358 Whitney's Geology of California. 
water infusoria. 
The term cement is often applied to certain forms of these 
consolidated volcanic materials, commonly to the breccia, or 
coarser materials; but the term-is used loosely, and is often © 
applied to true auriferous gravels now hardened. ‘To notice all 
the phases that these superficial volcanic deposits assume, or all 
the modifications they give rise to in mining, would exceed the 
limits of this article; we will therefore notice but one, “Table- 
Mountain Mining.” ‘ 
As before stated, the lava often flowed down the old river 
valleys, and then consolidated into very hard basaltic rock. 
Such a mass has withstood the denuding effects of later times 
much more completely than the slates on either side. Hence, 
the streams have cut new channels; and, at present, these 
mF) 
basalt, supporting a scanty growth of shrubs and stunted trees, 
in marked contrast with the hills of slate that have a more 
valley or mere gorge. And in other parts of the State evi 
dence is cited of even much greater denudation. On the Middle 
Pilot Peak and the adjacent heights, which lava is here about 
650 feet thick, Instances might be greatly multiplied in proof 
ation. 
Of course this lava now covers the auriferous gravels that 
i ‘flats,” “bars,” “! gule es 
and “bottoms,” that form the rich placer-grounds of those early | 
ages. Here it has been safely kept from harm and locked 
