292 GLACIAL GRAVELS OF MAINE. 



crystals and melts tliem, heat is inseparably connected with all the work of 

 the glacier. "Water is the heat transport of this heat engine. The waters 

 derived from the melting ice flow along the surface or gather in pools until 

 they find a crevasse down which they can escape. In passing from the 

 surface to the bottom of the ice they carry heat with them. The phe- 

 nomena of both subglacial and superglacial streams are largely determined 

 by the behavior of water with respect to radiant and molecular heat. The 

 most important of these relations are the following: 



1. Water is a poor conductor of molecular heat, but a good absorber 

 of radiant energy. 



2. Water, like all fluids, readily transmits and distributes molecular 

 heat by means of the convection currents so easily set in motion within it. 



3. The temperature of water at its greatest density is 39.1° F. 



4. The temperature both of melting ice and of freezing water (under 

 ordinary conditions) is 32° F, 



5. The specific heat of water is very g-reat. 



As a result of these properties of water, we have water above and 

 Ibelow the ice, and perhaps in some cases distributed everywhere through 

 it The glacial streams erode their banks and walls in a manner peculiarly 

 their own. Water is employed in the hydration of the clay which is formed 

 beneath the glacier. Grlaciers have their drainage systems as truly as does 

 the land, and no other form of stream erosion is so complex. In a word, 

 "we can not conceive of a glacier without its system of waters. The glacial 

 sediments are as important a matter of investigation as glaciated stones 

 themselves, if we are to detect former glacial periods. 



SIZES OF THE GLACIAL RIVERS OF MAINE. 



Many considerations prove that the precipitation over a large part of 

 North America was very great during glacial times. The occurrence of 

 Lakes Bonneville and Lahontan in the Great Basin and the observations 

 of Professor Wliitney in California unite with the facts as observed in many 

 other parts of the country to establish the general conclusion. 



Mr. Walter Wells, in his report on the water power of Maine, ^ pointed 

 out many circumstances favorable to a large average precipitation in the 



' Provisional Keport upon the Water Power of Maine, by Walter Wells, Secretary of the Hydro- 

 graphic Survey, Augusta, 327 pp., 1868, 8°. 



