The exterior stratum of red clay, with its ores and minerals, will be best understood by comparing it to a garment thrown over the rock-formations of the country. The search for ore has been generally confined to these clay diggings, which are pursued, very much, with the apparatus of common well-digging. If, on reaching the rock, no vein of ore is discovered, the work is generally dropped.
On viewing the district on a large scale, this external clay stratum appears to have originally derived its mineral contents from veins in the calcareous, lead-yielding rock. This metalliferous rock has evidently, in former ages, been scooped out by rivers and streams, forming valleys and vast diluvial plateaux, where the abraded materials were deposited. The original subterranean veins were concealed by these geological changes.
Some of the mines exhibit traits that may be mentioned. Mine La Motte is one of the oldest mines in the Territory, having been discovered in 1720, by the person whose name it bears. The mines are very extensive, and a large quantity of ore is annually raised. They are situated within two miles of St. Michael, Madison county, and on the head-waters of the river St. François. No spars are found accompanying the ore; iron pyrite is occasionally met with, and plumbago is found in the vicinity. The ore, which is less brilliant, and differs in other characters from any other in the mine tract, is at the same time more refractory; in some instances, the greatest difficulties have been experienced in the smelting. Hence, an idea has originated that it is combined with other metals; but no experiments, I believe, have been made to ascertain this point.
On a visit to these mines, I observed the inside of the ash-furnace beautifully tinged with a blue color of considerable intensity. This furnace is built of a white sandstone, which becomes vitrified on the surface, forming glass. We are acquainted with no substance which will communicate a blue color to glass in fusion but cobalt; hence, it is not unreasonable to infer that this metal is volatilized during the smelting, and is thus brought into contact with the liquefied surface of the stone, imparting to it the color noticed. That the ores of La Motte contain an unusual portion of sulphur, is very probable. I draw this inference both from its refractory nature and dull appearance. Sulphur always renders an ore refractory; for, when it is expelled by torrefaction, the ore melts easily. Its dull aspect is not less conclusive; for, the more an ore is roasted, and the more sulphur there is driven off, the brighter it grows. This is evident to every smelter, who cannot fail to observe the surprising brilliancy the ore assumes after it has gone through the first operation in the log furnace. That the difficulties daily experienced in smelting the La Motte ores are, therefore, attributable to the extraordinary quantity of sulphur they contain, is extremely probable; for, even if they were united with other metals, with silver or with cobalt, these would not increase their infusibility, except by the extra quantum of sulphur they brought with them. At least, we have no facts to prove that a simple alloy does not melt as easily as a pure metal, while there are many to show that alloys are of the most easy fusibility.
The quantity of ore raised at New Diggings has been very great, a regular vein having been found; but they were abandoned several years ago on account of the water, which rushed in with such rapidity, that to remove it every morning with a common windlass and bucket was found a work of such labor as to render the business unprofitable. The mines were left with the most flattering veins of ore in view. The general character of these mines is such as to justify the erection of a steam-engine, and other works for prosecuting the business on an extensive scale; and their revival at some future period may be confidently looked for.
Mine Renault is situated about six miles north-north-west of Mine à Burton, in a very rocky part of the country, which affords some of the most picturesque views of mountain scenery. The region is strongly marked by mineral appearances, rendering it probable that other substances of value, besides lead, may exist in that vicinity. Ores of zinc are abundant at this mine, and a body of micaceous oxide of iron is found in the neighborhood.
Bryan's Mines are seated on Hazel run, and are among the most recent discoveries of consequence. Near a million pounds of lead were made here during the first year of the discovery. The mine is characterized by yielding no heavy spar; sometimes a little calcareous spar is found, and then adhering to the ores; a circumstance which I have nowhere else observed. Much of the ore of these mines is found in tabular pieces, which are sonorous in a considerable degree; the ore is brilliant, and smelts readily, yielding the same as at Mine à Burton.
Gray's Mine, situated on Big river, in the northern extremity of the mine tract, is remarkable for a body of white clay, which was discovered in searching for ore. In sinking several pits at this mine, a stratum of clay of an unusual appearance was struck at the depth of from eight to ten feet, and no ore was procured at those places; the diggings were abandoned in consequence of the clay, which covers a considerable area of ground on the banks of Big river. This mineral substance bears a striking resemblance to specimens of a pyrous crucible clay.
Elliott's Mines lie upon the Mineral Fork, and are characterized by the abundance of pyrites, and the beauty of the calcareous spar found there. Considerable quantities of blende were also met with, and strong indications of the existence of copper are furnished. During the remarkable earthquakes of 1812, a fine spring of water at the mouth of the mines suddenly became warm and foul, and in a few days dried up entirely, and no water has run there since. Illuminations in the atmosphere (arising doubtless from phosphorus) are frequently observed in this vicinity on the approach of night.
At Mine à Burton, there is found adhering to the sides of the log-hearth furnace, a grayish-white sublimated matter, of great weight, which I take to be a sublimate of lead. It is considered as chiefly sulphur or arsenic by the lead-smelters, and is thrown by as useless. It is found at every furnace, and a very large quantity could be annually collected. This induced me to undertake some experiments on the subject. I was convinced, on reflection, that there could be no sulphur, at least no considerable quantity of sulphur, in it, from the fact that all sulphur, or other inflammable matter, expelled from the ore in the furnace, would undergo immediate combustion. This is also observable in the color of the flame while the ore is torrified. Indeed, every person conversant with the nature of this substance must know that it cannot be otherwise. The furnace is entirely open, and does not rise over seven or eight feet in height; consequently, there is no opportunity for it to condense. That the sulphuric acid is driven off, is undoubted; for, whenever sulphur is burned, this acid is set at liberty; but it has no opportunity for entering into a new combination within the body of a log furnace.