BASALT. 281 



which furnished some of the building material for the reduction furnaces. 

 It is well stratified and the beds are sliglitly inclined, showing a certain 

 amount of movement in the country since its deposition. This tufa carries 

 much brown o\r<i\ m the vertical cracks which intersect it in some direc- 

 tions. 



The Knoxville lava belongs to tlio older portion of the series of 

 basaltic eruptions of this region. At one point it shows remnants of what 

 was once probably a crater. This and the amount of erosion and weather- 

 ing seem to refer it to a date indistinguishably near that of the earlier por- 

 tion of the basalts near Clear Lake. Many bowlders have rolled from the 

 more elevated portions of the basalt to lower ground, and tlie area mapped 

 as basalt probably includes a fringe of such detritus, through which the 

 underlying metamorphics were not visible. The basalt area is somewhat 

 more than two miles long. 



All but one of the quicksilver mines and prospects of the districts are 

 separated from the edge of tlie basalt area by distances of less than half a 

 mile. The exception is the Andalusia, which lies nearly in the strike of the 

 Reed deposit and is probably on the same fissure. 



springs.—Near the edge of the basalt, particularly near the Redington 

 and Manhattan mines, there are numerous strong mineral springs. These 

 springs are not warm, but they carry so much mineral matter as to produce 

 beds of sinter and to cement surf\^ce gravel into hard conglomerates. The 

 sinters consist mainly of calcium carbonate. One of them showed, in ad- 

 dition to this substance, sodium, potassium, lithium, chlorine, boracic acid, 

 and a very little sulphuric acid. The boracic acid is no doubt combined 

 with sodium as borax, and it is evident that the water depositing this sinter 

 is closely analogous to that of Sulphur Bank. This is an important fact 

 when considered in connection with other phenomena and will be referred 



to again. 



Deposits of the district. — Threc propcrtles lu the district have produced impor- 

 tant quantities of quicksilver. These are the Redington, the Manhattan, and 

 the Reed mines. At the time of my visit the best days of these mines were 

 either long past or reserved for a remote future and the greater part of the 

 workings were entirely inaccessible. Only the somewhat extensive surface 



