By carefully studying the references to each congressionally-surveyed township in the county, it will be seen that the whole region lies within the great driftless area of the State, and that its surface contour has never been modified by glacial action.
We notice here high rolling ridges of land, intersected in all directions with deep ravines and valleys, often bordered with precipitous cliffs, --- the elevation of the ridges above the valleys being from 300 to 500 feet. The valleys in their length and breadth are the effect of erosion only; but it seems probable that the streams formerly were much larger and acted with greater rapidity and force. When we mentally reconstruct the country, as it must once have been, by filling up the valleys with the formations now found on their sides, and then add the formations whose outlines still remain, we can appreciate the immense denudation which the country has undergone.
Township 8, range 3 west (Marietta in part). This township is very hilly and rough land. The hills are high, steep, and covered with heavy timber of maple, elm, oak and basswood. The soil is a sandy clay. The formations are Potsdam, Lower Magnesian and St. Peters sandstone.
Township 9, range 3 west (Scott). The divide between Knapp creek and the Kickapoo passes irregularly through the township from section 31 to section 5. The ridge is, in some places, quite wide, and contains some good farming land. The township is well watered by numerous streams flowing from its center in all directions. The timber is very large and dense. The Potsdam covers one-third of the township, including all the valleys, and the Lower Magnesian the rest, excepting a narrow belt of St. Peters along the divide.
Township 10, range 3 west (Clayton in part). The divide mentioned in township 9 continues through township 10, from sections 32 to section 3, with numerous lateral spurs and ridges. The township consists chiefly of high, rolling, ridge land, with numerous ravines running down to the streams. The soil is clay, and the timber very dense and large, with but little underbrush. The principal trees are maple and elm. Along the crest of the divide, on sections 3, 9, 16 and 20, are some very conspicuous mounds formed by outliers of St. Peters sandstone. Sink holes are also of frequent occurrence. Water is obtained with difficulty on the ridges. In places wells are sunk from 100 to 165 feet. The formations are the same as in township 9.
Township 11, range 3 west (part of Clayton in Crawford county, and of Kickapoo in Vernon county). The eastern and central parts of this township consist of high, wide, rolling ridges; and the western part, of steep, rocky bluffs. The township is watered by the Kickapoo on the west and north. Fine springs are very numerous. The valley of the Kickapoo averages about a mile in width. The soil throughout the township is clay and the timber very heavy. The Potsdam covers about one-third of the township; the Lower Magnesian, one-half; and the St. Peters, one-sixth. Many loose bowlders of the St. Peters are found on the ridges where the formation cannot be found in place. The general section, in this township, of the formation is as follows:
Feet. St. Peters sandstone...............50 Lower Magnesian limestone.........150 Potsdam sandstone.................300 ----- From ridge to valley, total.......500
Township 7, range 4 west (Wauzeka in part). The part of this township which lies north of the Wisconsin river consists almost exclusively of the alluvial bottoms of that river and the Kickapoo. It is densely timbered with elm, maple, basswood, butternut, etc., with a deep, black, swampy soil. The hills which inclose the rivers are found along the north line of the township. The formations are Potsdam and Lower Magnesian.
Township 8, range 4 west (parts of Wauzeka, Marietta and Eastman). There is a high ridge running in a northeasterly course through this township, from which the ground slopes to the Kickapoo and Wisconsin rivers. The country is very hilly, the ridges narrow and broken by deep ravines. The soil is clay, and the timber very large and dense. The township is well watered by the Kickapoo and its several branches. There are a great many large springs in the valley of the Kickapoo. The Potsdam covers about one-sixth of the township; the Lower Magnesian, two-thirds; and the St. Peters sandstone and Trenton limestone, one sixth. The general section of this township, taken from the ridge of the Kickapoo is:
Feet. Trenton limestone..................30 St. Peters sandstone..............100 Lower Magnesian limestone.........180 Potsdam sandstone.................170 ----- Total from ridge to valley........480
Township 9, range 4 west (Haney). A large part of this township is occupied by the valley of the Kickapoo, which is from one-half to a mile wide. The stream is about 200 feet wide, very crooked and sluggish. On each side of the river the country is very hilly. The valley of the Kickapoo and the country to the east of it has the heavy timber --- maple, elm, etc.; but, west of the valley, the hills are smooth and bare, many of them showing terraces of the Potsdam, and the timber is white oak in grove, on the tops of the ridges. The formations are Potsdam, one-third; Lower Magnesian, two-thirds; and some ridges and mounds of St. Peters on the eastern side.
Township 10, range 4 west, (east part of Utica and west part of Clayton.) The general features of this township are similar to those of township 9. The valley of the Kickapoo is wider, more sandy, and less heavily timbered. Fine springs are very numerous. The formations are Potsdam and Lower Magnesian in about equal parts.
Township 11, range 4 west, (part of Utica in Crawford county, and of Franklin in Vernon county.) This township is composed chiefly of high, rolling ridge land, with a clay soil. In the central part of the township the soil is rather sandy, owing to a long belt of St. Peters which crosses the township from section 4 to section 34. The timber consists of groves of large white oaks. The formations are Potsdam one-sixth; Lower Magnesian two-thirds; and St. Peter's sandstone, one-sixth.
Township 7, range 5 west, (Wauzeka in part). This is a very hilly township. It is watered by the Wisconsin river, Grand Gris and Little Kickapoo. The valleys and sides of the ravines are heavily timbered with elm, maple, basswood, butternut, etc. There are two very high and wide ridges in the northern and northwestern parts of the township, where the soil is clay, rather shallow, and the timber smaller and more scattering. All the formations from the Potsdam to the Galena limestone, inclusive, are represented.
Township 8, range 5 west, (parts of Wauzeka and Eastman.) The high ridge which divides the Kickapoo and Mississippi rivers passes through the west side of this township. From it the country slopes to the east in wide, regular ridges, and deep narrow ravines. The soil throughout the township is clay. The timber is small and consists of groves of small black oak. Much of the country is prairie and devoid of timber. The geological formations are the same as in township 7. The general section of this township, from section 32 on the ridge to section 36, on the Kickapoo, is as follows:
Feet. Galena limestone...................20 Blue limestone.....................25 Bluff limestone....................20 St. Peter's sandstone.............100 Lower Magnesian limestone.........180 Potsdam sandstone.................100 ----- From ridge to river, total........445
Township 9, range 5 west, (Seneca in part.) The divide continues from the last township, from section 31 to section 3. It is very high, wide and rolling, with numerous subordinate ridges. The township is well watered by numerous small streams, and springs are found quite near the summit of the ridge, issuing from the numerous clay layers in the Trenton limestone. The soil is clay, frequently rather sandy. The timber is oak, small but quite abundant. All the formations from the Galena limestone to the Potsdam, are present; the St. Peter's and the Lower Magnesian are the prevailing ones.
Township 10, range 5 west, (parts of Utica, Freeman and Seneca.) The divide continues a nearly north and south course from section 34 to section 3. The general features of the country are very similar to those of township 9. Much of the township is prairie. The soil is a deep clay and the timber light. With the exception of the principal ridge, the country is very hilly and the valleys very deep and narrow. The formations are Potsdam, Lower Magnesian and St. Peter's; the last two being the principal ones.
Township 11, range 5 west, (parts of Utica and Freeman in Crawford county, and of Franklin and Sterling in Vernon county.) This is chiefly a prairie country; the divide is high, wide and rolling, extending from section 35 to section 1. There are no large streams in the township, but numerous small ravines running east and west from the divide. Small springs are quite numerous and the greater part of the township is available for agricultural purposes. The formations are St. Peters and Lower Magnesian in about equal parts.
Township 6, range 6 west (part of the town of Bridgeport and of the city of Prairie du Chien.) That part of this township which lies north of the Wisconsin river consists of the rich alluvial bottom lands of that stream, with numerous sloughs and swamps. The bluffs which inclose the river on the north commence near the north line of the township. The township is well timbered; soil, clay. The formation is Lower Magnesian.
Township 7, range 6 west, (parts of the towns of Bridgeport and Prairie du Chien and of the city of Prairie du Chien.) The high ridge which divides the Kickapoo and the Mississippi begins in this township and runs northeast, passing out at section 2. The ridge is wide, level and heavily timbered with white, black and burr oak. The soil is clay. The township is well watered and springs are quite numerous. On the west side is the valley of the Mississippi from one to two miles wide between the bluffs and the river. Its soil is sandy. All the formations are present from the Galena to the Lower Magnesian, inclusive.
Township 8, range 6 west, (part of Eastman.) The land in this township is very hilly and rough, being composed of long, straight ridges, which run east and west and become quite narrow as they approach the Mississippi on the west. There are a great many good springs arising near the ridge which in the course of a half mile sink into the ground, so that the large ravines although deep, seldom have any water in them. The soil is clay and in the western part quite stony. The timber is small and rather sparse. The formations are Galena limestone to Potsdam sandstone, inclusive. The general section of this township from section 23 to the Mississippi river is as follows:
Feet. Galena limestone.....................50 Trenton limestone (blue and buff)....40 St. Peters sandstone................110 Lower Magnesian limestone...........250 Potsdam sandstone....................20 ----- From ridge to valley, total.........470
Township 9, range 6 west, (part of Seneca). The bend of the Mississippi river causes this to be a fractional township, containing only about twelve square miles. It is composed of steep and rocky bluffs, forming the ends of ridges, often making perpendicular cliffs and escarpments of rock for long distances along the bank of the river. The township is covered with small timber. The ridges are very high, narrow and steep. The formations are the same as in township 9, just mentioned.
Township 10, range 6 west, (parts of Seneca and Freeman). This is also a fractional township and contains about twenty square miles. It is well watered by the Mississippi river and Sugar, Buck and Copper creeks. Fine large springs are very numerous. The soil throughout the township is clay and the timber small but abundant. The valleys and ridges are wide. The formations are the Potsdam and Lower Magnesian in about equal parts.
Township 11, range 6 west, (part of Freeman in Crawford county, and of Wheatland and Sterling in Vernon county). This township consists chiefly of high rolling, ridge land, having an elevation from 400 to 550 feet above the Mississippi. The principal ridge is very wide and runs east and west through the northern part of the township, with numerous smaller ridges running north and south. The soil is clay, in some parts rather sandy. The timber is small, but abundant. Water is very scarce on the ridges. The only stream is Rush creek in the southern part of the township; it has a rich and fertile valley about half a mile in width. The formations are Potsdam, Lower Magnesian and St. Peters; the two latter predominating.
Township 11, range 7 west, (part of Freeman in Crawford county, and Wheatland in Vernon county). This is a township made fractional by the Mississippi river, and contains about sixteen square miles. It is very hilly. The river runs close to the bluffs, which are high and precipitous. The soil is clay and the timber white oak. The formations are Potsdam, Lower Magnesian and St. Peters, the second being the prevailing one.
Fractional Townships, 6, (being a part of Bridgeport), 7, (being a portion of the city and town of Prairie du Chien), 8, (being a part of Eastman) and 10, (being a portion of Freeman), range 7 west. These fractional townships lie immediately upon the Mississippi river, the land being in many places subject to overflow in high water.
Fractional Townships 7, range 3 west, (in Marietta), and fractional township 6, range 7 west, (in Wauzeka), both lie immediately north of and are washed by the Wisconsin river.
There are some fine exposures of the Potsdam sandstone in Crawford county.
(1.) There is one on the northwest quarter of section 11, township 10, range 4 west, (Clayton), where a small creek enters the Kickapoo.
(2.) On the Kickapoo, on the southwest quarter of section 27, township 9, range 4 west, (Haney), where the top of the Potsdam is distinctly marked by a bed of white sandstone fifteen feet thick. Above it are the transition beds, and the lower beds of the Lower Magnesian. The Potsdam is also exposed for fifty feet below its junction with the Lower Magnesian, and consists of heavy-bedded white and yellow sandstones. The bluffs, in this vicinity, present this appearance for a distance of about a mile.
The productions of the Potsdam, which are of importance in an economical point of view, are iron, building stone and mineral waters. Iron, in the form usually of hematite, is found in Crawford county, but none is mined. Building stone and sand, for mortar and plastering, are obtainable; but it is in the mineral waters obtained by means of artesian wells that the Potsdam is most valuable as yet to the county. An account of these wells will be given hereafter.
This formation is an important one because by its decomposition it produces a rich and fertile soil on the ridges, and being washed down into the valleys, it fertilizes the otherwise barren sand derived from the Potsdam.
In the valley of the Mississippi there is no formation which presents finer or more frequent exposures. Its hardness, and the frequent joints which it contains, predispose it to form the lofty cliffs and precipices which form such an impressive feature in the scenery of the river.
At Prairie du Chien, the upper and middle portions are exposed, but the entire thickness is not seen until about six miles above, when the lower layers are exposed. Proceeding up the river, the formation constantly occupies a higher position in the bluffs.
This limestone is always light-colored, embracing all shades of yellow and gray, and is sometimes perfectly white. In texture it is hard and compact, the separate grains of which it is composed being seldom distinguishable. It usually presents an indistinct crystalline appearance, but the crystals are never large enough to present distinct faces or a clearage. Exposed surfaces of this formation always weather very irregularly by the removal of the lime through the usual atmospheric agencies. Small irregular cavities and hollows are thus formed in all parts, and in cliff exposures small holes and caves are sometimes seen, usually penetrating but a short distance.
The Lower Magnesian limestone always overlies the Potsdam conformably; that is, no denudation of the latter appears to have taken place before the former was deposited. The line of demarkation between the two formations is sometimes very distinctly defined by beds of limestone devoid of sand overlying the white sandstone of the Potsdam. The transition beds are, however, usually present, and the Lower Magnesian sometimes graduates almost insensibly into the Potsdam. The stratification of the Lower Magnesian is very regular and uniform; in some of the exposures, as in the cliffs along the Mississippi river, the same beds can be traced continuously for long distances. The greatest thickness which the Lower Magnesian is found to attain anywhere north of the Wisconsin river is 250 feet. The least thickness yet observed is 100 feet. This can be seen in the northwest quarter of section 5, township 9, range 5 west, (Seneca). Its average thickness may be stated at about 175 feet. These measures of thickness refer to localities where the formation is overlaid by the St. Peters.
The following is a list of localites in Crawford county where the exposures of the Lower Magnesian limestone offers facilities for the study of the formation:
(1.) At DeSoto, on the Mississippi river, where the formation affords a fine, close-grained and durable building stone. It is of a very light color, and often nearly white.
(2.) Section 6, township 7, range 6 west, (Prairie du Chien), where there are many fine cliff exposures overlaid with bluffs of St. Peters.
(3.) Section 18, township 8, range 6 west, (Eastman), where, along the Mississippi river, there are long, continuous cliff exposures of the formation, overlying the upper beds of the Potsdam, and affording good opportunities to examine the transition beds.
No very extensive or valuable deposits of metallic are found in the Lower Magnesian formation in Crawford county. A few localities of copper and lead exist, which show that the formation is not entirely destitute of metallic contents. Copper has been found on the northeast quarter of the southwest quarter, and the northwest quarter of the southeast quarter of section 26, township 8, range 5 west, (Eastman). This is in the valley of Plum creek, a small tributary of the Kickapoo, and about two miles above its junction with that stream. Here the copper has been mined.
The existence of copper ore here has been known for a number of years, and small quantities have been from time to time extracted; but it was not until 1860 that any systematic attempt at mining was begun. In 1858, the land was purchased by a company of five persons, residents of New York city, who commenced work in 1860, and abandoned it in 1861 on account of the war. Since then no work has been done in the Plum Creek Copper Mine, as it is called. About two car loads or ore were shipped. An analysis of some of the ore found at the mine gives only a little over ten per cent. of metallic copper, which is hardly a result to justify additional expense in developing this mine.
The Copper Creek mine is on the northeast quarter of section 34, township 10, range 5 west, (Utica). The mines of this locality are situate about three-quarters of a mile southwest of the village of Mt. Sterling, and on the side of a hill sloping toward one of the branches of Copper creek. The deposit of copper ore was discovered, in 1843, by William T Sterling. It was first worked by him and George Messersmith they paying a tribute of one-sixteenth to the United States. During this time, a specimen weighing 300 pounds was sent to the patent office. In the work performed by these men, 20,000 pounds of ore were taken out, when the best part of the deposit appeared to be exhausted and the work was suspended for two years. In 1846 the ground was leased to a German company who worked it about a year, their work being chiefly drifting and prospecting, after which time they abandoned it as unprofitable.
The property remained idle until 1856, when it was leased to a New York company, who worked it from May to September, producing 20,000 pounds of ore, at a cost of about $4000; since then the land has never been worked.
In an analysis of the ore made about thirty years ago less than twenty per cent. was metallic copper.
The existence of lead in Crawford county, in the Lower Magnesian formation, is confined to the vicinity of the lower part of the Kickapoo valley. The Little Kickapoo Lead Mine is located on the northwest quarter of section 10, township 7, range 5 west, (Wauzeka), in the upper part of the bluff on the north side of the Little Kickapoo, a small tributary of the Wisconsin. Lead ore was first discovered here in the year 1840, and was worked at intervals until the year 1850. There have been obtained from this mine from 25,000 to 50,000 pounds of ore. An analysis shows over eighty-two per cent. of metallic lead. This is equal to any found in Wisconsin. There are evidences of other deposits in the country round about.
Wherever the Lower Magnesian is exposed, there is always an abundance of good building stone. Some of the best quarries in the county are those at Prairie du Chien. This formation also affords lime with as much facility as building stone. All parts of the formation which are free from flint will produce lime on burning. There are several places in Crawford county where lime is burned in kilns of the simplest form and construction.
Owing to the elevation attained by the several formations, through their gradual rise in a northerly direction, and to the great and general denudation to which the country has been subjected, the St. Peters sandstone is only found in isolated areas of comparatively small extent and confined to the highest parts of the ridges. The area of this formation begins in township 6, range 6 west, (Bridgeport), and extends in a northerly direction through the county. On the west it approaches to the Mississippi in township 10, range 6 west, (parts of Seneca and Freeman), and may be traced along the bluffs of that river and all its tributary streams, in a belt varying from a mile in width on the north, to a quarter of a mile wide opposite Prairie du Chien; thence, along the bluffs of the Wisconsin and its tributaries to the Kickapoo. On the eastern side of the divide, it is seldom found more than two or three miles from the principal ridge, but as the country descends more gradually to the Kickapoo than to the Mississippi, it covers relatively a much larger area than on the western slope; and in township 10, range 5 west, (parts of Utica, Seneca and Freeman), it is the surface rock over about one-half of the township.
The country just described embraces many fine exposures among which may be mentioned the following:
1. The mounds near Mt. Sterling, which are chiefly composed of sandstone. 2. A ledge fifty feet high near the quarter post of sections 15 and 22, in township 8, range 5 west, (Eastman). 3. A mound on the southwest quarter of section 34, township 8, range 5 west, (Eastman).
The following exposures are situated on the ridge between Knapp creek and the Kickapoo:
1. In township 8, range 4 west, (Marietta), the St. Peters is the surface rock in parts of the following sections: 1, 2, 11, 12, 13, 14, 15, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32, 33 and 34. Its total area is a little more than seven square miles. There is one good exposure where it forms a mound in the southeast quarter of section 2.
2. In township 8, range 3 west, (Marietta), a branch of the same range is seen, extending through sections 6, 7, 16, 17, 18, 19, 20, 21 and 29, forming an area of about three square miles, with one fine ledge exposure near the center of section 7.
3. The same sandstone ridge continues in a northerly direction through sections 36, 25 and 24 in township 9, of range 4, (Haney), and through sections 31, 30, 19, 18, 17, 16, 15, 10, 9, 8, 4, 5 and 6, in township 9, of range 3 west, (Scott), and runs out in sections 31 and 32, of township 10, range 3 west, (Clayton), comprising a surface area of six sections. There is also an isolated area on sections 13, 14, 23, and 24 in township 9, range 3 west, (Scott), equal to one section.
4. In township 10, range 3 west, (Clayton), there are two large isolated areas: the first is on sections 22, 23, 26, 27, 35 and 36 having an extent of two square miles; the second is on sections 3, 4, 9, 16, 17 and 20 having an extent of one and a half square miles. On the latter are four prominent mounds of large size, which afford fine opportunities for studying the formation.
These two formations, which are usually considered collectively, are occasionally found north of the Wisconsin river. They usually attain their average thickness, which is about twenty-five feet each. There are no useful ores found in this formation north of the Wisconsin. The blue limestone would furnish an excellent material for burning to lime; but it is not used for that purpose.
A very singular deposit is to be seen at the village of Seneca, in the lower part of the buff limestone. It forms a small eminence a short distance north of the village. The deposit consists of a conglomerate, formed of quartz pebbles of small size, and sand in large rounded grains, firmly united with iron as a cementing material. The pebbles are seldom more than half an inch in the longest dimension, consisting always of white or transparent quartz, and always smoothly rounded, evidently having been rolled by the action of water.
The extent of the deposit is small, covering only about an acre and not exceeding five or six feet in depth. Several pits have been sunk in it, and numerous large masses of the conglomerate taken out in attempts to utilize it as iron ore; but, on account of the large amount of quartz ore material, which constitutes nearly one-half of the entire bulk, it is useless as an ore. This deposit derives its chief interest from the fact that it is the only ore of the kind found anywhere in the formation.
1. The Trenton forms the surface rock in sections 3, 10, 11, 15, 16, 17, 18, 19, 29, 21, 29, 30, 31 and 32, in township 9, of range 5 west, (Seneca). On section 20, the Galena limestone appears, and buff and blue form a belt surrounding it. This belt, commencing on section 20, runs southwest to the bluffs of the Mississippi; thence south along that stream and all its tributaries; thence east and north about the upper parts of the Grand Gris, Little Kickapoo and Plum creek; thence north to the head of Otter creek to the point of departure. Compared with this large tract all the other areas are small.
2. The blue limestone is found on sections 13, 14, 21, 22, 23 and 28 in township 8, of range 4 west, (Marietta), lying on the crest of the ridge in a long strip about half a mile in width, comprising an area of about two sections.
3. There is also a semi-circular strip, on sections 1 and 2, in the same township, extending into section 6, of township 8, in range 3 west, (Marietta), and forming an area equal to one square mile.
4. In township 10, range 5 west, (Utica), the two small mounds near the village of Mt. Sterling are capped with buff limestone.
5. In township 11, range 5 west, (Utica), is an area of about two square miles, surrounding the village of Rising Sun, lying on sections 14, 15, (in Vernon county), 21, 22, 23, 26, 27, 35, and on the divide between the Mississippi and Kickapoo rivers.
This sub-division of the Trenton period is found in a strip averaging about a mile in width, occupying the highest part of the ridge between the Kickapoo and Mississippi, extending from section 20, in township 9, of range 5 west (Seneca), to section 28, township 7, of range 6 west, (Prairie du Chien), a distance of about fourteen miles. From this ridge, the formation extends west, towards the Mississippi, in three small, subordinate ridges; and on the east, it extends for a short distance on the ridges between the Grand Gris, Little Kickapoo, Plum and Pine creeks. This formation is usually hard and compact in texture, of a yellow color and contains numerous flints disseminated through it. It is almost devoid of organic remains, and has not been found to contain any ores or minerals of value.
After the great Archaean upheaval, there followed a long period, concerning which very little is known --- a lost interval in geological history. It is only certain that immense erosion of the Archaean strata took place, and that in time the sea advanced upon the island, eroding its strata and re-depositing the wash and wear beneath its surface. The more resisting beds withstood this advance, and formed reefs and rocky islands off the ancient shore, about whose bases the sands and sediments accumulated, as they did over the bottom of the surrounding ocean. The breakers, dashing against the rocky cliffs, brought down masses of rock, which imbedded themselves in the sands, or were rolled and rounded on the beach, and at length were buried, in either case, to tell their own history, when they should be again disclosed by the ceaseless gnawings of the very elements that had buried them. In addition to the accumulations of wash and wear that have previously been the main agents of rock formations, abundant life now swarms in the ocean, and the sands become the great cemetery of its dead. Though the contribution of each little being was small, the myriad millions the waters brought forth, yielded by their remains, a large contribution to the accumulating sediments. Among plants there were sea-weeds, and among animals, protozoans, radiates, mollusks and articulates, all the sub-kingdoms except the vertebrates. Among these, the most remarkable, both in nature and number, were the trilobites, who have left their casts in countless multitudes in certain localities. The result of the action of these several agencies was the formation of extensive beds of sandstone, with interstratified layers of limestone and shale. These surrounded the Archaean nucleus on all sides, and reposed on its flanks. On the Lake Superior margin, the sea acted on the copper and iron-bearing series, which are highly ferruginous, and the result was the red Lake Superior sandstone. On the opposite side of the island, the wave-action was mainly upon quartzites, porphyries and granites and resulted in light-colored sandstones. The former is confined to the immediate vicinity of Lake Superior; the latter occupies a broad, irregular belt bordering on the Archaean area on the south, and, being widest in the central part of the State, is often likened to a rude crescent. It will be understood from the foregoing description, that the strata of this formation lies in a nearly horizontal position, and repose unconformably upon the worn surface of the crystalline rocks. The close of this period was not marked by any great upheaval; there was no crumpling or metamorphism of the strata, and they have remained to the present day very much the same as they were originally deposited, save a slight arching upward in the central portion of the State. The beds have been somewhat compacted by the pressure of superincumbent strata and solidified by the cementing action of calcareous and ferruginous waters, and by their own coherence, but the original character of the formation, as a great sand-bed, has not been obliterated. It still bears the ripple-marks, cross-lamination, worm-burrows, and similar markings that characterize a sandy beach. Its thickness is very irregular owing to the unevenness of its Archaean bottom, and may be said to range from 1000 feet downward. The strata slope gently away from the Archaean core of the State and underlie all the latter formations, and may be reached at any point in southern Wisconsin by penetrating to a sufficient depth, which can be calculated with an approximate correctness. As it is a water-bearing formation, and the source of fine artesian wells, this is a fact of much importance. The interbedded layers of limestone and shale, by supplying impervious strata, very much enhance its value as a source of fountains.
During the previous period, the accumulation of sandstone gave place for a time to the formation of limestone, and afterward the deposit of sandstone was resumed. At its close, without any very remarked disturbance of existing conditions, the formation of limestone was resumed, and progressed with little interruption till a thickness ranging from fifty to 250 feet was attained. This variation is due mainly to irregularities of the upper surface of the formation, which is undulating, and in some localities may appropriately be termed billowy, the surface rising and falling 100 feet in some cases, within a short distance. This, and the preceding similar deposit, have been spoken of as limestone simply, but they are really Dolomites, or Magnesian limestones, since they contain a large proportion of carbonate of magnesia. This rock also contains a notable quantity of silicia, which occurs disseminated through the mass of rock; or, variously, as nodules or masses of chert; as crystals of quartz, filling or lining drusy cavities, forming beautiful miniature grottoes; as the nucleus of oolitic concretions, or as sand. Some argillaceous matter also enters into its composition, and small quantities of the ores of iron, lead and copper, are sometimes found, but they give little promise of value. The evidences of life are very scanty. Some sea-weeds, a few mollusks, and an occasional indication of other forms of life, embrace the known list, except at a few favored localities where a somewhat ampler fauna is found. But it is not, therefore, safe to assume the absence of life in the depositing seas, for it is certain that most limestone has originated from the remains of animals and plants that secrete calcareous material, and it is most consistent to believe that such was the case in the present instance, and that the distinct traces of life were mostly obliterated. This formation occupies an irregular belt skirting the Potsdam area. It was, doubtless, originally a somewhat uniform band swinging around the nucleus of the state already formed, but it has since been eroded by streams to its present jagged outline.
At the close of this sandstone-making period there appears to have been an interval of which we have no record, and the next chapter of the history introduces us to another era of sand accumulation. The work began by the leveling up of the inequalities of the surface of the Lower Magnesian limestone, and it ceased before that was entirely accomplished in all parts of the State, for a few prominences were left projecting through the sand deposits. The material laid down consisted of a silicious sand, of uniform, well-rounded --- doubtless well-rolled --- grains. This was evidently deposited horizontally upon the uneven limestone surface, and so rests in a sense unconformably upon it. Where the sandstone abuts against the sides of the limestone prominences, it is mingled with material derived by wave action from them, which tells the story of its formation. But aside from these and other exceptional impurities, the formation is a very pure sandstone, and is used for glass manufacture. At most points the sandstone has never become firmly cemented and readily crumbles, so that it is used for mortar the simple handling with pick and shovel being sufficient to reduce it to a sand. Owing to the unevenness of its bottom, it varies greatly in thickness, the greatest yet observed being 212 feet, but the average is less than 100 feet. Until recently, no organic remains had ever been found in it, and the traces now collected are very meagre indeed, but they are sufficient to show the existence of marine life, and demonstrate that it is an oceanic deposit. The rarity of fossils is to be attributed to the porous nature of the rock, which is unfavorable to their preservation. This porosity, however, subserves a very useful purpose, as it renders this pre-eminently a water-bearing horizon, and supplies some of the finest artesian fountains in the State, and is competent to furnish many more. It occupies but a narrow area at the surface, fringing that of the Lower Magnesian limestone on the south.
A slight change in the oceanic conditions caused a return to limestone formation, accompanied with the deposit of considerable clayey material, which formed shale. The origin of the limestone is made evident by a close examination of it, which shows it to be full of fragments of shells, corals, and other organic remains, or the impressions they have left. Countless numbers of the lower forms of life flourished in the seas, and left their remains to be comminuted and consolidated into limestone. A part of the time the accumulation of clayey matter predominated, and so layers of shale alternate with the limestone beds, and shaly leaves and partings occur in the limestone layers. Unlike the calcareous strata above and below, a portion of these are true limestone containing but a very small proportion of magnesia. A sufficient amount of carbonaceous matter is present in some layers to cause them to burn readily. This formation is quite highly metalliferous in certain portions of the lead region, containing zinc especially, and considerable lead, with less quantities of other metals. The formation abounds in fossils, many of them well preserved, and, from their great antiquity, they possess uncommon interest. All the animal sub-kingdoms, except vertebrates, are represented. The surface area of this rock borders the St. Peter's sandstone. Its thickness reaches 120 feet.
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