TRANSVERSE SECTION OF BRISTOL COPPER MINE.

Showing the Contact of the Sandstone with the Crystalline Rocks, and the Position of the Great Flucan and Ore-ground of the Mine. Scale 60' to 1''.

greatest drawback on the prosperity of the mine, since the ore ground was too wide to be all taken down by the miners, and the distribution of the branches of ore in it was too irregular to admit of their being found without occasional expensive excavations in dead ground. In general, throughout the mine, a tendency to a concentration of the ore around the masses of granite may be remarked, and the latter are not unfrequently well filled with strings and bunches of ore, especially near their exterior.

The limits of the ore-ground to the west, or in the direction of the older rocks, the sandstone being to the east of the contact

line, have never been well ascertained, and must be somewhat irregular, as would be expected from the nature of the deposit. Eustis's level, going north from the 20-fathom cross-cut, has been driven along a well-marked and regular wall, which has been commonly called the foot wall of the mine. This dips, at an angle of 62° to the East, preserving a very near parallelism with the line of contact of the formations. The same kind of wall is seen in the 30-fathom level immediately beneath, where it is observed in the 20; but in neither level can it be traced for more than one or two hundred feet. There is nothing in the nature of the wall to indicate that ore might not be found beyond it, as appearances similar to this are observed in the ore-bearing ground of the mine. The excavations indicate that there was a tendency of the metalliferous matter towards this limit, and that there is not much probability of finding large bunches of ore beyond it. It is worthy of remark, however, regarding the ore-ground within the limits just described, that the average distribution of the vitreous copper is very uniform, so much so that for a long period it has been found profitable to crush and work over nearly every stone from this belt raised in working the mine.

The ore-ground just described was from the time the mine was first opened up to a recent period, considered as the only source in which the yield of copper was to be sought. Not long since, however, attention began to be called to a belt of soft rock, which lies next adjacent to the sandstone, and, of course, between it and the metalliferous belt just described. This belt is known as the "great flucan," (see diagram on previous page,) and it consists of a talco-micaceous slate completely disintegrated and softened by some chemical agency,' with the exception of a few bands and nodules of hard rock, but which are of very limited extent, compared with the softer portion. The flucan contains throughout its whole mass vitreous and other ores of copper, usually disseminated through it in small particles, so as hardly to be visible to the naked eye, but occasionally concentrated into bunches and strings of considerable size. The width of the great flucan is 27 feet in the 20-fathom level, but it increases rapidly as the workings descend, being respectively 38 and over 50 feet, in the 30 and 40fathom level. If this increase in width were to continue in depth, the flucan will meet the so-called foot-wall of the mine at or near the 80-fathom level, occupying in this place a width of about 120 feet. But that such an increase in its dimensions continues downwards indefinitely, seems hardly probable; it is more likely that it will be found to be a lenticular mass swelling out to great dimensions, and then gradually contracting again. The mass of flucan has been traced on the surface and opened at various points. At the distance of 700 feet to the southwest, from the engine-shaft, it has near the surface an inconsiderable width,

although it may increase in descending to the north, however, it holds its width as far as it has been explored. Jilbard's level was driven in this direction from the 20-fathom cross-cut, for a distance of over 300 feet, and the flucan there found to have a width of 41 feet. Still further to the north it has been cut at the surface, beyond Ives's level, but its width in this place was found to be at 30 feet from the surface much diminished.

The deposits of ore are not entirely confined to the primary. Within the sandstone, which at the line of junction is so broken up and irregular, that its stratification can with difficulty be made out, a small seam of ore was cut in the 20-fathom cross-cut from the engine-shaft. It has been driven on both-ways from the cross-cut to a distance of about 160 feet to the north, and 120 to the south. The upper part of this course of ore is still standing, showing a narrow seam of quartz rich in ore. The level to the north is at present inaccessible: to the south the ore appears to run out at a distance of about 50 feet from the cross-cut. (This seam of ore is shown in the cross section at A.)

History of the mine.-This locality has been known for a long period as a place furnishing copper, and was opened to a very limited extent many years since. In 1836 Mr. G. W. Bartholomew made an open cut in a spot where indications of ore were abundant, and the following account of its appearance is given in 1837, by Prof. C. U. Shepard, State Geologist, who saw it at that time:

"The trench has a nearly north and south course, and extends for twenty feet somewhat obliquely across alternations of vertical layers of granite and soft mica slate. The layers of granite áre from one to two feet in thickness, while those of the slate are generally much less. It was found on getting below the surface that the green malachite and brown iron ochre diminished in quantity, and that the rocks were less decomposed. Yellow copper pyrites began to make its appearance in the slate and variegated copper in the granite. The integrity of the rocks and the abundance of the ore increased regularly as the workmen de-. scended, till at the bottom the granite presented several almost continuous veins or layers of ore which in places had a thickness of two inches."-Report, p. 47.

Mr. Percival says: "The Bristol Mine is chiefly opened in a large vein of a coarse reddish sub-talcose granite, adjoining which the gneissoid micaceous rock, just referred to, is also sub-talcose or sub-chloritic, with decomposed greenish chloritic seams and nodules, and with more or less copper disseminated."-Report, p. 77.

The property subsequently passed into the hands of Mr. A. R. Miller, who drove various shallow levels near the surface, exploring for copper. While in his possession it was visited and re

ported on by Prof. Silliman, Senior, of Yale College, in 1839, and upon this report funds, to a small amount, were obtained in England for prosecuting the work. But the adventurers being unable to sustain the enterprise, the explorations were subsequently continued by Mr. L. C. Ives, who erected a small steam engine, and sunk the present engine shaft in the sandstone to the 20-fathom level. During this time, and prior to 1847, considerable shipments of the ore had been made to England, but exactly what quantity we have no means of ascertaining. It appears, however, from the information obtained from the last named proprietor, that it could not have been less than 100 to 125 tons.

It was not, however, until 1846-7, that the mine was opened and worked to any considerable extent. At that time it passed into the hands of Mr. Hezekiah Bradford and his associates. Since that period a large amount of money has been expended here, and over eighteen hundred tons of copper ore have been raised and sold. In 1851 the management of the mine passed into the hands of Mr. Henry R. Sheldon, as agent for the present owners. Mr. Sheldon (who is still the manager) has had the satisfaction of seeing the mine rise from a state of great depression in its affairs and prospects to a condition of prosperity and encouraging profits, with the certainty that by a judicious and moderate outlay, it can be made to return the whole cost of its plant and extraordinary expenses, with a wide margin of profit to the adventurer.

The value of the "great flucan" in ore appears from the average of all the trials which have been made upon it for a long period, including the actual results of stamping and crushing to be over 3 per cent of ore having 30 per cent copper. In a calculation made upon the probable future product of the mine, it is assumed that the average yield will be 2 per cent. The material composing the flucan is so soft and easily removed that no gunpowder is required in mining it. As soon as it is exposed to the action of air and moisture it runs as the miners express it and becomes , like a micaceous clay. It weighs a little more than 150 pounds to the cubic foot. In a careful examination of the fresh material, it is not difficult to see that it is chiefly the feldspathic portion of the original material which has undergone decomposition. The outline of the feldspathic portions is plainly discovered by the friable mass of mingled silica and clay of a white color loosely filling the space occupied by the feldspar. Small garnets, of a deep red color, and small black tourmalines are constantly to be seen when the material is washed-being apparently almost the only substances beside the vitreous ore of copper which have escaped the powerful decomposing influence which has produced this great zone of altered material.

This Report was in confirmation of one made in October, 1838, by Prof. C. U. Shepard, and which we have never seen.

In reflecting upon the probable cause of the decomposition of this extensive bed of talco-micaceous rock the suggestion naturally arises that it has probably a close connection with the injection of the trappean rocks among and beneath the sandstones of the secondary. This event it is certain was a subaqueous one, and the vast efflux of steam of high tension produced by the fiery injection of the molten trap, among rocks saturated with water must have left its traces in chemical changes produced by so powerful an agency. The irruption of the copper ores may have been and probably was an earlier event of segregation. But if the cause adduced for the decomposition of the flucan is the true one, it is pretty certain that the same decomposed material will be found at the greatest depth to which the mine will ever be explored. As it is now proposed to sink a shaft in the sandstone to the depth of 600 feet and to connect it at every 60 feet with the flucan by a cross-cut, we shall have the opportunity of studying these phenomena in detail as the explorations proceed. It is rather remarkable that the line of actual contact between the sandstone and the crystalline rocks is seldom visible and has still more rarely been carefully explored. We do not know of another example where this important feature in our geology has been explored with so much care as in the case before us.

Many statistical data embodied in our report and which are chiefly of economical value, are omitted here. It is proper to remark, however, that an important item in the present and future success of this mine is the employment of new and improved machinery, the most important of which are the ore separators and patent jigs, invented by Mr. H. Bradford. The separator is a shaking table of entirely new form and construction, on which by the rapid reciprocal motion of a copper plate the ore is by aid of water and gravity, thrown over one edge while the waste is projected over the other. After giving in detail the statistics of their operation, our report holds the following language :

Undoubtedly Bradford's separators are the most important mechanical invention ever produced for dressing what are called slime ores. The principle upon which they are constructed is truly philosophical, and has been most ingeniously applied by the talented inventor to the production of this machine. Like all accurate instruments they require careful adjustment in all particulars, but once adjusted they are completely self-acting, so that one attendant can easily oversee at least twenty of them.

Our "Report" concludes with the following observationsIn reviewing the condition of the Bristol Mine at the present time, the following are the most noteworthy points:

1. The mine is one of the few in the United States which is now worked at a profit.