GEOLOGICAL SURVEY OF THE TERRITORIES. 31 



Eange east of the source of the Gallatin Eiver, although the ridge con- 

 tinues on eastward, or south by east, to an unknown distance. 



The Carboniferous limestones are always well defined, not* only by 

 their texture, but from the fact that thej'' always contain fossils charac- 

 teristic of that age in greater or less quantities. In some localities 

 strata of considerable thickness are made up of an aggregate of fossils 

 in a fine state of preservation. The almost universal distribution of 

 these fossils would point to a uniform moderate depth for the waters of 

 the Old Carboniferous ocean. 



The Lower Caiion is about three miles in length, and the Yellowstone 

 has cut its way through the ridge at right angles, so that as complete a 

 section of the strata is shown on either side as one could desire. It was 

 this limestone ridge that checked the waters above which formed the 

 lake-basin, extending from the Lower Caiion to the Second Canon, 

 a distance of about thirty miles, and it was undoubtedly the slow wearing- 

 out of the channel or canon through the ridge that gradually drained the 

 lake-basins above. After leaving the Gallatin Eange, the older group of 

 beds, which we have called Lower Silurian, ceases to be as conspicuous. 

 The limestones of this group have a much older look, are more compact 

 and contain a greater per cent, of silica, are full of cavities lined with 

 crystals of quartz, and weather into much more rugged forms. The 

 lower portions, instead of being composed of clays, shales, sandstone, 

 <&:c., are quartzites or quartzose sandstones, entirely destitute of any 

 traces of organic forms. They seem gradually to change their chara(5ter 

 and thin out very much in their eastern extension, so that not more than 

 100 or 200 feet in thickness rest upon the gneissic rocks in the Yellow- 

 stone Eange east of the Lower Caiion. In the West Gallatin Canon the 

 same change in the Silurian group is observed. 



Above tlie caiion the Yellowstone Valley expands out to an average 

 width of ten miles, and was undoubtedly one of the old lake-basins 

 peculiar to the West. From any of the peaks of the Yellowstone Eange 

 on the east side, one may obtain a complete view of the eastern valley, 

 and the landscape thus presented to the eye is one of great beauty. 

 The sides of the valley slope like a dish, so that the immediate base 

 may be 800 to 1,200 feet above the bed of the river. These slopes are 

 grassed over, and to the eye at a distance they appear as smooth as a 

 lawn, gradually descending to the river-bottom. They are, however, 

 oftentimes very much cut up by the little mountain-streams that wear 

 deep channels through them. These channels afibrd excellent sections 

 of the-e modern deposits. 



On the east side of the Yellowstone Eiver, commencing near the Lower 

 Caiion, is one of the most symmetrical and beautiful ranges of mount- 

 ains in Montana. Id order that I might obtain a more definite knowl- 

 edge of the structure of this range, I ascended one of the highest 

 peaks that overlook the broad plains along the Yellowstone to the 

 northeast. Last year I had supposed, from an examination of Emigrant 

 Peak and its vicinity, that these mountains w^ere mostly of igneous ori- 

 gin, but found, on a more careful examination of the northern por- 

 tion, that the rocks are iirincipally granitic and of the kind characteristic 

 of the mountain-ranges generally. Our camp was located on the river- 

 bottom about three miles above the Lower Canon, and the peak which 

 we ascended is situated a little south of east of the caiion. For a dis- 

 tance of four miles we ascended the grassy slope, covered here and there 

 very thickly with roimded bowlders, which greatly impeded traveling • 

 scattered here and there are isolated hills of limestone, remnants left 

 after the erosion of the valley. The sides of these mountains are every- 



