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for the purpose, and being first deposited on the elevated peaks, 

 would rapidly spread over all those extended surfaces which glaciers 

 are thought once to have covered. Their subsequent disappearance 

 he accounted for, by supposing that the icy or snowy covering pre- 

 vented the loss by radiation of the heat received by the earth's crust 

 from the interior of the earth ; since this heat, gradually accumu- 

 lating below, would in time melt the icy masses at their lower ex- 

 tremities faster than they could be supplied from abovC; and thus 

 reduce them to their present dimensions. He illustrated this view, 

 by mentioning the fact, that the angular boulders, &c. are pretty 

 equally scattered over all the extended surfaces which glaciers are 

 thought formerly to have covered, but are rarely seen to form the 

 dykes or moraines seen at the terminations of glaciers at present in 

 existence ; this fact apparently proving that they must have com- 

 menced their decay very shortly after their formation. 



The author stated several other arguments in favour of the truth 

 of the sliding theory ; from all which he inferred, that the move- 

 ment was not a continuous, but an interrupted process ; — that when 

 the melting of the sides of the mass detached it fz-om its attachment 

 to the sides of the valley, and it became undermined below, by the 

 melting of its base, the force of gravity, unresisted by friction, was 

 brought into play, and it made a sudden progressive movement 

 (which might be only an inch or several feet), when it remained at 

 rest, till the same causes produced a renewal of the same result- 

 He shewed, that though many parts of these icy masses were nearly 

 level, all the upper portions, and many of the lower, were lyino- over 

 such inclined planes, that gravity could exert its full power in their 

 propulsion ; and as the whole icy mass was tolerably solid and con- 

 tinuous, the greater movement of one portion was communicated 

 more or less throughout its whole length, and tended to urge for- 

 wards and downwards those parts which had less tendency to move 

 onwards of themselves. 



The author also endeavoured to account for the advance of one 

 glacier, and the retirement of another along side of it, by supposinor 

 that it was caused by the snows being drifted away from the one 

 valley exposed to the blast, and from which the glacier, which was 

 retiring, descended, and being deposited in deep wreaths in the other, 

 which was probably more sheltered, and from which descended the 

 glacier, which was making destructive advances. The increased ac- 

 cumulation of snow, by furnishing a supply greater than the waste 



