GEOLOGICAL SUEVEY OF THE TERRITORIES. 229 



At the quartzite-outcrop, about a fourth of a mile west of our camp 

 on Pass Creek, another small creek comes out of the hills by an entirely- 

 distinct canon. Bat, on going up the pass about a half mile, the two 

 caiions unite into one valley, with barely enough divide to separate the 

 streams ; yet these continue distinct and come from very different direc- 

 tions. At this point, a stream -terrace of about 30 feet elevation is very 

 prominent ; but it is not continued out to the main valley. What could 

 have been the conditions under which these two canons were thus formed? 

 Porphyry appears in place high on the mountain-side at several points, 

 and in the stream-bottoms in this junction- valley, but only in the more 

 eastern canon, so far as I observed; so that I inferred that the outflow 

 of the porphyry had stopped up the original eastern caiion, and filled 

 up all the upper valley; that, in subsequent erosion, the new canon had 

 first been worn through the limestones and quartzites to the westward, 

 a terrace-like deposit of sand being meanwhile formed at the head of it 

 by the partially-checked stream; and that afterward, when the new 

 channel had been cut low enough to reach the old-stream gravel, and 

 the iKjrphyry had been eroded from the main valley outside, the per- 

 colation of water through the gravel of the old channel undermined the 

 overlying porphyry and opened the canon auQw for the more eastern 

 stream. 



The porphyry is now so much worn away from the pass that the out- 

 crops of the older rocks can be traced. Above the Quebec group, as 

 in the canons of the Teton range, we see the limestones continuous to 

 the highest summits. At one point, the castellated ruins of the Niag- 

 ara (?) limestone, with their intermediate pine-clad hollows, make a 

 prominent show upon the hill-sides. The Carboniferous limestones, from 

 which a few characteristic fossils were brought by Mr. West, are mainly 

 thin-bedded ; but one heavy bed caps some of the highest points. The 

 pass has very little timber and affords a good road. Yet, the largest 

 trees seen during the whole season stood near the summit of the pass. 

 No notes of their size were taken at the time, but I remember them as 

 about four feet through. They all seemed to be dying. 



On the Madison side of the range, the porphyry, which appears at 

 intervals all through the pass, is replaced by basalt. The broad bottoms 

 are covered with basaltic sand, bearing a thin growth of pines. The 

 streams have in many places bluff banks from 30 to 40 feet high, of vol- 

 canic sand, partially cemented into a loose sandstone. As we pass up 

 the valley the timber becomes more open, and, where not burned over, 

 resembles the artificial grouping of parks, with avenues opening in every 

 direction. There is, however, no turf, the volcanic sand being only 

 sparsely covered with a growth of coarse plants, often including much 

 sage-brush. Through a broad bottom, occupied by numerous beaver- 

 dams, a large stream, carrying perhaps 80 feet of water, comes in from 

 the south, which was afterward traced by Mr. Bechler to its source in 

 the mountains, where it grows rapidly from the large springs characteristic 

 of the porous volcanic sandstone. The Madison itself was carrying 

 possibly 200 feet of water, sometimes thinly spread out in a broad chan- 

 nel, sometimes narrow and deep, with dangerous holes. Trout were 

 shy and appeared to be few. Antelope and black-tailed deer were seen 

 in considerable numbers in this park-like region, which continued up to 

 the mouth of the upper canon of the Madison. 



The cafion is narrow, with lofty cliffs on either hand, running up to 

 800, 1,000, and 1,200 feet at different points. Passing up the north 

 bank, our trail lay for much of the distance along the edge of the river, 

 On the steep cfe6ris'-slopes of the mountain. The cliffs consist mainly of 



