BASALTIC GLASS. 253 



found beyond the crests of the hills surrounding the locality. Similar chips 

 are occasionally met with all over the district ; but this is in part due to 

 human agency, for a spearhead of this glass was found miles away. Most 

 such chips, however, are quite isolated and show no marks of artifice. Ex- 

 plosions attending the eruption may account for the greater part of the frag- 

 ments near the obsidian field ; how the more distant ones were transported 

 I cannot guess 



Another feature of the basalt of this district, somewhat unusual in 

 California, but not unknown in other portions of the State, is the formation 

 of regular crater-cones. Dense basalts, when in a state of fusion, are prob- 

 ably too fluid to build cones. Those at Sulphur Bank are composed of 

 extremely porous basalt, much of it in the condition of lapilli. Each of 

 them is broken through on one side, apparently by lava streams, not by 

 water. The lapilli are more or less oxidized, but have accumulated no 

 considerable quantity of soil and are not concealed by the scant herbaceous 

 vegetation, though trees, particularly conifers, have taken root among 

 them. Contorted forms of lava, too, are abundant at some of the croppings 

 and everything points to a very recent date of eruption. 



General description of the bank. — The Sulphur Bauk Is an area exhibiting most 

 manifest indications of solfataric action. It is not practicable to outline the 

 exact area of decomposition, which, however, is substantially coincident 

 with the southern half of the small basalt area in which it lies, including 

 all the more elevated portions of this area. The ore-bearing ground takes 

 in a narrow strip of the sedimentary area to the south. The surface indica- 

 tions of solfatarism consist in complete decomposition of a large portion of 

 the basalt to a \thite, pulverulent mass, sulphur deposits, and hot mineral 

 springs holding gases in solution. The locality was first worked for sulphur. 

 At a distance of a few yards below the surface, however, cinnabar was 

 found occurring with the sulphur, and lower still cinnabar was found in 

 large quantities. The property has been worked for the most part by open 

 cuts, with little regard to system. Its appearance is very peculiar. The 

 glare of white decomposition-products, the labyrinth of deep, open pits and 

 trenches, and the acrid dust and evil smells of the locality produce a strong 

 impression on the observer; but even to the geologist it is an interesting 



