LAKE-BASINS OP CUMBERLAND AND WESTMORELAND. 159 



many others in the country, was probably a rounded boss of rock, 

 with a thin covering of drift or moraine-matter. Supposing, how- 

 ever, the whole mass to be morainic, its presence does not explain 

 the formation of the deep rock-basin, unless we could suppose that 

 this groove, 40 feet beneath the sea-level, ran right on to the sea- 

 coast, and was now wholly filled up with drift, with the exception of 

 the present site of Wastewater, the drift-deposit being more than 

 250 feet thick near the lake-foot —altogether a supposition highly 

 improbable. Hence I think we may conclude that this lake is not 

 due to the presence of a terminal moraine. 



In 1865, the late Professor Phillips communicated a paper to 

 the British Association on " Glacial Striation (Wastdale)"*, in which, 

 from the great length of the lower, almost level tracts of ground, 

 and the shortness of the upper snow-slopes in ancient days, he con- 

 cluded that effective pressure could not be continued through the 

 length of Wastdale. Among other reasons for this, he instanced 

 the fact that under the pressure equivalent to 1000 or 1500 vertical 

 feet of ice, that substance would lose its solidity. He also showed 

 by a study of the relative grinding force of the icy weight under 

 different conditions of depth and inclination, that if such pressure 

 could be communicated, it would not be effective in excavating 

 the lake. It would not tend to make a hollow such as a lake 

 would fill, nor deepen such a hollow if previously placed in its path 

 in Wastdale. 



This is strong testimony against the idea of glacial erosion ; and 

 if it really w r ere the case that under a " pressure equivalent to 1000 

 or 1500 vertical feet of ice, that substance would lose its solidity," 

 the theory must, I suppose, be abandoned. But in Arctic and Ant- 

 arctic regions ice sheets of a much greater thickness than this have 

 been seen, apparently solid throughout, and regelation would soon 

 come into play if crushing were partially effected t. The lowering 

 of the melting-point by pressure must also be considered, which, 

 while tending to facilitate regelation, would not be likely to ma- 

 terially affect the solidity of the ice, especially if we may safely 

 assume that the temperature of the bottom layers of ice was well 

 below the freezing-point during the glacial period J. 



Now, I have already stated my belief that at one time the ice 

 coming down the Wastwater valley was fully 1500 feet thick, 

 measured from the present surface of the lake. In the longitudinal 

 section, however (PI. VII. A, fig. 1), I have made the thickness, above 

 the deepest part of the lake, only 1300 feet above the present lake- 

 surface. If we compare the relative thickness of ice and depth of 



* Rept. Brit. Assoc. 1865, Trans. Sect. p. 71. 



f See Croll, " On the Cause of the Motion of Glaciers," Phil. Mag. Sept. 1870. 



% Sir W. Thomson has found that " pressures of 8*1 and 16*8 atmospheres 

 lowered the melting-point of ice by 0"059° and 0-126° C. respectively. These 

 results justify the conclusion of Prof. J. Thomson, according to which an in- 

 crease of pressure of n atmospheres lowers the melting-point of ice by - 0074w° 

 C." (Ganot's Physics § 306, p. 249 : ed. 1872). Since a column of ice 1000 feet 

 thick very nearly equals 29 atmospheres, a pressure of 1000 feet of ice would lower 

 the melting-point -2146° C, and one of 5000 feet would only lower it 1° C. 



