
GLACIAL PHENOMENA AND SUPERFICIAL DEPOSITS. 259 
598. Dr. Hector concludes from the relations of the drift deposits of 
the west side of the Rocky Mountains with the Cascade Range, that the 
depression there cannot have exceeded about 4,000 feet.* The water 
which stood at this elevation can have been that of the ocean only, and 
though foreign drift is not met with on the Rocky Mountains, or their 
slopes, it is not to be concluded that the sea was free from ice ; for at 
this time the eastern granitic region, which had always been the great 
source of erratics, must have been deeply submerged. Its ponderous ice- 
cap may have maintained itself for some time after the water was 
actually above the level of the rocky substratum, but must ere this have 
succumbed. ’ 
599. Dr. Hayden speaking of regions further southward, where the 
elevated plains of the extreme west are higher, and stretch further 
from the mountains, insists on the same fact. He writes: “ As I have so 
often stated in my previous reports, I have never been able to find any 
evidence in the Rocky Mountain region of what is usually termed a 
northern drift.” + In mentioning the occurrence of terraces on the 
western tributaries of the Missouri, in the Rocky Mountains, he states his 
belief in the common origin of these, and those on the western side of the 
same range, and in the fact that the mountains may have been depressed, 
till only their highest peaks rose above the waters. f 
600. There is no evidence that this period of maximum depression 
endured long, nor that during the re-elevation of the continent, the waves 
acted long at any particular level; and though ice, bearing debris, no 
doubt still encumbered the waters, it does not seem necessary to suppose 
that any important additions to the deposits took place at this time. 
Some beds which may in part be composed of modified and re-arranged 
boulder-clay, such especially as those of the third prairie steppe, and of 
the plateau south of the Lake of the Woods, may perhaps, however, owe 
their present appearance to action at this time. 
601. On the retreat of the sea, each part of the country would again 
become for a short time a shore-line, and the rivers and streams on the 
emergence of the land, appear in most cases to have resumed their former 
channels, and began to re-excavate their beds in the drift material with 
which they had been filled. At one period, as Dr. Hector has pointed 
out, a great bay must have existed, bounded southward and westward by 
the curved line of the Coteau and third prairie escarpment, and north- 
* Exploration of British North America, p. 224. 
+ U, 8S. Geol, Surv, Territ., 1872. p. 85. t U.S. Geol, Surv. Territ., 1870. p. 174. 
