STEAMBOAT SPKINGS. 339 



saiall area of sinter in which there is now no evidence of activity. Much 

 of the main area of sinter is hkewise cohl and (h-y, but some three thousand 

 feet due west of the active g-roup of fissui'cs is a second group, now nearly 

 extinct, of which only one is shown on the map. From this small quantities 

 of steam and other gases still escape at a few points. At the mine only 

 small (piantities of sinter exist and the fissures are not superficially defined 

 as in the areas just mentioned, though it is clear that the lines of vent ex- 

 tended in a direction nearly north and south. In some of the excavations 

 the ground is moist and still hot enough to be painful to the touch. Gases 

 too, still es^-ape, but no water flows. The entire area of sinter and decom- 

 posed granite north and west of the basalt area is continuous and manifestly 

 has a common origin. There can of course be no question that the thermal 

 action of this locality is volcanic. The area of thermal activity is at the 

 foot of a stream of comparatively recent basalt, which was the last rock 

 ejected. The relations tlius point very clearly to an immediate connection 

 between the Ijasalt eruption and hot springs. 



In discussing the solfatarism of the Washoe district I inferred that it 

 was prabaldy of later date than the eruption of later hornblende-ando- 

 site, while of its time-relations to the basalt eruption there was no means 

 of judging.' I was not then aware of the evidence that the activity at 

 Steamboat was directly referable to the eruption of basalt. Tlie thermal 

 action on the Comstock has advanced somewhat farther towards extinction 

 than that at Steamboat; for, while the water on the 3,00(»-foot level of the 

 Comstock is cliarged with carbonic and sulph}'dric acids and has a tempera- 

 ture of 70.7^ C, most of the vents at the surface at Steamboat show still 

 liigher temperatures and the water at a distance of half a mile below must 

 be greatly superheated. Nevertheless the thermal action in each of tiie 

 districts must be of approximately the san\e age, as are also the basalt erup- 

 tions of the two areas; and the fact that the origin of the spring In the one 

 case is directly traceable to the eruption of basalt makes it extremely prol)- 

 able that in the other also the basalt eruption gave rise to the thermal ac- 

 tivity. The relations of the lava to the springs at Steamboat are strikingly 



' Geology of the Comstock Lode, p. 207. 



