These mighty changes have gradually been accomplished, and the accumulated
denudations of the mineral zones have defended themselves by strata of
crystallized silicates of quartz of various thicknesses, and thus in
places beneath such system of defense, or by their own concretion, have
preserved in many localities a thickness of from 500 to 600 feet of
conglomerate, but without this 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.
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