36 REPORT UNITED STATES GEOLOGICAL SURVEY. 



Eange as a gap for the reason that on the east side of the canon there 

 is a low, rounded ridge that seems to be a geological continuation of the 

 Washburn Eange. The canon is everywhere quite abrupt, the walls 

 descending from the general level of the jjlateau to the bed of the river 

 without the interruption of shelves or terraces, yet the slopes are not so 

 steep as to prevent the growth of dense forests over a larger part of 

 their surface. 



The exposed rocks are generally yellowish or brownish in color, and 

 present very regular and continuous walls, Indented by numbers of 

 notches, very few of which cut back far into the plateau. All the 

 tributary streams excepting Jasper and Broad Greeks run upon the 

 upper surface of the plateau, or have but shallow valleys. All of the 

 walls that can be seen from Washburn seem to be formed of rhyolite. 

 In the cliffs about the mouth of the caiion of Broad Creek there are 

 immense walls of yellowish-gray rhyolite which exhibit a marked 

 columnar structure. The neighboring plateau up to the very brink of 

 the canon is densely timbered with the usual pine forest. The northern 

 slopes of Washburn and the southern slopes of Amethyst Mountain 

 beyond Agate Creek present a delightful contrast, however, to the 

 somber forest, and abound in rich, grassy parks. The ujjper surface of 

 the plateau at the falls has an elevation of 8,000 feet 5 at the base of 

 Washburn also 8,000 feet, and between this and a point opposite the 

 mouth of Tower Creek 7,200 feet. The depth of the canon at the base 

 of the Great Falls is 801) feet at the base of Mount Washburn 1,200 

 feet, and at Tower Creek 900 feet. The depth of the canon may be 

 therefore pretty fairly stated as 1,000 feet. The width is almost as 

 uniform as the depth, varying from less than one-half mile to one mile. 

 This caiion is without a doubt entirely one of erosion, and has been cut 

 by the waters of the Yellowstone since the flow of the rhyolites and 

 probably very greatly since the conglomerate-forming era. 



On the 3d and 4th days of September we were in camp on Cascade 

 Creek, near the Upper Falls of the Yellowstone. Heavy rains descended 

 continuously and but little could be done. Early on the morning of the 

 4th a small party, consisting of Mr. James Eccles, an English geologist, 

 Mr. Gannett, Mr. West, andmyself forded theriveratthehead of therapids 

 and proceeded to the brink of the canon, below the Great Falls. About two 

 hours were spent in an attempt to measure the height of the falls. We 

 descended a narrow, crevice-like gulch, and after considerable difficulty 

 in the descent and a very dangerous passage along the face of the slimy 

 walls that hug the torrent, found ourselves at the base of the falls, but 

 such was the force of the whirling spray that we completed our work 

 and retreated in the greatest haste, completely drenched. I should not 

 advise any visitor to attemi)t the passage to this point without the use 

 of ropes, as there is almost no hold for the hands and feet and a single 

 slip on the damp, smooth rocks would j)recipitate him, without hope of 

 rescue, into one of the wildest torrents that the world can show. The 

 falls from below are inimitable, and, taken together with the caiion, 

 form a picture without a rival. The lithologic characters of the caiion 

 walls are very interesting and extraordinary. The formations consist 

 almost exclusively of igneous rocks, which include a very great variety 

 of rhyolites and pitchstones. Oaptain Button describes two specimens 

 in his catalogue, ISTos. 10 and 11. A feature of the walls. below the falls 

 is the occurrence of fragments of horizontal strata which have been built 

 into irregularrecesses and are thus shiehled from erosion. They are gen- 

 erally coarse-grained sandstones or conglomerates and have very much 

 the appearance of the lake beds which occur on the upper surface of the 



