THE NONMETALLIC MINERALS. 177 



The difficulties in development lie in the -quicksands and gravel, 

 which are wet and soft, and in the soft rock (hole 1), which yields sul- 

 phurous waters under a head, at the surface, of about 15 feet. 



The Nevada deposits occupy the craters of extinct hot springs near 

 Humboldt House. These craters are described by Russell 1 as situated 

 on the open desert, above the surface of which they rise to a height of 

 from 20 to 50 feet. 



Nearly all of the cones are weathered and broken down, and are all extinct, the water 

 now rising to the surface for miles around. The outer surface of the cones is composed 

 of calcareous tufa and siliceous sinter, forming irregular imbricated sheets that slope 

 away at a low angle from the orifice at the top. The interiors of these structures are 

 filled with crystalline gypsum, that in at least two instances is impregnated with sul- 

 phur. One of the cones has been opened by a cut from the side in such a manner as 

 to expose a good section of the material filling the interior, and a few tons of the sul- 

 phur and gypsurn removed. The percentage of sulphur is small, and the economic 

 importance of the deposit, as shown by the excavation already made, will not war- 

 rant the further expenditure of capital. The cone that has been opened is surrounded 

 on all sides by a large deposit of calcareous and siliceous material, thus forming a low 

 dome or crater, with a base many times as great in diameter as the height of the 

 deposit. These cones correspond in all their essential features with the structures 

 that surround hot springs that are still active in various parts of the Great Basin, 

 thus leaving no question as to their origin. They are situated within the basin of 

 Lake Lahontan, and must have been formed and become extinct since the old lake 

 evaporated away. 



Sulphur is reported as occurring in the chemically formed deposits 

 that surrounded Steamboat Springs, situated midway between Carson 

 and Reno, Nevada. The conditions at these springs must be very simi- 

 lar to those that existed near Humboldt House at the time the cones 

 containing the sulphur were formed. Sulphur is also said to occur in 

 the Sweetwater Mountains, situated on the boundary between Cali- 

 fornia and Nevada, in latitude 38 30'. The extent and geological 

 relations of these deposits are unknown. 



Another illustration of sulphur deposits of the volcanic type is that 

 furnished by the Rabbit-Hole Sulphur Mines (Specimen No. 16092, 

 U.S.N.M.). These are located in northwestern Nevada, on the eastern 

 border of the Black Rock Desert, and derive their name from the Rab- 

 bit-Hole Springs, a few miles to the southward. The hills bordering 

 the Black Rock Desert on the east are mainly of rhyolite, with a narrow 

 band of volcanic tufa along the immediate edge of the desert. These 

 beds of tufa are stratified and evidently water-lain, and are identical with 

 tufa deposits that occur over an immense area in Oregon and Nevada. 

 At the sulphur mines the tufas contain angular fragments of volcanic 

 rock, and have been cemented by opal and other siliceous infiltrations 

 since their deposition, so that they now form brittle siliceous rocks, 

 with pebbles and fragments of older rocks scattered through the mass. 



1 Transactions of the New York Academy of Sciences, I, 1881-1882, p. 172. 

 NAT MUS 99 12 



