GEOLOGICAL SURVEY OF THE- TERRITORIES. ' 75 



Range is the central and the largest one. On the east side, between 

 the Gallatiu Eange and the intermediate valley of Shields's River, there 

 is a belt of country ten to fifteen miles in width, made up of Cretaceous 

 and Tertiary beds, with an unusual somber brown color, as if they had 

 been affected more or less by heat. Here and there are iudications of 

 the effusion of basalt, usually in the form of a dike, without generally 

 affecting to any great extent the position of the sedimentary strata, but 

 sometimes throwing them into various positions. The highest hills are 

 from 800 to 1,200 feet above the surrounding country, but descend west- 

 ward in step-like ridges. The belt is exceedingly rugged from the nature 

 of the upheaval, the beds having beenlifted up at var.ous elevations; but 

 in addition they are cut down in every direction by the little streams 

 that How into Shields's River on one side and into the Gallatiu on the 

 other. A large portion of this belt is covered with thick pines, with 

 patches of asi)en, and the remainder thickly grassed over, forming most 

 excellent pasturage for stock of all kinds.. In the valley of iShields's 

 River are hundreds of excellent farms, which would long -since have 

 been taken up by farmers had it not been for fear of hostile Indians. 



The Flat-Head Pass is the great thoroughfare for the Flat-Head and 

 Baunack Indians on tlieir way to the buffalo-districts on the Muscle- 

 shell, Missouri, and Lower Yellowstone. The hostile Sioux have made 

 several raids through this pass into the Gallatin Valley, nuirdering the 

 settlers and running off' their stock. The illustrative-section which was 

 taken at Flat-Head Pass shows the situatiou of the range with great 

 clearness. Passing along the west base of the range from Flat-Head 

 Pass to Fort Ellis, we find the slope from the Gallatiu River to the im- 

 mediate foot of the mountains dotted with cultivated farms. Where the 

 superficial deposits are cut through by the numerous small streams, a 

 great thickness of the modern lake-deposits and drift is exposed. lu 

 some instances the modern beds are hardened iuto a calcareous sand- 

 stone that is used for buildiug purposes. These de[)Osits jut up against 

 the sides of the mountain in such a manner that the old shore-line is 

 distinctly marked. From Flat-Head Pass to Union Pass, a distance of 

 about fifteen mile^s, the abrupt foot hills are composed entirely of the 

 Siluriau group, lifted up in such a manner as to incline past a vertical. 

 The character, as well as the order of superposition of the beds, must 

 be the sanje as of those noted along the Gallatiu a few miles below, but the 

 hills are so covered with detritus and grassed over that I found it im- 

 possible to obtain a consecutive section. Nearly all the more compact 

 strata crop out at different points, so that the principal beds were de- 

 tected. In Union Pass the streams have worn a passage through the 

 range, so that the strata are well exposed, and we find here underneath 

 the Silurian group a granitic base, as shown in the section. In the mas- 

 sive limestones of Union Pass, which are probably of the Potsdam epoch, 

 there is a singular illustration of jointage, well shown iu Fig. 23, which 

 would at once arrest the attention of the geologist. x\t first, one 

 would be much puzzled to determine the true stratificatiou from the 

 false. It forms a portion of Liberty Peak, which rises about 8,000 feet, 

 and is probably due to partial metamorphic action. The granitic 

 rocks contimie to increase in thickness up to Bridger Caiion, a distance 

 of fifteen miles. Here there seems to have been a less powerful force 

 exerted, so that only the limestones are exposed, and the Cretaceous 

 and Coal strata are found on the summits of the range. Bridger and 

 Bozeman Passes are low depressions in the range. As we* i)ass across 

 the numerous branches of the Gallatin, as they emerge from the mount- 

 ains, we see the Carboniferous and Siluriau limestones inclining from 



