166 



ation of the upper part of the Yorkshire Dales has been as intense as 

 the glaciation of the country around Shap, it seems a fair inference 

 tliat the quantity of rock removed from the surface of the lower 

 lying Dale rocks must be at least equal, area for area, to what was 

 removed from Wastdale Crag. Hence we are led to the conclusion 

 that the ice-sheet effected some very important modifications of 

 form in the old preglacial valleys. Where the ice remained for 

 long periods, there can hardly be any doubt that many of the 

 valleys were both deepened and widened, in some instances to a 

 considerable extent ; and also that the peculiar mode of action of 

 the ice tended everywhere to modify the pre-existing form of the 

 surface, and even to replace part of this by sculpturing that is very 

 different from anything that, under existing physical conditions, 

 could possibly be produced by any kind of Subaerial Erosion. 



The remarkable development of the limestone terraces in Wens- 

 leydale is almost certainly due to the fact that the movements of 

 the ice, all through the Glacial Period, were mainly in the same 

 direction, and did not veer about to anything like the same extent 

 as the ice certainly did elsewhere. While it was partly effacing 

 some of its earlier work in Edenside and VVensleydale, it continued 

 to carry its action still further, and to intensify effects already 

 accomplished. 



In the original papers further arguments bearing upon the same 

 subject were discussed in considerable detail ; and an attempt was 

 made to show that the present form of the rock surface in this, 

 and in the adjoining areas, was due to extensive modifications of 

 old features of subaerial origin by the prolonged action of glacial 

 erosion. 



Among the features impressed upon the rock surface by these 

 causes the writer is still, as much as ever, disposed to include 

 those remarkable semicircular hollows so common in glaciated 

 mountain areas, and known under the names of Coums, Corries, 

 or Cirques. In the original articles special reference is made to 

 the origin of some most remarkable phenomena of this nature 

 occurring near Melmerby, which illustrate in a very striking 

 manner, the more characteristic of these singular features. 



