74 GEOLOGICAL SURVEY OF THE TERRITORIES. 



deposits, with here and there a lar^e amount of modern drift. The 

 surface is covered with water-worn bowlders, the remains of the last 

 acts in the drama. I have so often called attention to these very- 

 modern drift-deposits that it is only necessary to state that they 

 cover the entire surface of the country, except the summits of the high- 

 est peaks. The origin of the forces that transported these bowlders 

 and scattered them over the surface in this irregular manner will be 

 discusjsed in another place. The details of the structure of the Gallatin 

 Eauge are numerous, and could be best presented by an account of the 

 different routes traveled in exploring it, but I will only describe the two 

 sides in general terms. The range itself is i)iobably a monoclinal, that is, 

 it is an elevated ridge with the strata all inclining in the same direction, 

 and th(? position of the opposite portion is not yet known with certainty. 

 The older beds on the west side have a marked reversed dip, but the* 

 central beds of limestone are nearly vertical, while the Jurassic, Cre- 

 taceous, and Coal strata, inclining at various angles from 5° to 5(P, 

 gradually descend in step-like ridges from the summit of the range to 

 Shields's River, eastward a distance of about fifteen or twenty miles. The 

 aggregate inclination seems to be about northeast. Bridger Creek, near 

 the Union Pass, flows southward along the east base of the main ridge 

 for about ten miles, and bends around, wearing a very deep canon 

 through the south end of the range througli the limestones, and enters 

 the East Gallatin about five miles below Bozeman. The Jurassic beds 

 are crushed together in the uplift to such an extent that they are quite 

 obscure, and do not appear to much advantage, but in Union and Flat- 

 Head Passes they are much better exposed, but the Cretaceous and Coal 

 gi'oups are enormously developed, reaching an aggregate thickness of 

 more than 10,000 feet. By the Coal group I always mean the series "of 

 beds which are probably Cretaceous in i)art, passing up into Lower Ter- 

 tiary and containing the coal-beds of the West. The axis of the Gal- 

 latin Range is somewhat zig-zag in its trend. The great mass of the 

 mountain inclines eastward or northeastward, but bends abruptly west 

 in two or three places, forming interesting passes, as Union and Flat- 

 Head Passes. The outcropping edges of the limestone-strata have 

 been rounded off by atmospheric agencies, yet for a wide belt along the 

 very summit each layer is clearly shown, like irregular bands from one 

 end of the range to the other, a distance of about twenty-five miles. 

 The highest peak, whicii is nearly 9,000 feet, shows the upturned 

 edges of the limestone-laj^ers most clearly. As I have before remarked, 

 the central mass aiul the highest portions are those whi(;h seem to have 

 resisted erosion best. These beds are usually nearly vertical in posi- 

 tion, seldom inclining past a vertical, while the Silurian group has a 

 reversed inclination Irom 5° to 15°. On the west side of Union Pass 

 the underlying granitoid rocks are exposed, dipping in the opposite di- 

 rection, as if in the uplift there had been forces acting not only vertically 

 but tangentially. The Silurian group is exposed on the foot-hills, vary- 

 ing from 800 to 1,200 feet in height from Bridger's Pass across to a 

 point about five miles north of Flat-Head Pass, a distance of nearly 

 twenty miles. The consecutiveness of the beds is much obscured by 

 the great thickness of detritus and grass, but the rocks crop out all 

 over the hills, so that they can be studied with confidence. Then we 

 know that they are only an extension southward of the same group of 

 beds which is so admirably well shown along the Gallatin, and which has 

 been descril*)ed in a previous portion of this chapter. From the Mis- 

 souri River southeast to the Yellowstone River, there is a series of 

 rather low, broken ranges of mountain-ridges, of which the Gallatin 



