GEOLOGICAL SUEVEY OF THE TEREITOEIES. 101 



bank, where the orifice comes up, a considerable distance, through the 

 soft superficial clays. The constant thud may be heard at our camj;) night 

 and day from half a dozen of these mud-puffs. (Fig. 35.) They have built 

 up a large number of small circular mounds about 2 feet high. These 

 springs do not differ essentially from the others which have been described. 

 There are some two hundred or three hundred in all, of all sizes, and of 

 variable temperatures. Some of them are 50 feet in diameter, and when 

 sounded with a lead showed a depth of 40 to 50 feet. One of them was as 

 clear as crystal, and the funnel-shaped basin was 45 feet in depth. So 

 clear was the water that the smallest object could be seen on the sides of 

 the basin, so that, as the breeze swept across the surface, the ultramarine 

 hue of the transparent depth in the bright sunlight was the most daz- 

 zlingly beautiful sight I have ever beheld. There were a number of 

 these large clear springs, but not more than two or three that exhib- 

 ited all those brilliant shades, from deep-sea green to ultramarine, in 

 the sunlight. The surface in some i^laces is covered with a most singu- 

 lar substance, which seems to have been precipitated by the overflow of 

 the springs ; it is very prettily variegated, every shade of green, yellow, 

 or pink and rose color, but not as vivid as in some other localities. 

 The deposit is about two inches in thickness, and breaks easily; it 

 seems to the touch like jelly ; it is largely vegetable, without doubt 

 composed of diatoms. 



Underneath this silicious deposit, and along the shore of the lake on 

 either side of this group of springs, are fine exposures of the strata of 

 the modern lake deposit which I have so often alluded to. Sandstones, 

 padding-stones, and indurated clays, all formed of decomx^osed vol- 

 canic rocks, present fine exposures. They extend high up on the bor- 

 ders of the lake. Within half a mile of this camij there is a small 

 lake, hidden among the dense forests, ab^ut a mile in length, and half 

 a mile wide, and iDcrhaps 30 or 40 feet higher than the main lake. It 

 seems to occupy a depression, and, though entirely isolated at present, 

 was once, no doubt, a portion of the great lake. I believe that the 

 rivers and lakes, large and small, which are distributed among the 

 dense forests around the lakes, are sim]Dly fragments, that have been 

 cut off by the decrease of the area occupied by the old lake basin. 

 There are a few hot springs near Heart Lake, one of which is a moder- 

 ate-sized geyser, but the group is not one of much importance. 



CHAPTEE yi. 



FROM YELLOWSTONE LAKE TO THE GEYSER BASINS OF FIEE-HOLE 



EIVEE, AND EETUEN. 



On the morning of July 31, 1 detailed a small party from our camp on 

 the northwest shore of the lake to make the examination of the far- 

 famed geyser basin of the Fire-Hole Eiver. Mr. Schonborn, topographer, 

 Mr. Elliott, artist, and Dr. Peale, mineralogist, accompanied me. We 

 took a southwesterly course, intending to strike some of the branches 

 of the Madison, and follow them down until we came to the springs. 

 Having no guide, we became involved in the net- work of fallen timber, 

 which at times threatened to obstruct our passage altogether. We 

 traveled thirty-one and one-half miles that day, and at least twelve of 

 them were among the fallen pines, where we were obliged to wind our 

 way wherever we could find the prostrate trees low enough for our 



