16 



GLACIERS AND DRIFT ICE. 



CtSSSt For th ? {a *^v guidance of those who may wish to ex- 



V&^. + 7 ine thlS Sub J ec * for themselves, I must add a little about 

 n Recess 41. the appearance of the Dolish on * n »v s «„^i *i „ . 



of glaciated surfaces. 



In the Alps, when glacier ice is freshly removed, the 

 rock underneath, whether of limestone, gneiss, granite or 

 even quartz, though striated, often possesses the polish of >x 

 sheet of glass. In our own country, when the impervious 

 covering of till has been taken away, the surfaces of lime 

 stone (as at North Berwick), though grooved and striated 

 are often beautifully smooth. In a country so low this 

 may have been due to the grating of icebergs. In other 

 cases, as in some parts of Wales, when the turf and "lacier 

 debris is lifted, the underlying surfaces of slate stiir re tain 

 a perfect glassy polish, marked sometimes by flutin-s and 

 sometimes by numerous scratches as fine as if they' had 

 been made by the point of a diamond. After long exposure 

 these finer markings disappear, and " ' 



though the general 



rounded form perfectly remains, the surface becomes rough- 

 ened, and the planes of the highly-inclined cleavage present 

 on their edires a - 1 ' * " 



slightly 



. . serrated aspect. The deeper 

 fiutings, however, often for a long time remain, but even 

 these at length vanish, though it is not until long after 

 this has been effected that the general rounded form of the 

 Toches moutonnees is entirely obliterated. Phenomena of 

 the same general nature are observable in the igneous un- 



cleaved rocks over which 



a glacier has passed. 



The 



original polished surface, on exposure, becomes roughened 

 by atmospheric disintegration ; but the general form remains 

 to attest its glacial origin, and in no case is there any 

 danger of the experienced eye confounding this with those 

 forms produced by spherical decomposition about which so 

 much has been written. Finally, in the long lapse of time, 

 the air, water, and repeated frosts tell their tale, the rock 

 splits at its joints, crumbles, masses fall off; and it assumes 

 an irregular and craggy outline, altogether distinct from 

 the glaciated surface produced by the long-continued passage 





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