the South and Middle Yuba, California. 5 
where it is protected from such action. Probably 120 feet is 
not an over-statement for its average thickness in the marginal 
portions, where it has been exposed by working the deep dig- 
gings or sparc claims. This vast gravel bed is com 
of rounded masses of quartz, greenstone, ee onan the metamor- 
phic rocks which are found in the high Sie 
It is often locally a aaa but I could ‘find no evidence of 
any continuity in its ings. The lower portions are com- 
posed of larger boudders than the upper, as a general rule, but 
this does not exclude the occasional presence of huge boulders 
in the central and upper portions. In a fresh fracture of the 
whole thickness of these deposits, such as may be seen daily in 
the ‘claims,’ which are being actively areas a striking con- 
trast of aolee-4 is seen between the lower and upper portions of 
sition of pyrites, and rect the gravel of a lively red and 
yellow coior in g lines and bande, contrasting ona 
with the blue color ‘of the unoxydized portions. e 
firm as sc unniaaee requiring the force of orem to break 
it u 
In the upper — of these beds are frequent isolated 
patches, often of considerable extent, composed of fine sand, 
bby 
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note on the hills of auriferous gravel. Some of meee which 
I measured, were fifteen to eighteen inches in diameter and ten 
to fifteen feet in length. Occasionally the mass of this ancient 
driftwood accumulated in these eddies of the current, where 
they were deposited with the fine sands, amount almost to a 
continuous bed of lignite 
Wedge-shaped and lenticular masses of tough yellow and 
whitish « clay also occur in the ancient drift, replacing the gravel 
and affording, by their resisting power, a ‘great impediment to 
— Saget of minin 
exposure of the hard gravel ‘cement’ produces, is due mainly, 
if net entirely, to the decomposition of the associated pyr 
before noted. It is remarkable how peg nt a A sac the 
smoothed and beautifully rounded large 
e- 
own’ or disintegration which a few months ~ 
