78 EEPOKT UNITED STATES GEOLOGICAL SURVEY. 



back of this spring there is a deposit of sulphur in the main mass of 

 the sediments. 



ITo. 18 is a pure white basin 12 feet by 20 feet in its dimensions, with 

 three centers of ebullition. The water has a temperature of 161° F., 

 and a portion of it flows out into ISTo. 19. 



No. 19 is a yellowish-white flat basin, with a fissure in the center 

 and several holes in which the water bubbles and boils. The size of the 

 spring is indefinite, as it opens oufc into Ko. 20. In that direction are 

 yellow sulphur-tinged filaments which radiate from the margin of the 

 spring. The temperature was 164° F. 



]^o. 20 is a hole in a basin that measures about 6 feet in width and 

 a foot in depth. It receives water from the springs above (19 and 20), 

 but iu the active portion of the spring has a temperature of 165° F. 

 Below it are the radiating sulphury filaments that are seen between it and 

 No. 19. They spread out on flat, shallow basins, which are white and red 

 in color, and are very handsome in some places. These are best appreci- 

 ated by a reference to the accompanying plates (Plates Yb and Vc), 

 which show the general appearance of the terrace in 1878, This group 

 in 1871 was much nearer the base of the ridge, and the water spread 

 over the greater part of the terrace so that it was only on the edges 

 that we could walk. We can now go over the very place where the 

 spring then was without any danger. There was a great change from 

 1871 to 1872, and even more to 1878, as a comparison of Plates Ya, Yb, 

 and Yc will show. The highest temperature in this group in 1871 was 

 only 162° F., because we could get only the temperature at the edge 

 of the spring and not in the center of ebullition. Near the springs are 

 several fissures and cavities, the chambers of extinct springs, in which 

 are fragile stalactitic masses of deposit of pure white and light yellow- 

 ish colors. They have been formed by the percolation of water through 

 the mass of sediment. At the foot of the ridge back of these springs 

 is a mass pulpit-shaped, from which we called it the Pulpit. It marks 

 the site of a former spring. The changes from 1871 to 1878 iu the 

 springs of this portion of the terrace are best shown by the photographs 

 taken in the two years (Plates Ya, Yb, and Vc), although they were taken 

 from slightly different points in order to best show the springs. Plates 

 Ya and Yc are from nearly the safne point of view, the latter being 

 taken from a point a little more to the right. 



No. 21. Main spring. — This spring occupies very nearly the same posi- 

 tion it did in 1871 and 1872. It may, perhaps, reach back a little farther 

 from the edge, but the change in position, if any, has been slight. It is 

 a large pool-like spring about 100 by 200 feet. It reaches back to the 

 white basins that spread out below the group just described. It is 10 

 feet lower than they are, and the basins between are empty. Sur- 

 rounding the spring are large shallow basins and pools, some of which 

 are lined with a red deposit. East of the spring, on the slopes leading 

 down from the edge of the terrace, are some of the handsomest basins 

 to be found at the locality (Plate VI). The tubs are irregular in size 

 and sha])e, and extend far down the sides. The edges of many are 

 tinged of a rusty color. The temperature of the water could be ob- 

 tained only at the edge, where it was 147° F. In 1871 a temperature 

 of 155° F." was recorded for this spring ; 162° was recorded in 1872. 

 These temperatures were probably all at different points. The line of 

 tubs extending down the ravine between the main spring and group 

 of 11-15 has been mentioned when speaking of the latter. 



No. 22 is a sulphur spring on a mound of deposit at the south end of 

 the ninth terrace, above the general level of which it is raised 12 feet. It 



