636 WM, P. BLAKE 
conclusion would, I think, be a fair one that both the mammalian 
remains and flint implements occur in the same gravels, or horizon, 
in which the skull is claimed to have been found. So far as my 
knowledge extends this is not so. J am not aware that it has 
been claimed that flint implements, or even the remains of the 
mammoth and the mastodon have been found where the skull 
was said to occur. That flint implements have been found in 
association with the remains of the large mammals there is little 
doubt, but as to the age of such gravels, and whether or not the 
implements may not have been washed in from higher levels or 
superficial deposits of a far later origin I am not able to bear 
conclusive testimony. The subject requires most careful and 
extended investigation, the fact being always kept in mind that 
in the gigantic placer mining operations of California there is a 
concentration upon the bedrock of all heavy objects which may 
have been originally in the surface soil or any part of the banks 
of gravel between the soil and the bed of the ancient river. 
In all river and creek channels of modern streams, and even 
in what are called dry arroyos or gulches, there is a possibility that 
in seasons of flood or of great accumulation of rushing water 
from showers or cloud-bursts objects lying on the surface, such 
as stone implements, pestles, mortars, metates, flint chips, etc., 
may be swept onwards in the gravel and sunk to the very bed- 
rock and become buried by deposits twenty feet thick, and pos- 
sibly more and all in the space of an hour or less. The loss of 
iron safes in different places in California and Arizona, the safes 
wholly disappearing, and similarly the loss of quicksilver in 
flasks while crossing a swollen torrent are familiar examples. 
Heavy objects, like gold, in swiftly moving water are carried to 
the lowest point possible and are covered from view by heavy 
deposits of gravel and bowlders. The finding, therefore, of 
Indian stone mortars at a considerable depth in gravel in a 
modern stream valley is not good evidence of antiquity. 
In regard to the concentration of objects on the bedrock of 
placers, when there is sluicing or washing by the hydraulic 
method on a large scale, miners are familiar with the fact that 
