752 



DYNAMICAL GEOLOGY. 



facts prove a sympathy between different vents ; and the same was illustrated in other 

 parts of the region. 



Bradley also states that, during the eruption of some of the larger geysers, there 

 are pulsating sounds or thumps, in the depths of the geyser conduits, which have no 

 parallel movement in the jet; and that, in an eruption of the " Giantess," there were 

 seventy-three of these pulsations a minute; and in that of "Grand" geyser, at first 

 seventy-two or seventy-three, but in the course of twenty minutes they decreased to 

 seventy, and became gradually fainter. 



These and other geysers, and additional hot-spring phenomena, are described in the 

 Reports of the expedition under Hayden for the years 1871 and 1872. 



The siliceous geyser-cones are all beautiful concretionary work; and the beauty of 

 form and rexture and pearly lustre is often greatly enhanced hy the delicate shades 

 of pink, buff, yellow, and other tints, mingled with white, over their surfaces. Peb- 



bles, in the bottom of the small basins 

 formed about the cones, are commonly 

 concretions of the opal, like the rosettes 

 of the bottom and sides. 



In the eruption of a geyser, the jet is 

 first water; then much steam with the 

 water; and, at last, mostly or wholly 

 steam, the water having been all thrown 

 out; and, when the water partly falls or 

 runs back into the basin, the eruption 

 is sometimes renewed successively, be- 

 fore finally stopping. 



The action of geysers is ow- 

 ing (1) to the access of subter- 

 ranean waters to hot rocks, pro- 

 ducing steam, which seeks exit 

 by conduits upward ; (2) to 

 cooler superficial waters de- 

 scending those conduits to where 

 the steam prevents farther de- 

 scent, and gradually accumulat- 

 ing, until the conduit is filled to 

 the top ; (3) to the heating up 

 of these upper waters by the 

 steam from below, to near the 

 boiling point ; when (4) the 

 lower portion of these upper 



Water-and-gas Geyser. waterg becomeg convert ed into 



steam, and the jet of water or eruption ensues. This is nearly the 

 explanation given by Bunsen. The deposit of silica in the throat 

 of the conduit, after an eruption, tends to diminish its size, and some- 

 times closes it completely, so that the waters are obliged to open a 

 new vent. 



Hot springs also occur at many other points in, and west of, the 

 Rocky Mountains. There is a region of springs of hot water and 



