DRIFTS OF FLAMBOROTJGH HEAD. 421 



this quarter, "by the washinf^ of debris off the ice, and from the land 

 also, where the ground sloped towards the glacier. Under such 

 conditions thick mounds of stratified drift, like those on the escarp- 

 ment at Speeton, might be piled up by surface-waters coursing down 

 the marginal slopes of the glacier. 



Quite favourable to this view are the alternations of chalky and 

 chalklcss gravels at the lower levels of the headland. With the 

 glacier to the north and east sending, in summer, streams laden 

 with drift detritus into the ice-dammed hollows on its flanks, and 

 to the westward the bare Chalk Wolds weathering rapidly and 

 supplying a fresh burden to every flood, the interstratiflcation of 

 beds of varying appearance near the margin of the glacier can be 

 readilv understood. 



It is clear that the ice which formed the Basement Clay must have 

 been charged with marine debris* (caught up by some method not 

 yet, perhaps, clearly explained), and wherever the solid residuum of 

 that ice has accumulated, whether as Boulder-clay or as gravel, traces 

 of the marine deposits destroyed by it are almost certain to occur, 

 precisely as we find traces of the other older deposits which the ice 

 has similarly laid under contribution. The presence of these shell- 

 fragments in the gravels is therefore no more proof of the marine 

 origin of the beds than the Liassic or Carboniferous fossils are 

 proof of their Carboniferous or Liassic aget. And the greater 

 abundance of the fragments generally, and of Cardimn edule in par- 

 ticular, at the lower levels in North Holderness is exactly what we 

 might expect to find after the ice had passed across a sandy bay J, 

 such as we know to have existed there. 



To the washing of morainic material at the margin of the ice, 

 then, may be ascribed the origin of the Intermediate beds of Flam- 

 borough Head and of the north of Holderness. 



With regard, however, to the deposits of this age in the neighbour- 

 hood of the Humber, it is possible that here the pre-existing marine 

 beds may not have been so greatly modified by the action of the ice, 

 and that the sea was not altogether shut out by the glacier during 

 the formation of the gravels. In the w^ell-known Kelsea-Hill pits, 

 the shells are present in far greater numbers and in much better 

 preservation than farther north, and include Cyrena jlmnhmlis and 

 other peculiar species. But even here, though I have examined the 

 section many times, I have never felt convinced that the shells 

 represent a contemporaneous fauna. The general character of the 



* Geol. Mag. (1890) p. 07. 



t There is, of course, nothing new in this argument, which has been frequently- 

 applied to account for the presence of shells in glacial gravels, as for instance 

 by Mr. H. B. Woodward in discussing the ' Middle Glacial ' of Norfolk (Proc. 

 Geol. Assoc, vol. ix. (1886) p. Ill); Mr. T. F. Jamieson for shelly gravels in 

 Aberdeenshire (Quart. Journ. Geol. Soc. vol. xxxviii. (1882) p. 145), which seem 

 to bear a very close I'esemblance to the Flaniborough beds; T. Belt ('Nature,' 

 May 14, 1874) and various other observers, for the Moel-Tuyfaen and Maccles- 

 field beds ; and the late Prof. H. Carvill Lewis for the drifts generally, Eep. 

 Brit. Assoc. (18S7) p. 092. 



I As bhown by the blown sands of the Sewerby Cliff. 



