necessary cementation its further removal
is very certain when again attacked by water. An example of this
continuous process is very observable in "Death Valley," Lower California,
where a width of about 100 miles has been filled up from the hills to the
gulf of same name, invading and occupying its former bed; and this
activity is still proceeding, and a temporary formation of tableland
above it is in course of removal, although already overgrown with forest
trees, which are toppling over the side which is being attacked. But
eternal snow now only covers a small portion of these Sierras, and a
period of comparative repose may be expected, as the distribution has
already been far advanced by the excessive reduction of the mountains.

The deep and extensive depositions which I now attempt to describe
attracted the early attention of the mining adventurers, and were called
"hill diggings," but not being properly understood were therefore not
immediately operated upon, and remained in abeyance, while the lower,
richer, and more manifest alluvials endured. They were designated "blue
gravel," the color being due to the action of sulphuret of iron and other
salts, the cementing auxiliaries requisite to form the hard conglomerate,
and on exposure to the atmosphere changes color to yellow and violet,
losing also its firmness by oxidation.

The "great blue lead" is another important mining term and designates the
alluvium found reposing in a well-defined channel on the bed rock, being
the well-worn path of an ancient river; and it is obvious that the
material in these channels should be richer than the general mass beyond
their limits.

"Rim rock" is the boundary line of the banks of the old channel, and, like
the bottom, is well worn and corrugated by the running water into cavities
and "pot holes," where the force of the stream eddied. The width of these
channels varies from 60 to 400 feet, and the cement near the rim and
bottom is always richer than elsewhere. The wider and deeper channels
generally course from N. to N.W. The richest and most explored belt of
gold-bearing alluvium in California lies between the South and Middle Yuba
Rivers, commencing near Eureka, in Nevada county, and extends downwards to
Smartsville and Timbuctoo, in Yuba county, a distance of 40 miles; and
from among snowy mountains the country falls gradually from where the
ravines or canons are cut by the actual rivers, which are 2,000 feet
beneath th