Rev. Edtvin Hill — Lifting by Ice-melting. 13 



over the upper sniface. Sun lieat attacks only the upper surface ; 

 wind and rain attack onl}' the upper surface; the flow off from 

 melting will not for some time have any melting power. Even 

 a warmer current, so long as Avater above freezing is denser than 

 water at freezing, is likely to pass below the water in contact with 

 the ice : the lower surface will be likely for a while to escape its 

 influence. In considering only cases of melting from the upper 

 surface we shall be considering, I think, a large majority of the cases 

 which actually occur. That ice does melt on its upper surface every 

 skater knows by experience of thaw, and accounts of Polar explora- 

 tions describe summer alterations of the surface even in the regions 

 of greatest cold. Wherever ice is formed melting must be verj" 

 frequent. There are incessant alterations of temperature, by changes 

 of wind and cloud, by changes of night and day, by changes of winter 

 and summer. Melting is an action of very frequent occurrence. 

 Lifting by melting must be a very frequent result. It may 

 produce a variety of consequences, according to the variety of 

 circumstances. 



In shallow waters the ice-crust will, over parts, touch the bottom. 

 Parts of the sodden bottom may, and doubtless will, be frozen to it, 

 will when its surface melts be lifted by it, may when it breaks up 

 and floats away be carried away with it. Fi-om a bottom undulating 

 in ridges or mounds, if the ice be in contact with such ridges or 

 mounds, the highest parts will be lifted and removed. Thus the 

 depth will be made more uniform ; the effect will be as if tops were 

 planed away. The bottom will be levelled and the average depth 

 increased. Ice melting and lifting is an agent of levelling and of 

 denudation. 



When the ice floats away materials attached to it will be floated 

 away : the ice melting and lifting will become an agent of trans- 

 portation. If a portion strands, where it rests the attached materials 

 may rest. If a portion melts, where it melts the attached materials 

 may be deposited. Ice melting and lifting will have become an agent 

 of deposition. 



AVhen an ice-crust has enveloped any objects projecting from the 

 bottom, as it rises it tends to pull them up. The lifting power of 

 flotation is well known : it has been employed to tear up piles, 

 barges lashed to them raising them with a rising tide. An ice-crust 

 melting exerts the same action. Horizontal force on such objects 

 would be resisted by the strength of the matrix in which they are 

 embedded ; but vertical lift is resisted only by their weight and 

 adhesion. Ice melting and rising exerts the action which has been 

 attributed to glaciers under the name of ' plucking ', and exerts it in 

 the most favourable direction. 



When an ice-crust forms against a bank or cliff portions will adhere 

 to it : portions may be broken away as it rises, and will be carried 

 away if it moves. This action will steepen banks and undermine 

 cliffs. It is the action which has been attrib\ited to glaciers under 

 the name of ' sapping '. 



Ice melting and lifting will elevate. Boulders attached to its 

 under surface will rise with that surface, and if stranded will be left 



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