Near the head of the Third Cañon a stream flows into the Yellowstone from the northeast, bearing the sonorous title, Hell-Roaring River. It is quite a large stream, rising high among the mountains, and flowing with tremendous impetuosity down the deep gorges. The mountains on either side come close down to the channel of the Yellowstone, and are among the most rugged in this rugged region. A huge peak of this sort, composed of stratified gneiss, with deep strata of massive red and grey granite, stands at the mouth of Hell-Roaring River, and takes to itself the same imposing name. A short distance above the mouth of Hell Roaring River, the East Fork of the Yellowstone comes in from the southeast. Its sources are high up among the most rugged and inaccessible portions of the basaltic range, several jagged peaks which rise from 10,000 to 11,000 feet above the sea. "The summits of these high peaks," observes Mr. Hayden, "are all close, compact trachyte, while all around the sides are built up walls of stratified conglomerate. It is plain that all of them are the nuclei of old volcanoes. The trachyte may sometimes be concealed by the conglomerates, but I am inclined to think that each one has formed a centre of effusion. Large quantities of silicified wood are found among the conglomerates, mostly inclosed in the volcanic cement, evidently thrown out of the active craters with the fragments of basalt. My impression is, that when the old volcanoes disgorged their contents into the great lake of waters around, they threw out also portions from the sedimentary formations, and thus the silicified wood comes from the Tertiary or Cretaceous beds, which may have formed the upper part of the walls of the crater. At any rate, these woods belong to the Coal Series of the West, and they are scattered profusely among the conglomerates. Interlaced among the massive beds of volcanic conglomerates are some layers of a light-grey or whitish sandy clay, which show that the whole breccia or conglomerates, with the intercalated layers of clay or sand, were deposited in water like any sedimentary water rocks." Interesting ruins of ancient springs abound in this valley. Mr. Hayden describes one, a very curious mammiform mound of calcareous deposit, about forty feet high, built up by overlapping layers like those of Liberty Cap on Gardiner's River.