BASALT. 247 



Sulphur Bank, on Indian Island, on Red Hill, and west of Lower Lake 

 contorted masses of lava remain on the surface, where they chilled after 

 oozing from vents or from cracks in the lava streams. It is also indicative 

 of the lateness of the basalt eruptions tliat fragments of the rock are 

 usually to be found only in the immediate neighborhood of the main areas. 

 There does not seem to have been time enough since the eruptions to effect 

 any general or even widespread distribution of pebbles. At Sulphur Bank 

 it is also said that the Indians have traditions of eruptions. While this fact 

 might liave little significance were any portion of California now the seat 

 of volcanic activity, it seems not without weight when it is remembered 

 that the nearest volcano now active is very ftir away. At all events, it 

 seems to me by no means impossible that the latest eruption may have 

 occurred within a thousand years or even less. 



The relations of the basalt areas to the general structure of the under- 

 lying metamorphic rocks are not easily studied, for lack of exposures. I 

 have endeavored to make out the fissure system which no doubt connected 

 the various vents of the basaltic eruptions, but have failed to reach any sat- 

 isfactory conclusion. 



There are but two places in the district where basalt tables occur. Of 

 these one is at the extreme eastern end of the McPike area, where the lava 

 appears to have followed the bed of the north fork of Cache Creek and to 

 have been subsequently undermined by the stream. The rock has fallen 

 off in columns, leaving perpendicular walls. The other bluffs are com- 

 prised in the area northeast of Red Hill, and, like all similar occurrences, are 

 a result of undermining. In both cases I can but suppose that the lava 

 represents much earlier eruptions than those which left the unimpaired cra- 

 ters nearer the Sulphur Bank, tliough they are both Post-Pliocene, resting 

 unconformably upon the uplifted Caclie Lake beds. 



Clear Lake. — Botli the topograpliy and an examination of the soils show 

 that Clear Lake formerly occupied a considerably greater area than it now 

 does. The flat land about Sulphur Bank once formed a portion of the lake 

 bottorti, and would again do so were the lake to rise 50 or 70 feet. A 

 much smaller rise would flood the valley now in part occupied by Borax 

 Lake, the surface of wliich is but a few inches above the level of the lake. 



