440 Laws of Glacier Motion and Regelatio?i. 



Ice experiments could be well tried on a large scale in Switzerland, Norway, 

 Russia, or in Canada, where the temperature of the air is low. 



By your permission I would attempt a new explanation, to show a possible 

 mode in which lakes high above the sea level are formed by the action of ice ; 

 that is, by glacial action. The motion is due to vis a tergo, like the slope 

 movement of marshy ground when loaded by an embankment. 



(5) The outlets of all such lakes in mountainous districts are high above the 

 lowest part of the bottom of the lakes themselves. Deep lakes as Fig. 2 are 

 always embosomed in the mountains by whose glaciers they were formed. 

 Deep lakes are purely the mechanical consequence of high and steep mountains 

 from the poles to the equator. Given the position and depth of the lakes, it is 

 often possible to predict the position of the mountains. 



I have shown, in Fig. I, a lake which you may suppose to be that of Zurich 

 or Lucerne. The outlet, or outfall, of this lake is in hard rock, and it is 

 evident that the whole of the material which formerly occupied the lake must 

 have been, at some time or other, excavated, or dug out, as it is not possible 

 to suppose any other hypothesis. 



I hope to show how glaciers — that is, ice holdingboulders or rocky blocks firmly 

 in its grasp, dragging along the bottom— can perform this difficult operation. 



As glaciers have a considerable motion, although a slow one, these rocks 

 shown in the diagram are like tools or shears, which plough up the surface of 

 the earth and push the loosened material up a slope into the outfall. 



It is possible to explain by this drawing how a glacier, having hard boulders 

 firmly embedded in the bottom, can drag these along the bottom and cut out 

 the rock and push it up the lake-bottom against gravity, over the* outfall, from 

 which it woidd be removed in the usual way, if the glacier can move forward 

 from top to bottom. In the glacial period the mean temperature of the ice 

 must be assumed at ten or twenty degrees below freezing, although now near 

 the freezing point in modern glaciers. 



There is one condition necessary to be admitted, and that accords with 

 observation — viz. that the bottom of the glaciers must be wet, and at 32 

 Fahr., or about that temperature. If colder, the ice would freeze to the bot- 

 tom and no motion would ensue, and if warmer the ice holding the boulders 

 would be thawed and there would be no erosion taking place. 



All observations show that all modern glaciers move in constrained, and not 

 in free motion, and more in summer than in winter, and that there is a thin 

 wet or watery surface between the glacier bottom and the ground of the valley 

 it moves in. There are greater deviations in glaciers from their mean motion 

 than in rivers from their mean motion, but still glaciers move forward in a 

 mass, and the front ice is not overtaken by the back ice. 



Now the fact of the greater motion in the day than in the night, and in sum- 

 mer than in winter, is an indication that the greater the quantity of water 

 present in the glacier the greater is the motion. The action of a quantity of 

 water at the bottom of the lake, and in the fissures of the glacier, would tend to 

 float the lake glacier to some small extent, or at least to place it in the unstable 

 condition of marshy ground. We know that when a railway embankment or 

 a large building is erected on a marsh, elevation of the surface of the marsh 

 takes place at a long distance from the point where the weight is applied. 



In order to render the motion of the lake glacier possible, such as that repre- 

 sented Fig. 1, we want a certain quantity of water constantly produced, 

 and that part should soon freeze, so as not to increase the stock of water. I think 

 the congelation-dilatation theory of De Charpentier, with some modifications, 

 helps to explain lake glaciers. Although Sir H. Davy pointed out that ice 

 rubbed against ice produced heat, yet this has not been taken into account in 

 any of the theories of glacier motion, and I mention it now for the first time in 

 a public lecture, that there is a possible source of heat to produce the water 



