3i6 On Ihi/ish Drifls and the fn/cro/acid/ Problem. 



the I'pper boulder-chi}- or Hessle Clay of Holderness. The 

 character and fauna of the warp show that it must have been 

 hiid down between tide-marks, and we therefore g^ain an exact 

 measure of the sea-level at the time of its accumulation, and 

 also, I think, of the hijj^hest limit of marine submerg-ence in this 

 part of Eng-land during- any stage of the Glacial Period. 



The position of the deposit, at the fringe of the great sheet 

 of drift which covers the lowland east of the Wolds and on the 

 edge of an area west of the Wolds which appears to have 

 escaped glaciation, sustains me in the opinion that it was 

 accumulated during that temporary recession of the East British 

 ice-lobe of which we have other evidence. Its proposed correla- 

 tion with the Holderness gravels seems hardly tenable in the 

 light of the fuller information which we now possess regarding 

 the section. That the East-British ice-lobe, during one of its 

 phases, had the sea at its margin, has always appeared to me 

 to be probable,* and, I think, supplies an adequate explanation 

 of the facts. 



Under this interpretation the complex drifts between the 

 Basement Clay and the Hessle Clay are regarded as the marginal 

 products of the ice-lobe which filled the North Sea Basin during 

 a stage when its western border began to lose ground by rapid 

 wasting. By this recession a broad hollow was left between 

 the hills and the ice-sheet, and into this hollow were swept the 

 abundant washings from the glacier on the one side and from 

 the bare land on the other, thus forming the irregular mounds 

 and broad fans of stratified material which run parallel with the 

 receding ice-border. The sea at this time encircled the southern 

 end of the ice-lobe, but its waters were restricted, in the area 

 under consideration, to narrow estuarine inlets between the ice 

 luid the land. 



The Upper Bouhh'r day. —Concurrently with this shrinkage 

 of the East British ice-lobe there appears to have been a steady 

 increase in the ice-caps which covered the broader upland tracks 

 of the northern Eng-lish counties. But all the evidence tends to 

 show that the tongues descending eastward from these caps, 

 from the time of the Basement Clay onward to the close of the 

 glaciation, were persistently prevented from passing freely 

 outward by the presence of the main lobe in the North Sea 

 Basin. Upon the shrinkage of the main lobe thev were deflected 



* ' Drifts of Fl;unbori)u^-li Head.' Ouiirt. Juurn. iUol. Soc, vol. .\l\ii. 

 (1891), p. 421. 



Naturalist, 



