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believe that the advent of the Glacial Period found the rock 

 surfaces over a large part of this area as deeply buried beneath a 

 covering of their own material, weathered and disintegrated in situ, 

 as are any of the rock surfaces at the present day where subaerial 

 waste has gone on without interruption from preglacial times. To 

 appreciate the significance of this, we have but to compare the 

 character of the surface rocks of granitic areas in highly-glaciated 

 districts, as, for example, at Shap, with rocks in similar positions 

 that have not been swept clean by an invasion of land ice, as in 

 the case of the Cornish granites. The bare masses of hard and 

 solid rock at the surface in the granite areas of the northern parts 

 of the kingdom contrast strongly in this respect with the deeply- 

 weathered rock, and its accompanying thick superficial mass of 

 china clay, resulting from prolonged disintegration, that are associ- 

 ated with the granites of Cornwall, and other nonglaciated areas. 

 Or, again, we may compare the surface of the Chalk of Yorkshire 

 with that seen upon the North Downs, where thick deposits of 

 Clay-with-flints have gone on accumulating for long ages, almost 

 undisturbed by land ice, and thus bear forcible witness equally to 

 the continuous subaerial waste of the rock from a period long 

 anterior to the Glacial Epoch. (Geol. Mag. 1875, p. 360, and 

 Pro. Geol. Assoc, ix.. No. 3.) 



The Precursors of the Ice Sheet, and the earlier periods of Glaci- 

 ation. — It is not possible to do more than hazard a conjecture 

 regarding the precise sequence of events that led up to that 

 succession of periods of extreme cold that together characterized 

 what we call the Glacial Period. It is possible that, from early 

 Pleistocene times — or even from late Pliocene, as we know was the 

 case in East Anglia — periods of greater cold, alternating with more 

 temperate conditions, may have nourished glaciers in all the moun- 

 tainous districts of the North. And it is not unlikely that these 

 precursors of the great Ice Sheet may, time after time, have pushed 

 their respective moraines out far beyond the mountain regions 

 themselves. Or they may even, under climatal conditions of 

 excessive rigour, have extended as far as the sea, especially in the 



