GENERAL DISTRIBUTION OF THE GRAVELS. 305 
type of the uncovered deposits, spread over broad areas, and with difficulty 
to be connected together into any one continuous channel, those between 
the South and Middle Yuba furnish, probably, the finest example to be found 
anywhere of a detrital mass possessing all those peculiar characteristics 
which mark the work of ancient rivers in the Sierra. The deposits of gravel 
are of great thickness, and may be traced almost continuously from high up 
in the range down almost to its very base. Large portions of it are un- 
covered, so that the banks can be washed by the hydraulic method; the 
auriferous particles are probably more uniformly scattered through the de- 
trital masses than anywhere else on the slope of the Sierra; and the topo- 
graphical conditions at and near the summit are favorable for securing large 
and permanent supplies of water. Hence we have in this region the largest 
and most important hydraulic mines in the world, which promise to hold 
their own for a considerable number of years to come. From Snow Point, 
at an elevation of 4,200 feet, to French Corral, 1,579 feet, the gravel has 
been traced not continuously, but sufficiently so to make it certain that it 
belongs essentially to one channel, although not without lateral branches, 
the position of which has not yet been clearly made out. This channel is 
extensively covered in its upper portion by volcanic materials, but below - 
Columbia the gravel is entirely free from any lava capping; and although 
there is a break in its continuity, between Cherokee and North San Juan, of 
a little over three miles, yet there can be no doubt of the former existence 
of a connecting deposit, which has been washed away and disappeared. It 
is not necessary, however, to dwell on the peculiar features of this great 
deposit on the summit between the Yubas, because it has already been quite 
fully described in the preceding pages.* Certain questions connected with 
it will come up for consideration further on, after the present general sketch 
of the occurrence of gravels has been completed. 
The divide between the Middle and North forks of the alles is very differ- 
ently situated, with reference to the gravel deposits, from that between the 
Middle and South branches of the same river. There are two quite decidedly 
marked channels, and possibly a third; but we have them now for the first 
time exhibiting a direction not, in the main, coincident with that of the 
present lines of drainage; but, on the other hand, decidedly transverse to it. 
The gravel deposits occur on this divide in quite isolated patches, which are 
not of extensive area; but their position with regard to each other is such 
* See ante, pp. 196-208, and Appendix A. 
