J. LeConte—Old River-beds of California. 183 
limits of its energy. This principle is well understood by 
hydraulic miners. The amount of water gathered in the sluices 
from the hydraulic jets must be duly related to the amount of 
earth removed. If the water is in excess, the precious water 
is wasted and the erosion of the sluices is very great; if the 
earth is in excess the sluice is choked, even though the velocity 
under proper conditions is sufficient to carry bowlders of severa 
cubic feet.. The water must be well-loaded but not over-loaded. 
The same important principle is well illustrated by the pheno- 
mena of the floods of the tributaries of the Sacramento River. 
As I learn from my nephew, Julian LeConte, who has been 
engaged in the hydrographical survey of this river, at the time 
of flood, the rushing waters first come down Feather River 
bringing only fine silt and clay; the water rises and increases 
proportionally in depth. Next comes the great mass of coarse 
sediment, sand, gravel and pebbles creeping slowly along the 
bottom and filling up the bed twenty feet deep; the water 
though in full flood is but little deeper (though much wider) 
than before the flood.* Lastly, as the water falls and has less 
sediment to carry, it again takes up the sediment previously 
deposited and scours out the channel even though its general 
velocity is now far less than when the same was deposited. In 
this case the filling is not permanent; but cases are not want- 
Ing of steady building up by rivers of very high velocity. 
According to the authority already mentioned the Yuba River 
at Marysville has permanently filled up its beds 30 feet deep, 
and 15 miles above Marysville 115 feet deep, in the last 
years. This is wholly due to the large increase of transported 
matter produced by the operations of hydraulic mining. Again, 
according to Captain Dutton,+ the Colorado River through its 
cafion and the Platte River over the plains have about the 
same slope, viz: eight feet per mile; but while the Colorado 
has cut its wonderful cation and is still cutting, the Platte has 
water varies at so high a rate that a very slight change in con- 
ditions affects enormously the amount of deposit. While they 
build, therefore, they build rapidly but are liable under even 
* The rise of the surface is about 23 feet ; the filling of the bed 20 feet. 
t Nature, vol. xix, p. 274, 1879 | 
