GEOLOGICAL SUEVEY OF THE TEKRITORIES. 259 



A short distauce sontliwest of Beulah Lakes, over a divide about 300 

 feet high, aud at a level about 100 feet lower, Mr. Bechler found two other 

 small lakes, at the head of a branch of the stream which enters Falls 

 Eiver from the south, just above the Great Falls. The upper one has an 

 area of something over one hundred acres, with rocky banks, aud flows 

 to the lower, which occupies about 40 acres in the center of a marshy 

 basin of perhaps a hundred and forty acres. 



Southeast of these latter lakes, over a divide about 350 feet high, 

 we reach the head of a valley runniug eastward to the main Snake. Its 

 upper portion is a flat basin, about one and a half miles long by a mile 

 wide, bounded on the east and north by from 400 to 500 feet of volcanic 

 rocks, of which the upper 200 feet present a vertical front, while the 

 remainder is mainly covered by a slope of tumbling rubbish down to 

 the stream. The other slopes are rounded, as are also most of those 

 along the lower course of the stream down to its junction with the Snake. 



All this wide area, from these northern slopes of the Teton Eange 

 nearly to the Tyghee Pass aud to the mountains on the north side of 

 the Upper Madison, though actually quite elevated, is relatively much 

 depressed below the summits of the limestone, quartzite, and granite 

 mountains on either side. From the general distribution of the volcanic 

 rocks, as well as from facts observed elsewhere, I am inclined to believe 

 that, before the ejection of these immense bodies of lavas, there was 

 here a broad valley, through which the drainage of the upper mount- 

 ain-region to the eastward found its way out to the great basin of the 

 Snake, while the canon by which it now escapes through the high 

 mountain-mass south of the Tetons had not been cut down. 



Immediately opposite the camp at the mouth of Lake Fork, there is 

 a considerable cluster of dead and dying hot springs. Several mounds 

 indicate the former i^ositions of geysers of considerable size. The temper- 

 atures often springs were taken by Mr. Taggart, varying from 103° to 

 158°. Three were above 150°. The deposits are now rapidly disintegrat- 

 ing. Upon one large conical mound this process had developed a col- 

 umnar or fibrous condition of the g^yserite. Similar spring-deposits 

 also occur on the west side of the river, from one to four miles below 

 this camp, and some of the mire-holes so common in the Fire-Hole 

 basins were also encountered. Upon looking back from below, two 

 large columns of steam were seeu, about a mile up the Beaver-Dam 

 Creek, which seemed to indicate the possibility of geysers still existing 

 there. The lower iDart of that stream was full of puri^le-nacred unios, 

 apparently like, or closely allied to, those found in the branches of 

 Henry's Fork. 



Aloug the east side of the river, the face of the high ridge shows the 

 folio v.iug rocks, according to notes taken and specimens brought in by 

 Mr. Taggart : — At the base lie about 200 feet of white and light-gray 

 quartziies, overlaid by from 500 to 000 feet of light-drab and dark-gray 

 limestones, and about 100 feet of gray sandstones, followed by heavy 

 beds of red, shaly sandstones, apparently the same as those seen higher 

 up the river. I am not satisfied as to the age of either the limestone or 

 the quartzite. The ridge is capped with beds of porphyritic trachytes, 

 having a dip of about 30° to the southeast, while the limestoues beneath 

 dip about 40° in the same direction, showing that their tilting com- 

 menced before the deposition of the trachytes. 



The main trail crosses the Snake about a mile below camp, and 

 passes over the hills so as to cut off a considerable bend of the river. 

 From six to eight miles below the forks, a spur, which runs nearly to 

 the west bank of the river, shows a high bluff face of porphyritic* 



