298 GLACIAL GRAVELS OF MAINE. 



water would find imusual facilities for flowing in almost any direction by zig- 

 zagging along crevases. We can not therefore consider this case typical of 

 the behavior of the subglacial waters under thicker and less broken glaciers. 



We know that the subglacial streams of ordinary valley glaciers must 

 flow approximately parallel to the ice, for the very obvio,us reason that they 

 are confined between the sides of the valleys and can not wander out of 

 them. But such a statement adds nothing to our knowledge of glacial con- 

 ditions and can not satisfy us. We wish to know more of the laws that 

 govern the formation and maintenance of subglacial channels. For instance, 

 in the case of glaciers flowing in meandering valleys, it is well known that 

 the line of swiftest ice flow is a curve more crooked than the axis of the 

 glacier. Are there conditions under which a corresponding deflection of 

 the subglacial rivers takes place along the lines of swiftest motion, or do 

 they follow a less crooked course than the axis of the glacier f This and 

 many similar questions need to be answered observationally before we can 

 understand the drainage systems of existing glaciers, still less of extinct 

 ice-sheets. 



We ma)^ form two A'ery different conceptions of the relation of the ice 

 of the glacier to its waters. 



First, we may consider the ice as static, like the stationary land. The 

 waters falling on the earth cut into it valleys and canyons, as do the super- 

 ficial streams on the ice. They penetrate its pores and crevices, as glacial 

 waters do the snow and ice. They eiilarge the subterranean passages into 

 watercourses like the subglacial and englacial channels, and in both land 

 and glacier these internal channels often overflow on the surface as foun- 

 tains. In short, tlie waters falling on the land, though often employing 

 difiFerent forces, yet in the end achieve substantially the same results as the 

 supei-ficial waters of the glacier. But in all this the land is stationary; it is 

 simply obstructive, holding back the water or modifying its flow by friction 

 or direct pressure. So also glacial ice as static is nothing but an obstruc- 

 tion to its waters. But for the ice the waters would follow the drainage 

 slopes of the land; whereas the ice, by simply standing in the way, often 

 forces the water to follow crevasses or other channels along lines very dif- 

 ferent from the land slopes. In fact, on this conception the ice is simply 

 regarded as a rock and its internal water system a part of the subterranean 

 drainage. 



