and
the old river gravels, with their protecting caps of volcanic rock, are
now seen running out as spurs from the Sierras and forming the divides
between the modern streams. The latter have formed their own more
recent gravels, from the wear, partly of the old deposits and partly of
the mountain sides, as at first. The surface-diggings and placers of
the early prospecting days of California were, of course, in these
modern gravels and bars. The older gravels, equally rich, are worked
either by the hydraulic process, or when compacted into what are called
" cement-beds," by stamp-mills. It is in these deposits that the
diamonds have been found, picked from the sluices and flumes. In the
case of the cement-beds, only fragments are obtained, as the
diamond-crystals have been crushed under the stamps. There is much in
the mode of their occurrence that recalls, at first sight, the diamond
mines of Brazil and South Africa. In Brazil the matrix is also a
gravel, and is frequently cemented into a conglomerate (" cascalho ")
by oxide of iron. In Africa the diamond gravels contain associated
minerals similar to those found in some of the California placers,
notably in those of Butte County, where zircons, garnets, and rutile
are met with. But these are not important relations, and afford no
ground for assuming either a similar richness of yield or an identity
of geological origin.
The
first recognition of diamonds in the State goes back to the early
gold-seeking days of 1850. In that year, Mr. Lyman, a clergyman from
New England, was shown a crystal about the size of a small pea, with
convex faces, and of a straw-colored tint. He saw it for a moment only,
yet its general aspect was enough to identify it as a true diamond, and
the interesting fact was published.1 The first diamond from
the Cherokee district, Butte County, was obtained in 1853. This has
since proved one of the principal localities in the State. In 1854
Melville Attwood called attention, in a newspaper article, to the
general similarity of the California deposits to the diamantiferous
gravel and conglomerate of Brazil, with which he had become familiar
by a residence there of some years. He advised that search be made and
care exercised, lest diamonds should pass unheeded in the
gold-washings. Since then diamonds have been reported from
1 Am. J. Sci., II, Vol. 8, p. 294. Sept. 1849.
