GEOLOGICAL SURVEY OF TflE TEERITOEIES. 7o 



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

 the Galhitiu Eange and the intermediate valley of Shields'sEiver, there 

 is a helt 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 indications 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 SOO 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 been lifted up at various elevations; but 

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

 that flow into Shields's Eiver oh one side and into the Gallatin on the 

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

 patches of aspen, and the remainder thickly grassed over, forming most 

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

 Eiver are hundreds of excellent farms, which would long since have 

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



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

 Bannack Indians on their 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, murdering the 

 settlers and running off their stock. The illustrative-section w^hich was 

 taken at Flat-Head Pass shows the situation 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 Gallatin Eiver to the im- 

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

 sui^erficial deposits are cut through by the numerous small streams, a 

 great thickness of the modern lake-deposits and drift is exi>osed. In 

 some instances the modern beds are, hardened into a calcareous sauil- 

 stone that is used for building purposes. Tl^ese deposits 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 miles, the abrupt foot-hills are composed entirely of the 

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

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

 be the same as of those noted along the Gallatin a few miles below, but the 

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

 possible to obtain a consecuti^^e section, l«^'early 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. At first, one 

 would be much puzzled to determine the true stratification from the 

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

 and is i)robably due to partial metamorphic action. The granitic 

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

 of fifteen miles. Here there seems to have been a less povrerful 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 pass across 

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

 ains, we see the Carboniferous and Silurian limestones incliniug from 



