GEOLOGICAL SURVEY OF THE TERRITORIES. 53 



9,000 to 9,500 feet above the sea. The northwest end of this Snowy 

 Range is formed of roof-shaped peaks, with slopes toward the northwest, 

 and summits running up like a wedge, easily distinguished by their 

 shape from the more symmetrical basaltic peaks in the same range. 

 Separated by an interval of about twenty-five miles to the northwest, 

 tbere is a beautiful group of conical p^aks, 9,000 to 10,000 feet high, 

 occupying an area of not more than fifteen miles square, called Crazy' 

 Woman Mountains ; I did not visit them, but I should judge that they 

 might be a local upheaval on the same line of fracture with the Snow}- 

 Eange. The two ranges are entirely separate, and each independent of . 

 any other, and surrounded by sedimentary formations which incline from ', 

 their sides at various angles. The valley, or park, as it might be called, 

 below the canon, is extremely beautiful to the eye, as all these oval 

 valleys are. The same proofs of an old lake basin, which we have before 

 described, are seen everywhere, with gray and cream marls and sands, 

 with great quantities of local drift, and the step-like terraces are well 

 shown ; there is a uniformity not only in the materials, but also in the 

 deposition of them, which must show an intimate connection and a com- 

 mon origin. The canon is about three miles long 5 the river has cut its 

 way through the limestone ridge nearly at right angles, forming a- per- 

 fect cross-section, so that the character of the rocks down to the gran- 

 ites maybe examined. On the east side of the Yellowstone, a little above 

 the canon,' the junction of the Carboniferous with the granitoid series 

 may be seen with great clearness. There is no method that I could de- 

 vise to arrive at the exact thickness of the Carboniferous group, but, 

 with the aid of the best data I could secure, I estimated it at 1,500 to 

 2,000 feet. Where rocks are thrown up in such confusion, and the streams 

 cut channels through mountains, forming caiions with vertical walls 

 1,000 to 1,500 feet, the grandeur of the operations will oftentimes pro- 

 duce such an eifect on the mind as to lead to an exaggerated idea of 

 the thickness, but my estimates have been checked so far as possible by 

 the use of the barometer. Passing through the canon, we came into a 

 broad, open valley again, much larger but similar to one already de- 

 scribed. 



We may now return to the valley of Trail Creek. We have 

 already stated that the range of hills on the left or north side of the 

 valley is the ridge of limestone through which the Yellowstone Eiver 

 has carved out its lower canon ; the little stream, therefore, flows into 

 the Yellowstone Eiver just above the canon. As we descend the valley 

 of Trail Creek, we meet with a conspicuous isolated hill of basalt in the 

 center of the valley, the east side bordering immediately on the valley 

 of the Yellowstone. A minute descrij)tion of this hill would apply to 

 nearly all the volcanic phenomena of the Yellowstone Valley. It will be 

 seen, therefore, that it is not only important, but necessary, to repeat 

 the substance of many of our descriptions from time to time, in order 

 to do any kind of justice to the subject. Basalt Butte is about 800 feet 

 in height above the plains below, and overlooks the valley in every di- 

 rection ; it is evidently a huge mass cut off by Trail Creek Yalley from 

 the volcanic range on the south side. The huite is composed of volcanic 

 conglomerate, or breccia ; that is, the matrix is a steel-gray volcanic 

 sand and dust, slightly calcareous, inclosing fragments of igneous rocks 

 of varied character and texture. These inclosed masses vary in size 

 from an inch to several feet in diameter; in most cases they are angu- 

 lar, and the aggregate 1 have called a breccia, but in this htitte, and in 

 some other localities, the masses are more or less rounded by attritioa 

 in v/ater, showing that they have been transported some distance from 



