TESTS OF SUBGLACIAL OR SUPERFICIAL DEPOSITION. 437 



stream lies approximately parallel to the ice surface EB. As the ice melts, 

 the bed will come to occupy the position of the dotted line and dip beneath 

 the horizontal line AB. A marginal lake will form in front of the ice, just 

 as in the supposed case of a subglacial stream. The melting will be most 

 rapid along the bed of the stream and near the mouth where it enters the 

 lake, and thus the form of the lake will probably not differ much from that 

 when a subglacial stream flows into it. In this broad .channel or lake we 

 might have reticulated ridges or an osar-plain deposited. As the ice 

 retreated toward the bottom of the valley it would seem that the glacial 

 gravel ought to be more abundant in that region than anywhere on the 

 northern slope. It certainly would be so, and of frontal or overwash char- 

 acter, unless the superficial stream forms a glacial lake at some point 

 toward the north, which arrested the transportation of sediments from the 

 north. We can admit transverse escape over the ice to the east or west or 

 around the front of the ice next the hills, but not subglacial or englacial 

 escape, since this would be inconsistent with the supposed conditions, i. e., 



Fig. 33.— Section of valley between Sherman and Springfieia. M, at Macwahoc ; K, at Kingman ; P. at Prentiss. 



ice so stagnant that the crevasses were not sufficient to enable a subglacial 

 tunnel to be formed. This is a large demand to make so near the ice front, 

 but my purpose is to give the theory every possible chance to account for 

 the field phenomena. 



These general principles have been discussed with a view to their 

 application to certain localities. 



The great Seboois-Kingman-Columbia osar system descends the valley 

 of Molunkus Stream from Sherman to Kingman, where it crosses the Mat- 

 tawamkeag River nearly at right angles, and then ascends the other side of 

 the Mattawamkeag basin, through Webster, Prentiss, and Springfield, where 

 it crosses a divide near 200 feet higher than the river at Kingman. This 

 great osar river has left gravels for 40 miles or more north of Kingman, 

 where it crossed the deep transverse valley of the Mattawamkeag. Fig. 33 

 represents the system in this part of its course. The slope of the Molunkus 

 Stream is moderately steep from Sherman to Macwahoc ; then the valley 



