History of Green County, Wisconsin. Together with sketches of its towns and villages, educational, civil, military and political history; portraits of prominent persons, and biographies of representative citizens, Part 12

Author: Union publishing company, Springfield, Ill., pub. [from old catalog]
Publication date: 1884
Publisher: Springfield, Ill., Union publishing company
Number of Pages: 1168

USA > Wisconsin > Green County > History of Green County, Wisconsin. Together with sketches of its towns and villages, educational, civil, military and political history; portraits of prominent persons, and biographies of representative citizens > Part 12

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HISTORY OF GREEN COUNTY.

do not exhibit any distinctive morainic appear- ance.

Gravel beds are not very frequent, although they are found in several places in the county. There is one situated very near the boundary of the drift, on the northwest quarter of section 4, in township 1 north, of range 7 east (town of Clarno), where there is a bed of gravel about eight feet thick, underlaid by a bed of stratified sand and clay about four feet thick. This sand is very fine, and has just enough clay mixed with it to make a good article of moulding sand for iron foundries; it would give a fine impres- sion and make a smooth casting. A similar bed is seen about two miles east of the preceding, on the southwest quarter of section 2, in town- ship 1 north, of range 7 east, (town of Clarno), where the drift sand and gravel have accumu- lated to a thickness of about twelve feet. An- other bed, like the other two, is in existence on the northwest quarter of section 2, in township 1 north, of range 7 east, (town of Clarno). There are several other beds in various portions of the county.

The amount of drift clay in this county is comparatively small, it probably having been dissolved out and washed away from the greater portion of the surface. It is to be found how- ever; and particularly on the northwest quarter of section 25, in township 3 north, of range 7 east, (town of Washington), where a well has been sunk in the drift. There is here a thick- ness of about twenty feet of slate-colored clay, full of small pebbles.

III .- GEOLOGICAL FORMATIONS.

The geological formations underlying Green county are : (I.) the Potsdam sandstone ; (II.) the Lower Magnesian limestone; (III.) St. Peters sandstone ; (IV.) Trenton (Buff and Blue) lime- stone; and (V.) Galena limestone. It is pro- posed, in this connection, before describing the geographical boundaries, lithological character- istics and paleontology of these formations in Green county, to give a brief history of their origin:

I .- Potsdam Sandstone.

After the great Archæan upheaval, there fol- lowed a long period, concerning which very little is known-a lost interval in geological history. It is only certain that immense erosion of the Archæan strata took place, and that in time the sea advanced upon the island, eroding its strata and redepos- iting the wash and wear beneath its surface. The more resisting beds withstood this ad- vance, 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 ac- cumulating 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 num- ber, were the trilobites, who have left their casts in countless multitudes in certain locali- ties. The result of the action of these several agencies was the formation of extensive beds of sandstone, with interstratified layers of lime- stone and shale. These surrounded the Ar- chæan 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

HISTORY OF GREEN COUNTY.

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, ir- regular belt bordering on the Archæan 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 de- scription, that the strata of this formation lies in a nearly horizontal position,and repose uncon- formably upon the worn surface of the crystal- line rocks. The close of this period was not marked by any great upheaval ; there was no crumbling 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 une- venness of its Archæan bottom, and may be said to range from 1,000 feet downward. The strata slope gently away from the Archæan core of the State and underlie all the lat- ter 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 impor- tance. The interbedded layers of limestone and shale, by supplying impervious strata, very much enhance its value as a source of fountains.

II .- Lower Magnesian Limestone.

During the previous period, the accumulation of sandstone gave place for a time to the for- mation of limestouc, and afterward the deposit

of sandstone was resumed. At its close, with- out any very remarked disturbance of existing conditions, the formation of limestone was re- sumed, and progressed with little interruption till a thickness ranging from fifty to 250 feet was attained. This variation is due mainly to irreg- ularities 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 sim- ilar deposit, have been spoken of as limestone simply, but they are really Dolomites, or Mag- nesian 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 cavi- ties, 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 am- pler fauna is found. But it is not, therefore, safe to assume the absence of life in the depos- iting 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 dis- tinct traces of life were mostly obliterated. This formation occupies an irregular belt skirt- ing the Potsdam area. It was, doubtless, origi- nally 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.

HISTORY OF GREEN COUNTY.

III .- St. Peter's Sandstone.

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 ac- cumulation. 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 project- ing through the sand deposits. The material laid down consisted of a silicious sand, of uni- form, well-rounded-doubtless well-rolled- grains. This was evidently deposited horizon- tally 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 ma- terial derived by wave action from them, which tells the story of its formation. But aside from these and other exceptional impurities, the for- mation is a very pure sandstone, and is used for glass manufacture. At most points the sand- stone 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. Un- til 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 demon- strate 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 pres- ervation. This porosity, however, subserves a very useful purpose, as it renders this pre-emi- nently 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.

IV .- Trenton Limestone.

A slight change in the oceanie conditions caused a return to limestone formation, accom- panied with the deposit of considerable clayey material, which formed shale. The origin of the limestone is made evident by a close exami- nation of it, which shows it to be full of frag- ments of shells, corals, and other organic re- mains, or the impressions they have left. Count- less numbers of the lower forms of life flourished in the seas, and left their remains to be com- minuted and consolidated into limestone. A part of the time the accumulation of clayey matter predominated, and so layers of shale al- ternate with the limestone beds, and shaly leaves and partings occur in the limestone lay- ers. Unlike the calcareous strata above and below, a portion of these are true limestone with less quantities of other metals. The for- mation 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 repre- sented. The surface area of this rock borders the St. Peter's sandstone, but, to avoid too great complexity on the map, it is not distin- guished from the next formation to which it is closely allied. Its thickness reaches 120 feet.

It it here appropriate to consider the geo- graphical boundaries, lithological characteris- tics, and paleontology of the several formations in Green county, in the same order as has been followed in giving the history of their origin.

Potsdam Sandstone .*- This formation is not exposed anywhere in Green county; but south of the Wisconsin river, it is found as the bed rock of Otter, Mill and Blue Mounds creeks and their various tributaries, as far south as township 7, of the various ranges. Here it dis- appears owing to the southerly dip of the for- mation, and the sudden rise of the country to

*Because of the Potsdam sandstone being an underlying formation of Green county, though not exposed anywhere, so far as is known, within its limits, it is thought best to give its geographical boundaries, etc., in the Lead Region.

HISTORY OF GREEN COUNTY.

the south. This explains why it nowhere ap- pears in Green county. The valley of the Wis- consin river lies in this sandstone, forming a very level plain, from two to three miles wide and extending from Sauk City to a point about four miles above the mouth of the river. Good nat- ural exposures are seen in the bluffs on each side of the river, in which the various strata may be traced uninterruptedly for miles.

The sandstone beds of the Potsdam are usu- ally composed of a very soft and friable sand, frequently crumbling readily between the fingers, especially if it is white. The upper beds are more frequently white than the others, although white beds are not uncommon in all parts of the formation. In general, the lower beds are yellow or brownish in color. The great inequality in the hardness of the several strata of the Potsdam is frequently the cause of the formation of terraces by erosion, which are often a conspicuous feature of the valleys in the vicinity of the Wisconsin river.

South of the Wisconsin river, about the head- waters of Blue Mounds creek and Mill creek, the upper bed of the Potsdam consists of a red and very ferruginous sandstone, often contain- ing seams of iron ore and iron concretions. The coloring matter appears to be partially soluble, and, becoming washed out by the rain, colors the soil in some places to a considerable extent.

The fossil remains of this formation seem to be chiefly confined to the calcareous strata and argillaceous shales. These remains consist chief- ly of Lingula Aurora and Dicellocephelus Min- nesotensis,-the former being quite small and usually having the shell remaining; sometimes, however, the shells have been ground up so that only a few fragments are found, disseminated through the shales. The trilobites are seldom or never found entire, but usually the cephalic portion, the pygidium, or still smaller fragments. The various sandstone beds of the Potsdam are usually unfossiliferous. The upper bed of sand- stone seldom contains anything but Scolithus, which, in some localities, is very numerous.

This fossil is also frequently found in all the sandstone beds.

Lower Magnesian Limestone .- South of the Wisconsin river and north of the main water- shed, the Lower Magnesian limestone occupies a tract of land lying about the heads of all the smaller tributary streams, although seldom found so far back as their springs. Passing down any of the streams, we gradually pass be- low its surface, and its outcrops are seen gradu- ally higher in the hills, until, on reaching the Wisconsin river, it forms the cap of all the bluffs from Sauk City to Boscobel, usually ap- pearing in bold and rugged cliffs, lending a very picturesque effect to the scenery of the river. It forms also the valley of the Mississippi as far south as Glen Haven where it passes under the surface. Passing south of the divide which separates the waters which flow into the Wis- consin from the Pecatonica, it is found in the branches of the latter stream as far north as the north line of township 5, in ranges 5 and 6 east. Proceeding westward, it is not again encountered until the Platte and Grant rivers are reached, where it is found as the bed-rock of those streams; and, in township 5 north, of range 3 west, it covers a large portion of the township.

In Green county, there is but one exposure of the formation. It is in the valley of the Sugar river, about three miles above Brodhead. It commences a short distance north of the center of section 15, in township 2 north, of range 9 east, (town of Decatur), where it has a width of about half a mile. In passing into township 3, in the same range (town of Albany) it widens to nearly two miles. It then becomes narrower; attains its greatest elevation above the river at the village of Albany; and finally disappears be- neath the surface of the river about a mile and a half above that place.

After passing through the transition beds separating it from the Potsdam sandstone, the Lower Magnesian assumes all the qualities char- acterizing dolomite. It is very hard, compact, and close-grained, of a grayish-white color.

HISTORY OF GREEN COUNTY.

Beds of flint or chert are contained in all the strata, irrespective of geological position, differ- ing, however, considerably from the flint found in the Galena limestone, in that they are more regularly segregated, forming layers by them- selves, and are not so promiscuously distributed through the formation.

The flint of the Lower Magnesian limestone is much whiter and more liable to decomposition than that of the Galena. There are also geodes and cavities lined with drusy quartz-crystals, which have never been seen in the Galena lime- stone, but are very abundant in the Lower Mag- nesian. The crystals are of many colors- white, yellow and rose color predominating and often affording beautiful cabinet specimens.

The Lower Magnesian is a formation of ex- tremely variable thickness; the greatest known in the lead region is about 250 feet; this, how- ever, is seldom seen. This formation is charac- terized by the extreme rarity of its organic re- mains. The few fossils seen have been found imbedded in the drusy quartz with which the formation abounds and usually in the form of casts. Some, however, have been found in the limestone.

St. Peter's Sandstone .- The formation known as the St. Peter's sandstone is found in the val- leys of the Grant, Platte and Pecatonica rivers and their tributaries. In Green county, it forms the valley of the Sugar river and its branches, this valley being, in many places, as wide as that of the Mississippi. North of the dividing ridge it is found about the headwaters of the streams which flow into the Wisconsin, having its north- ern outcrop usually within two or three miles of the river and as far east as Boscobel forming a portion of the bluffs which inclose the river valley.

The St. Peters sandstone differs from the Potsdam sandstone in that it contains no beds of limestone or shales interstratified with it, but presents at any given locality a homo- geneous structure through its entire thickness. Its color varies from snow white, through all

the shades of yellow, to a very dark red, and in texture, from friable crumbling sand, to com- pact and fine-grained stone. Beneath the micro- scope, the particles of sand appear rounded and and water-worn. The same color and texture usually exist through the entire thickness at any given place.

The St. Peters formation frequently impresses npon the surface of the country an appearance of terraces, although no traces of terraces, such as are formed in river valleys by changes of level, have anywhere been observed. This is most readily seen in those districts where it becomes the surface rock over any extended portion of country.

The exposures of St. Peter's are very frequent in Green county, where, in addition to the con- tinuous exposures, small hills are frequently seen with flat tops, which have been denuded nearly down to the formation under considera- tion.

The varying hardness of the upper bed of the St. Peters, some portions, especially the white, being quite soft and friable, and others nearly as hard as quartzite, due, perhaps, to its greater or less impregnation with iron, appear to have caused an unequal resistance to disintegration, which has resulted in the formation of knobs, as they are called. These are isolated pillars of sandstone, which shoot up in picturesque castel- lated forms, frequently exposing the entire thickness of the formation and forming very conspicuous objects in the landscape.

The peculiarity of the hardness of the upper beds of the St. Peters proves of great assistance in tracing the outlines of the formation, in de- termining its thickness and in detecting irregu- larities in the surface contour. This formation differs very much in its thickness in different localities, although this does not appear to be the case so much in the Lead Region as near the northern outcrop of the formation, where it is in some places as thin as forty feet, and in oth- ers, not more than a mile or two distant, it is 100 or even 150 feet thick, depending, seem-

HISTORY OF GREEN COUNTY.

ingly, on the varying thickness of the underly- ing Lower Magnesian limestone. The layers consist of subordinate parts of very various lamination, dipping in various directions.

There are several points in the lead region, where slight upheavals of the formation appear to have taken place. The sandstone on the small branch on sections 35 and 36, in township 2 north, of range 6 east, (town of Jordan, Green county), slopes gently toward Skinner creek, which appears to lie in a slight depression or synclinal valley. Passing over the ridge be- tween Skinner and Jordan creeks, a slight an- ticlinal ridge is seen by means of observations on the top of the St. Peters, which is exposed in numerous small dry runs. The top of the formation is found to be thirty feet higher on the ridge than at either of the creeks. Although disturbances of this kind are extremely rare and infrequent, yet in this case, as in a few others, the variations from the normal dip are too plain to be mistaken.

The St. Peters sandstone seems everywhere to be perfectly destitute of organic remains. The only indication of metal seen in this for- mation is the presence of small concretions of sandstone, cemented by a ferruginous substance. This is due to the decomposition of iron pyrites or marcasite, as is proved by its existence in va- rions stages of decay. These concretions are not confined to any. particular part of the for- mation, but are much more abundant in the up- per beds. They are frequently perfectly spherical, and, when they occur in the dark col- ored sandstone, are often surrounded by a white ring about half an inch in width, from which the coloring matter seems to have been ab- sorbed. They have been noticed with more or less frequency in various places. They can be seen in abundance in the road near the center of section 3, in township 1 north, of range 6 east (town of Cadiz, Green county). The lower bed is full of irregular cavities and small round holes about one-fourth of an inch in di- ameter. The upper bed of the sandstone is col-

ored green by some salt of iron, and in it is a seam of green and ferruginous matter.

It is a peculiarity of this formation that the stone hardens on exposure to the weather. In examining any natural exposure, it is found to consist of an outer indurated shell and an inner and softer sandstone. This is a valuable qual- ity, causing it to be easily quarried and dressed, and enabling it afterward to withstand the in- fluences of the weather. In addition to this, it is easy to find almost any color that may be de- sired.

Trenton (Buff and Blue) Limestones .- It will not be necessary to enter into a detailed descrip- tion of the ground covered by this formation. It is sufficient to say that it is always found be- tween the lowest bed of the Galena limestone (hereafter to be described) and the top of the St. Peters sandstone, and having an average thickness of about fifty feet.

The Blue limestone is remarkable as being the purest in the Lead Region, and the nearest approach to the Trenton limestone of the east- ern States, both in its lithological and paleonto- logical characteristics. A very noticeable feature is its marked division into two parts; one very heavy-bedded, in layers of two or three feet thick, known as the glass rock, which constitutes the lower half; and the other, thin- bedded, in layers of two or three inches, gradu- ating sometimes without much change into thin- bedded Galena limestone above. It is at this point that the stratum of carbonaceous shale occurs, which is the line of demarkation be- tween the Blue and Galena limestones, and as such, is an unfailing guide. It varies very much in its thickness, being from a quarter of an inch to a foot or more, but wherever a good exposure of the two formations is seen, it has uniformly been found.

East of range 3 east (that is, east of a north and sonth line drawn twelve miles west of the east boundary lines of the counties of Iowa and Lafayette) the presence of the Blue limestone

HISTORY OF GREEN COUNTY.

is nowhere so clearly marked as west of this line. It is usually recognized by the outerop- ping of a quantity of highly fossiliferous frag- ments scattered through the soil, having a worn and bleached appearance. East of range 3, the fossiliferous Blue limestone has not been found; hence, none has been discovered in Green county which lies still farther eastward. It is replaced by a yellowish limestone, containing but very few fossils and in all respects similar to the Buff limestone. The thickness between the Galena limestone and St. Peters sandstone remains as usual about fifty feet.

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History of Green County, Wisconsin. Together with sketches of its towns and villages, educational, civil, military and political history; portraits of prominent persons, and biographies of representative citizens, Part 12

Author: Union publishing company, Springfield, Ill., pub. [from old catalog] Publication date: 1884 Publisher: Springfield, Ill., Union publishing company Number of Pages: 1168

Author: Union publishing company, Springfield, Ill., pub. [from old catalog]
Publication date: 1884
Publisher: Springfield, Ill., Union publishing company
Number of Pages: 1168