30 GEOLOGICAL SURVEY OF THE TERRITOEIES. 



very abrupt, rising at once to a height of 800 to 1,200 feet, while the 

 peaks and the sharp ridges are 2,000 to 2,500 feet above the valley below. 

 On the east side the hills, composed of the more modern groups, descend 

 gradually to the immediate valley of Shields's River. 



We thus see that this range constitutes the east portion of an anti- 

 clinal, and, so far as we know, a huge monoclinal. We may hereafter 

 discover fragments of the west portion. So far as the line of uplift is 

 concerned, the Gallatin continued southeastward, crossing the Yellow- 

 stone River, forming what we have located on the map as the Lower 

 Canon. The mountains about the sources of the branches of the East 

 Gallatin, and those between the East and West Gallatin Rivers, are 

 largely composed of the limestones thrown up in great confusion appa- 

 rently; but really all having an inclination in the same' general direction.. 



In my report of last year, I stated that there seemed to be a true anti- 

 clinal extending over to the Yellowstone, and that Trail Creek might flow 

 in the valley between the two portions, but the more caieful explorations 

 of the past season have shown that all the uplifts belong to one side of the 

 anticlinal, however chaotic the strata may appear. This great monoclinal 

 is very remarkable. It commences down below the Three Forks, with a 

 trend'east by south, indicating greater irregularity in form. Sometimes 

 the beds are inverted, and the whole series exposed down to the granitic, 

 then again all are concealed except the coal strata. From Bridger CaQon 

 to Spring Caiion, a distance of four miles, there is a complete break in the 

 range, forming several passes, which are easily traversed with wagon- 

 roads, in which no rocks older than the Coal group are seen. Then in 

 Spring Caiion the older rocks are again brought to the surface in full 

 force. 



The investigations of the present season have shown that what appeared 

 to be fragments of the western jiortion of an anticlinal are only frag- 

 ments of the one great mass which have been broken off in the uplift 

 and now lie scattered around in the valleys, on the foot-hills and mount- 

 ain sides, in apparent coniusion. As I have before remarked, the main 

 range of sedimentary beds continues east by south, forming the high 

 divide between the waters of the Gallatin on one side and those of 

 Shields's River and the Yellowstone on the other, but crosses the Yellow- 

 stone, forming the Lower Caiion, and inclining from the east side of 

 the great range of mountains in which the Bowlder, Rosebud, and 

 Clark's Fork, with their numerous branches, take their rise. In the in- 

 termediate space, sometimes low down in the yailey of Trail Creek, and 

 sometimes on the mountain-sides, are beds of coal, the strata above and 

 below being vertical or horizontal, as the case may be. This region has 

 been very carefully prospected for coal. The artificial excavations that 

 were made threw great light on the position of those fragments, which 

 seem to have been broken off and fallen down in the general uplift. At 

 the present time it is only by most carefully following the channels of 

 the streams as they cut down into the sides of the mountains, or by 

 studying the artificial excavations, that we can gain any of the details 

 of structure. With the exception of the main ridges of upheaval, the 

 strata are mostly concealed by modern superficial deposits, which are 

 covered with a thick growth of grass. Occasionally, also, these frag- 

 ments crop out from beneath the mountains of trachyte, and volcanic 

 breccia, which are so remarkable in this region. As previously stated, 

 the limestone seems to have yielded less re«dily to atmospheric agencies, 

 and consequently projects high up above the surrounding hills, and 

 forms the leading topographical feature. In tracing it across the coun- 

 try, we may call it a limestone ridge, as it loses the name of Gallatin 



