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Report of Doctor Houghton on the Copper of Lake Superior.

Fredonia, N. Y., November 14, 1831.

Hon. Lewis Cass, Secretary of War.

Sir:

In fulfilment of the duties assigned to me in the late expedition into the Indian country, under the direction of H. R. Schoolcraft, Esq., Indian agent, I would beg leave to transmit to you the following observations relative to the existence of copper in the country bordering on the southern shore of Lake Superior.

It is without doubt true that this subject has long been viewed with an interest far beyond its actual merit. Each mass of native copper which this country has produced, however insulated, or however it may have been separated from its original position, appears to have been considered a sure indication of the existence of that metal in beds; and hence we occasionally see, upon maps of that section of our country, particular portions marked as containing “copper mines,” where no copper now exists. But while it is certain that a combination of circumstances has served to mislead the public mind with regard to the geological situation and existing quantity of that metal, it is no less certain that a greater quantity of insulated native copper has been discovered upon the borders of Lake Superior, than in any other equal portion of North America.

Among the masses of native copper which have engaged the attention of travellers in this section of country, one, which from its great size was early noticed, is situated on the Ontonagon River, a stream which empties its waters into the southern part of Lake Superior, 331 miles above the falls of the Ste. Marie. The Ontonagon River is, with some difficulty, navigable by bateaux 36 miles, at which place by the union of two smaller streams, one from an easterly, and the other from a westerly direction, the main stream is formed. The mass of copper is situated on the western fork, at a distance of six or eight miles from the junction.

The face of the country through the upper half of the distance from Lake Superior is uneven, and the irregularity is given it by hills of marly clay, which occasionally rise quite abruptly to the height of one or two hundred feet. No rock was observed in situ, except in one place, where, for a distance, the red sandstone was observed, forming the bed of the river.

The mass of copper lies partly covered by water, directly at the foot of a clay hill, from which, together with numerous boulders of the primitive rocks, it has undoubtedly been washed by the action of the water of the river. Although it is completely insulated, there is much to interest in its examination. Its largest surface measures three and a half by four feet, and this, which is of malleable copper, is kept bright by the action of the water, and has the usual appearance of that metal when worn. To one surface is attached a small quantity of rock, singularly bound together by threads of copper, which pass through it in all directions. This rock, although many of its distinctive characters are lost, is evidently a dark colored serpentine, with small interspersed masses of milky quartz.

The mass of copper is so situated as to afford but little that would enable us to judge of its original geological position. In examining the eastern fork of the river, I discovered small water-worn masses of trap-rock, in which were specks of imbedded carbonate of copper and copper black; and with them were occasionally associated minute specks of serpentine, in some respects resembling that which is attached to the large mass of copper; and facts would lead us to infer that the trap formation which appears on Lake Superior east of the Ontonagon River, crosses this section of country at or near the source of that river and at length forms one of the spurs of the Porcupine Mountains.

Several smaller masses of insulated native copper have been discovered on the borders of Lake Superior, but that upon Ontonagon River is the only one which is now known to remain.

At as early a period as before the American revolution, an English mining company directed their operations to the country bordering on Lake Superior, and Ontonagon River was one point to which their attention was immediately directed. Traces of a shaft, sunk in the clay hill, near a mass of copper, are still visible, a memento of ignorance and folly.

Operations were also commenced on the southern shore of Lake Superior, near the mouth of a small stream, which, from that circumstance, is called Miners’ River. Parts of the names of the miners, carved upon the sandstone rock at the mouth of the river are still visible. What circumstance led to the selection of this spot does not now appear. No mineral traces are at this day perceptible, except occasional discolorations of the sandstone rock by what is apparently a mixture of the carbonate of iron and copper; and this is only to be observed where water, holding in solution an extremely minute portion of these salts, has trickled slowly over those rocks.

It does not, in fact, appear that the red sandstone, which constitutes the principal rock formation of the southern shore, of Lake Superior, is in any instance metalliferous in any considerable degree. If this be true, it would require but little reflection to convince one of the inexpediency of conducting mining operations at either of the points selected for that purpose; and it is beyond a doubt true, that the company did not receive the least inducement to continue their labors.

In addition to these masses of native copper, an ore of that metal has long been known to the lake traders as the green rock, in which the characteristic substances are the green and blue carbonate of copper, accompanied by copper black. It is situated upon Keweena Point, 280 miles above the falls of the Ste. Marie. The ore is embraced by what is apparently a recently formed crag; and although it is of a kind, and so situated as to make an imposing appearance, there is little certainty of its existence in large quantities in this formation. The ore forms a thin covering to the pebbles of which the body of the rock is composed, and is rarely observed in masses separate from it. The crag is composed of angular fragments of trap-rock; and the formation is occasionally traversed by broad and continuous belts of calc. spar, here and there tinged with copper. Although the ore was not observed in any considerable quantity, except at one point, it apparently exists in minute specks through a greater part of the crag formation, which extends several miles, forming the shore of the lake.

This examination of the crag threw new interest upon the trap formation, which had been first observed to take the place of the sandstone at the bottom of a deep bay, called Montreal Bay, on the easterly side of Keweena Point. The trap-rock continues for a few miles, when the crag before noticed appears to lie directly upon it, and to form the extremity of the point; the crag, in turn, disappears, and the trap-rock is continued for a distance of six or eight miles upon the westerly side of the point, when the sandstone again reappears.

The trap-rock is of a compact granular texture, occasionally running into the amygdaloid and toadstone varieties, and is rich in imbedded minerals, such as amethystine quartz, smoky quartz, cornelian, chalcedony, agate, &c., together with several of the ores of copper. Traces of copper ore in the trap-rock were first noticed on the easterly side of Keweena Point, and near the commencement of the trap formation. This ore, which is an impure copper black, was observed in a vein of variable thickness, but not in any part exceeding 2½ inches; it is sufficiently compact and hard to receive a firm polish, but it is rather disposed to break into small irregular masses. A specimen furnished, upon analysis, 47.5 per cent. of pure copper.

On the western side of Keweena Point, the same ore appears under different circumstances, being disseminated through the body of the trap-rock, in grains varying in size from a pin’s head to a pea. Although many of these grains are wholly copper black, they are occasionally only depositions of the mineral upon specks of cornelian, chalcedony, or agate, or are more frequently composed, in part, of what is apparently an imperfect steatite. The ore is so connected with, and so much resembles in colour the rock, of which it may be said to be a constituent part, that they might easily, during a hasty examination, be confounded. A random specimen of the rock furnished, upon analysis, 3.2 per cent. of pure copper. The rock continues combined with that mineral for nearly the space of three miles. Extremely thin veins of copper black were observed to traverse this same rock; and in enlargements of these were discovered several masses of amorphous native copper. The latter mineral appeared in two forms—the one consisting of compact and malleable masses, carrying from 4 to 10 ounces each; and the other, of specks and fasciculi of pure copper, binding together confused masses of copper green, and partially disintegrated trap-rock: the latter was of several pounds’ weight. Each variety was closely embraced by the rock, although the action of the water upon the rock had occasionally exposed to view points of the metal. In addition to the accompanying copper green, which was in a disintegrated state, small specks of the oxyd of copper were associated in most of the native specimens.

Circumstances would not permit an examination of any portion of the trap formation, except that bordering directly upon the lake. But facts would lead us to infer that that formation extends from one side of Keweena Point to the other, and that a range of thickly wooded hills, which traverses the point, is based upon, if not formed of, that rock. An Indian information which, particularly upon such a subject, must be adopted with caution, would sanction the opinion that the prominent constituents are the same wherever the rock is observed.

After having duly considered the facts which are presented, I would not hesitate to offer, as an opinion, that the trap-rock formation was the original source of the masses of copper which have been observed in the country bordering on Lake Superior; and that at the present day, examinations for the ores of copper could not be made in that country with hopes of success, except in the trap-rock itself; which rock is not certainly known to exist upon any place upon Lake Superior, other than Keweena Point.

If this opinion be a correct one, the cause of failure of the mining company in this region is rendered plain. Having considered each insulated mass of pure metal as a true indication of the existence of a bed in the vicinity, operations were directed to wrong points; when, having failed to realize their anticipations, the project was abandoned without further actual investigation. We would be induced to infer, that no attempts were made to learn the original source of the metal which was discovered, and thus, while the attention was drawn to insulated masses, the ores, ordinary in appearance, but more important in situ, were neglected; and perhaps from the close analogy in appearance to the rock with which they were associated, no distinction was observed.

What quantity of ore the trap-rock of Keweena Point may be capable of producing, can only be determined by minute and laborious examination. The indications which were presented by a hasty investigation are here imbodied, and, with deference, submitted to your consideration.

I have the honor to be,

Sir, your obedient servant,

Douglass Houghton.