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to the action of subaerial agencies, the sound rock in the low 

 ground would be long in being affected, even where it was not 

 covered by drift, while at the higher points subaerial denudation 

 would soon remove the slightly-glaciated surface and replace it by 

 surface features of a different kind, so these parts would eventually 

 appear to have been always out of the reach of the ice. Thus it is 

 that in the Dale District the higher lying rock surfaces show more 

 decided traces of the action of the weather than are to be fouud 

 nearer the bottoms of the valleys. The thorough glaciation of the 

 low ground caused all the preglacially weathered rock — swallow 

 holes, widened joints, and all— to be removed; whilst at higher 

 levels even a considerable portion of the preglacially weathered 

 rock was left. In the one case the weather has had to begin its 

 work anew ; in the other it resumed work almost where it ceased. 

 The same remarks will of course apply equally to those parts of 

 Mid and Southern England where the presence of glacial drift 

 marks the former extension of the ice-sheet. AVhen compared with 

 its duration in the Northern parts of England, the stay of the 

 ice-sheet in the South was probably brief Hence there would be 

 less modification of the rock surface than was effected where the 

 ice had a longer stay. Consequently, the slight amount of erosion 

 that the rocks underwent would favour the rapid replacement of an 

 ice-worn surface by one that to all appearance had been produced 

 solely by atmospheric causes. 



When we consider the immense number of the boulders of 

 almost every rock of marked lithological character that have been 

 dispersed far and wide from outcrops of small extent, it becomes 

 evident that other rocks that, as boulders, are not so easily followed, 

 have, under a like amount of glaciation, suffered denudation to as 

 great an extent. The enormous quantity of rock material removed 

 in the shape of boulders from the Shap Granite at Wastdale Crag 

 has been already more than once referred to ; and this, taken with 

 the other instances mentioned, will suffice to prove this point. It 

 would therefore necessarily follow that what is known to be true 

 of any particular rocks like those mentioned, must be equally true, ' 

 cceteris paribus, of other rocks associated with it. And as the glaci- 



