GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 49 



On the IStli of July we bade farewell to the hospitable officers of Fort 

 Ellis, and with an excellent outfit, for which we were greatly indebted 

 to their kindness, started, with confidence and hope, toward the wonder- 

 land of tbe Yellowstone Valley. We followed a well-traveled road, 

 which wound around among the hills, diverging by numerous branches 

 in almost every direction. After passing behind the main range to the 

 north, we turned our course to the east, up the valley of a little branch 

 of Mill Creek, and soon passed over the divide into the waters of the 

 Yellowstone. The water-shed and the geological divide are by no means 

 identical. The little stream cuts directly through the heart of the anti- 

 clinal, and rises high up in the coal group eaet of the limestones. East 

 of the narrow belt of limestones the coal strata occupy the greater por- 

 tion of the interval to the Yellowstone Eiver. These beds incline at 

 various angles east and northeast. A large quantity of finely preserved 

 impressions of leaves of deciduous trees were found. The texture of 

 the rocks was quite varied, and the examples of oblique lamina of 

 deposition were quite conspicuous. The sandstones were usually quite 

 fine and close-grained, but sometimes they passed into a fine pudding- 

 stone. Interstratified with these rocks are layers of compact basalt, 

 and not unfrequently on the summits of the hills are thick masses of it. 

 It will be seen at once that the dark brown or somber hue of this great 

 group of strata (1,200 to 1,500 feet) is not the original color, but caused 

 by the subjection of the strata to a greater or less heat during the period 

 of volcanic activity. Wherever the igneous matter has come in direct 

 contact with the sedimentary rocks they have been more or less changed. 

 Some of the sandstones have become compact quartzites, but the same 

 dark, gloomy appearance pervades them all. 



From the divide between the Gallatin and Yellowstone Eivers, the 

 view is wonderfully fine in every direction. On the north side the 

 hills rise up 600 to 800 feet. The elevation of the divide over which 

 the road passes is 5,681 feet. The principal range of mountains 

 on the south side is mostly of volcanic origin, and rises 800 to 1,200 feet. 

 The belt of Carboniferous limestone seems to have a trend northeast 

 and southwest, preserving its anticlinal character to the Yellowstone 

 Valley, then, crossing the Yellowstone Eiver, is seen only on the sides 

 of the Snowy Eange, inclining northwest. Although the general 

 character of the geological structure of the country lying between the 

 sources of the Gallatin and the Yellowstone Eiver ajjpears so simple, 

 yet months of earnest labor would be required to work it out in all its 

 details. The distance is yot more than thirty miles. The sediment- 

 ary beds are thrown into almost inextricable confusion. I shall en- 

 deavor to unravel it in pnvt as I proceed step by step on our journey 

 up the Yellowstone. 



It is probable that in general terms the rocks of the country be-- 

 long only to about half a dozen groups, and yet these are so multi- 

 plied into a diversity of forms, and then by subsequent elevation, so 

 mingled together, that at the first glance there seems only confusion; 

 and yet, with the exception of themore.modern volcanic forces, there has 

 been a method in their action. So far as the rocks of Carboniferous and 

 Jurassic age are concerned, we may rely with some confidence on their 

 uniformity of character wherever they may occur, but all the others are 

 modified more or less even in their mineral texture at different localities. 

 For example, on our route from Fort Ellis to the Yellowstone Eiver, a 

 distance of about thirty miles, we find the summits of the highest hills 

 covered with a greater or less thickness of a local drift, and wherever 

 the rocks are shown they appear to belong mostly to the Coal Series, 

 4 a s 



