obtained, of which 18 are unknown in any part of the Crag ; and of 

 these 59, two forms only (or rather more than 3 per cent.) are not 

 known living, viz., Nucida Gohboldice and Tellina ohliqua. The 



^ Some concliologists regard this shell as identical with Nucula insignis from 

 Japan, and some with N. LyalK, from Vancouver; while others, my father and 

 myself among them, regard it as different from both. Even supposing, however, 

 that one or other of these living Nuculce he identical with Gohboldim, yet, for such a 

 test as the comparison of the fauna of the East Anglian beds with that of the Scotch, 

 it is much the same whether we regard the shell as not known living, or as living in 

 so remote a sea as the North Pacific. 



2 The first four of these shells are new species, figured and described in the Supple- 

 ment to the Crag Mollusca now awaiting the next issue of the Palseontographical 

 Society. Some of these may probably turn out to be living forms, which would 

 reduce the 12^ per-centage of extinct ones. Trophon Billockbiensis may possibly be 

 the young of Purpura tetragona, an extinct Crag species. 



