Chapter XXI: Section II

TOPOGRAPHICAL AND GEOLOGICAL OUTLINE OF THE MINE COUNTRY.

The district of country formerly known as the lead-mines of Louisiana, extends from the head waters of the St. Francis, in a north-west direction, to the Maramec, a distance of seventy miles, by about forty-five in width, having the Mississippi on its eastern borders. It is included, very nearly, between 37 deg. and 38 deg. north latitude, and comprises an area of about three thousand square miles. Most of the mines are situated within a circle of this general area, of which Potosi and Mine a Burton constitute a centre.

The rock formation of the country appears to be simple and uniform. At the lowest depths observed in valleys, there is a crystalline sandstone, which often consists of transparent quartzose grains, adhering by the force of aggregation. The lead-bearing limestone reposes upon this. Both formations are deposited in perfectly horizontal strata. Valleys which carry streams have been worn down into this formation, presenting this order of arrangement very satisfactorily. A stratum of red, marly clay, spreads over the limestone. Above this, constituting the top layer, or surface soil, rests a bed of diluvial materials, filled with broken-down fragments of rock, masses of radiated quartz, and chips of hornstone. Vegetable matter and black sand form a covering over such parts of this diluvial deposit as constitute valleys and agricultural plains. The Mississippi river lays open this formation along its western banks, from the influx of the Missouri to Cape Girardeau.

Beneath this metalliferous column lie the primitive rocks. The most striking feature of this kind is found in the occurrence of a primitive formation at the sources of the river St. Francis. My attention was arrested by this fact, soon after I began to examine the mine country. This formation consists of sienite, rather than granite; the mica being generally replaced or represented by hornblende. The feldspar, which constitutes three-fourths of the mass, is of a dull red hue. The rock in connection is greenstone trap, which is sometimes porphyritic. I observed small masses of sulphuret of iron in some parts of this rock. The upheaval of this formation appears to have been of the most ancient era of geological action; for the stratified limestones and sandstones, which lie upon or in juxtaposition to these elevations, have not been disturbed in their horizontality. The altitude of this primitive tract does not probably exceed one thousand feet above the waters of the St. Francis river. Vast blocks of the red sienite have been detached, and scattered southwardly over the secondary rocks, apparently by the force of some antique deluge, setting from the north. The whole series of formations may be judged of by the following diagram:

The general aspect of the country is sterile, though not mountainous. The lands lie rolling, like a body of water in gentle agitation. In some places they rise into abrupt cliffs, where the rock formations appear. Generally, they present the form of diluvial ridges, sparingly covered with forest, and bearing a growth of prairie-grass and herbage. The western banks of the Mississippi, between St. Genevieve and Herculaneum, present a mural front to this district, in a series of elevated perpendicular cliffs of compact limestone. The whole coast extending to St. Louis, appears to be sufficiently elevated to have served as a former barrier to waters covering the low grounds of Illinois. The strata exhibit ancient water-marks of a diluvial character. They are broken through, from the west, by small streams draining the mine country.

No indications of lead-ore have been found in these cliffs. The mines are situated at considerable distances west of them; and when the observer has arrived at their localities, he finds the ore often lying in the unconsolidated soil. This soil is a stiff, reddish-colored clay, filled with fragments of cherty stones, quartz, and small gravel, clearly attesting its diluvial character. This soil extends to the depth of from ten to twenty feet, or more, and is based on limestone rock. It is so firm, in some places, as almost to resist the pick-axe; in others, it partakes more fully of marl, and is readily penetrated. The ore lies in this marly clay, and is often accompanied by sulphate of barytes and calcareous spar. The country is particularly characterized by radiated quartz, which is strewn in detached pieces over the ground, and is also found imbedded in the soil at all depths. This substance is here called _blossom of lead_, or _mineral blossom_. Pyrites, and some other ores of iron, are also found in detached masses upon the surface, and, very rarely, lead-ore.

Such is the general character of the mineral lands, which are covered with a stunted growth of oaks, denominated post-oaks. Walnut is found in some instances out of the valleys. A ridge of yellow pine extends west of the mines, between the St. Francis and Maramec, and is more decidedly barren than the grounds covered with oak. All the open, elevated tracts, are clothed with herbage, which hides their flinty aspect, and gives the country a picturesque appearance. The minor slopes and ravines are often rendered almost impassable by hazel, vines, and other bramble, which appear to be indicative of a better, or rather a deeper soil. The whole area of upland soil, which rests as a mantle over the rocks, is a diluvium, which must, we think, be referred to an early period of diluvial action.

The only true alluvium of the mines appears to be confined to the valleys or plains, which are, consequently, the principal seats of cultivation, and thus derive an additional value from their contiguity to the barren tracts. This alluvium rests on the red marl-clay, or mineral diluvium; the latter of which is uniformly found on penetrating it. Some of the mines exist in, and have been pursued beneath, this top alluvion, across the valleys. Others are seated beneath an arable soil, bearing a forest. Many of the most barren and stony parts of the elevated lands are, on the contrary, destitute of mines. The depth of the mineral soil varies exceedingly. It barely conceals the rock formations in many of the more elevated positions, and frequently does not conceal them. It is deepest in the plains and depressed grounds, being accumulated much in the manner we should expect, on the supposition of a general diluvial submersion.

The principal objection to a general diluvial action, involving the whole Mississippi valley, appears to arise from the admission of the limestone rock's being the true locality of the ore. But we think there are too many facts in support of this opinion, to leave any reasonable grounds for questioning it. Several of the mines in the mineral soil have been traced down into the rock, and have been pursued through apertures, closing and expanding in the manner of true veins. In the numerous cases where the rock has put a stop to further mining, and it has exhibited no signs of ore, it may be supposed that the ore has been moved, by diluvial force, from the original position of the mine, and been finally deposited, with the soil, upon unmetalliferous portions of the rock. And could we with certainty determine the course of diluvial action, the principles of mining might be, in some respects, employed in searching for the original vein. It is evident, from the unscratched and unbroken surface of much of the ore and its spars, that it could not have been transported far; while the portions of it called gravel ore, which evince its diluvial character, are manifest proofs of a change, more or less extensive, in the general position of the ore.

With respect to the character of the limestone, we have been perplexed with its protean character, and, to avoid apparent contradictions, were led, at first, to adopt distinctions of strata, which we very soon saw were untenable. It is evidently the American equivalent for the metalliferous limestone of England, and, as a formation, is of the transition era. In a specimen of this rock, now before us, taken from a fresh excavation at Potosi, forty feet below the surface of the soil, and thirty-one feet below the original surface of the rock, the structure is in part compact, and in part granular; the compact portions having minute shining crystalline points, and the granular being without any appearance of crystallization, but changing, in the width of about forty lines, from compact granular to a dull arenaceous structure, quite friable between the fingers. Part of the mass is vesicular, and the vesicles are studded over with minute crystals of white opaque quartz. The two extremes of this specimen have the appearance of totally different formations, yet are both calcareous. By experiment, I found a portion of the lower arenaceous part almost completely soluble, in the cold, in nitro-sulphuric acid; and the actual residuum was, in part, owing to a defect in trituration.

Most of the limestone rock disclosed by excavation in the mines, is of the granulated kind; while the structure of the rock above the surface, where the strata are exposed to the weather, as in cliffs and hill-sides, is of the solid, glistening, pseudo-compact variety. Both these varieties, as shown in the specimen, are geologically identical, notwithstanding their striking differences in hardness, structure, colour, and particularly in crystalline lustre. This lustre is, however, as shown by examination with the magnet, owing almost exclusively to minute facets of calcareous crystals, which render it rather sparry than crystalline.

We have examined large portions of this rock, in all its varieties, for organic remains; but have not succeeded in finding any well-characterized species, although a further and fuller search might, and probably would, disclose some species. We observed a single mass of the rock, an imperfectly columniform structure, apparently organic. The rock is rather vesicular than cavernous in its structure. The heavy deposit of diluvium conceals the surface. But if the appearances in the mine-diggings are to be received as general indicia, the surface of the concealed rock is extremely rough and irregular, standing up, in the mineral soil, in huge lumps, which renders the general depth at which it may be reached, a question of great uncertainty.

It has been intimated that the sparry-compact, and the dull granulated varieties of the limestone, are often contiguous; and we have seen, by the examination of a hard specimen, that they are geologically identical as a formation. If this compact variety from the mines be compared with the principal formation in the precipitous cliffs forming the western banks of the Mississippi, in front of the mine tract, they will be found to coincide in so many points, that these two localities may be deemed parts of the same formation, and as being identical in age. The principal differences consist in the occurrence of organic remains in the strata along the banks of the Mississippi; a discovery attributable to the more full exposure of these cliffs to observation. There is also an apparent absence of the granulated, or sand-lime variety. These two calcareous tracts are not, however, continuous, being separated by a formation of granular quartz, or white crystalline sandstone, which runs nearly parallel with the Mississippi for a distance, a few miles west of it. This stratum of rock, which appears to be rather a quartzose sandstone than a granular quartz, reappears west of Potosi, in the barren area called the Pinery, and is also apparent at several localities between the waters of the Maramec and the St. Francis.

At a point thirty miles west of the Mississippi, in about the latitude of St. Genevieve, the primitive formation reveals itself in a series of mountain masses of granite, which cover a comparatively extensive area. This tract appears to be the nucleus of the country, rising through the great secondary formations which intervene between the Alleghany and the Rocky mountains. Its western limits have not yet been explored; but it probably covers an area of not less than a hundred square miles. The mines lie north of it. This granite is composed almost exclusively of reddish feldspar and quartz. The proportion of mica is small, and this mineral is often absent. It has been employed as a material for millstones. It is connected with greenstone, which is sometimes porphyritic.

We have now three formations of rock, as constituting the mine series; and it only remains to point out their relative position and extent, with the best means at our command. This might seem to be a very simple process, and would indeed be so, were it not that the area over which the formations extend is extensive, and is covered with deep formations of the diluvial and alluvial character, bearing a forest. The primitive is immediately succeeded by the two latter. Mine a La Motte is situated in the mineral diluvium, and is distant about two miles from the granite on Blackford's fork. The first appearance of rock, in situ, north of this point, is at Rock creek, a few miles distant, where the granular quartzose sandstone appears. There is no further appearance of rock in this direction for many miles. The white crystalline sand-caves of St. Genevieve are seated in this formation. It is again disclosed on the Platten creek, and in the elevations west of the Joachim creek, called Fort Rock, and in the white sand-caves near Herculaneum. Whether it is continued farther in the approach to the Maramec, cannot be stated; but the line of country which is thus traversed by it, is probably sixty miles. The only point where this rock appears on the banks of the Mississippi, is in the range of the Cornice Rocks.

Proceeding west across this formation, the mineral diluvium succeeds, and conceals the rock formations; but, wherever they are disclosed by the action of the streams, and by excavations, the metalliferous limestone appears, which constitutes the lowest stratum yet found in the mine region proper. But it is to be observed, that no excavations of any considerable depth have been made; the rock has not been penetrated to any great depth. The principal seat of the mines consists of the area included within the circuits of the Grand river and Mineral Fork, constituting the main tributaries of the Maramec. These streams extend something in the shape of a horse-shoe around the mines. Immediately west and south-west of this area, the white sandstone reappears, extending south towards the granite. The position of the two formations may be represented by a pair of expanded dividers, opening northward; the two shanks of which denote the sandstone ridges, and the head, or rivet, the primitive.

The most valuable mineral products of the mines, in addition to lead, are iron and salt; the latter of which is made, in limited quantities, at a saline spring at Madansburgh, in the county of St. Genevieve. Other indications of it exist at one or two localities in the township of Bellevieu, and on the Maramec river, where efforts were formerly made to manufacture salt.

Iron-ores are found at numerous points; but no body of the ores of this metal is known, comparable, in extent or value, to the locality of Bellevieu, called the Iron Mountain. The ore exists, at this place, in a very massive form. It is in the state of a micaceous oxide. It has been tried in a slag furnace, and smelted easily, without a flux. The iron obtained was of a very malleable quality, and spread freely under the hammer. This locality is embraced by the waters of Cedar creek, which, at the distance of seven miles, are stated to afford a water-power adequate for the reduction and working of the ore. About five miles distant, at Stout's settlement, occurs another body of this ore.

Zinc is found, in the form of a sulphuret, in small quantities, at several of the lead-mines in Washington county. A single mass of the sulphuret of antimony has been discovered in the granitical district, which affords also a locality of coarse graphite, and some other minerals, which will be noticed in the sequel.

A sulphur spring exists a few miles west of the Mississippi, in Jefferson county. The water issues, in a copious stream, from an aperture, situated near a cliff of the compact limestone. It is of a bright, transparent quality, but indicates, by its taste, its sulphureous impregnation, and deposits sulphur, in a whitish pulpy form, on the pebble-stones and fallen vegetation of the brook which issues from the spring.

Topographically considered, the mine country is a hilly and uneven tract, having a considerable elevation above the waters of the Mississippi. It is well watered, with numerous springs, brooks, and streams, and, from the prevalence of a firm diluvial soil, affords facilities for roads. The climate is favorable to health. The manner in which the smelting of the ores is performed, being in the open air, is probably less injurious to those engaged in it, than if the furnaces were enclosed with buildings.

Some losses are sustained in the death of cattle, which die with a disease called the mine sickness. Cows and horses, which are frequently seen licking around old furnaces, often die without any apparent cause. Cats and dogs are taken with violent fits, which never fail, in a short time, to terminate their lives. This is usually attributed, by the inhabitants, to the effects of sulphur, driven off from the ores in smelting. It is more probable that it arises from the sulphurous acid in its combination with barytes, which may operate as a poison to animals. The sickness is wholly confined to quadrupeds.[16]

The soil thrown out of the pits, at the abandoned mines, is found to produce some plants, and even trees, which are not peculiar to the surface. Such are the cotton-wood and the beech-grape, species which are usually confined to the arenaceous alluvions of valleys. And we think their growth here is not promoted by the mineral clay, which is manifestly of a fertilizing property, when cast on the surface; but to the disintegration of the sand-lime, producing a soil favorable to such productions. The sensitive brier, observed in the mine district, is evidently not of this class, as it is found remote from any mine excavations.