, GEOLOGICAL SURVEY OF THE TEREITOEIES. 57 



second canon, noting, step by step, the principal features of interest. 

 We have attempted to describe the lower caiion, the valley above as 

 far as the mouth of Trail Creek, and the magnificent range of snow- 

 mountains, of which Emigrant Peak forms a part. From the upper jjor- 

 tion of the lower canon to Trail Creek is about five miles ; and from the 

 mouth of Trail Creek to Bottler's Eanch, ten miles ; and from the latter 

 place to the second canon, about twelve miles. We have stated that this 

 valley was one of the lake-basins that formed a series of chain-like links, 

 extending probably throughout all the great hydrographic basins of the 

 West. A little above Trail Creek, on the west side of the Yellowstone, 

 there is an exposure of Carboniferous limestones, 200 to 300 feet thick, 

 occupying only a small area, but enough to show that the sedimentary 

 . beds extend under the vast mass of basalt and breccia. On the road 

 across the broad upland bottoms of the Yellowstone, a number of fine 

 streams, six to ten feet wide, which have their origin in springs at the 

 base of the range of mountains on the west side, flow across the table- 

 like bottoms, almost on the surface, overflowing in many places, 

 so that they form natural acequias. There is so little channel 

 that they are quite noticeable. Basaltic bowlders of immense size 

 are scattered all over the plain, and the finer detritus forms the cov- 

 ering of the entire surface. Some of these bowlders stand out in the 

 plain far from any water at the present time, and are six to ten feet in 

 diameter. It is possible that water alone has been the agent that has 

 moved them to their present position, by slow degrees, at some period 

 far back in the past, but it is also possible that ice may have aided in 

 the work. 



From the mouth of Trail Creek to Bottler's Eanch, the modern 

 basalt makes its appearance on the west side of the valley from time 

 to time. In some localities it is quite prominent and breaks off in reg- 

 ular columns. It is possible that this sheet or floor of basalt extended 

 all over the valley at one time, as the appearance of the portions that 

 are now left would seem to indicate. If so, the disintegration and 

 removal of the basalt must have been very great. This basalt is visible 

 in greater or less force all the way up to the foot of the second canon, 

 and on the east side of the Yellowstone there is a bluff wall, cut by the 

 river, which shows, at the top at least, three different beds of basalt, 

 indicating as many different outflows. Underneath the basalt are 100 to 

 150 feet of light-gray marly sand and sandstone, clearly belonging to 

 the modern lake deposit. These are the rocks which may be said to 

 fofm the valley proper — first, the Pliocene, or lake deposits ; secondly, the 

 broad sheet or floor of basalt ; thirdly, the detritus, or local drift. On 

 the sides of the main valley, and sometimes intrenching upon it, are the 

 materials of the volcanic breccia, which must have been thrown out of 

 fissures and vents in the mountain ranges on one side of the valley or 

 the other, or perhaps both, into the waters of the lake, and then re- 

 arranged and cemented together. If we delay a moment, and study this 

 basaltic breccia on the east side of the valley just back of our camp at 

 Bottler's Eanch, we shall be able to form some conception of its char- 

 acter. We find here, that the foot-hills are entirely composed of it 5 and 

 as the erosion has in some instances cut some excellent sections in it, it 

 is- easily studied. The general hue is the usual somber-gray or brown 

 of most igneous rocks, but still there are a great variety of colors ; some- 

 times there are thin seams of milky-white and cream marly clay, then 

 a mixture of materials which, when disintegrated, leave debris like the 

 ashes of an old furnace ; at other places the rocks have a dull brick-red 

 color, as if the volcanic fires had raged only yesterday. The whole as- 



