338 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



the edge of the basalt, and I can see no reason to doubt that they result 

 from the volcanic action of which the lava eruption was one manifestation. 



The springs. — Thc preseut vents of the springs lie along a series of fissures 

 about a mile in length, shown on the map nearly parallel to the railroad. 

 These cracks have formed in a mass of sinter deposited from earlier vents and 

 are in part choked up by detritus, in part covered by recent deposits, but 

 they are nevertheless traceable for long distances. The vents in numy cases 

 retain their fissure character and the water mny be seen and heard boiling 

 in ojjcnings, evidently of great depth, from an incli to two feet in width and 

 many yards in length. At other points the cracks are closed, with the ex- 

 ception of pipe-like openings, through which the water reaches the surface. 

 At vents of the latter class there often form smooth mounds of sinter, from 

 the summit of which the water escapes continuously or fitfully. Some of 

 the springs have a true geyser character, though on a very small scale, 

 alternately disappearing from their basins and returning to them with noise 

 and agitation at short intervals of time. It is said by the inhabitants that 

 in some seasons the water returns to certain of the basins with sufficient 

 violence to be thrown several feet into the air, but during my visits the 

 maximum action did not exceed a plentiful overflow. 



It is very clear that tliese springs are short-lived. In the most active 

 area they are to bj found in every approach to extinction. Some have 

 completely covered their own vents with sinter, though when tlie crust is 

 broken hot water is still found below, while otlier mounds and cracks are 

 completely cold. Some very active vents are also manifestly extremely 

 recent and have only lately begun to form new deposits. The extinction 

 and subsequent formation of springs has certainly been in progress for a 

 long time and the accumulation of sinter is large. The u{)per line of vents 

 is about one hundred feet above the railroad, which runs along the base 

 of the mass of sinter. The ground beneath the sintei-, however, evidently 

 slopes outward from the hills, and the maximum thickness of the deposits is 

 probably about fifty feet. Active springs formerly existed at many other 

 points. The map extends eastward to the foot of the Virginia Eange. The 

 rocks of this range a little farther eastward are greatly decomposed, apparent- 

 ly by solfataric action. There is also on the map east of the railroad one 



