GEOLOGICAL SURVEY OF THE TERRITORIES. 55 



camped the niglit of August 21 in a very romantic place, at the junc- 

 tion of Gibbon's Fork with the Madison. Gibbon's Fork is a beautiful 

 stream that flows into the Madison on the east side, about 100 feet wide, 

 quite unknown on any of our maps. We have named this stream in 

 honor of General John Gibbon, United States Army, who has been in 

 military command of Montana for some years, and has, on many occa- 

 sions, rendered the survey most important services. 



About half a mile up Gibbon's Fork on the west side are some very 

 interesting hot springs. They are located near the immediate base of 

 the hills that inclose the valley, elevated about 100 feet above the bed 

 of the stream, and cover several acres with their peculiar deposit. The 

 varied colors of the jelly-like substance were fine, and other vegetable 

 forms are abundant. Several quite large streams flow away from the 

 springs in winding channels, with beautifully-scalloped edges. One 

 large spring forms a reservoir about 200 feet long, and on an average 

 50 feet wide. At one end of this reservoir are two orifices, one quite 

 large in mass, two feet or more, boiling constantly. There is also a 

 Small side-orifice. From the sides of the hill" several small hot springs 

 flow into the reservoir along most elegantly-ornamented channels. If 

 it. were not for the greater and more important group of siblings above, 

 this small group would attract much attention at some future period. 

 The old deposit has now become dry, but it was formed into quite large 

 terraces, somewhat like those made by the calcareous springs, with 

 larger reservoirs or pools, instead of the more delicate ones in the 

 Geyser Basin. In the reservoirs and along the channels of the living 

 springs are most beautiful masses or locks of vivid green confer void 

 vegetation, floating in the water lilie locks of wool. Thei'e are several 

 other fine springs, but mostly of low temperature, with the inner surface 

 of the basins covered over with a thick, deep, rusty -yellow, leathery sub- 

 stance, which gives them the look of a tan vat. The rocks on either side 

 of the Madison are trachyte, but apparently arranged in vertical layers, 

 so that the river seems to have worn its channel through them. The 

 rocks appear as if they had originally been formed in horizontal layers, 

 but had been tilted up subsequently into a nearly vertical position ; but 

 it is probable that this slaty fracture is due to some process of cooling. 

 In the canon where the walls rise on either side to a vertical height of 

 800 to 1,400 feet, there is no evidence of any tilting of the rocks of mod- 

 ern date. The valley through tiie canon is about 300 yards wide, cov- 

 ered thickly with small pines. About five miles down the canon on the 

 right side, there are rather imperfect basaltic columns. In one instance 

 a most picturesque arch is formed. On the summit of the canon there 

 is a bed of somber-brown rock that looks like basalt. The lower por- 

 tions, which we have usually called trachyte, probably cooled under 

 considerable pressure and is older, while the basalt is the result of a 

 second outflow under far less pressure, is less compact and yields 

 readily to meteoric agencies. 



After passing through the caGon, which is about eight miles in length, 

 we came out into a vast basin with a remarkable system of terraces on 

 both sides of the JMadison. The river is beautiful in its quiet flow. 

 The water is shallow, clear, and at the bottom the bright vegetation 

 may be seen like little green islands. As we come out of the caijon we 

 have the bold basaltic peaks about the sources of Gardiner's River, 

 extending down between the Yellowstone and the Madison ; on the 

 south is the long, low wooded divide between the waters of the Madison 

 and Snake Rivers, very seldom rising above 7,000 or 8,000 feet; on the 

 west side of the basin is the grand range, which extends on both sides of 



