DRIFTS OF FL.VAIIWROUGII HEAD. 419 



south of Bridliriixton, seems to ho now the most northerly of the 

 Holderness moujids, tliough I think tliere is evidence that others 

 have existed still nearer to Bridlington *, and have heen destroyed 

 by Huviatile action and ])y the encroachments of the sea, which 

 have once linked lieacon Hill (tig. 0) or Totter Hill (tig. :5) to the 

 Holderness range. From iJarmston the line may be followed inland 

 (though not ([uite uninterruptedly) by Stonehills, Gransmoor, Kelk, 

 lirigham, Frodingham, and Ih'andesbnrton. The structure of tlie 

 mounds is evidently everywhere similar to that of Beacon Hill. 

 They are based on Boulder-clay, and their flanks wrapped by an upper 

 red Jioulder-elay which genenfUy thins out before reaching the crest 

 of the hill t. In southern Holderness the range becomes broader 

 and more complex and broken, and may have been formed under 

 somewhat different conditions. 



In going southwards from Barmston shell-fragments occur in the 

 gravels in constantly increasing numbers ; but until we reach the 

 neighbourhood of the Humber the species are always the same as 

 those that occur at Flamborough, though Cardium edale becomes 

 relatively more abundant. 



These beds have been described as '' marine gravels of inter- 

 glacial age " (Geol. Survey Mem. " Holderness "), apparently chiefly 

 because of the presence of shell-fragments in them, but I think that, 

 at any rate in Northern Holderness, they can scarcely have had a 

 marine origin. Even where the shells are most plentiful, the valves 

 are always separate, unbroken specimens very rare, and all much 

 waterworn ; moreover they all occur among the fine gravel, and 

 none in the silty beds. I believe that a section east and west across 

 Holderness would reveal the passage of the Purple Clays into these 

 beds (as shown in the left half of the diagram, fig. 15), just as the 

 north and south cliff-section reveals the passage of the clays into 

 the stratified beds of Flamborough Head. 



The position of the Intermediate Beds on the crest of the escarp- 

 ment at Speeton has arrested the attention of many observers. 

 They were first described by AVood and Kome as " denudation 

 gravels of jDost-Glacial age," and supposed to have been formed 

 during a great submergence J. But it is so extremely improbable 

 that a marine gravel could have accumulated in such a position 

 that we are not surprised to find S. V. Wood, in his later memoir §, 

 refer them (in parenthesis) to " the melting there of the Furple-Clay 

 ice." This latter explanation I believe to be the true one, and, as 

 1 have already mentioned, the opinion of the late Prof. Caivill 

 Lewis was essentially the same. 



With ice filling up the bed of the Xorth Sea to the extent indi- 



* The sandy rising ground on which Hilderthorpe stands probably belongs 

 to this range, having been eroded and its outline destroyed during the lorma- 

 tioii of the recent freshwater gravels, &c., which surround it. 



t See Geol. Survey Mem. ' Holderness,' pp. 52-53. The beds are described 

 as ' ^lariue Interglacial Gravels,' see above ; also ' Driffield,' pp. 14 & 15. 



+ Quart. Journ. Geol. Soc. vol. xxiv. (1808) p. 175. 



§ Ibid. vol. xxxvi. (188U) p. 520. 



