802 WALLACE W. ATWOOD 
elevation above the stream bed for several miles up the canyon from 
the terminal moraines, until, near the basin region, the canyon walls 
become too steep to permit the lodgment of loose débris. The eleva- 
tion of the lateral moraines indicates that the ice in many of the 
canyons was but 600 or 700 feet thick, but where the larger glaciers 
existed the ice was from 1,500 to 2,000 feet thick, and in one case 
2,500 feet thick. ‘The extensive terraces extending down stream from 
the terminal moraines are remnants of valley trains deposited by the 
waters associated with the glaciers. 
POLISHED AND STRIATED SURFACES 
The polished and striated surfaces of bed rock are restricted 
almost exclusively to the basin regions. In the areas where the drift 
is scarce, striae, grooves, polishings, and roches moutonnées are 
common. Square miles of bed rock are exposed in the higher por- 
tions of the range, where the signs of ice action are beautifully shown. 
In many of the passes in the main crest-line, glaciated surfaces appear. 
Striae have been found as high on some of the peaks as any other 
signs of ice action, and about the marginal portions of the basin 
regions ice action is often recorded both in glaciated surfaces and ice- 
gouged basins in the hard quartzite rock. A few striated rock 
surfaces have been found deep in the Senay O18 and on benches or 
shoulders on canyon walls. 
INFLUENCE OF GLACIATION ON DRAINAGE 
The hundreds of glacial lakes and marshes indicate, especially in 
the basin region of the range, how generally the drainage has been 
modified by the ice. Scarcely a basin exists where waters are not 
yet ponded by the morainic deposits or retained in rock basins gouged 
out by the ice. In a few cases tributary streams in unglaciated 
valleys have been ponded by lateral moraines of a main canyon. 
Terminal and recessional moraines have in some canyons blocked 
the courses of the main streams and caused the formation of chains 
of lakes. At the close of the glacial period such chains were much 
more common than they are today, but in their places are chains of 
meadows, separated from each other, as the former lakes were, by 
morainic ridges. ‘There are now more than 550 glacial lakes among 
