Douglass : A Geological Reconnaissance. 249 



the foot of the steep western slope of the mountains, lying stretched 

 out like a relief-map, checkered with pastures, meadows, fallow land, 

 and rich fields of grain, and traversed by wood-fringed streams, is one 

 of the most productive spots in the west, the far-famed Gallatin Valley, 

 North of this valley is a broken country, south is a maze of rugged 

 mountains reaching to the horizon, and on the west, range beyond 

 range of mountains gradually fade away toward the horizon until they 

 blend with the sky. These mountains are composed of rocks, which 

 vary in age from the gneisses of the Archaean epoch, to strata of Cre- 

 taceous times. The foot-hills are sometimes composed of older rocks, 

 principally Cretaceous, but great portions of the valleys have been 

 filled, sometimes to a depth of several hundreds of feet, with later 

 Tertiary deposits, in which in some places have been imbedded the 

 bones of a few of the many mammals, which have successively occupied 

 this region for many hundreds of thousands of years. 



After leaving Bozeman, a pleasantly located town on the East Gal- 

 latin River in the eastern part of the Gallatin Valley, the train passes 

 for about twenty-five miles through the poorer portion of the valley to 

 the small town of Logan, where the railroad branches, one line going 

 through Helena and the other through Butte. Logan is situated in a 

 narrow portion of the Gallatin Valley just before it expands into the 

 large flat, where the streams of the Gallatin from the east, the Madison 

 from the south, and the Jefferson from the southwestward unite to 

 form the Missouri River. 



The greater portions of the river valleys in this region have been 

 excavated in Tertiary rocks, the remains of which form bluffs, benches, 

 and quite large, nearly level, or undulating plains. These later Ter- 

 tiary deposits in their turn occupy old river valleys, which in Eocene 

 times had been eroded in Mesozoic and older rocks. 



The Gallatin, Madison, and Jefferson rivers unite in the northern 

 portion of the valley, and the Missouri River, which they form, starts 

 on its northern course through a canon in the Palaeozoic rocks. This 

 river, like other streams in western Montana, ignoring to a great 

 extent the old valleys made by Eocene streams, carves its way through 

 soft clays, incoherent sands, and gravel of Tertiary age, through Meso- 

 zoic sandstones. Palaeozoic limestones, Algonkian shales and quartzites, 

 and through lava-flows, with apparent indifference. It first flows 

 northward for about twenty miles through a cafion carved in Palaeozoic 

 and Algonkian rocks, then for about sixty miles plays at "hide and 



