444 A Description of the Process of [August, 
sierras, and a period of comparative repose may be ex- 
pected, as the distribution has already been far advanced y 
the excessive reduction of the mountains. 
The deep and extensive depositions which I now. attemp 
to describe attracted the early attention of, the mining ad- 
venturers, and were called hill diggings, but not being 
properly understood were therefore not immediately operated 
upon, and remained in abeyance, whilst the lower,. richer, 
and more manifest alluvials endured. They were designated 
“ blue gravel,” the colour being due to the aCtion of sui- 
phuret of iron and other salts, the cementing auxiliaries 
requisite to form the hard conglomerate, and on exposure 
to the atmosphere changes colour 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 oi an 
ancient river ; and it is obvious that the material m these 
channels should be richer than the general mass beyond 
“ Ri m 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 chan- 
nels 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 NAY. the 
richest and most explored belt of gold bearing alluvium in 
California lies between the South and Middle Yuba Riveis, 
commencing near Eureka, in Nevada county, and extends 
downwards to Smartsville and Timbudtoo, in Yuba county, 
a distance of 40 miles, and from amongst snowy mountains 
the country falls gradually from where the ravines or canons 
are cut by the attual rivers, which are 2000 feet beneath the 
auriferous gravel and region near Smartsville, and 2000 feet 
above the Yuba River, where snow is unknown, and near its 
terminus the ancient river bed courses more westerly than 
it does above it, and crosses Yuba below Timbuftoo, where 
the auriferous depositions disappear. The whole distance 
of 40 miles has been ransacked by the earlier adventurers, 
and around the village of Timbudtoo was a centre famed loi 
its wonderful yield of gold, obtained chiefly in the ravines 
in holes and depressions in the bed rock. These hollow 
detained the concentrations of the denudated alluvium tiom 
the altitudes, and were generally closely beneath the surface, 
and by such guidance and means of discovery the miners 
