312 On lirilisJi Diifls ciiid Ihv Inlcnyhicinl Problem. 



The 'Purple' Boulder-Clays and Si rati tied Drifts. — The 

 drifts overlyiiiif the Basement Clay in East Yorkshire consist of 

 a complex and very variable series, in which bands of boulder- 

 clay predominate in some places and lenticular sheets of 

 well-stratified materials in others. In the cliff-sections of the 

 Holderness plain certain bands of boulder-clay, known as the 

 Upper and Lower Purple Clays, are persistent for many miles ; 

 but when the series approaches the rising g-round of the Wolds 

 the individuality of the beds is lost, and they are often replaced 

 entirely by irregular mounds of sand and gravel. 



I began work on these sections with the then-prevalent idea 

 that every separate band of boulder-clay above the Basement 

 Clay might indicate a separate glacial epoch, and that warm 

 interglacial epochs might be represented by the partings of 

 sand and gravel between these boulder-clays ; and the object 

 of one of my early papers was to show that more of these 

 divisions were present than had found place in the scheme of 

 classification then in vogue. But after struggling for a time 

 under an ever-increasing load of epochs I was compelled, in 

 tracing the separate bands northwards, to recognise, as my 

 friend Mr. J. R. Dakyns had previously recognised, that the 

 whole series underwent protean changes, the boulder-clays 

 sometimes splitting into numerous shreds amid thick sheets of 

 sand and gravel, at other times merging into a single mass to 

 the exclusion of all stratified material, and not rarely presenting 

 a passage from uncomprising ' till ' to stratified gravel, sand 

 and clay. Hence I was driven to conclude that stratified and 

 unstratified drift must often have been forming simultaneously 

 at places very little distance apart ; and on finding, also, that 

 the whole of the deposits between the Basement Clay and the 

 Upper or ' Hessle ' Clay were not only knit together in this 

 fashion, but were similarly interwoven with the top and bottom 

 of these boulder-cla\s, I had finally to abandon the Interglacial 

 hypothesis altogether so far as the coast-sections were con- 

 cerned. 1 mention this experience in order to show that my 

 present scepticism respecting the Helvetian Interglacial Epoch 

 is based, not upon any preconceived objection to the idea, but 

 upon the failure of the hypothesis when I have put it to the test 

 in this and other districts; and I find also that my experience 

 in this particular runs parallel with thai of many other investi- 

 gators of the so-called ' middle glacial ' deposits of England. 



Marine Detritus in Glaeial Gnrvels.—V rom certain 

 characters of the- mound)' graxi-ls on I'himhorough Head and in 



Naturalist, 



