206 



north and soutli, as will be seen by examination of the map. We will 

 commence at the lower or north end of the caSon, and follow up through 

 the several continuous sections and note the principal points of interest. 

 At c c, the Carboniferous limestones appear with their peculiar tj^pe of 

 weathering. The distant hills are underlaid by the granitic or meta- 

 morphic rocks. The limestones seem to have dropped down so that a 

 fault of some importance exists. These Carboniferous limestones rest on 

 Silurian beds. In Section iSTo. 2, still farther up the caiiou, we find the 

 Silurian arenaceous limestones forming a rugged escarpment at the base, 

 while on the rather rounded hills the Carboniferous limestones crop out. 

 These hills rise about 1,000 feet above the bed of the river. We thus 

 see that the metamorphic rocks, the Carboniferous and Silurian lime- 

 stones, present three quite distinct types or forms of erosion, thus giving 

 considerable variety to the scenery. 



In Section No. 3, Plate V, the Silurian beds overlaid with Carbonif- 

 erous limestones continue and pass over the summits of the hills, while 

 from beneath them rise up the reddish feldspathic quartzites, which 

 have weathered into peculiar sharp pinnacles. The river runs for about 

 three miles through a narrow gorge, with vertical walls on either side 

 rising up a thousand feet or more, beset with these sharp angular pin- 

 nacles. Above this point, the surface features are softened down, the 

 rocks ])artially covered with earth, but cropping out in numerous places. 



On looking at the geological map of Montana, «S:c., prepared from the 

 results of the Survey in 1872, it will be seen that there is a small stream 

 flowing into the West Gallatin on the west side, one branch of which 

 rises in Lone Mountain, and the other branch in the Sphynx. Kear 

 the mouth of this stream, a high ridge of limestone crosses the Galla- 

 tin with a trend about northwest and southeast. On the east side of 

 the Gallatin, the sharp ridges rise up to a height of 1,500 to 2,000 feet, 

 with an inclination 50° southwest. Section No. 5, Plate VI, shows this 

 ridge as it appears on the east side of the river, with the somewhat 

 rounded granitic hills below, on which the limestones lean. The river 

 has cut its channel directly through this ridge, and on the bottom, the 

 worn edges of the upturned shales may be traced across the channel 

 with perfect distinctness. In the section we see the Carboniferous, 

 limestones at b underlaid with Silurian rocks, resting directly on the 

 granites ; and lying against the Carboniferous beds are the Jurassic at 

 c c, and at d patches of Cretaceous, which seem to have dropped down, 

 113 it were, in a sort of Jurassic synclinal. 



The Silurian and Carboniferous, with a portion of the Jurassic group, 

 appear to have been lifted up by a vertical force that broke the beds as 

 if they were layers of lumber. In the depression which seems to have 

 been produced by this movement, the Jurassic and Cretaceous beds are 

 seen ; but at a distance of about tive miles, where, as shown in section 

 No. 6, the Carboniferous limestones rise from beneath the Jurassic in a 

 nearly horizontal position, it would appear that the elevation of the 

 metamorphic rocks, pushing off, as it were, from the sides the sediment- 

 ary beds, produced a depression which formed an excellent reservoir 

 for the drainage of the higher lands around, thus giving origin to a 

 stream of water on both sides of the Gallatin. In the background in 

 section 5, we see the group of volcanic peaks which form the divide be- 

 tween the Gallatin and the Yellowstone Kivers. In section 6, the rounded 

 grassy character of the summits of the hills shows the more yielding 

 nature of the Jurassic beds. It is not certain that the true red beds 

 occur in this immediate vicinity. In section 7, we find another dropping- 

 down or faulting of the strata. At b the Carboniferous limestones are 



