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ledge is very limited, and we must be careful not to assume too 

 much from observations that may not be entirely accurate. 



It is known that Greenland, speaking generally, is covered 

 with one vast mantle of ice, which in places attains enormous 

 thickness. Snow falling inland is converted sooner or later into 

 ice, and the drainage of the country is carried on by means of an 

 unceasing downward motion of the ice towards the sea ; but in 

 thus acting, hills are crossed over, and valleys filled to an extra- 

 ordinary degree, so that the upper surface of the ice is comparatively 

 level, as compared with the actual contour of the country. As the 

 ice sweeps down to the coast it will be thinner on the high ground, 

 assuming that it covers the crests, but the valleys will be filled up 

 with ice to a depth that we can hardly appreciate. As the huge 

 streams of ice, which may be two thousand feet thick, come down 

 to the shore, they press onwards over the sea-bottom. The farther 

 they go, the greater is the inclination of this seaward portion to rise 

 to the surface, owing to the greater lightness of ice as compared 

 with water, until the moment finally arrives, more frequently in the 

 summer, when the cohesion of the mass fails, enormous fragments 

 break off, rise in the water, and float away to melt on the banks of 

 Newfoundland. Any examination of these bergs is a difficult 

 matter ; but we may assume that though they frequently contain 

 considerable quantities of rock materials, yet, comparatively, this 

 amount must be very trifling. Grottoes in Swiss glaciers show the 

 ice almost free from visible impurities, and we may well believe 

 that Greenland icebergs are no less pure than Swiss glaciers. 

 Nevertheless, though the ice be clear as crystal, and though we 

 know nothing at present as to deposits forming in front of these 

 ice sheets, there must be enormous denudation going on, caused 

 by the unceasing movement over the surface of the land of its icy 

 shroud, ever scraping off irregularities, and rounding every pro- 

 tuberance. If we attempt to imagine this ice action in Greenland, 

 we may perhaps suppose that it has so long continued, that most 

 of the irregularities are now planed off", and that the work of the 

 ice will be mainly confined to grinding the rounded or level 

 surfaces of the rocks. Weathering will doubtless bring down 



