174 GEOLOGICAL SURVEY OF THE TERRITORIES. 



apparently a uniform elevation as far as the eye can extend — formations which, hastily 

 examined, seem no less unmistakably than the former to indicate their shore origin. 

 They are elevated from two hundred or three hundred to six hundred or eight hundred 

 feet above the present lake, and may on careful examination afford the means of de- 

 termining the character of the sea by which they were formed, whether an internal 

 one, subsequently drained off by the breaking or wearing away of the rim of the basin, 

 or an arm of the main sea, which with the continent has been elevated to its present 

 position and drained by the successive steps indicated by these shores. 



These terraces seem to be a marked feature of the valleys of streams 

 on both sides of the Rocky Mountains. In the valleys of the Missouri 

 River and its tributaries, even the smallest branch, they are to be seen 

 more or less conspicuous. Professor Dana describes them with much 

 care, as universal on the Pacific coast. So far as those terraces are con- 

 cerned which occur on the Pacific coast and the eastern slope of the 

 Rocky Mountains, I believe they have a common origin ; but the ter- 

 races of this great inland basin might be synchronous or quite independ- 

 ent of the others. Still, as both must have been formed near the close 

 of the quarternary period, constituting the last act in the drama, we 

 might consider them all as having a common origin. If we were to ex- 

 amine the whole country west of the Mississippi, the broad plains of the 

 eastern slope rising gradually to the foot of the mountains and to the 

 very summits of the loftiest ranges, descend into the plains on the oppo- 

 site side, and explore the valleys of the inland streams, the parks and ba- 

 sins, we shall find everywhere, to a greater or lesser extent, the proofs of a 

 very modern drift deposit, or that among the latest events in the geo- 

 graphical history of our continent is the evidence that it was nearly or 

 quite submerged with water. Some of the highest peaks may have pro- 

 jected above the almost universal sea of waters ; but the tops of the 

 highest mountains, as the Wind River, Big Horn, Uinta, show the drift 

 boulders at an elevation of twelve thousand feet above the sea. So far 

 as my own observations are concerned, all the evidences I have been able 

 to detect show that the superficial or quarternary deposits of the West are 

 of local origin. In the vicinity of the mountain ranges the proofs of the 

 origin of the vast mass of the boulder drift is very apparent. The hills at 

 the base of the mountains are often covered with masses of rocks, usually 

 out slightly worn. And as we recede from the mountains these rocks 

 become smaller and more worn, until far out in the plains they are re- 

 duced to mere pebbles. But it is in the inland plains and parks, as 

 Laramie Plains, the Great Salt Lake Basin, North, Middle, and South 

 Parks, &c, that the greatest exhibition of this local drift action is best 

 shown. In the Missouri Valley, and especially north in Minnesota and 

 Dakota, these stray masses are scattered in the greatest profusion all 

 over the surface of those broad, treeless plains. The character of the 

 rocks themselves shows that they came from the mountains. Sometimes 

 these rocks are strewn in belts across the country, taking a uniform 

 direction. North of the Missouri River, from the Big Sioux River to 

 Fort Clark, there are districts where one might walk for miles ncross 

 the plains and over the hills without stepping upon the ground, so 

 closely paved is it with worn or partially-worn boulders. The cele- 

 brated Coteau de Prairie was no doubt outlined by these drift forces, and 

 scattered over the hills are masses of these rocks. The accompanying 

 figure 17 will convey an idea of a strip of country whicli forms a sort of 

 water divide between the drainage of the Missouri, Mississippi, and the 

 Red River of the North. 



As we have previously remarked, we believe that the quaternary 

 period, although more difficult to study, will be found to be scarcely 

 second in importance to any of the previous great epochs in g ology. 



