r^^o 



08 GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 



pect IS moderu, and one feels, as lie winds Ms way among these high 

 basaltic hills, that he is in a region where the great volcanic forces 

 which have given form to this entire region, ceased at a x>eriod so recent, 

 that a recnrrence of the same events might be looked for at any time. 

 Indeed, earthqnake-shocks have been felt in the vicinity of Emigrant 

 Gnlch several times since the discovery of gold there in 1864. Immense 

 masses of the basaltic breccia have fallen down from themountains among 

 the foot-hills ; and in the valley some of the included masses are slightly 

 worn, as if they had been roUed about in the waters for a time, but 

 most of them are angular; some of them are red, like pumice, 

 others black, compact, close in texture, like obsidian. There is, indeed, in 

 this breccia almost every possible variety 01 basalt. The cement is rather 

 firm, resisting the atmosphere well, looking much like volcanic ashes. 

 Scattered through the bottoms and on tbe sides of the hiUs are quite 

 abundant gneiss bowlders, some of them of gTeat size, and most of them 

 considerably worn. 



From Fort Ellis to within a mile of the foot of the second caiion 

 not an exposure of the metamorphic rocks was seen on the right 

 or west side of our road; and, after leaving Trail Creek, the igneous 

 rocks arose 2,000 to 2,500 feet above the valtey, and some of the higher 

 l^eaks were at least 3,000 feet above the plain As soon as we reach the 

 foot of the second caiion, we find the mountains are made up of the 

 same granitoid rocks. Two of the streams that flow down from the 

 divide, that must have their sources at least ten or fifteen miles in the 

 heart of the mountains west of the river, have brought down in their 

 channels detached portions of the granitic rocks, showing that the cen- 

 tral mass of the range between the second caiion and the sources of 

 the west branch of the Gallatin is metamorphic. The size, abundance, 

 and position of these rounded granite bowlders are such that no forces 

 now in operation in this region could have moved them high up on tbe 

 sides of the valley, where no water is found or can reach at the present 

 time. They cover a space a mile in length and one-fourth of a mile in 

 width, as thick as they can lie on the ground. 



I have already referred to the section of the foot-hills cut by tbe 

 Yellowstone Eiver, about a mile above Bottler's Eancli, and that this 

 section would seem to show the thickness and character of the original 

 lake deposits. From the water up there is about one hundred feet of a 

 light-cream marly, indurated clay, with some concretions, from a few 

 inches to two feet in diameter. Above this there are 40 feet detritus, 

 composed of rounded pebbles, and above this very modern local drift, 

 there are 30 to CO feet of the basalt. This fact shows the very modern 

 character of this outflow, as I have endeavored to show in other por- 

 tions of this report. Just opposite this bluff", on the west side of the 

 valley, there is another feature which is quite a conspicuous one in the 

 landscape. There is here a series of terraces, five in number, which 

 rise, step by step, with remarkable regularity. The usual terrace Sys- 

 tem is undeveloped in this valley ; but in this locabty there is a series 

 of regular steps, rising about 200 feet above the channel of the river. 

 They probably belong to the system of terraces that was formed during 

 the period of drainage of these mountain lakes ; but why they should 

 be divided in so marked a way as at this point I could not explain. 



Before closing this chapter, I will note, very briefly, some of the re- 

 sources of this valley. It is about fifteen miles long, and will average 

 three miles in width ; is well watered, soil fertile, and in every respect 

 one of the most desirable portions of Montana. We may not look for 

 any districts favorable for agriculture in the Yellowstone Valley above 



