GOODCHILD : GEOLOGICAL HISTORY OF UPPER SWALEDALE. 247 



within the ice at least as far as the Yorkshire coast; but the material 

 detached from the rock surface by the ice did not all go out of the 

 Dale. Some of it was released when the ice melted — released as if 

 it were a kind of sediment — and it is this glacial sediment of stones, 

 mud, sand and boulders, that now constitutes the glacial drift, in 

 every one of its many different forms. Till, sand and gravel, and 

 washed drifts of all kinds here are simply so much material that was 

 formerly dispersed throughout the body of the ice (not on it, or 

 under it, but wiihiti the ice) and when this ice melted the drift are 

 the sediments it left behind. 



In Swaledale, as elsewhere, there is abundant evidence that the 

 Ice Sheet ceased to move somewhat abruptly, and that it began to 

 melt away on the spot soon after the icy flood attained its maximum. 

 Why it did so has not yet been satisfactorily explained ; but so it 

 did ; and it certainly did not wane in reverse order through all the 

 changes that marked its waxing. The striae left by the ice when at 

 its maximum have hardly ever been effaced by later movements in 

 different directions. It would seem, however, that some time after 

 temperate conditions had taken the place of the rigorous arctic 

 conditions just referred to, a later period of cold, very much less 

 intense than what preceded it, did obtain here. Here and there 

 in the heart of the larger mountain areas, a tiny glacier seems to 

 have been nourished, and this may really have, locally, pushed out 

 some of the older glacial sediments, and striated the rock surface in 

 new directions. But it is doubtful, very, whether this can be shown 

 to have been the case in Swaledale. 



At no time during the Glacial Period, or since then, does the 

 Dale appear to have been submerged a single foot beneath the sea. 

 Nor is there any evidence whatever of the transportal into Swaledale 

 of any of the far-travelled boulders that represent the stream netted 

 out of the Stainmoor current of the Ice Sheet. 



After the close of the Glacial Period (at the most not more than 

 20,000 years ago) sub-aerial denudation renewed its attacks upon the 

 rock-surface of Swaledale. Waterfalls again started into existence, 

 and have had time to cut back into long ravines ; scars began to 

 crumble away, and again to weather into something like their pre- 

 glacial contours ; vegetation gained a footing ; Neolithic man entered 

 upon the tracts whence — untold ages before — his Palaeolithic fore- 

 runner had been driven by the advance of the Ice Sheet ; and, 

 finally, the Dale gradually began to assume, under the action of sub- 

 aerial forces, something of the varied and beautiful aspect which 

 characterizes it at the present day. 



August 1890. 



