Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean: Vol. 5, Pt. 2

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board-sluice is generally twelve or fifteen inches in width, and from eight to ten inches deep,
and is made in convenient lengths, so that one can be added to another until a length of two or
three hundred feet or more is obtained. False bottoms of boards pierced with holes, or a series
of raised cleats, are placed in the bottom of the sluice, and are intended to receive and retain the
gold, while the stones and gravel are washed away. Long bars, or a grating with the spaces
parallel with the sluice, are, however, generally preferred to the cross cleats or holes. The fall
or rate of descent of the sluice is varied according to circumstances, being arranged to suit the
size of the gold and the nature of the drift. One or two feet in a rod is a common inclination,
and with a good supply of water is sufficient to cause stones two or three inches in diameter to
roll from one end of the sluice to the other.
The earth, stones, and gold, as they enter these sluices with the water, are all mingled
together, but the current soon effects a separation; the lighter portions are swept on in advance
and the gold remains behind and moves slowly forward until it drops down between the cleats
or bars. The larger stones and coarse gravel are swept on by the current, and after traversing
the whole length of the sluice are thrown out at the lower end. The operation, as in the case
of washing down the bank, is a continuous one, and requires little labor or attention, except to
keep the sluice from clogging. This is done by one or two men, who walk up and down and
throw out the large stones with forks.
The water for these operations at such a height above the river, and for the elevated placers
or "dry diggings" generally, is brought in aqueducts from the sources of the streams many
miles distant in the mountains. The water at Michigan City is supplied by the E1 Dorado
Company's aqueduct, at this time over ten miles in length, but soon to be extended so as to
reach other sources of water. After traversing the aqueduct, the water is received into a
reservoir above the level of the claims, and from thence distributed to the consumers. It is sold
by the inch, being delivered from a horizontal aperture one inch high and twenty-four inches
long. This opening is at the side of a box twenty-four inches square and six inches deep, and is
opened or shut by a slide. This box is kept full of water by making a slight dam on the sides
of the ditch coming from the reservoir, and the stream is thus delivered under a constant
pressure of six inches. The opening is graduated to half inches, and for each inch of water
the miner pays fifty cents for each day of ten hours; but in the summer, or dry season, it is worth
seventy-five cents.
MICHIGAN CITY TO NEVADA AND GRASS VALLEY.
Aigtgst 15.-Michigan Oity to Iowa Hill.-On leaving Michigan City we rode back for several
miles over the road by which we came, and then turned off to cross over the divide to the valley
of the North Fork. Several miles from the river, serpentine was observed outcropping in slaty
masses along the trail. The surface was also strewn with great numbers of spherical or globular
masses, which had been liberated by the weathering of the rock. In this respect, and in its
lithological characters, the rock greatly resembles the serpentine of Fort Point, at the Golden
Gate. The rock at this place attains a great development, and forms a series of knob-like hills
that are bare and barren, and look like the Bare Hills near Baltimore, Maryland. These bare
tracts in the midst of a wooded region are familiarly known as Brimstone Plains.
We at length reached the margin of the divide above the North Fork, and looked off into the
chasm of the river. The rapid, but to us silent, current was winding about, over 2,000 feet
SLUICES-AQUEDUCTS-SERPENTINE.