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Show 207 idA nearly horizontal, while at c c the Jurassic beds present a reversed dip, forming a kind of synclinal valley. At d d are caps of volcanic material by the eruption of which these remarkable dislocations of the beds may Jkave been produced. There is here an open valley for a short distance Sphere the Gallatin again flows between high vertical walls of Carboniferous limestones with a dip of not more than 1° to 3°. These lime- /^ Stones are weathered into remarkably picturesque forms, castles with '^ pinnacles, turrets, & c. Great quantities of fossils were found here which i/ yMxed the age of the rocks beyond any doubt. Plate X is composed of llt | wo isolated but very characteristic views of the scenery of this portiou r^ if Montana. The upper sketch represents with remarkable perfection yu& forms produced byerosiouof the immense volcanic breccia beds V | bont the sources of the Yellowstqne. The sketch was taken from a v Joint looking up Soda Butte Creek, a braueh of the East Fork of the . A Yellowstone. This small stream may lie followed to its source, near the head of llark's Fork, between nearly vertical walls of volcanic breccia, stratified, ,500 to 2,000 feet in height. From beneath these mountains of breccia, ds of Carboniferous limestones crop out here and there, sometimes 1y a few feet above the bed of the stream, again rising to a height of eral hundred feet. The hundreds of high mountain- peaks, 10,000 to 000 feet elevation abovte sea- level, which form the divide between the Uowstone River and the sources of Clark's Fork, Stinkingwater, and y Bull Rivers, are composed of volcanic breccia, underlaid with Car-niferous limestones. This sketch may be said to represent a type of most remarkable seen- Caly, which covers a large portion of the country about the sources of the fcllowstoue and the western branches of the Big Horn. Similar forms fere been carved out of the breccias and trachyte around the sources t the East Gallatin near Mount Blackmore, of which Palace Butte is p example. A more detailed description of the East Fork and Soda fctte Creeks can be found in the Annual Report of the Survey for 1872, papter III, commencing on page 44. The sketch of the terraces of the middle valley of the Madison may k found described in considerable detail in the same report on page f. A more connected view is here presented, with the high range of untains which forms the high divide between the Madison and the * v. rf est Gallatin Rivers. The middle valley is an expansion or basin about Iky miles in length, and with an average width of five miles. The Ver thirty miles presents the most remarkable system of terraces I ive ever seen in the West, and I regard them as one of the wonders - j this wonder- land. This valley was once the bed of a lake, and the _ v^ Jk5Q8trine deposits lap on to the base of the mountains at an elevatiou " J. about 400 or 500 feet above the bed of the river. The surfaee of the ^^| rrace8 is composed of superficial drift or the usual Quaternary depos- _ j j of this country. Underneath them, especially at the lower end of ^^ Ibasin, the Lacustrine deposits are seen. VWrom our study of the mountain- ranges in Montana, as well as in ^ per portions of the West, it would appear that the outflow of the _'_ ieous rocks is synchronous with their elevations. This is especially - I case with those ranges which have a granite nucleus. _ X_ f he igneous rocks are of different ages. The evidence about the trees of. the Missouri and the Yellowstone is that the igneous material m formed more or less through all the periods from the very com-r jfMerorot of the general elevation of the country, which culminated 1 1 pur present mountains. It may not at all times have come to the PI I \ > |
