14 Rev. Edivin Hill — Lifting hy Ice-melting. 



at a higher level. The elevation by a single operation cannot exceed 

 the thickness of the ice. But where land is sinking repetitions of 

 the operation might elevate to the total extent of subsidence. Also, 

 any snowfall will sink the ice by its superincumbent weight.^ 

 Should the periodic snowfall exceed the periodic melting the under 

 surface will continue to sink. In an ice-age lakes thus easily 

 may, probably wdll, become solid masses of ice. When milder times 

 return materials from their very bottoms may be brought to their 

 surfaces. 



On land, when ice filling a rock-basin moves through it, materials 

 may be moved from the lower levels to the level of outflow. But 

 even when the ice does not move through, on melting it may bring 

 up materials from the very bottom to the surface. 



When an ice-floe with attached pebbles or rock-fragments strands, 

 scratches and striations on pebbles, fragments, and bottom may result, 

 as has often and long ago been suggested. 



This action of ice-lifting by melting should produce its maximum 

 effects in groups of conditions, different for different effects. For 

 removal of material, planing down, denudation in general, the most 

 favourable conditions while climate remains unaltered seem to be, 

 a land undergoing alterations of level ; either rising, whereby fresh 

 bottom is being brought within reach of the ice, or sinking, whereby 

 fresh stretches of margin are being submerged. 



In lifting boulders to points above their place of origin, the greatest 

 possible lift is from the lowest point reached by ice in the period to 

 the highest. 



For accumulation of a thick deposit favourable conditions seem, 

 a wide area of shallow water alternately frozen and thawed, which 

 should drain into an area of warmer water sufficiently deep. 



The action described does not necessarily require a low mean 

 annual temperature. Favourable conditions would be, severe winter 

 cold, with summer warmth sufficient to melt ice at the surface and 

 to break it up. The action would be vigorous during the incoming 

 of a glacial period. When cold grew so severe that there was no 

 summer break up the action might cease, but would recommence 

 when the cold began to pass away. During every part of such 

 period the action, though suspended over the interior of the cold 

 area, would probably still be going on over the outskirts. Even now 

 it must be going on in several parts of the earth. 



The amount of work which could be done in this way might be 

 considerable in a sufficient time. Thousands of years are claimed for 

 the durations of ice-ages : if so, work done in them should be the 

 average work of a year multiplied by thousands. An ice-raft able 

 to support an inch of material would not need to be very thick. 

 Anything attached to the lower surface would be buoyed up by the 

 water and lose part of its weight. Consider material of sp. gr. 2*50. 

 An inch-thick layer on the upper surface would require about 

 30 inches of ice, but if attached below could be supported by about 



^ Scott's Voyage of Discovery, vol. ii, p. 4.58. Shackleton's Heart of 

 Antarctic, vol. ii, p. 289. Also Lyell's Principles, oh. xi (there of drifted 

 snow). 



