GEOLOGICAL SUEVEY OF THE TEREITOKIES. 269 



down stream dips of 17°, appareutly implying great rapidity of current 

 over a. rapid into a deep pool at some former period. 



About two miles below, Salt River also enters the Snake, through a 

 broad-terraced valley, which looks as if it were really the continuation 

 of the lower valley of the Snake. But for misinformation as to dis- 

 tances, we should have explored this valley up to the salt-works before 

 descendiug the Snake. It seems to afford an easy passage thit)ugh a 

 valuable region. The caiion through which we had just come, though 

 having a reputation for very difficult traveling, was passed by us with 

 ease, and really presents but very slight obstacles to building a railroad, 

 if one were desired from this point to Yellowstone Lake or beyond, or 

 merely to give convenient access to the rich basins of Jackson's Hole 

 and Little Hole. Furthermore, a road, reaching this point from either 

 the lower or the upper Bear River Valley, would have then the alterna- 

 tion of passing down the Snake with easy grades to the east side of the 

 valley of Henry's Fork, with the advantage of crossing the river where 

 its channel is narrow and its banks far above any floods. 



The Snake here turns sharply northward into the continuation of the 

 valley of Salt River, with high mountains of Carboniferous limestones 

 on the east, showing some castellated walls, and lower and more 

 rounded ones on the west. Two or three miles below the mouth of Salt 

 River, a small stream from the west was thick with mud from the 

 Caribou gold- washings. 



The valley is here located by an anticlinal fold ; and the nearly ver- 

 tical limestones of its axis are linely exposed along the foot of the west- 

 ern hills. Here, also, is located a cluster of warm springs, making cal- 

 careous, sulphurous, and saline deposits. The largest spring, the 

 Wash-tub, has built up a flaring table, 1 foot high, of an oval form, 

 measuring about 4J by 7^- feet, upon a mound consisting of calcareous 

 mud, scarcely solidified, of from 5 to 7 feet above the creek-bottom in 

 which it stands. The central table has contracted so as to crack across 

 diagonally, and the flow now escapes at its western base, depositing a 

 fine mud tinged in the full pools with a faint sulphur-yellow, but pure 

 white in the dry ones. These pools cover the mound in descending 

 steps of great beauty. The present flow is southward, though it has 

 been on all sides in succession. The deposit on the surface of the 

 mound is still very soft, and showed at the time of our visit (October 6) 

 the tracks of a small bear, who had receutl}' investigated the wonders 

 of the mound, even setting his foot on the central table. One mound, 

 no longer active, is 5 feet high, with a circular base of about 5 feet 

 diameter and an oval summit of about 1 foot by 6 inches. Many small 

 spiiugs escape along the bank for a hundred yards or more. The 

 deposits vary greatly in color. At some points, the odors of sulphurous 

 acid and of sulphureted hydrogen were quite noticeable. The older 

 deposits have built up a bank 10 feet high, along the base of the terrace ; 

 and the beavers have taken possession and have dammed up on it the 

 waters of the cold springs which flow from the second terrace at short 

 intervals along this plain. On the opposite shore, two considerable 

 springs have built up their deposits against the foot of the mountain, 

 one of which appears to be nearly dead. The highest temi^erature 

 observed here was 144°. The \Yash-tub gave 142° and others 142°, 

 140°, 90°, 88°, i&c. 



The deep channel, seen through all the lower part of the canon, con- 

 tituies for several miles down the valley, and fords are at all i)oints 

 much rarer than in the upper valley. The stream is narrower on the 

 average, and the amount of water has been much increased. 



