102 GEOLOGICAL SURVEY OF THE TERRITORIES. 



mules to pass over them. Now and then we would come out into an 

 open giade, and start on at a brisk pace with fresh hope, when we 

 would come again to a belt of this remarkable net- work of fallen i)ines. 

 In all our journey we found but two kinds of rock, the black obsidian 

 and the usual trachyte. At one point, soon after leaving camp, we 

 found a most singular natural bridge of the trachyte, which gives 

 passage to a small stream, wbich we called Bridge Creek. There 

 is barely room across it for a trail about two feet wide, which is 

 used only by herds of elk that are passing daily. The descent on 

 either side is so great that a fall from it would be fatal to man or beast. 

 Every few minutes we met with a grouiD of dead or dying springs ; very 

 few of them contain water at the present time, but steam was issuing 

 from hundreds of vents. There was one locality where the deposit cov- 

 ered several acres that presented a most attractive picture. The entire 

 area Avas thickly covered with conical mounds of various sizes, ranging 

 in diameter from a few inches to a hundred feet or more, and these cones, 

 or hillocks, were full of orifices from which steam was issuing. All 

 these little chimneys, or orifices, Avere lined Avith the most brilliant crys- 

 tals of sulphur, and, when the heated crust was removed, we found the 

 under side adorned in the same manner. The basis of the deposit was 

 silica, as Avhite as snow ; but it was variegated with every shade of yel- 

 low from sulphur, and with scarlet or rose color from oxide of iron. In 

 the distant view the appearance of the whole country may be not un- 

 aptly compared to a vast limekiln in full operation. Most of the 

 countrj- passed over has been washed into rounded hills from 50 to 200 

 feet in height, composed of the whitish, yellow, pinkish clays and sands 

 of the modern lake deposits. This deposit seems to prevail, more or 

 less, all around the rim of the basin, reaching several hundred feet above 

 the present level of the lake. At another locality there was quite a 

 large stream of hot water, formed by the overflow of a group of springs. 

 One of the springs was constantly throwing up a column of water sev- 

 eral feet. In this deposit tliere was a large amount of calcareous mat- 

 ter, which is quite unusual in the Yellowstone Basin. We know, how.- 

 ever, that there are i)atches of the Carboniferous limestone here and 

 there, remnants of the great series of strata that once covered the entire 

 region. There is no doubt that if sufficient time was given to explore 

 all the country about the sources of the Yellowstone, ]\Iissouri, and 

 Snake Eivers, great numbers of other groups of springs of greater or 

 less importance would be found, which, as yet, have never been seen by 

 human eye. Fortunately for us, in our wanderings we struck the sources 

 of the East Fork of the Madison instead of those of the Fire-Hole, and, 

 in consequence, saw many line springs and much interesting country 

 which would otherwise have escaped our attention. 



Crossing the divide, Ave at once descended a steep declivity 1,000 feet 

 into a valley about ten miles below the extreme source of the East Fork, 

 and there camped for the night. The next morning, August 1, there 

 was a heavy frost and ice a sixteenth of an inch thick. The ther- 

 mometer frequently falls to 20^ during the months of July, August, and 

 September. The East Fork, near the point where we struck it, is 

 about 30 feet wide and, on an average, 10 feet deep. The water flows 

 Avith great velocity, is quite warm, 60° to 70°, at one camp 78°, and is 

 fed almost entirely by warm or hot springs. The entire A^alley, from its 

 source to its junction with the Madison, extending over an area twenty- 

 five miles long and an average of half a mile in width, is covered AAith the 

 siliceous deposits of the hot springs, ancient or modern. The bed of the 

 stream is lined with the white silica, and the valley itself looks like an 



