246 GOODCHILD : GEOLOGICAL HISTORY OF UPPER SWALEDALE. 



Glacial Period and the formation of the great Ice Sheet. Throughout 

 all the earlier part of the Glacial Period the Dale seems to have been 

 occupied by simple glaciers, which flowed down the valleys, or from 

 the heart of the mountains, towards the lowlands. The prolonged 

 excavation arising from this cause resulted in the removal of the 

 whole of the weathered rock disintegrated by exposure during pre- 

 glacial times. Necessarily, the greater part of the weathered rock so 

 removed was eroded where the ice acted with greater force, so that the 

 bottoms of the valleys were considerably deepened by this cause 

 alone. Another result followed — ice, in eroding a rock surface, acts 

 differently from water, and the results are therefore different in their 

 kind from what would have been effected by simple weathering. 

 It is to this cause that the present writer attributes the formation of 

 the remarkable terraces and scars of limestone, etc., so well displayed 

 in the adjoining dales. To this cause also he attributed the forma- 

 tion of the coums and other hollows with sweeping curvature, which 

 form some of the most characteristic features of the district. The 

 general effect of the ice-erosion was to impart to the newly-carved 

 rock surface a flowing contour, and an association of scars and 

 terraces which are quite different from what would naturally result 

 from simple atmospheric erosion. These features are much more 

 strongly marked in such districts as Wensleydale, where the flow of 

 the ice from first to last did not vary much in direction, if it ever 

 varied at all. 



Near the climax of the Glacial Period, when the glaciers had 

 become confluent, and their conjoinal surface rose to its highest 

 level, the prevailing directions of movement of the ice in the upper 

 parts of Swaledale were influenced by causes acting from outside the 

 district. As a consequence, the flow of the ice in all the area 

 referred to, instead of being along the valley and downhill, was 

 towards the north-east, across the valleys, and in many cases uphill. 

 This transverse movement of the ice extended even to its bottom 

 strata, which, even at the very lowest parts of the valleys traversed, 

 here impelled across the low ground and up the hills on the opposite 

 side. The valley of the Swale above Keld is thus striated right 

 across, in the very bed of the river itself; and the ice that effected 

 this striation certainly moved steadily up the hill on the north-side 

 of the Swale, and thence right away over the fells until its direction 

 was merged into that of the ice-currents then prevailing on Stainmoor. 

 Complicated results followed from this change of direction ; but with 

 these we are not concerned here. 



What became of all the preglacially weathered rock thus removed 

 by the outward flow of the ice ? Some of it, certainly, flowed away 



Naturalist, 



