and sometimes at other points, the "under current sluice" is usually introduced, being constructed and arranged as follows: At the end of the last sluice box above the under current, a grating of iron bars is placed lengthwise in the bottom of the box, through which a portion of the water and finer material falls, upon a series of more gently graded sluices below, from two to five times the width of the main sluice. These sluices are placed at right angles to the other, and are often lined with amalgamated copper plates, and provided with mercurial riffles, which, in connection with the gentler current, materially assist in saving the finer gold. The great body of the gravel with the large boulders meantime go dashing forward, being precipitated in places over falls from twenty to fifty feet in height, thus producing by the crushing and grinding effect a great disintegrating power. From the bottom of this fall the materials are immediately taken up by a series of boxes, and being again joined by the stream from the under current, flow on, the process being repeated, often many times, before the bottom of the ravine is reached.

The water from the canal is brought by side flumes to the head of the mining ground with an elevation of from one to two hundred feet above the bed-rock, whence it is conveyed to the bottom in iron pipes, sometimes sustained by a strong incline of timber. These pipes are of sheet iron of adequate strength, riveted at the joints and measure from twelve to twenty inches in diameter. They communicate at the bottom with a strong prismatic box of cast iron, in the top and sides of which are openings for the adaptation of flexible pipes made of a very strong fabric of canvas, strengthened by cording, and terminating in metallic nozzles of from two and a half to three inches in diameter. From these nozzles the streams are directed against the face of the gravel to be washed, with immense force.

The volume of water employed varies with the work to be done; though frequently four different streams, each conveying a hundred inches or more of water, are brought to bear simultaneously on the face of the same bank. Five hundred miners' inches of water, approximately equal to 53,000 cubic feet per hour, are often discharged against the face of the bank, with the great velocity and pressure due to the head employed.

Under the continuous action of this enormous mechanical force, aided by the softening power of the water, large sections of the gravelly mass are readily broken down and washed away. The débris speedily dissolving and disappearing under the force of the torrent, is hurried forward in the sluices to the mouth of the shaft, down which it is pre

cipitated with the whole volume of water. Boulders weighing hundreds of pounds, accompanied by masses of the harder cement, are carried forward, encountering everywhere on their passage, and especially in the plunge over the fall, the crushing agencies necessary for their disintegration.

The heavier banks, of eighty feet and upwards, are usually worked in two benches; the upper and poorer, being also less firm, is worked away with greater rapidity. The lower section is usually much more compact the stratum on the bed-rock being strongly cemented by sulphuret of iron and resisting even the full force of the water until it has been loosened by powder. For this purpose a tunnel is driven in on the bed-rock, from forty to seventy feet from the face of the bank, from the inner extremity of which another is extended to some distance on each side and at right angles to the first. In this cross tunnel is placed the charge, consisting of from one hundred to five hundred kegs of powder, fired as a single blast. The effect in shattering and loosening, in all directions, the heavy mass of conglomerate, is tremendous-fitting it for the ready and efficient action of the water.

Sometimes in the softer, upper stratum, a sytem of cross tunnels is extended, as practiced in coal mining, leaving blocks, which are then washed away; after which the whole mass settles and disintegrates easily under the influence of the water. A double set of sluices is usually placed in these long tunnels, in order that one set may be cleaned up while the other is in action.

The process of cleaning up is performed at intervals of from twenty to forty days, according to the size of the works and the richness of the earth. Advantage is taken of this occasion to reverse the position of the blocks and stones when they are worn irregularly, and to substitute new ones for those which are worn out. The action of the washing upon the blocks is rapid and severe, demanding a complete renewal of them once in eight or ten weeks. Some miners prefer a pavement consisting entirely of cobble stones, though most of the sluices are paved with wooden blocks, with or without alternating sections of stones.

Rude as this method of saving the gold by hydraulic washing may appear, experience has shown that more is saved by it than by any other mode yet devised, while its economical advantages are incomparably greater than those of any other. In fact it would be utterly impossible to handle such masses of poor material with profit in any other manner, or by any other agency than that of water.

To show the advantages possessed by this system as compared with

those formerly in use, assuming wages to be three dollars per day, the cost of handling a cubic yard of auriferous gravel is approximately as follows: with the pan, $15; with the rocker, $3 75; with the long tom, $1; with the hydraulic process, 15 cts.

By no other means does man more completely change the face of nature than by this process of hydraulic mining. Hills melt away and disappear under its influence, every winter's freshets carrying to lower and yet lower points portions of the detritus, while whole valleys are filled with clean washed boulders of quartz and other rocks. Meanwhile the Sacramento and its branches, as well as the San Joaquin, flow turbid with mud. Bars are formed where none existed before, and the hydrography of the bay of San Francisco is changing under the influence of the same causes. The desolation which remains after the ground, thus washed, is abandoned, is remediless and appalling. The rounded surface of the bed rock, torn with picks and strewn with immense boulders too large to be removed, shows here and there islands of the poorer gravel rising in vertical cliffs with red and blue stains, serving to mark the former levels, and filling the mind with astonishment at the changes, geologic in their nature and extent, which the hand of man has wrought.

QUARTZ, OR VEIN MINING.

Before proceeding to treat particularly of the means and methods employed in the mining and subsequent treatment of auriferous quartz, something may be said, in a general way, as to the modes of occurrence of gold in the rocks, and of the more prominent features and characteristics of auriferous veins, or "ledges," as they are usually styled by the California miner.

It has been stated in the early part of this chapter, that when gold occurs in situ in the rocks, it is usually found in veins of quartz. It has also been stated, in the chapter devoted to geology, that the great gold-bearing region of the State, viz: the western flanks of the Sierra Nevada, is of comparatively recent geological age; that it consists almost entirely of slates, varying largely in lithological character, but having a remarkable uniformity of strike and dip, the former being, with few exceptions, approximately parallel to the central axis of the Sierras, while the latter inclines generally at a high angle to the east, or towards this central axis.

The innumerable veins of quartz with which this region is filled, do not, in general, form a network cutting each other and the strata in various directions, and dipping at all imaginable angles, as is com

monly the case in other regions, more particularly in many of the mineral districts of Europe. On the contrary, the veins here lie parallel with the stratification of the slates, being enclosed between the beds, with which they conform both in strike and dip. There are, however, exceptions to this general rule, a vein occasionally cutting the strata with a strike and dip, entirely independent of them-these cases, in some localities, being rather frequent.

The gangue of the auriferous veins is almost always quartz. Near the surface, the associate minerals are chiefly the oxidized ores of iron, copper, lead and zinc; the sulphurets of these metals, at depths beyond the reach of atmospheric influences, being of general occurrence: the latter are sometimes accompanied by arseniurets of iron, etc., and occasionally by rarer combinations, such as the tellurides of Carson Hill and other localities. Sometimes the gold in the veins is distributed with remarkable uniformity throughout the whole mass of the gangue, while in other and more numerous cases the reverse is true. In some instances, portions of the foot-wall prove the richest, while in others, that next the hanging wall is the more highly auriferous.

Often the veins are more or less banded in structure, in which case the gold is apt to lie in streaks parallel with the banding of the quartz. Occasionally it lies mainly in "chimneys," or "chutes," having a pitch in the direction of the strike of the vein; and not infrequently there is the greatest possible irregularity in its distribution, some portions of the vein matter being extremely rich, while others immediately adjacent are almost entirely barren. In some spots the gold is coarse, while in others it is impalpably fine much of the rock that pays well to work showing no gold whatever to the naked eye. Sometimes the vein-stuff adheres strongly to the walls of the adjoining country rock; so that the former cannot be removed without breaking off much of the latter, while, again, the cleavage or parting between the two is perfect and clean. Frequently the vein and the country rock are separated by a selvage or clay band an inch or two in thickness; a condition that greatly facilitates the removal of the former. Often the walls, as well as the surface of the vein, are marked with parallel striæ, showing the direction of dynamic action, the surface often being not only worn smooth, but even beautifully polished by this movement. The gold occurs distributed more or less throughout not only the hardest and most compact quartz, but also in the more soft and cellular portions thereof, it being also present to a greater or less extent in the various metallic sulphurets scattered through the veins, particularly in iron

and arsenical pyrites where the latter occurs, both of these minerals being often extremely rich.

The gold is not, however, entirely confined to the limits of the metaliferous vein; frequently existing as well in adjacent portions of the wall rocks-sometimes to such an extent as to remunerate well the cost of extracting and working it. Cases have occurred, as at Carson Hill, where the soft slates adjoining the veins, for a foot or more in thickness, were found to be immensely rich, equalling in this respect even the richest portions of the quartz itself. But, although the quartz veins are everywhere the chief matrix of gold, they are not its invariable accompaniments. Within the past few years this metal has been found at certain localities in considerable quantity, distributed throughout broad bands or patches of the metamorphic slates, unaccompanied either by quartz in notable quantity, or by any distinct and definite vein formation. In these cases the rocks are shown to have been highly impregnated with metallic sulphurets of various kinds, the most prominent of which, however, was iron pyrites. The slow decomposition and oxidation of these sulphurets, as the result chiefly of atmospheric causes, have in many places entirely changed the chemical character and consistence of the rocks, replacing many of their original constituents by others of a very different kind. By this process, too, the whole mass of rock has sometimes been so softened as to set free the particles of gold once contained in the sulphurets, leaving the rocks often stained with a variety of brilliant colors, due to the metallic oxides and salts resulting from their decomposition.

But this subject of the modes of occurrence of gold in situ in the rocks, and other questions connected therewith, although exceedingly interesting, form too broad a field to permit of further consideration here; therefore, we proceed to notice briefly the principal means and methods employed in the mining and subsequent treatment of the ore.

MINING OPERATIONS.

As the extraction of auriferous quartz does not vary materially from other vein mining as practiced in different parts of the world, it hardly requires a special description in this place. When the vein is so situated that it can be reached, at a considerable depth below its outcrop, by means of a tunnel extending nearly horizontally from the hill-side or from an adjoining valley, such a tunnel or adit is first driven, drifts being afterwards extended from it in each direction along the vein. The auriferous quartz above is then stoped out, and conveyed in cars through the tunnel to its mouth, and thence to the mill.