130 GEOLOGICAL SURVEY OF THE TEEEITOEIES. 



hangs the water and coated with a deposit of sulphur, which is deposited 

 by the sulphuretted hydrogen gas. The water here is cleaner than in 

 any of the' surrounding springs. The center of the spring is in violent 

 ebullition from the escape of steam. The temperature of the water at 

 the edge of the spring was 184° F., the air behig 78o. The second 

 group has a general elevation of about 150 feet above the first, and 

 is also situated on the slope of a hill. The first spring in this group 

 we called the "Mush-Pot." It is about 20 feet in diameter, and has three 

 openings, each about 10 feet in depth. The mud at the bottom of these 

 holes is very thick and of a bluish-black color. The mass heaves and 

 throbs as the steam escapes through it. It was impossible to take the 

 temperature of the mud, as the steam scattered it in all directions, ren- 

 dering it impossible even to look into it with safety. 



j!!To. 2 was named the "Paint-Pot," the mud in it resembling lead- 

 colored paint. The entire surface was in violent agitation. The 

 diameter of this spring is narrower at the top than at the surface of the 

 mud, which was eight feet below the surface of the ground. The mud 

 is scattered in all directions, as in the last-mentioned spring, rendering 

 it impossible'to obtain its temperature. At intervals of about three 

 minutes it seems to take a rest, remaining quite for a few seconds. 



No. 3 is a fissure of nearly 100 feet in length, in the course of which 

 there are a number of black-mud springs, their average temperature 

 being 185° F., while the air was 79° F. This fissure is about 100 feet 

 above spring No. 1. 



No. 4 is a similar fissure of about the same length. It is about 100 

 feet above the preceding one, and contains mud-springs of the same 

 character, the average temperature being 190° F. The boiling-point at 

 this elevation is 197°.6 F. All around this fissure there is an abundant 

 deposit of sulphur and alum, the sulphur-crystals being exceedingly 

 brilliant and delicate. 



No. 5 is a blue-mud spring of about three feet in diameter, having a 

 temperature of 190° F. Nos. 6, 7, 8, 9, and 10 form a small group 

 distinguished by the abundance of sulphur surrounding them. The 

 mud in them was very thick and varied in color from blue to black. 

 The ground about them was too treacherous to allow of a near approach, 

 but their temperature would probably average about 185°-190o. Be- 

 sides the springs I have described above there were numerous smaller 

 ones and a great many steam vents. I have only mentioned the most 

 important springs. Both the groups are situated in banks of clay, and 

 the deposits consist mainly of clay, alum, and sulphur. All the springs 

 are acid in reaction from the presence of sulphuric acid. The sulphur 

 results from the. decomposition of the sulphuretted hydrogen which is 

 so abundant in this locality. The oxidation of the sulphur and its 

 union with the alumina and iron gives us the alum which we find here. 



Our next camp (No. 11) was on Cascade Creek, a few miles from the 

 Lower Falls of the Yellowstone and the Grand Caiion. Cascade Creek, 

 near our camp, flows through a valley covered with sedimentary rocks, 

 into which it has cut a short distance. It is made up partly of sand 

 and particles of volcanic material. It is jirobably Pliocene in its origin, 

 and was deposited at the bottom of a lake which was very likely a pro- 

 longation of the ancient Yellowstone Lake, and existed here at a 

 comparatively recent period. The strata are soft and contain particles 

 of obsidian in abundance, and are also in part contributed to by volcanic 

 ashes, for here we find ourselves in the midst of a volcanic country. This 

 sedimentary deposit extends over the entire valley of the Yellowstone at 



