1909.] RKCEXT BIOLOGY OF SOME LIVING SHELLS. 763 



Before liiin, these sands were treated as true Crag. The difficulty 

 of separating them is in fact very considerable, and it must be 

 allowed that the separation was made on most unsatisfactory 

 grounds, and Mr. Whitaker quite admits in a letter to myself 

 that much which was once thought to be drift has been shown to 

 be Crag. 



When Wood and Harmer separated the so-called Middle Sands 

 of East Anglia fi'om the Norwich Crag and its several subordinate 

 divisions, the Weymouth Crag, Chillesfoi'd Crag, etc., they pro- 

 ceeded to constitute them a new biological horizon and to treat 

 their molluscan contents as glacial shells. This view Wood sub- 

 sequently somewhat modified. It was Mr. Horace Woodward 

 who first threw a flood of light on the subject by his suggestion 

 that the shell-fragments, &c., of the drift beds of Eastern England 

 were in no sense at home there, and did not constitute a special 

 biological horizon, but were in every case derivative. In his 

 various papers and memoirs on the East Anglian drifts he has 

 emphasized the point, and I have been indebted to him for much 

 information on the subject. 



In his paper on the Glacial Drifts of Norfolk he calls attention 

 to the fact that the fragments of shells found in them represent 

 moi'e than a hundred species identified by Messrs. Wood and 

 Harmer as Crag shells, a considerable number of them belonging 

 to the Coralline Crag. It was this discovery, which seemed to 

 point to warmer conditions, that first started the notion of warm 

 inter-glacial periods interposed in the so-called glacial age. 

 Mr. Woodward entirely disputed the cogency of this evidence. 

 He said : " The aspect of the shells alone makes one sceptical, and 

 it is admitted that they did not live on the spots where they have 

 been accumulated." These beds, he says, " pass southward into 

 gravels which underlie the chalky boulder-clay " ; and he urges 

 that the fragmentary shells in them have been largely derived 

 from old Crag formations which were entirely destroyed or buried 

 beneath the waters of the North Sea. Mr. Clement Reid, who 

 once held a diff"erent opinion, wrote to me many years ago saying : 

 " The fauna of the Middle Glacial sands of Norfolk, I now have 

 no doubt, is entirely derivative," and proceeded to show very 

 clearly that Searles Wood's theory about their contemporaneity 

 would not hold water. See the whole subject discussed at greater 

 length in my ' Glacial Nightmare,' p. 430 ; ' Ice and Water,' ii. 

 pp. 104-106 and p. 206. If derivative, I cannot for a moment 

 doubt that they were derived, as Gunn and the earlier Norfolk 

 geologists urged, from the Crag beds, being merely redeposited 

 Crag shells. Wood himself was constrained to admit that they 

 were deiived, but argued that they came from some other 

 otherwise unknown glacial beds. 



Wha,t is true of the East Anglian drifts is almost certainly 

 true also of the drift of Lincolnshire, the shells in which are very 

 fiugmentary and rubbed : see Survey Memoir on East Lincoln- 

 shire, p. 91, for a long list and description of them ; see also the 



