646 TRANSACTIONS OF SECTION C. 



toward the west than toward the east, until finally the eastern portions were 

 shrunken for want of sustenance, while the westerly lobes were still waxing 

 thicker and stronger. The recent researches of Mr. F. W. Harmer into the 

 probable meteorological conditions of the Glacial Period ' are full of suggestion in 

 their bearing upon the changes which must have been brought about by the 

 expansion of the ice-sheets. The subject is one of peculiar difficulty, but I believe 

 that the solution of many of the problems connected with the Glacial Period are 

 to be found along the lines of Mr. Harmer's investigations. 



In considering this factor it is also especially interesting to find that Captain 

 R. F. Scott is of opinion that the great shrinkage in the Antarctic laud ice, of which 

 he obtained such convincing evidence during the recent expedition, is due to the 

 present excessive coldness, and consequent dryness, of the climate ; and he assigns 

 the former extension of the southern ice-sheets to a period of warmer and moister 

 conditions.- It would have been easy, had time permitted, to bring together 

 numerous illustrations from Polar lands to show how strongly localised in many 

 places are the conditions of existing glaciation ; and such conditions must have 

 tjeen still more effective at lower latitudes. Hence we can readily imagine 

 that, during the Glacial Period, differential growth and shrinkage might be 

 brought about concurrently in areas not very wide apart, by local circumstances. 



Waning Ice-sheets. — So far as the eastern side of England is concerned, I think 

 that the epoch of maximum glaciation was reached, not when the East British 

 lobe pressed farthest westward, but when the Pennine and North British ice 

 advanced southward along its receding flank ; and this stage is, I presume, 

 equivalent to the ' Polandian Glacial Epoch ' of Professor Geikie's classification. 

 It was at this time that the ice lapped highest around the slopes of the Jurassic 

 and Cretaceous uplands of Yorkshire, causing that radical diversion of the surface- 

 drainage which produced the remarkable efi'ects first made known to us by the 

 brilliant researches of Professor P. F. Kendall in Cleveland,^ and since traced by 

 him and his fellow-workers at intervals wherever the margins of the ice-sheets 

 have abutted against the slope of the land. 



Farther southward this ice, augmented by the snowfall on its own broad 

 surface, appears to have spread over the lower ground far beyond the bounds of 

 the former invasion, covering most of East Anglia and the East Midland counties 

 with a moving ice-cap, beneath which the Chalky boulder-clay was accumulated. 

 The Upper boulder-clay of Yorkshire I consider to be the product of the same 

 ice-sheet at its waning. 



This final waning of the British ice-sheets, as I have elsewhere attempted to 

 show,' must have been accompanied by conditions very different from the waxing 

 stages. It appears from the evidence that the great ice-plateaus still lingered 

 in their basins even after the amelioration of the climate had progressed so far that 

 no permanent snow could remain on hills that rose considerably 'above their level. 

 Deprived of reinforcement, and wasting ever more rapidly as their surfaces were 

 brought lower, the lobes must in aU their embayments have passed into that con- 

 dition of ' dead ice ' with which the explorers of Polar regions have made us familiar. 

 The ' englacial ' load of detritus which the ice was powerless farther to transport 

 was gradually dropped to the ground, and often modified and spread by gravita- 

 tional movement in the saturated mass.^ The peculiar features of the upper 

 part of the lowland drifts were thus explained many years ago by the late J. G. 



' 'The Influence of Winds upon Climate during the Pleistocene Epoch.' Quart. 

 Juurn. Geol. Soc, vol. Ivii. (1901), pp. 403-476. 



^ ' Results of the National Antarctic Expedition.' Gcogra/ph. Journ., vol. xxv. 

 (1905), p. 30G. 



' ' A System of Glacier-Lakes in the Cleveland Hills.' Quart. Juurn. Geol. Sue, 

 vol. Iviii. (1902), pp. 471-571. 



* 'The Geology of the Isle of Man.' Mem. Geol. Survey (1903), pp. 395-397. 



^ The flow of loose material at the surface when saturated by water has been 

 recently studied by J. G. Andersson (Upsala), who cites many remarkable illustia- 

 lions of the phenomenon, and proposes to apply to it the term ' solifluction.' Journ, 

 Geol., vol, xiv. (1906), pp. 91-112. 



