HOLMES. 1 THE WASHBURN RANGE. 33 



pass and the main peak, and nothing like an analysis of the geologic 

 structure has been attempted. The writer also unfortunately made but 

 little advance over the information previously gained, not, however, for 

 want of effort. 



Our first passage of the range was made on the 6th of September, 

 while en route to the supply camp at the Springs. The storms had effect- 

 ually iDrevented a satisfactory study of the region about the falls and 

 the upper i^art of the canon, and I was glad to get a i)artially clear day 

 to make a panoramic view from Mount Washburn. I was even pre- 

 vented from completing my sketches by the storms of wind and snow, 

 and close geologic study was out of the question. Our second visit to 

 this region was rendered totally fruitless by the heavy snow-storms 

 which finally drove us from the Park. - 



Topographically this range is very simple. A narrow range of rounded 

 crests extends from Mount Washburn to the west for a distance of ten 

 miles ; thence an equal distance to the northward 5 and thence to the 

 east about eight miles, thus forming three sides of a hollow square. 

 Tower Creek drains the inclosed area, jjassingout to the northeast into 

 the Yellowstone. The drainage on the north is into the Yellowstone by 

 Black-tail-deer, Elk, and Geode Creeks ; of the west and southwest, 

 into the East Fork of Gardiner River, and on the south into Cascade 

 Creek and the Grand Canon. The range rests ui)on the floor of the great 

 rhyolite plateau as a base, and has a general elevation of about 9,000 

 feet above the sea and 1,000 above the plateau. 



With the geologic structure of this range I had considerable difficulty. 

 A little additional study at a few points would clear up the obscurity 

 that yet envelops the relations of the various groups of the volcanic 

 Tertiary formations. 



I shall first give briefly the details of my visits. On the 5th day of 

 September I followed the Grand Canon from the falls to the mouth of 

 Sulphur Creek, and thence passed to the west across a broken table- 

 land to the head of the Cascade Creek meadows. The rocks of the canon 

 are mostly compact rhyolites. On the higher parts of the plateau, be- 

 tween the canon and Cascade Creek, there are heavy deposits of Obsid- 

 ian strata. At the point where the trail reaches the base of the mountain 

 there are considerable deposits of drift, composed of the disintegrated 

 rocks of the range. A belt of this drift extends all along the base of 

 the range, and at every point visited obscures the junction of the pla- 

 teau formations with the formations of the mountains. The larger 

 masses of the drift are compact hornblendic trachyte and andesite, 

 such as occur on all parts of the range. The lower slopes are 

 smooth and partially tree-covered. Higher up, dark, gnarled, massive 

 rocks project from the slopes. The first outcrops observed along the 

 trail are within perhaps a mile of the summit of the pass. They seem 

 to consist of stratified eruptive rocks that dip at various angles and 

 have a generally uorth-and-south strike. Beds of compact hornblendic 

 trachyte alternate with basalts, compact conglomerates, and other rocks 

 of poorly-defined species. None of these rocks, however, resemble in 

 the least the horizontally bedded sheets that form the plateau. To the 

 right and left of the pass we have the same formations, with probably 

 some coarse conglomerates and breccias overlying them. In descend- 

 ing the northern slope, in the valley of Tower Creek, the upper 900 feet 

 consist, so far as can be seen, of the same rocks. In the bed of a small 

 branch of Tower Creek, which descends from the northern face of Mount 

 Washburn, we came suddenly upon the horizontal rhyolites, at a level 

 which corresponds very closely with the disappearance of the same 

 3 H, PT 11 



