occur where the vertical plates, or combs, as they are there called, exhibit crystals so dovetailed as to prove that the same fissure has been often enlarged. Sir H. De la Beche gives the following curious and instructive example (fig. 516)

Fig. 516.

from a copper mine in granite, near Redruth. Each of the plates or combs (a, b, c, d, e, f) are double, having the points of their crystals turned inwards along the axis of the comb. The sides or walls (2, 3, 4, 5, and 6) are parted by a thin covering of ochreous clay, so that each comb is readily separable from another by a moderate blow of the hammer. The breadth of each represents the whole width of the fissure at six successive periods, and the outer walls of the vein, where the first Copper lode, near Redruth, enlarged at six suc- narrow rent was formed, consisted of the cessive periods. granitic surfaces 1 and 7.

A somewhat analogous interpretation is applicable to numbers of other cases, where clay, sand, or angular detritus, alternate with ores and vein-stones. Thus, we may imagine the sides of a fissure to be encrusted with siliceous matter, as Von Buch observed, in Lancerote, the walls of a volcanic crater formed in 1731 to be traversed by an open rent in which hot vapors had deposited hydrate of silica, the incrustation nearly extending to the middle. Such a vein may then be filled with clay or sand, and afterwards reopened, the new rent dividing the argillaceous deposit, and allowing a quantity of rubbish to fall down. Various metals and spars may then be precipitated from aqueous solutions among the interstices of this heterogeneous mass.

That such changes have repeatedly occurred, is demonstrated by occasional cross-veins, implying the oblique fracture of previously formed chemical and mechanical deposits. Thus, for example, M. Fournet, in his description of some mines in Auvergne worked under his superintendence, observes, that the granite of that country was first penetrated by veins of granite, and then dislocated, so that open rents crossed both the granite and the granitic veins. Into such openings, quartz, accompanied by sulphurets of iron and arsenical pyrites, was introduced. Another convulsion then burst open the rocks along the old line of fracture, and the first set of deposits was cracked and often shattered, so that the new rent was filled, not only with angular fragments of the adjoining rocks, but with pieces of the older vein-stones. Polished and striated surfaces on the sides or in the contents of the vein also attest the reality of these movements. A new period of repose then ensued, during which various sulphurets were introduced, together with horn-stone quartz, by which angular fragments of the older quartz before mentioned were cemented into a breccia. This period was followed by other dilatations of the same veins, and other sets of mineral deposits, until, at last, pebbles of the basaltic lavas of Auvergne, derived from superficial alluviums, probably of Miocene or older Pliocene date, were swept into the veins. I have not space to enumerate all the changes minutely detailed by M. Fournet, but they are valuable, both to the miner and geologist, as showing how the supposed signs of violent catastrophes may be the monuments, not of one paroxysmal shock, but of reiterated movements.

"On the swelling out and contraction of veins," we make the following extracts:

A large proportion of metalliferous veins have their opposite walls nearly parallel, and sometimes over a wide extent of country. There is a fine example of this in the celebrated vein of Andreasburg in the Hartz, which has been worked for a depth of 500 yards perpendicularly, and 200 horizontally, retaining almost every where a width of 3 feet. But many lodes in Cornwall and elsewhere are extremely variable in size, being one or two inches in one part, and then eight or ten feet in another, at the distance of a few fathoms, and

then again narrowing as before. Such alternate swelling and contraction is so often characteristic as to require explanation. The walls of fissures in general, observes Sir H. De la Beche, are rarely perfect planes throughout their entire course, nor could we well expect them to be so, since they commonly pass through rocks of unequal hardness and different mineral composition. If, therefore, the opposite sides of such irregular fissures slide upon each other, that is to say, if there be a fault, as in the case of so many mineral veins, the parallelism of the opposite walls is at once entirely destroyed, as will be readily seen by studying the annexed diagrams.

Let a b, fig. 517, be a line of fracture traversing a rock, and let a b, fig. 518, represent the same line. Now, if we cut a piece of paper representing this line, and then move the lower portion of this cut paper sideways from a to à', taking care that the two pieces of paper still touch each other at the points 1, 2, 3, 4, 5, we obtain an irregular aperture at c, and the isolated cavities at d d d, and when we compare such figures with nature we find that, with certain modifications, they represent the interior of faults and mineral veins. If, instead of sliding the cut paper to the right hand, we move the lower part towards the left, about the same distance that it was previously slid to the right, we obtain considerable variation in the cavities so produced, two long irregular open spaces, ff, fig. 519, being then formed. This will serve to show to what slight circumstances considerable variations in the character of the openings between unevenly fractured surfaces may be due, such surfaces being moved upon each other, so as to have numerous points of contact.

Fig. 520.

Most lodes are perpendicular to the horizon, or nearly so; but some of them have a considerable inclination or "hade," as it is termed, the angles of dip varying from 15° to 45°. The course of a vein is frequently very straight; but if tortuous, it is found to be choked up with clay, stones, and pebbles, at points where it departs most widely from verticality. Hence at places, such as a, fig. 520, the miner complains that the ores are "nipped," or greatly reduced in quantity, the space for their free deposition having been interferred with in consequence of the pre-occupancy of the lode by earthy materials. When lodes are many fathoms wide, they are usually filled for the most part with earthy matter, and fragments of rock, through which the ores are much disseminated. metallic substances frequently coat or encircle detached pieces of rock, which our miners call "horses" or "riders." That we should find some mineral veins which split into branches is also natural, for we observe the same in regard to open fissures.

The

Passing over all that is said relative to "chemical deposits in veins," we conclude with one further extract on the " relative age of the different metals:"

Relative age of the different metals.-After duly reflecting on the facts above described, we cannot doubt that mineral veins, like eruptions of granite or trap, are referable to many distinct periods of the earth's history, although it may be more difficult to determine the precise age of veins; because they have often remained open for ages, and because, as we have seen, the same

fissure, after having been once filled, has frequently been reopened or enlarged. But besides this diversity of age, it has been supposed by some geologists that certain metals have been produced exclusively in earlier, others in more modern times, that tin, for example, is of higher antiquity than copper, copper than lead or silver, and all of them more ancient than gold. I shall first point out that the facts once relied upon in support of some of these views are contradicted by later experience, and then consider how far any chronological order of arrangement can be recognized in the position of the precious and other metals in the earth's crust. In the first place, it is not true that veins in which tin abounds are the oldest lodes worked in Great Britain. The government survey of Ireland has demonstrated, that in Wexford veins of copper and lead (the latter as usual being argentiferous) are much older than the tin of Cornwall. In each of the two countries a very similar series of geological changes has occurred at two distinct epochs,-in Wexford, before the Devonshire strata were deposited; in Cornwall, after the carboniferous epoch. To begin with the Irish mining district: We have granite in Wexford, traversed by granite veins, which veins also intrude themselves into the Silurian strata, the same Silurian rocks as well as the veins having been denuded before the Devonshire beds were superimposed. Next we find, in the same county, that elvans, or straight dikes of porphyritic granite, have cut through the granite and the veins before mentioned, but have not penetrated the Devonian rocks. Subsequently to these elvans, veins of copper and lead were produced, being of a date certainly posterior to the Silurian, and anterior to the Devonian; for they do not enter the latter, and, what is still more decisive, streaks or layers of derivative copper have been found near Wexford in the Devonian, not far from points where mines of copper are worked in the Silurian strata.

Although the precise age of such copper lodes cannot be defined, we may safely affirm that they were either filled at the close of the Silurian or commencement of the Devonian period. Besides copper, lead, and silver, there is some gold in these ancient or primary metalliferous veins. A few fragments also of tin found in Wicklow in the drift are supposed to have been derived from veins of the same age.

Next, if we turn to Cornwall, we find there also the monuments of a very analogous sequence of events. First the granite was formed; then, about the same period, veins of fine-grained granite, often tortuous, penetrating both the outer crust of granite and the adjoining fossiliferous or primary rocks, including the coal-measures; thirdly, elvans, holding their course straight through granite, granitic veins, and fossiliferous slates; fourthly, veins of tin also containing copper, the first of those eight systems of fissures of different ages already alluded to. Here, then, the tin lodes are newer than the elvans. It has indeed been stated by some Cornish miners that the elvans are in some few instances posterior to the oldest tin-bearing lodes, but the observations of Sir H. de la Beche during the survey led him to an opposite conclusion, and he has shown how the cases referred to in corroboration can be otherwise interpreted. We may, therefore, assert that the most ancient Cornish lodes are younger than the coal-measures of that part of England, and it follows that they are of a much later date than the Irish copper and lead of Wexford and some adjoining counties. How much later it is not so easy to declare, although probably they are not newer than the beginning of the Permian period, as no tin lodes have been discovered in any red sandstone of the Poikilitic group, which overlies the coal in the southwest of England.

There are lead veins in the Mendip hills which extend through the mountain limestone into the Permian or Dolomitic conglomerate, and others in Glamorganshire which enter the lias. Those worked near Frome, in Somersetshire, have been traced into the Inferior Oolite. In Bohemia, the rich veins of silver of Joachimsthal cut through basalt containing olivine, which overlies tertiary lignite, in which are leaves of dicotyledonous trees. This silver, therefore, is decidedly a tertiary formation. In regard to the age of the gold of the

Ural Mountains, in Russia, which, like that of California, is obtained chiefly from auriferous alluvium, we can merely affirm that it occurs in veins of quartz in the schistose and granitic rocks of that chain. Sir R. Murchison observes, that no gold has yet been found in the Permian conglomerates which lie at the base of the Ural Mountains, although large quantities of iron and copper detritus are mixed with the rolled pebbles of these same Permian strata. Hence it seems that the Uralian quartz veins, containing gold and platinum, were not exposed to aqueous denudation during the Permian era. But we can

not feel sure, from any data yet before us, that such auriferous veins of quartz may not be as old as the tin lodes of Cornwall, in which, as well as the more ancient copper lodes of Ireland, some gold has been detected. We are also unable at present to assign to the gold veins of Brazil, Peru, or California, their respective geological dates. But, although enough is known to show that Ovid's line about the "Age of Gold," "Aurea prima sata est ætas," would, by no means, be an apt motto for a treatise on mining, it would be equally rash in the present state of our inquiries to affirm, as some have done, that gold was the last-formed of metals.

It has been remarked by M. de Beaumont, that lead and some other metals are found in dikes of basalt and green-stone, as well as in mineral veins connected with trap rocks, whereas tin is met with in granite and in veins associated with the granitic series. If this rule hold true generally, the geological position of tin in localities accessible to the miners will belong, for the most part, to rocks older than those bearing lead. The tin veins will be of higher relative antiquity for the same reason that the "underlying" igneous formations or granites which are visible to man are older, on the whole, than the overlying or trappean formations.

If different sets of fissures, originating simultaneously at different levels in the earth's crust, and communicating, some of them, with volcanic, others with heated plutonic masses, be filled with different metals, it will follow that those formed farthest from the surface will usually require the longest time before they can be exposed superficially. In order to bring them into view, or within reach of the miner, a greater amount of upheaval and denudation must take place in proportion as they have lain deeper when first formed. A considerable series of geological revolutions must intervene before any part of the fissure, which has been for ages in the proximity of the plutonic rocks, so as to receive the gases discharged from it when it was cooling, can emerge into the atmosphere. But I need not enlarge on this subject, as the reader will remember what was said in the 30th, 34th, and 37th chapters, on the chronology of the volcanic and hypogene formations.

ART. VII.-QUARTZ MINING OPERATIONS IN CALIFORNIA.

GOLD is found in crystalline primitive rocks, transition rocks, trap rocks and alluvial grounds. It never predominates to such an extent as to constitute distinct veins by itself. It is either disseminated, and as it were impasted, in strong masses, or spread out in thin plates or grains on the surface, or lastly implanted in their cavities under the shape of filaments or crystallized twigs. The minerals composing the veins are either quartz, calcspar, or sulphate of baryta.

With the exception of iron, it may be safely asserted that the geological districts, within which gold occurs, embrace a larger

aggregate area than that of any other metal. Yet the proportion of gold to that of the substances from which it must be separated for the use of mankind is so moderate, that the cost of eliminating it must necessarily be such as to maintain a high commercial value in all future time.

The gold-bearing veins of rock usually consist of quartz, a white vitreous stone, and one of the ingredients of granite. These, like all true veins, are generally inclined at a large angle to the plane of the horizon, and are often vertical or nearly so. In thickness they vary considerably; the same vein is sometimes contracted to the width of a few inches, whilst at other points it is expanded in thickness to many yards. They extend downwards to greater depths than the miner has ever reached.

By far the largest portion of gold hitherto has been procured from the deposits of diluvium and alluvium in the valleys and ravines which have been formed in those regions where metallic veins existed prior to the formation of such valleys and ravines.

Notwithstanding the apparently large quantity of gold hitherto procured in these deposits, from the most remote periods, we may safely assume that it bears an infinitely small proportion to what yet remains imprisoned within the rocks, at no greater distance from the surface than has already been reached by the industrious miner in other researches. The small amount of space occupied by the ravines and valleys of excavation in metalliferous regions, compared with that remaining below and between them, clearly proves the correctness of this opinion.

In our remarks upon gold mining in this article, we shall confine our attention strictly to the method of obtaining the metal from the rock, or quartz mining, as it is called.

The first attempts at quartz mining in the State were made on the Mariposa in the southern section of the gold region, some details of which are described in the following letter from a friend:

In regard to the commencement of quartz mining in California, Capt. Wm. Jackson and Mr. Eliason, both natives of Virginia, were about the first that attempted any thing. I had often, while at San Francisco, heard men who pretended to be competent judges, say that there were no such things as veins of auriferous or gold-bearing quartz in California, and even if there ever had been, they were all broken up by some great eruption, and had since been decomposed. After hearing such opinions expressed, I visited Stockton in the latter part of May, 1850, in company with Joseph C. Palmer, of the firm of Palmer, Cook & Co.; and Mr. Warbass, of the firm of Warbass & Co., of Sacramento. While at Stockton we met with Capt. Jackson, who had just come down from Mariposa. He had some rich quartz specimens, taken from the big Mariposa vein. He wished us to go up and see the vein, and offered to sell the greater part of it to us. Some of us went, and found Capt. Jackson's partner, Mr. Eliason, and eight men at work (three of them Mexicans and the rest Americans). They were pulverizing the quartz dry in iron mortars with spring poles. The weight of the mortars was about 100 lbs. After pulverizing the ore, they amalgamated it in a Virginia rocker. The ore that they were stamping was very rich, yieldVOL. I.-10