207 



nearly horizontal, while at c e the Jurassic beds present a reversed dip, 

 forming a kind of synclinal valley. At r/ d are caps of volcanic material 

 by the eruption of which these remarkable dislocations of the beds may 

 have been |)roduced. There is here an open valley for a short distance 

 where the Gallatin a<iain flows between high vertical walls of Carbon- 

 iferous limestones witii a dip of iu)t more than 1^ to .'P. These lime- 

 stones are weathered into remaikably pictur(\s(pic ibrms, castles with 

 pinnacles, t^urrets, &c. (ireat (piantities of fossils were found lier(* which 

 tixed the age of tlie rocks beyond any doul)t. IMate X is composed of 

 two isolated but very characteristic views of the scenery of this portion 

 of Montana. The upi)er sketch represents with remarkable perfection 

 the forms produced by erosion of the immense volcanic breccia beds 

 about the sources of the Yellowstone. The sketch was taken from a 

 l)oint looking up Sodn Butte Creek, a branch of the East Fork of the 

 Yellowstone. 



This small stream may be followed to its source, near the head of 

 Clark's Fork, between nearly vertical walls of volcanic breccia, stratified, 

 1,500 to 2,000 feet in height. From beneath these mountains of breccia, 

 beds of Carboniferous lin;estones crop out here and there, sometimes 

 only a few feet above the bed of the stream, again rising to a height of 

 several hundred leet. The hundreds of high mountain-i>eaks, 10,000 to 

 12,000 feet elevation above sea level, which form the divide between the 

 Yellowstone Kiver and the sources of Clark's Fork, tStinkingwater, and 

 Grey Bull Kivers, are composed of volcanic breccia, underlaid with Car- 

 bouiferous limestones. 



This sketch may be said to represent a type of most remarkable scen- 

 ery, which covers a large portion of the country about the sources of the 

 I'ellowstone aod the western branches of the Big Horn. Similar forms 

 have been carved out of the breccias and trachyte around the sources 

 of the East Gallatin near Mount Blackmore, of which Palace Butte is 

 an example. A more detailed description of the East Fork and Soda 

 Butte Creeks can be found in the Annual Beport of the Survey for 1872, 

 Chapter III, commencing on page 44. 



The sketch of the terraces of the middle valley of the Madison may 

 be found described in considerable detail in the same rei)ort on page 

 ()2. A more connected view is here ])resented, with the high range of 

 mountains which forms the high divide between the Madison and the 

 West Gallatin Kivers. The middle valley is an expansion or basin about 

 fifty miles in length, and with an average width of five miles. The 

 lower thirty miles presents the most remarlrablc system of terraces 1 

 have ever seen in the ^Vest, and 1 regard them as one of the wonders 

 in this wonder-land. This valley was once the bed of a lake, and the 

 Lacustrine (h'i)osits lap on to the base of the mountains at an elevation 

 of about 400 or 500 feet above the bed of the river. The surface of the 

 terraces is composed of superficial drift or the usual (^>uaternary depos- 

 its of this country. Underneath them, especially at the lower end of 

 the basin, the Lacustrine deposits are seen. 



From our study of the mountain-ranges in Montana, as well as in 

 other portions of the West, it would appear that the outflow of the 

 igneous rocks is synchronous with their elevations. This is especiall^v 

 the case with those ranges which have a granit** nucleus. 



The igneous rocks are of difVeicnt ages. The evidence alxMit the 

 sources of the Missouri and the Yellowstone is that the igneous material 

 was formed more or less through all the i)eriods from the very com- 

 mencement of the general elevation of the country, which culminated 

 in our present mountains. It may not at all times have come to the 



