and chemical, that one familiar with it from any one locality can hardly fail to recognize it when coming from others. The iron produced from it is always "cold-short," on account of the large content of phosphorus; but, mingled with siliceous ores free from phosphorus, it yields always a most excellent foundry iron. It is mined at numerous points from New York to Tennessee, and at some points reaches a very great total thickness. In Wisconsin the Clinton rocks merge into the great Niagara limestone series of the eastern part of the state, but at the bottom of the series, in a few places, the Clinton ore is found immediately overlying the Cincinnati shales. The most important locality is that known as Iron Ridge, on sections twelve and thirteen in the town of Hubbard, in Dodge county. Here a north-and-south ledge of Niagara limestone overlooks lower land to the west. Underneath, at the foot of the ridge, is the ore bed, fifteen to eighteen feet in thickness, consisting of horizontally bedded ore, in layers three to fourteen inches thick. The ore has a concretionary structure, being composed of lenticular grains, one twenty-fifth of an inch in diameter, but the top layer is without this structure, having a dark purplish color, and in places a slight metallic appearance. Much of the lower ore is somewhat hydrated. Three quarters of a mile north of Iron Ridge, at Mayville, there is a total thickness of as much as forty feet. According to Mr. E. T. Sweet, the percentages of the several constituents of the Iron Ridge ore are as follows: iron peroxide, 66.38; carbonate of lime, 10.42; carbonate of magnesia, 2.79; silica, 4.72; alumina, 5.54; manganese oxide, 0.44; sulphur, 0.23; phosphoric acid, 0.73; water, 8.75 100: metallic iron, 46.66.

Two small charcoal furnaces at Mayville and Iron Ridge smelt a considerable quantity of these ores alone, producing an iron very rich in phosphorus. An analysis of the Mayville pig iron, also by Mr. Sweet, shows the following composition: iron, 95.784 per cent; phosphorus, 1.675: carbon, 0.849; silicon, 0.108 = 100.286. The average furnace yield of the ore is fortyfive per cent. By far the larger part of the ore, however, is sent away to mingle with other ores. It goes to Chicago, Joliet and Springfield, Ill., St. Louis, Mo., Wyandotte and Jackson, Mich., and Appleton, Green Bay and Milwaukee, Wis. In 1872, the Iron Ridge mines yielded 82,371 tons. The Clinton ore is found at other places farther north along the outcrop of the base of the Niagara formation in Wisconsin, but no one of these appears to promise any great quantity of good ore. Red hematite is found at numerous places in Wisconsin, highly charging certain layers of the Potsdam sandstone series, the lowest one of the horizontal Wisconsin formations. In the eastern part of the town of Westfield, Sauk county, the iron ore excludes the sandstone. forming an excellent ore. No developments have been made in this district, so that the size of the deposit is not definitely known.

BROWN HEMATITES.

These ores contain their iron as the hydrated, or brown, sesquioxide, which, when pure, has about sixty per cent. of the metal; the ordinary brown hematites, however, seldom contain over forty per cent. Bog iron ore, a porous brown hematite that forms by deposition from the water of bogs, occurs somewhat widely scattered underneath the large marshes of Portage, Wood and Juneau counties. Very excellent bog ore, containing nearly 50 per cent. of iron, is found near Necedah, Juneau county, and near Grand Rapids, Wood county, but the amount obtainable is not definitely known. The Necedah ore contains: silica, 8.52; alumina, 3.77; iron peroxide, 71.40; manganese oxide, 0.27; lime, 0.58; magnesia, trace; phosphoric acid, 0.21; sulphur, 0.02; organic matter, 1.62; water, 13.46=99.85; metallic iron, 49.98according to Mr. E. T. Sweet's analysis. An ore from section 34, twp. 23, range 6 east, Wood county, yielded, to Mr. Oliver Matthews, silica, 4.81; alumina, 1.00; iron peroxide, 73.23; lime, 0.11, magnesia, 0.25; sulphuric acid, 0.07; phosphoric acid, 0.10; organic matter, 5.88; water,

14.24; 99.69: metallic iron, 51.26.

Brown hematite, mingled with more or less red ore, occurs also in some quantity filling cracks and irregular cavities in certain portions of the Potsdam series in northwestern Sauk county and the adjoining portion of Richland. A small charcoal furnace has been in operation on this ore at Ironton, Sauk county, for a number of years, and recently another one has been erected at Cazenovia in the same district.

MAGNETIC ORES AND SPECULAR HEMATITES.

These are taken together here, because their geological occurrence is the same, the two ores occurring not only in the same group of rocks, but even intimately mingled with one another. These ores are not now produced in Wisconsin; but it is quite probable that they may before many years become its principal mineral production. In magnetic iron ore, the iron is in the shape of the mineral magnetite, an oxide of iron containing 72 4 per cent of iron when pure, and this is the highest percentage of iron that any ore can ever have. Specular hematite is the same as red hematite, but is crystalline, has a bright, metallic luster, and a considerable hardness. As mined the richest magnetic and specular ores rarely run over 65 per cent., while in most regions. where they are mined they commonly do not reach 50 per cent. The amount of rich ores of this kind in the northern peninsula of Michigan is so great, however, that an ore with less than 50 per cent. finds no sale; and the same must be true in the adjoining states. So largely does this matter of richness affect the value of an ore, that an owner of a mine of 45 per cent. "hard" ore in Wisconsin would find it cheaper to import and smelt Michigan 65 per cent. ore, than to smelt his own, even if his furnace and mine were side by side.

The specular and magnetic ores of Wisconsin occur in two districts the Penokee iron district, ten to twenty miles south of Lake Superior, in Bayfield, Ashland and Lincoln counties, and the Menomonee iron district, near the head waters of the Menomonee river, in township 40, ranges 17 and 18 east, Oconto county. Specular iron in veins and nests is found in small quantities with the quartz rocks of the Baraboo valley, Sauk county, and Necedah, Juneau county; and very large quantities of a peculiar quartz-schist, charged with more or less of the magnetic and specular iron oxides, occur in the vicinity of Black River Falls, Jackson county; but in none of these places is there any promise of the existence of valuable ore.

In the Penokee and Menomonee regions, the iron ores occur in a series of slaty and quartzose rocks known to geologists as the Haronian series. The rocks of these districts are really the extensions westward of a great rock series, which in the northern Michigan peninsula contains the rich iron ores that have made that region so famous. In position, this rock series may be likened to a great elongated parabola, the head of which is in the Marquette iron district and the two ends in the Penokee and Menomonee regions of Wisconsin. In all of its extent, this rock series holds great beds of lean magnetic and specular ores. These contain large quantities of quartz, which, from its great hardness, renders them very resistant to the action of atmospheric erosion. As a result, these lean ores are found forming high and bold ridges. Such ridges of lean ores have deceived many explorers, and not a few geologists. In the same rock series, for the most part occupying portions of a higher layer, are found, however, ores of extraordinary richness and purity, which, from their comparative softness, very rarely outcrop. The existence in quantity of these very rich ores in the Menomonee region has been definitely proven. One deposit, laid open during the Summer of 1877, shows a width of over 150 feet of first class specular ore; and exceeding in size the greatest of the famous deposits of Michigan. In the Penokee region, however, though the indications are favorable, the existence of the richer ores is as yet an inference only. The Penokee range itself is a wonderful development of

lean ore, which forms a continuous belt several hundred feet in width and over thirty miles in length. Occasionally portions of this belt are richer than the rest, and become almost merchantable ores. The probability is, however, that the rich ores of this region will be found in the lower country immediately north of the Penokee range, where the rocks are buried beneath heavy accumulations of drift material.

COPPER.

The only copper ore at present raised in Wisconsin is obtained near Mineral Point, in the lead region of the southwestern part of the state, where small quantities of chalcopyrite, the yellow sulphide of copper and iron, are obtained from pockets and limited crevices in the Galena limestone. Copper pyrites is known to occur in this way throughout the lead region, but it does not appear that the quantity at any point is sufficient to warrant exploration.

Copper occurs also in the northernmost portions of Wisconsin, where it is found under altogether different circumstances. The great copper-bearing series of rocks of Keweenaw point and Isle Royale stretch southwestward into and entirely across the state of Wisconsin, in two parallel belts. One of these belts enters Wisconsin at the mouth of the Montreal river, and immediately leaving the shore of Lake Superior, crosses Ashland and Bayfield counties, and then widening greatly, occupies a large area in Douglas, St. Croix, Barron and Chippewa counties. The other belt forms the backbone of the Bayfield peninsula, and crosses the northern part of Douglas county, forming a bold ridge, to the Minnesota line. The rocks of this great series appear to be for the most part of igneous origin, but they are distinctly bedded, and even interstratified with sandstone, shales, and coarse boulder-conglomerate, the whole series having generally a tilted position. In veins crossing the rock-beds, and scattered also promiscuously through the layers of both conglomerates and igneous rocks, pure metallic copper in fine flakes is often found. Mining on a small scale has been attempted at numbers of points where the rivers flowing northward into Lake Superior make gorges across the rock series, but at none of them has sufficient work been done to prove or disprove the existence of copper in paying quantity.

GOLD AND SILVER.

Small traces of gold have been detected by the writer in quartz from the crystalline rocks of Clark county, but there is no probability that any quantity of this metal will ever be found in the state. Traces of silver have also been found in certain layers of the copper series in Ashland county. Judging from the occurrence of silver in the same series not far to the east in Michigan, it seems not improbable that this metal may be found also in Wisconsin.

BRICK CLAYS.

These constitute a very important resource in Wisconsin. Extending inland for many miles from the shores of Lakes Michigan and Superior are stratified beds of clay of lacustrine origin, having been deposited by the lakes when greatly expanded beyond their present sizes. All of these clays are characterized by the presence of a large amount of carbonate of lime. Along Lake Superior they have not yet been utilized, but all through the belt of country bordering. Lake Michigan they are dug and burned, fully 50,000,000 bricks being made annually in this region. A large proportion of these bricks are white or cream-colored, and these are widely known under the name of "Milwaukee brick," though by no means altogether made at Milwaukee. Others are ordinary red brick. The difference between the light-colored and red bricks is ordinarily attributed to the greater amount of iron in the clay from which the latter are

burned, but it has been shown by Mr. E. T. Sweet that the white bricks are burned from clay which often contains more iron than that from which the red bricks are made, but which also contains a very large amont of carbonate of lime. The following analyses show (1) the composition of the clay from which cream-colored brick are burned at Milwaukee, (2) the composition. of a red-brick clay from near Madison, and (3) the composition of the unutilized clay from Ashland, Lake Superior. Nos. 1 and 2 are by Mr. E. T. Sweet, No. 3 by Professor W. W.

Daniells:

At Milwaukee 24,000,000 cream-colored brick are made annually; at Racine, 3,500,000; at Appleton and Menasha, 1,800,000 each; at Neenah, 1,600,000; at Clifton, 1,700,000; at Waterloo, 1,600,000; and in smaller quantities at Jefferson, Ft. Atkinson, Edgerton, Whitewater, Geneva, Ozaukee, Sheboygan Falls, Manitowoc, Kewaunee, and other places. In most cases the cream-colored bricks are made from a bright-red clay, although occasionally the clay is lightcolored. At Whitewater and other places tile and pottery are also made from this clay.

Although these lacustrine clays are much the most important in Wisconsin, excellent brick clays are also found in the interior of the state. In numbers of places along the Yahara valley, in Dane county, an excellent stratified clay occurs. At Madison this is burned to a red brick ; at Stoughton and Oregon to a fine cream-colored brick. At Platteville, Lancaster, and other points in the southwestern part of the state, red bricks are made from clays found in the vicinity.

KAOLIN (PORCELAIN - CLAY-FIRE - CLAY).

The word "kaolin" is applied by geologists to a clay-like material which is used in making chinaware in this country and in Europe. The word is of Chinese origin, and is applied by the Chinese to the substance from which the famous porcelain of China is made. Its application to the European porcelain-clay was made under the mistaken idea-one which has prevailed among scientists until very recently-that the Chinese material is the same as the European. This we now know to be an error, the Chinese and Japanese wares being both made altogether from a solid rock.

True kaolin, using the word in its European sense, is unlike other ordinary clays, in being the result of the disintegration of felspathic crystalline rocks "in place," that is without being removed from the place of its first formation. The base of kaolin is a mineral known as kaolinite, a compound of silica, alumina and water, which results from a change or decay of the felspar of felspar-bearing rocks. Felspar contains silica, alumina, and soda or potash, or both. By percolation through the rocks of surface water carrying carbonic acid, the potash and soda are removed and kaolinite results. Mingled with the kaolinite are, however, always the other ingredients of the rock, quartz, mica, etc., and also always some undecomposed, or only partly decomposed felspar. These foreign ingredients can all, however, be more or less perfectly removed by a system of levigation, when a pure white clay results, composed almost wholly of the scales of

the mineral kaolinite. Prepared in this way the kaolin has a high value as a refractory material, and for forming the base of fine porcelain wares.

The crystalline rocks, which, by decomposition, would produce a kaolin, are widely spread over the northern part of Wisconsin; but over the most of the region occupied by them there is no sign of the existence of kaolin, the softened rock having apparently been removed by glacial action. In a belt of country, however, which extends from Grand Rapids on the Wisconsin, westward to Black river, in Jackson county, the drift is insignificant or entirely absent; the glacial forces have not acted, and the crystalline rocks are, or once were, overlaid by sandstone, along whose line of junction with the underlying formation numerous water-courses have existed, the result being an unusual amount of disintegration. Here we find, in the beds of the Wisconsin, Yellow, and Black rivers, large exposures of crystalline rocks, which between the rivers are overlaid by sandstone. The crystalline rocks are in distinct layers, tilted at high angles, and in numerous places decomposed into a soft white kaolin. Inasmuch as these layers strike across the country in long, straight lines, patches of kaolin are found ranging themselves into similar lines. The kaolin patches are most abundant on the Wisconsin in the vicinity of the city of Grand Rapids, in Wood county. They vary greatly in size, one deposit even varying from a fraction of an inch to a number of feet in thickness. The kaolin varies, also, greatly in character, some being quite impure and easily fusible from a large content of iron oxide or from partial decomposition only, while much of it is very pure and refractory. There is no doubt, however, that a large amount of kaolin exists in this region, and that by selection and levigation an excellent material may be obtained, which, by mingling with powdered quartz, may be made to yield a fire-brick of unusual refractoriness, and which may even be employed in making fine porcelain ware.

The following table gives the composition of the raw clay, the fine clay obtained from it by levigation, and the coarse residue from the same operation, the sample having been taken from the opening on the land of Mr. C. B. Garrison, section 5, town 22, range 6 east, Wood county:

Certain layers of the Lower Magnesian limestone, as at Ripon, and other points in the eastern part of the state, are known to produce a lime which has in some degree the hydraulic property, and the same is true of certain layers of the Blue limestone of the Trenton group, in the southwestern part of the state; the most valuable material of this kind, however, that is as yet known to exist in Wisconsin, is found near Milwaukee, and has become very recently somewhat widely known as the "Milwaukee" cement-rock. This rock belongs to the Hamilton formation, and is found near the Washington street bridge, at Brown Deer, on the lake shore at Whitefish