92 



GEOLOGICAL SUEVEY OF THE TEREITOEIES. 



with considerable force, the temperature is only 96°, showing that the 

 bubbling was due to the escape of gas. The bubbles stand all over the 

 surface. About 20 feet from the last, is a small mud-spring, with an 

 orifice 10 inches in diameter, with whitish-brown mud, 182°. Another 

 basin near the last has two orifices, the one throwing out the mud with 

 a dull thud about once in three seconds, spurting the mud out 3 or 4 

 feet ; the other is content to boil up quite violently, occasionally throw- 

 ing the mud 10 to 12 inches. This mud, which has been wrought in 

 these caldrons for perhaps hundreds of years, is so fine and pure that 

 the manufacturer of porcelain- ware would go into ecstacy at the sight. 

 The contents of many of the springs are of such a snowy whiteness that, 

 when dried in cakes in the sun or by a fire, they resemble the finest 

 meerschaum. The color of the mud depends upon the superficial de- 

 posits which cover the ground, through which the waters of the springs 

 reach the surface. They were all clear hot springs originally, perhaps 

 geysers even ; but the continual caving in of the sides has produced a 

 sort of mud-pot, exactly the same as the process of preparing a kettle 

 of mush. The water is at first clear and hot; then it becomes turbid 

 from the mingling of the loose earth around the sides of the orifice, 

 until, by continued accessions of earth, the contents of the basin become 

 of the consistency of thick mush, and, as the gas bursts up through it, 

 the dull, thud-like noise is produced. Every possible variation of con- 

 dition of the contents is found, from simple milky turbidness to a stiff 

 mortar. On the east side of the Yellowstone, close to the margin of the 

 river, are a few turbid and mud springs, strong! j^ impregnated with alum. 

 The mud is quite yellow, and contains much sulphur. This we called a 

 mud-sulphur spriug. The basin is 15 by 30 feet, and has three centers 

 of ebullition, showing that deep down underneath the superficial earth, 

 there are three separate orifices, not connected with each other, for the 

 emission of the heated waters. Just opposite this spring, on the west 

 side of the river, is a singular vertical wall of rather Coarse basalt, which 

 looks like huge mason-work, separated by the jointage into nearly rec- 

 tangular blocks. The wall is about 50 feet high, and is important in 



giving us an exposure of the basis rock 

 of this region. The surface is mostly 

 covered with a thick deposit of clay of 

 modern origin ; but the heated waters 

 must pass a great distance through 

 these igneous rocks, dissolving .from 

 them great quantities of silica and 

 other chemical materials which we find 

 so abundantly around the springs. 

 The next interesting spriug we called 

 the Grotto. (Fig. 28.) A vast column 

 of steam issues froui a cavern in the 

 side of the hill, with an oiJeuing about 

 5 feet in diameter. The roaring of 

 the waters in the cavern, and the noise 

 of the waves as they surge up to the 

 mouth of the opening, are like that 

 of the billows lashing the sea-shore. 

 The water is as clear as crystal, and 

 the steam is so hot that it is only when a breeze wafts it aside for a 

 moment one can venture tp take a look into the opening. From the 

 tremendous roaring and dashing of the waters against the sides of the 

 cavern, one would suppose that the amount must be great, but not 



Fig, 28, 



GROTTO, YELLOWSTONE RIVER. 



