Douglass : A Geological Reconnaissance. 247 



The land around the base of the mountains, especially the eastern 

 portion, forms an elevated plain, which has been carved into various 

 forms by the streams issuing from the ranges. The different kinds 

 of rocks are exposed, series after series, from doubtful Jurassic to 

 Lower Tertiary, and are inclined in different directions and at various 

 angles, so that erosion has produced a varied topography. 



The streams, carving their way through rocks of different kinds and 

 different grades of hardness, make valleys, which vary from narrow 

 canons to quite extensive flats or plains. Some formations, like the 

 Eagle sandstones, and the Fox Hills or l^ower Laramie sandstones, 

 form ridges, which can be traced eastward or southeastward from the 

 mountains to a distance of sixty miles, and I know not how much 

 farther. Others, like the Pierre shales, form ravines or broad depres- 

 sions according to the degree of dip of the rock. 



From Big Timber to Bozeman. 



Big Timber, which is the county-seat of Sweetgrass County, is 

 built on a large alluvial fan, consisting principally of sand, gravel, and 

 boulders of granite, which have been deposited by Big Boulder Creek. 

 This stream rises in the Granite and Snow mountains, between forty 

 and fifty miles to the soutward, and flows through a rough tract of 

 country. Where it enters the Yellowstone valley, it has during a 

 long period of time deposited its heavy loads of water-worn boulders. 



I do not know that characteristic fossils have been found in the 

 stratified rocks, which form the bluffs on both sides of the river above 

 Big Timber, though I have examined them hastily. They do pot 

 differ much in appearance from those of Fort Union age to the north- 

 ward and northeastward. Farther up the river is a series of beds of 

 considerable thickness, which are in part massive and composed of 

 volcanic breccia, and in part made up of a large series of somber look- 

 ing rocks, which have the appearance of being stratified. These are 

 the Livingstone beds of Weed, descriptions of which may be found in 

 Bulletin No. 105, and in the Livingstone Atlas Folio, No. i,of the 

 United States Geological Survey. 



At Livingstone the main line of the railway leaves the valley of the 

 Yellowstone River and ascends the steep grade toward Mullen Pass in 

 the Gallatin-Bridger range. These are the first mountains over which 

 we pass in our westward journey on the Northern Pacific Railroad. 

 Stretched behind us are the vast plains, elevated in the western por- 



