GEOLOGICAL SURVEY OF THE TEREITOKIES. 217 



EIVEE SYSTEMS. 



As I have repeatedly stated, and as is well known, the chief divide of 

 the waters is the main ridge of the Rocky Mountains, running generally 

 a northwest and southeast course, separating the waters of the Atlantic 

 from those of the Pacific, consequently giving two general sloj)es, one 

 to the east, the other to the west, modified by lateral ranges, mount- 

 ains, &c. I have already alluded to the north and south course of the 

 minor ranges as modifying the influence of the general slope, crossing, 

 at right angles, the natural direction of the water coming down from 

 the chief divide, turning the minor streams north and south. But there 

 is also another very important modifying feature, which has much to 

 do with giving form to the water-basins and the general course of their 

 water drainage. This is a great transverse divide, which, though not 

 so prominent and perceptible as the great longitudinal one, is equally 

 potent, so far as acting as a dividing water-shed is concerned. 



Starting near the northwest corner of JSTebraska, it runs westward to 

 the northwest corner of ISTevada, making a sharp bend northward along 

 the west boundary of Wyoming, around the upper arm of the Green 

 Eiver Basin. 



By examining a good map, the influence of this almost imperceptible 

 divide upon the water systems of this region will be seen at once from the 

 direction the principal streams flow to reach their respective reservoirs. 

 By crossing the Eocky Mountains somewhat at right angles, it forms four 

 great basins, the one sloping to the northeast, the waters of which are 

 drained by the Upper Missouri, the one to the northwest being drained 

 by the Columbia, the one to the southeast being drained by the Platte, 

 the one to the southwest being double, the Great Salt Lake Basin and 

 the Green River Valley. 



The waters of the northeast and southeast basins reach the Missis- 

 sippi through the same channel, the Missouri. The plains at the base 

 of the mountains in Montana having a much less elevation than those 

 lying along the east base of the range in Wyoming and Colorado, and 

 the distance the waters of the former have to traverse to reach the junc- 

 tion of the two being much greater than that of the latter, it follows 

 that the descent of the former is much less rapid than that of the latter. 

 Hence, we find that while the Plattes have a descent on the plains of 

 from five or six to eight feet to the mile, that of the Missouri east of 

 Fort Benton is only about two feet to the mile. Therefore, while it will 

 be possible, by extensive canals, to utilize the waters of the former 

 streams in irrigating the plains which border them, the same thing 

 would seem to be impossible in regard to the waters of the Missouri, or 

 its chief tributary, the Yellowstone. Possibly something may hereafter 

 be done in the way of raising water by machinery, but this can be made 

 remunerative only at certain points, and to a very limited extent. Hus- 

 banding the water during freshets, when a higher level is reached, may 

 also be practicable, to a limited extent i but I know too little in regard 

 to the rises in this stream to express any opinion on this point. 



Lewis's Fork of the Columbia, (Snake River,) whicli, in the southern 

 part of Idaho, traverses an extensive plain, has a descent of certainly 

 not less than six or eight feet to the mile ; and as the bordering lands are 

 low and comparatively level, there is no apparent reason why its waters 

 may not be utilized to their full extent in irrigating this plain. 



How far the waters of these streams may be rendered useful as a 

 means of transportation, I cannot say. That the Plattes and Snake 

 Eiver, as they now are, are not navigable, is quite certain ; but I see no 



