240 GEOLOGICAL ,SUEVEY OF THE TERRITORIES. 



Basin, we find fewer of the mire-lioles which render travel difficult and 

 even dangerous in some parts of the Lower Basin. The surface is made 

 up largely of the thinly-laminated sinter, broken up by frost and sun, 

 and partly of the clay left behind in the disintegration of the volcanic 

 rocks and the removal of the silica by the hot waters. 



The larger geysers, so far as yet known, are clustered within a rather 

 limited area, so that one can generally watch three or four at once. The 

 different ones have very different periods of eruption ; and, in many, 

 the successive intervals of any one vary considerably. The violence of 

 eruptions also varies greatly ; but no law of connection between relative 

 violence and length of interval has yet been determined. Many of the 

 geysers erupt without any noise, other than the mere rush of water and 

 steam ; but the eruptions of several of the larger ones are constantly 

 accompanied by violent regular pulsations, audible to a considerable 

 distance, and shaking the earth for many rods, as if a fifty-thousand- 

 horse-power steam-pump were in full action down below. In one erup- 

 tion of Giantess, five or six pulsations were heard before the water be- 

 gan to rise. Their rate was at first seventy-three per minute, but 

 slightly decreased toward the close of the eruption. One eruption of 

 Grand started with seventy-two pulsations per minute, which decreased 

 to seventy, in the course of twenty minutes, and became fainter and 

 fainter. Another, of the same geyser, started at seventy-three per min- 

 ute, slowing gradually. In most instances, these pulsations cease when 

 the flow of water ceases ; but they were once observed to continue for 

 some minutes after the opening of the final rush of steam. This escape 

 of steam often comes with greater velocity and noise than that of the 

 water, and is really a j^art of the eruption, though generally not so con- 

 sidered. 



The erosion effected by the erupted water is generally very slight, 

 being confined, even in case of the most abundant flow, to the channels 

 by which the water escapes and to the space immediately about the 

 vent, where, however, the sinter is generally very compact, and is in- 

 creased by deposition from evaporation rather than eroded by the fall- 

 ing jet. In the case of Fan Geyser, the main jet, instead of being ver- 

 tical or nearly so, escapes at an angle of about 60° with the horizon, 

 and the falling water has hollowed out the disintegrating sinter quite 

 deeply for a space of about 115 feet from the vent. 



In some of the shallower hot pools, we find beautiful rosettes of sin- 

 ter, of variable thickness, slightly attached to the bottom. In their 

 earliest stages, these are extremely thin, and from the lower side small 

 spiny processes fall to the bottom, much like the rooting-processes of 

 the bryozoans, or the roots which depend from the branches of the 

 mangrove and the banyan. Judging by their general appearance and 

 conditions, these probably originate as fragments of very thin pellicles 

 formed by evaporation upon the very surface of the pool, and, broken up 

 by the wind, each fragment tends to sink; but some of them escape that 

 fate, and more material accumulates by evaporation upon their wet edges, 

 so that they become basin-shaped and float securely. I cannot account 

 for the basal spires, about which a solid pedestal finally accumulates, ex- 

 cept by supposing that they have central nuclei of the small fibers of 

 myeelimn, which are floating in all these pools in greater or less abun- 

 dance. 



With the exception of these low-grade vegetables, and the larves of 

 Helicopsyche, found by Mr. Taggart in water of temperature of 180^, we 

 saw no evidence of the existence of living forms in these very hot 

 pools. 



