420 ME. G. W. LAMPLTJGH ON THE 



cated by the Basement Clay, and this ice not of local origin but an 

 extraneous mass (for it is clear that the Yorkshire Wolds and the 

 eastern moorlands added nothing to it, and were not entirely sub- 

 merged by it), there must have been a time when the great sheet 

 rested with its flank upon this bold coast-line while its main, 

 current sw^ept southwards, follow^ing the deepest part of the sea- 

 bottom. The basin of the North iSea has been so greatly modified 

 by material deposited in it during Glacial times that it is not pos- 

 sible now to trace its pre-Glacial features, liut there are reasons 

 for supposing that the deepest hollow lay at some distance from our 

 coast *, especially south of Elamborough, and therefore that the main 

 ice-current would probably flow southwards unimpeded by the coast- 

 line, while only the right wing of the great glacier, augmented by the 

 Teesdale and other Pennine ice, expanded sluggishly westward upon 

 our shores. At the time of its greatest extension the ice seems to 

 have been five or six hundred feet thick at Speeton, and a thin flange 

 from the top of the glacier probably passed, during the deposition of 

 the Basement Clay, over the crest of the clitt' there, and made its way 

 down the Bempton valley ; meanw'hile the chief portion was deflected 

 eastwards along the line of cliffs, bearing hard upon the bottom 

 and tearing up the Speeton Clay in its course, because of this 

 obstruction, until it reached the lower ground near Plamborough, 

 which it overrode. 



Porty miles farther north, in the neighbourhood of Whitby, the 

 ice seems during its greatest extension to have reached a height 

 of about 800 feet above sea-level f. But south of Plamborough, as 

 the efiect of the shelter aflbrded by the headland, and probably also 

 because of the shallowness of the Bay of Holderness and the distance 

 of its shores from the main current of the glacier, the level attained 

 by the glacial deposits, and therefore presumably by the ice, sinks at 

 once to between 200 and 270 feet J, and does not again exceed this 

 elevation north of the Humber, In South Lincolnshire, however, 

 where the Wolds protrude eastward again, and would therefore lie 

 more directl}' in the path of the ice, the current seems to have over- 

 ridden them in places where they are as high as 400 feet above 

 sea-level §. I regard these differences of level as strong evidence 

 for the ''land-ice" origin of the drifts, and also for the stability of 

 the relative levels of the east of England during the Glacial period. 



So long as the edge of the ice was advancing, no great accumula- 

 tion of material could very well take place at its margin, for any- 

 thing lodging in front of it would soon be overridden and mingled 

 with the basal moraine. But as soon as its growth was arrested and 

 it began to decline there must have been considerable deposition in 



* During part of the Pliocene period tbe bed of the J^orth Sea seems to have 

 been dry laud, wherein the Rhine and Thames united to How northwards (Geol. 

 Survey Mem. ' Cromer,' p. 57). The river-valley then eroded would probably 

 lie at some distance from the Yorkshire coast-line. 



t Geol. Survey Mem. 'Geol. ofEskdale, &c.,' p. 51. 



\ Geol. Survey Mem. ' Driffield,' p. 13. 



§ A. J. Jukes-Browne, 'The Boidder-claya of Lincolnshire,' Quart. Journ. 

 Geol. Soc. vol. xli. (1885) p. 117. 



