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which has hitherto attended the search after lead ore within its confines, render it doubtful. As this formation occupies but a small corner of the district, the examinations were necessarily too limited to enable me to pronounce, with confidence, upon its lead-bearing character.
All the valuable deposites of lead ore which have as yet been discovered, occur either in fissures or rents in the cliff rock, or else are found imbedded in the recent deposites which overlie these rocks. These fissures vary from the thickness of a wafer to thirty or even fifty feet in thickness; and many of them extend to a very great, and at present unknown, depth.
The most common diameter of fissures filled with solid ore is from one to four inches. • In the Apple-river diggings, one vein filled up with ore was reported to me as being, where then worked, four feet across; but an experienced miner, living close to the Illinois line, in one of the richest spots in the district, informed me that he had never seen a solid vein continue, for any considerable distance, of greater thickness than one foot.
In the spring of 1828 there was a mass of lead ore found in an eastand-west crevice, at the Vinegar-hill diggings, about thirty-five feet in length, expanding in the centre to the width of six or eight feet, and terminating in a point at each end. It was hollow, and its walls averaged about a foot in thickness, forming, as it were, a huge shell of mineral. This extraordinary natural chamber was cleared out; a table spread within it on the 4th of July; and a considerable company celebrated the national anniversary within its leaden walls, about sixty feet below the surface of the earth.
The formation of caverns, by the occasional expansion of the lead bearing crevice to a considerable width and height, is not uncominon. The ceiling of such a subterranean chamber is commonly adorned with large, pendant, icicle-like stalactites, which conceal from the eye of the spectator the rich lead ore which they encrust.
A regular vein of ore, half an inch thick, can be worked profitably in a solid rock that requires blasting. But where the crevice is filled with clay or loose rock, a regular vein of but a quarter of an inch will pay well for working.
The fissures which bear productive lead veins generally run east and West; or, rather, a little south of east, and north of west. In but a few
instances are they found quartering (say) northeast and southwest. On the · west of the Mississippi, the north-and-south lodes are always very thin;
generally not thicker than a knife.blade; and are seldom followed, except in drifting from one east-and-west vein to another.
Exceptions to this are found east of the Mississippi. In the neighborhood of Mineral Point and Dodgeville, north-and south lodes have been found equally productive with those running east and west.
The downward inclination of these crevices has scarcely any uniformity. The same fissure may have an inclination, for ten feet, of forty-five degrees; the next ten be vertical; then it may be arrested at some particular stratum, and strike off horizontally, between the strata, for from one to twenty feet; when it may again resume its vertical direction. Thus the hade of the lead veins is very irregular.
The ore does not, in general, fill the entire crevice, but is commonly surrounded by, and imbedded in, either clay or sand, Crys:allized carbonate
.. of lime (calcareous spar) frequently accompanies the ore, and may be considered ihe veinstone or gangue of these lead-mines.*
The most usual position of the ore in the fissures is in detached pieces, most commonly of a cubical form, varying from the size of a pea up to · masses of one thousand pounds and upwards in weight. The clav in
which it is imbedded is usually ferruginous ; sometimes of a jet black, owing to the presence of manganese. Sometimes the ore reposes in a tine sandy-looking powder, the result of the decomposition of the rock. A portion of the crevice is also often filled with masses of rock which have falec from the walls of the fissure. - Though the ore be found, as above stated, usually in detached masses,
yet these assume, in the fissure, a certain degree of regularity; often occur• ring in regularly descending steps, as represented in this sketch. (see sketch " No. 8,) exhibiting a vertical section of a lead mine, and bringing into view
the surface soil superincumbent on the cap-rock, below which is shown a longitudinal section of the lead bearing fissure-the gangie shaded dark,
and the lead ore somewhat lighter; showing also the mode of drifting, 2, and of ascending and descending in the shaft. Although the above is the í most common position of the lead ore, it is sometimes found in a solid
sheet, compressed between the sills of the crevice; and is then called by :: the miners " sheet mineral.”. When found in detached masses, as above 's described, it is commonly termed by the workmen "chunk ore."
" The lead bearing fissures frequently do not reach within many feet of ti the upper surface of the rock, but are overcapped by a thick and solid · stratum. (See sketch No. 8.) Occasionally, however, they extend to the
surface, and open externally. At other times, they terminate upwards in a
contracted funnel, which alone, chimney-like, reaches the surface. It is ... remarkable, that though the lead ore is never found attached to the walls is of the fissure, it frequently occurs completely imbedded in the superincum3. bent cap-rock.
Much lead is raised from what are called "clay diggings.” In these the ore is commonly found in detached fragments, but occasionally in regular ; sheets; and it is covered up, sometimes to a very inconsiderable depth, by
ferruginous clay, sand, or detrites, (crumbled rock.) The ore in these localities appears to have dropped into its present position, in proportion as the rock which originally encased it gradually sunk under decaying influences; and the veins, in some places, have retained their former contin
uity, and may still occasionally be traced horizontally for some distance • along the ground where they may be supposed to have fallen, until they
dip into a vertical fissure; the upper portion of which fissure, now decayed and gone, they doubtless formerly occupied.
There are only one or two instances, in Iowa or Wiskonsin, where the lead ore is fun! associated with sulphate of barytes, (near Mineral Point, and at Gratioi's Grore mine :) though this is the most common gangue in Missouri, and in many other lead-mines, Boris
stance, those in the Hartz mountains, in the south of Hanover. Neither was the ore lund Ni associated with the fluate of lime, (fluor spar,) as in Scotland it frequently is. The only lo
cality of this mineral in these western Stales is, I believe, near Shawneetown, in the Suate 3 : Illinois, where it is found along with galena.
The clay which, with the ore and loose rocks, fills the fissures, appears to render them water. tight, and obstructs the flow of water through the rocks formation; a circumstance which w be of great importance when the mines are worked deep enongh to require draining, as it will divide the lead-bearing rock into water tight compariments in the same manner
a in other mining districts present the influx of water from one inine to another. Were ibis auf sto so, it would be impossible to keep the mines drained, even witb powerful steam-edgides,
... The ore thus found has been denominated float mineral; incorrectly, ** however, if by that term is to be understood ore which has been transported
from other distant localities to its present position. Drop minerat would 11. have been a more correct expression.
" It is a remark made by geologists, that mineral veins generally occur in ** proximity to the sources of subterranean heat; and trap dikes, toadstone, 40greenstone, and other ancient volcanic rocks, frequently intersect metal75 liferous rock formations. In sowa and Wiskonsin, however, careful exammination and inquiry resulted in no discovery of any effects of volcanic action, poi except only in the undulation and irregular dip of the rock; and perhaps
in the existence of the fissures themselves, if their origin may correctly be "!, referred to dislocation-a doubisul point.
The symptoms of lead ore in Wiskonsin are various and important.
Inasmuch as the ore is chiefly found in fissures, whatever indicates the !" vicinity of a fissure may be considered as indicating also the neighborhood 44 of lead ore. Thus, when the outline of a hill presents a sort of bench, or "" step, or slight undulation, like this: (see sketch No. 9,) even if but small, and
not readily remarked, yet as indicating a slight slip from an internal rent, it 13 becomes a symptom of lead, which the experienced miner's eye instantly t; detects. For the same reason, a small longitudinal depression, or miniature *34 ravine, on a hill-side, may also be considered a symptom.
Again: sink-holes ranging either in an east-and-west, or in a north-and2 south.course, are an indication. So also is a rank growth of vegetation in ' a linear direction ; especially of plants with deep-reaching radicals.
The discovery on the surface of fragments of calcareous spar (crystal09!. lized carbonate of lime) is also an indication of lead, that spar being, as 1561: already stated, the gangue of these lead-mines ; but if found in large quan
tities, as in the southern and western portions of the district, it is an unfaIX**vorable sign, as indicating that the fissures are chiefly, or entirely, filled up " with this vein-stone, to the exclusion of ore.
The red appearance of the surface, indicating the ferruginous clay in , . which the mineral is often imbedded, may be considered an indication ; I though it is not so striking a feature here as in the Missouri lead region. 13. Indeed, the surface signs generally in the Wiskonsin lead district are less
distinctly marked than in that of Missouri. In some of the spots most pro4444 ductive in minerals, nothing appears but the rich black vegetable mould, ' 'with occasional pieces of chert interspersed, and the rock showing itself 191 'only occasionally in the cuts of the adjacent streams.
But, of all surface indications, the discovery of (so called)“gravel mineral," 19! (small pieces of lead ore,) in connexion with the crumbling and arenaceous si appearance of the adjacent magnesian limestone, is the most trustworthy.
To this may be added minute dark specks distributed over the rock, often assuming the form of delicate miniature feros.
The only coralline which I detected in the true productive lead-benring
rock is a reticulated fossil, resembling the coscinopora sulcata of Goldsuss. .HR/ See skelch No. 10.) Its presence may be considered a good indication of
mobilead. After a productive lode has once been struck, so muilorm is generally 11 the direction of the crevice which contains it, that, by taking its bearing by alij icompass, "additional shafts may be sunk without prospecting, and yet with aff assurance of striking the lode, even though at cousiderable distance Irom the
When a miner sets out in search of lead ore, he usually begins by what is called prospecting;" that is, on those spots where surface or other indications lead him to expect a discovery of ore, he commences digging holes or sins og shafts, usually on the summit or the declivity of a hill. Should he ta. i the first attempt to reach gravel mineral, or to come upon any signs of neighborhood to a fissure, he soon abandons the spot, and begins to dig ese where. The ground in niany portions of the lead district is found riddiad with such pits, called, in the language of the Wiskonsin miner. “ prospect holes.” Should he reach encouraging symptoms, or actually strike upon ! vein, or upon detached pieces of ore ranging downwards, he continues bis labor, often with very great profit.
When, after preliminary examinations, he decides to sink a shait, with the view of striking a crevice, he is compelled, until he reaches the rock, to rall ' up the shaft with logs.
These shafts, of irregular form, usually approaching a cylinder, are generally from four to five feet across. Sometimes the rock is soit enough to be quarried with hammer, gad, and pickaxe; at others, it is found neces. sary to blast it with gunpower.
The mode of descending is by means of a rope of raw hide, and a cosmon windlass worked by one or two men. (See sketch No. 8.) By the same simple contrivance, the ore is raised to the surface. Sometimes, bu: rarely, ladders are used to ascend and descend.
When a miner is fortunate enough to discover a productive vein accessible from a hill side, he forms a drift, and very conveniently conveys be ore out in wheelbarrows-of course, at a very trifling expense.
The shafts are sunk in this lead region to the depth of fifty, one hue. dred, or one hundred and fifty feet. They are usually abandoned as seca as the mine is inundated with water, unless the miner, by drifung (that is, working horizontally) until the external surface of the hill is reached, can readily drain the mine. There is but a single instance in the district where a mine has been prosecuted after being flooded with water, which could not thus be got rid of: namely, at Hamilton's diggings, near the Peccatonnica, where the mine is readily drained by a small steam-engine. The water in this mine was struck at the depth of thirty feet, and the mine has been worked with profit thirty-five feet below that point.
In the deeper diggings, the damp (carbonic acid gas) sometimes accumulates in such quantities towards the bottom as to render it dangerous to work. This happens chiefly in the hot months of summer; and at such seasons the miners are frequently compelled to discontinue their labors.
The means of ventilation yet employed are very simple. A cloth funnel, its upper portion so placed as to receive the breeze and deflect it into the shaft, is the only contrivance.
The lead ore which, with a few local exceptions, is alone found or work. ed in this district, is the galena, or sulphuret of lead; the same species of ore from which nearly all the lead of commerce is derived.
One of these local exceptions, however, is to be found at Mr. Brighan's mines, near the Blue Mounds, where carbonate of lead is raised in consider able quantities along with the galena. This carbonate is also found in other portions of the district. It is very easily reduced ; more so than the sulphuret, inasmuch as the carbonic acid is more readily expelled than the sulphur,
The ores of this lead region are, in general, remarkably pure,* and free from adhering gangne. In a few localities the sulphuret ot lead is intermixed with black-jack, (sulphuret of zinc,) and occasionally with carbonate of zinc and oxide of iron.
The process for reducing the lead ore has of late been much improved. Instead of the old log and ash furnaces, (which consumed the best timber in lavish quantities,) cupola, blast, and reverbatory furnaces, have been introduced, which demand comparatively little fuel; an economy of vast importance in a country scantily timbered, devoid of coal, where wood is often sold at five dollars a cord.
STATISTICS OF THE LEAD REGION. In proportion as I proceeded with the geological survey of the Wiskonsin lead region, I became more and more strongly impressed with its great value and rich promise of commercial importance. This conviction urged me to the task of carefully collecting and collating such facts as might supply materials for a comparison between the geological character of this region, and that of the richest lead district in Europe—the Cross Fell country of the North of England. That comparison has been briefly made in a previous section of this report. So far as it goes, it is in a pecuniary and commercial view highly satisfactory; for the strong similarity between the two formations furnishes an encouraging item in an estimate of the value of the mineral tract now under examination.
But other and more direct proof of that value yet remains. The statistics of this American lead region, so lately settled ; so imperfectly known even now; so inefficiently worked, for lack of force, even in those locations where a cursory survey had chanced upon rich lead veins : these statistics (uncertain though they be) of a country so new and rude, impel us to the conclusion that the Wiskonsin lead region may compare, if not in present productiveness, at least in future prospects, with any other in the known world. * The analysis of two average specimens of galena resulted as follows:
16.00 Lead" :
100.00 The specific gravity of these ores is ·
7.52 In the reduction of sulphuret of lead, great care should be taken, while roasting, never to raise the heat so high as to melt the ore. If the ore be melted before all the sulphur is expelled, it is almost impossible enthly to get rid of the sulphur. Free access of air should be allowed during the roasting process, so as to furnish oxygen for the conversion of the sulphur into salphurous acid, the form under which it must be expelled from the lead. The melted lead, on the contrary, should not be unnecessarily exposed to currents of air, which, in a state of fusion, rapidly oxydizes this metal. The analysis of the carbonate of lead gave: Carbonic acid
. - 16.00 Lead
. 72.06 ) Oxygen
- 5.56 protoxide of lead 77.62 Oxide of iron .
2.00 Insoluble residuum
1.80 Lime -
1.00 Water of absorption
The specific gravity of this ore is 6.04.