HOLMES.] EAST FORK AND AMETHYST MOUNTAIN. 47 



before reaching the open upland, the materials are mucli coarser, con- 

 sisting frequently of great angular masses of basalt and probably also 

 andesitic and sedimentary rocks. There are also considerable columns 

 of dark and ferrnginous basalt. Geodes of banded agate and chal- 

 cedony are very abundant. The basalts are very abundant on the 

 rather gentle slopes that extend from the trail downward to the canon. 

 The Tertiary strata, however, appear frequently, and even extend down 

 to the bed of the river in a few places. As mentioned before, the river 

 is mostly in the granites, but near Hell Eoaring Creek it is in the con- 

 glomerates. At one point they form a sort of gateway of i)icturesque 

 cliffs. In a number of places the basalts reach down to the river, and 

 in a few instances occur in small bodies on the north side. 



I have not seen this region thoroughly enough to make a good map 

 of it, as the conglomerates, basalts, trachytes, and schists occur without 

 the least regularity. My study of this locality has unfortunately in 

 every case been of the twenty-flve-mile-a-day kind. My knowledge of 

 the caiion between Garnet Hill and the mouth of the Black-tail-deer 

 Creek is limited to the memories of a hurried trip in 1872, and such 

 glimpses as were afforded by a visit to Garnet Hill in 1878. 



One of the most noticeable features of this valley is the occurrence of 

 drift deposits, and especially of huge masses of granite on the various 

 benches about the forks from the river bed to the level of the great 

 plateau 1,000 feet above. These granite masses have doubtless been 

 brought down from the valley of the East Fork, as they correspond in 

 lithologic characters to the massive granites that occur from 8 to 10 

 miles above the junction. Their transportation has begun with the 

 beginning of the erosion of the valleys, and they have been deposited 

 on the various flood-plains formed as the river descended through the 

 rhyolitic plateau and its underlying formations. 



EAST FORK AND AMETHYST MOUNTAIN. 



Tlie valley of the East Fork of the Yellowstone is one of the most en- 

 chanting in the Park. For nearly 20 miles above Junction Yalley it is 

 broad and smooth, abounding in meadows and terraced grass lands. 

 On the north rises the massive range of the Yellowstone Mountains, and 

 on the south the i^eculiarly interesting walls of Amethyst Mountain. 

 Twent.y miles above the bridge the valley narrows up and is pretty 

 densel,^' timbered, but the u])land region about the headwaters abounds 

 in delightful parks. The beds of the various tributary streams are gen- 

 erally in rather precipitous valleys from 500 to 1,000 feet in dei)th. 



The two main tributaries from the north, Slough Creek and Soda 

 Creek, emerge from deep-caSoned valleys, which they have cut in the 

 massive volcanic formations of the Yellowstone Eange. On the south 

 side a dozen or more small streams of clear w^ater descend from Amethyst 

 liidge. 



In the lower part of its course the river is in the granites, which here, 

 as at the forks and belov/, have a strong dip to the east. About 9 miles 

 abovethejunctiona massive stratum of reddish, feldspathic granite forms 

 a low ridge across the valley, this seems to have offered very determined 

 resistance to the progress of erosion. The valley is here more than a 

 mile wide, and the river seems, in times past, to have oscillated from side 

 to side, descending.with great force over the granite ledge, detaching 

 the great bowlders that now appear so plentifully ni all the valleys 

 below. At present the river has cut a deep and narrow passage through 

 this belt of granite far over toward the north side of the valkn'. Above 



