USA > Wisconsin > Sauk County > A standard history of Sauk County, Wisconsin, Volume I > Part 5
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Immediately following the deposition of the sand, thick beds of clay, and over the clay thick deposits of limestone and iron ore were laid down. These beds are now changed to slate and iron formation, and the latter is the source of the iron ores of the district. These beds of slate and iron formation are now found only in the valley between the quartzite ranges, but when originally formed they lay everywhere horizontally over the sands of the quartzite, and all of these formations extended over the surrounding region in flat lying beds.
Following the period when these formations lay in their original horizontal position, there was a time of extensive uplift and mountain- making movements throughout the region, and it was during this period of extensive uplift, probably accompanied by slight volcanie eruptions, extensive folding and faulting, that the onee horizontal beds of sand, clay, and iron ore were uplifted into mountain ranges and the beds folded and metamorphesed into formations of hard quartzite, slate, and iron formation.
Accompanying this period of uplift and following it, there was a long period of erosion of the uplifted region, and as a final result the mountains were gradually worn down nearly to sea level, leaving only the very hardest and most resistant rocks to stand out as low ridges, as illustrated in the eross section. The degradation of the mountains to a nearly level plain was reached near the elose of the Archean Age, and at this stage the Baraboo Bluffs stood out as mere remnants of a mountainous tract, only abont 1,000 to 1,500 feet above the surrounding lower plain of Archean land.
PALEOZOIC GEOLOGY
When the early Paleozoic sea advanced, due to the low sinking of the land, the Baraboo quartzite bluffs had been formed essentially
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as they stand today. The quartzite ridges stood as islands in the sea, and about the rocky shores were formed the sandstone and conglom- erate that lie against the eroded beds of quartzite. The first deposits formed against the quartzite was coarse gravel and boulders, now hardened into conglomerate. Examples of the conglomerate are well exposed in the. ravines at Parfrey's Glen, in Durward's Glen, and on the north face of quartzite at the Upper Narrows at Ableman, as well as many other places along the sides of the bluffs.
Over the coarse beds of conglomerate, and sometimes between them, are thick beds of sandstone and shale, all of which lie in a horizontal position against the tilted strata of the old quartzite.
The sandstone formation and the conglomerate beds associated with it belong to the Upper Cambrian period and has very generally been called the Potsdam sandstone, because it is the same age as the sandstone occurring at Potsdam, New York. The thickness of the sandstone is about 700 to 800 feet a short distance away from the bluffs, but on the slopes of the quartzite ridges it is necessarily much thinner, because the ridges stood as islands in the sea in which the sands accumulated.
Thin beds of limestone, ten to fifteen feet thick, occur in the upper portion of the Potsdam sandstone, well exposed at the old lime kilns at Eiky's quarry in section 25, Greenfield, and at Wood's quarry in section 10, Baraboo. The limestone of these old quarries is no longer used for burned lime, but. at present is crushed and used for road purposes.
In the western part of the county there are much later limestone beds forming the highest portions of the uplands which belong to the Lower Magnesian formation. This limestone is found also in a few places on the uplands in the northwest part and in the southern part of the county. Above the Lower Magnesian limestone occur in a few places beds of the St. Peter sandstone. It is very probable that still later deposits of Paleozoic formation, such as the Trenton limestone and the Niagara limestone, may have been deposited above the St. Peter formation, but if so all traces have been removed by subsequent erosion.
The deposition of the various formations of the Paleozoic was not a continuous or unbroken series of events. Uplifts of the land took place, causing retreats of the seas, during which erosion of land would take place instead of the continuous accumulation of sediment in the sea bottoms.
While the 700 to 800 feet of Upper Cambrian (Potsdam) sandstone formation was being formed, only minor breaks in the progress of sedimentation took place. The Upper Cambrian may be divided into four or five minor formations which appear to be separated by slight intervals of erosion. Between the Upper Cambrian and the Lower Magnesian limestone, however, there was probably an important break
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in sedimentation, and in many places in Wisconsin the Lower Magnesian itself may be divided into two formations-the Oneota and the Shakopee, which are distinctly separated by a marked unconformity and break 'in sedimentation. Between the Lower Magnesian and the St. Peter sandstone there was a very long interval of erosion, and likewise between the various formations that succeed the St. Peter formation.
EARLY PALEOZOIC LIFE
Before the Upper Cambrian sandstone was formed, when the quartzite, slate, and iron formation of the Archean was deposited, no forms of life existed, and hence no fossils are preserved in the Archean rocks. Some organisms may have existed during the latter part of the Archean, but if so the forms of life were of a low order, and no well- defined fossils have been preserved.
The life of the period when the Upper Cambrian sandstone and the Lower Magnesian limestone was formed, however, was fairly abundant, considering the type of organisms existing at that time. At that stage in geologie history the vertebrate animals had not been developed, hence the remains of fishes, the earliest of the vertebrates, have not been found in the strata of Sauk County. However, the invertebrates were well developed, and many species of erustacea, brachiopoda, gas- tropoda, and corals lived in the sca of that period.
Not all the beds of sandstone and limestone, however, contain fossils. The fossils appear to be concentrated in considerable abundance in certain beds and are not present in others. Following a break in sedi- mentation, when the sea again advanced over the land, life appears to have been especially abundant.
Not all the forms of life when the Paleozoic sandstone and lime- stone was formed can be mentioned. Trilobites, three-lobed forms of crustacea, were very abundant in the sea when the Potsdam sandstone was formed, and it may be of special interest to state that an important genus of trilobites has been named Saukia, after Sauk County. Thirteen species have been described as belonging to the genus, many of which occur in Sauk County and in other counties of Wisconsin, but some occur as far away as Texas, Colorado, Nevada, New York, and Nova Scotia.
A new species of brachiopod, an oyster-like organism, has been named Eorthis winfieldensis, from the fact of its discovery in the town of Winfield.
GLACIAL GEOLOGY
The eastern part of the county, east of Baraboo, is covered with glacial drift, but the western part contains no drift except a few
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boulders. The terminal moraine at the border of the drift area con- sists of ridges and hummocks of loose boulders, gravel, sand, and elay. The moraine runs north and south from a short distance east of Delton, through Lyons and Devil's Lake, and crosses the Wisconsin River at the big dam at Prairie du Sae. Where the moraine crosses the East Bluffs at Devil's Lake a wide detour is made to the eastward as far as Point Sauk, because of the high elevation of the bluff.
West of the terminal moraine are a few boulders, scattered over the surface as far as Reedsburg. These boulders were probably deposited by an invasion of ice much earlier than the one that formed the terminal moraine.
The ice sheets that invaded Sauk County were parts of great ice sheets that covered a large portion of North America, north of the Ohio and Missouri Rivers. The terminal moraine, formed by the latest ice sheet, has been traced across the entire continent, from Long Island on the Atlantic to Puget Sound on the Pacific.
Although the glacial deposits directly overlie the hard rock forma- tions of sandstone and quartzite in Sauk County, a very long period elapsed between the deposition of these rock formations and of the glacial drift. In other parts of America many thiek formations were deposited after the Paleozoie rocks were formed and before the Glacial period began. This long period between the deposition of the Early Paleozoic sandstone and limestone and the Glacial drift is represented by nearly the whole of the Paleozoic age, the whole of the Mesozoic age, and a large part of the Cenozoic age-a period of time variously estimated at 100,000,000 to 200,000,000 of years in length.
The Glacial period itself is a relatively short and very recent epoch in geology as compared with the time which has elapsed sinee the sand- stone was laid down against the rocky shores of the island of quartzite. The beginning of the glacial period, however, found the valleys of the distriet about 225 feet below their present levels, and these were filled with boulders, gravel, and sand carried by the ice and waters of the Ice age from the regions to the northward and northeastward. There- fore important changes in the superficial features of the county have been wrought even during the Glacial period, and very probably the earliest of the glacial deposits were formed as long ago as several hundred thousand or a million years.
Since glacial time the ordinary agents of erosion and weathering have been at work upon the drift and older rocks, weathering them into soils and removing them to lower levels, as in all the earlier periods of land degradation. Especially rapid has been the change in the aspect of the region since the land has been cleared, through the natural forces of erosion combined with action of man in the cultivation of the soil and in other active pursuits of our modern civilization.
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THE HISTORY OF SCENIC FEATURES
The hills and valleys and other landscape features of Sauk County owe their origin to various geologic agencies that have been in operation from almost the very beginning of geologic history. Volcanism, mountain-making movements, marine sedimentation, erosion by the sea, the rivers, the wind, and the ice have all been active at various times, and to a varying degree, hence the final results observable today as the natural scenery are the inheritance of all the geological forces active in the past.
THE BARABOO BLUFFS
Nowhere in Southern Wisconsin or in the surrounding region are there elevations which so nearly approach mountains as the ranges of the Baraboo Bluffs. The usual altitude of the bluffs reach up to 1,200 and 1,500 feet above sea level, the highest, Point Sauk, reaching an altitude of 1,620 fcet. The surrounding lowlands in the valley bottoms are usually from 800 to 900 feet above sea level, hence the bluffs gen- erally rise from 400 to 800 feet above their surroundings.
The history of the bluffs involves the following stages: (1) The formation of the volcanic rocks, portions of which are exposed at the Lower Narrows and in the vicinity of Denzer, Devil's Nose, and Alloa; (2) the deposition of sands 'over the volcanic rocks in the Archcan sea bottom; (3) the deposition of clays, limestone beds, and iron ore over the sand; (4) the uplift and folding of the Archean beds, forming a canoe-shaped structural basin in a mountain range, accompanied by igneous intrusions, faulting, crushing, and shearing, resulting in the metamorphism of the sandstone to hard quartzite and of the clays and iron ore to hard slates and iron formation; (5) a prolonged period of erosion of the Archean mountains during which the folds of the quartzite were largely worn away, leaving only high ridges of quartzite along the rim of the canoe-shaped basin standing above the surrounding Archean land; (6) the submergence of the region by the Early Paleo- zoic (Upper Cambrian) sea finally covering even the crests of the ridges of quartzite; (7) a protracted period of deposition, during which the Potsdam sandstone, Lower Magnesian limestone and probably later Paleozoic formations were laid down about and finally over the quartzite, completely burying the mountainous ridges; (8) the eleva- tion of the Paleozoic sea bottom, again converting the region into land; (9) a long period of land erosion, during which the Paleozoic forma- tions were largely worn away and the quartzite ridges partly uncovered, as they appear today.
The Baraboo Bluffs are, therefore, a "resurrected" mountain, though not with the full height which they attained in Archean time. When the Archean beds were folded by the mountain-making forces,
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stage 4, the region probably reached the height of the Alps or the Rockies; after the Archean mountains had been worn down and sub- mergence by the Paleozoic sea began (stage 6), the' quartzite ridges, as mere remnants of the Archean mountains, stood only 1,000 to 1,500 feet above the surrounding Archean plains; while at the present time the bluffs stand only 400 to 800 feet above the surrounding lower land.
The Baraboo Bluffs, therefore, represent a fossil mountain of the Archean age, and as such is now so well known in the literature of geology and physiography that fossil mountains of a similar nature in other regions are often referred to as "baraboos."
THE NARROWS
These are four narrows or passes across the quartzite ranges, all of which are striking scenic features. Two of these are occupied by the Baraboo River, one by Narrows Creek, and one by Devil's Lake.
The Upper Narrows of the Baraboo River are located at Ableman, through which pass the river, the C. & N. W. Railroad, and the publie highway. It has a depth of about 200 feet and a width of one-eighth to one-fourth of a mile. The slopes of the Upper Narrows are rugged and precipitous. The quartzite on the north side of the narrows is covered with Potsdam conglomerate, which overlies the truncated beds of vertical quartzite with unconformable contact. So clear an example of unconformity in the rock strata is not often seen, and for this reason the locality is a popular one for university classes in geology. An additional attraction is the quartzite breccia on the east wall of this narrows.
The narrows of Narrows Creek are located 11/2 miles west of Able- man, where a narrow pass in the quartzite is developed. This pass is narrower than the others. Its walls are nearly vertical and possess the same rugged beauty as those at Ableman.
The Lower Narrows, located about six miles northeast of Baraboo, is a conspicuous pass in the quartzite range about 400 feet deep and one-fourth of a mile wide, through which the Baraboo River flows. The north face of the range at the Lower Narrows is formed of volcanic rock, but the main part of the ridge is quartzite. The Lower Narrows is a much more prominent notch in the quartzite range than the narrows at Ableman.
The most prominent pass across the quartzite, however, is the one in the South Range in which lies Devil's Lake. This pass has a depth of about 600 feet and a width of about one-half mile, and because of its occupaney by the lake it is the center of interest for the whole region.
The history of each of these several narrows is much the same. They are gaps cut into the quartzite ranges by the erosive work of
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rivers. The erosion of the passes, however, was not accomplished by the rivers that now flow through them, but by rivers belonging to an earlier drainage cycle.
The history of the narrows appears to involve the following stages : (1) Erosion of the passes in the quartzite during Archean time, when the Baraboo Bluffs were being worn down from a mountain range; (2) the submergence of the quartzite ranges and the filling of the passes with the Potsdam sandstone and the complete burial of the quartzite ridges; (3) a second period of erosion, during which the quartzite ridges were again exposed by removal of the sandstone and overlying beds, and the passes again occupied by streams and narrows cleaned out and deepened.
Although the pass in which lies Devil's Lake is not now occupied by a river, the form of this gap across the range is such as to leave no doubt about its origin through the work of a great river which slowly carved its way across the quartzite as erosion sank deeper and deeper into the quartzite and surrounding rocks.
DEVIL'S LAKE
The origin of Devil's Lake is but a short episode in the history of the gorge in which it lies. The lake has a maximum depth of about forty fect. It was not formed in any manner by the action of volcanism. The huge blocks of rock that lie against the surround- ing cliffs, and which add greatly to the wonder and beauty of the lake, are not of volcanic origin, but consist of quartzite blocks accu- mulated as loose talus on the slopes of the gorge by the ordinary action of weathering and erosion. When the great river flowed through the gorge the talus deposits were carried away, but since the gorge is no longer occupied by a river the blocks of loose rock and soil, fallen from the higher slopes of the rock walls, slowly accumulate on the lower slopes of the cliffs.
The lake is of glacial origin and was formed by the deposition of terminal moraine in the old river gorge, forming dams of glacial drift at the ends of the lake. The moraine at the north end of the lake lies very near the lake shore, but at the south end the moraine lies about a half-mile east of the lake. Between these drift dams the basin was formed, and the lake therefore occupies an unfilled portion of the old river valley. The lake was formed in the relatively recent glacial history of the region, and its origin is therefore only a very recent and short episode as compared with the long history of the gorge in which it lies.
Glens. Important scenie features are the numerous glens that lie along the sides of the Baraboo Bluffs. Parfrey's Glen and Durward's Glen are probably the best known of these, but there are many others
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that are almost equally as attractive from the scenie point of view. The glens owe their origin to the work of erosion of small streams, which have carved deep gorges in the sandstone and conglomerate that lie against the quartzite bluffs.
The Dalles of the Wisconsin. The Dalles are a narrow canyon-like stretch of the Wisconsin Valley, seven miles in length, on the border of Sauk County, near Kilbourn. The depth of the gorge is from 50 to 100 feet. The part above the bridge at Kilbourn is the Upper Dalles, and that below, the Lower Dalles. The sides of the Dalles are nearly vertical much of the way, and usually so steep that landing
EAST BLUFF. DEVIL'S LAKE
is impossible. Between the walls the Wisconsin River formerly swiftly flowed, but since the construction of the dam at Kilbourn, still-water extends through the reaches of the Upper Dalles.
The Dalles was formed by the relatively rapid erosion by the river of the sandstone forming the walls of the gorge. The weathering and erosion processes follow largely along joint planes. The relative hard- ness of the sandstone beds also greatly affect the rate of erosion and largely control the development of the peculiar shapes formed by the erosion and weathering processes.
The beds of sandstone out of which the Dalles have been carved plainly show well-defined features of stratification developed when laid down in the Potsdam sea. The beds lie in an essentially hori- zontal position, and many show striking eross stratification, due to the strong currents along the shores of the sea in which they were deposited.
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The main gorge of the Dalles is not only a feature of great beauty.
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but it contains also many small gulches and canyons which add greatly to the charm of the whole. Witch's Gulch and Cold Water Canyon not only deserve special mention because of their beauty, but also because of the striking features of rapid erosion which they illustrate. They are much the same in their character and origin as the larger gorge of the Dalles, to which they are tributary, and are due wholly to the sculpture of stream erosion.
PROFESSOR EATON'S PAPER
Among the other widely known scientists of the state, Prof. James H. Eaton, of Beloit College, has made a thorough investigation of the region about Devil's Lake. His conclusions, which have been reported in the Transactions of the Wisconsin Academy of Sciences, Arts and Letters, were as follows:
"The formation of Sauk county is the Potsdam sandstone (Pots- dam epoch of the New York Survey). It lies nearly horizontal, with a gentle dip to the southeast. The higher elevations, especially in the southern parts of the county, are capped with conformable layers of the lower magnesian limestone (Calcareous epoch of the New York Sur- veys). Running east and west through the center of the county are two parallel ridges, with an average elevation of 400 to 500 feet and a base of two to four miles. The distance between them is three to four miles. The Baraboo river runs in this valley and empties cast into the Wisconsin. A north and south valley cuts half way through the eastern end of the southern ridge, and then trends east towards the valley of the Wisconsin. In the north end of this valley lies Devil's Lake.
"They are compact, crystalline sandstone, without cement or quartz- ite. The predominant colors are pink and red, often banded with straight or contorted parallel lines of lighter and darker colors. In some places the rock is an homogeneous white quartz, with distinet and well-formed crystals.
ORIGIN OF THE QUARTZITE
"Both the nature of the rock and its position give evidence that it is metamorphic Potsdam sandstone. The rock presents all grada- tions from the simple sandstone to the perfectly crystallized quartz. The Potsdam sandstone consists of small round grains of quartz, and is very loosely cemented. It can easily be crumbled with the fingers. Hand pieces of the quartzite may be obtained in all stages from this friable sandstone, to that where the grains are apparent and the rock is less friable, to that where the homogeneousness is here nearly approached, but the small grains ean still be seen, and finally to the
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perfeet homogeneous quartz. No sharp geographical line of demarca- tion between the sandstone and quartzite, and no gradation in any direction, were observed.
"The homogeneousness of the colored quartzite is not as perfeet as it appears. Whenever a surface has been subjected to the weather, the small grains come to view again. The bandings of the quartzite are very similar to those in the undisturbed sandstone. These bands sometimes consist of layers of fine grains of sand. Some of the great blocks of quartzite which have fallen down the sides of the valley are most beautifully covered with regular ripple marks. They must have been first made in the moving sands.
SLOW UPHEAVAL OF THE SANDSTONE AND QUARTZITE STRATA
"The layers are nearly as perfect as in the sandstone, and have a dip equal to the inelination of the ridges. The dip on either side can be seen best from the opposite side. The antielinal ridge on the cast side of the lake is removed by the valley, which trends to the east, and on the west by another valley, which comes down to the lake. Ver- tical joints also lead to the conclusion that the ridge has been formed by the upheaval of the horizontal layers of sandstone. The layers were not traced north and south to determine whether they are continu- ous horizontally.
"Both the nature of the rock and its position forbid the idea of aqueous fusion or active voleanie agency. The change must have taken place by the purely wet way of partial solution and crystallization, or by a low degree of heat, working for a long series of years through the moisture in the sandstone, probably aided by the pressure which lifted the ridges. If the latter, the change and elevation of the rock took place at the same time, and both effects were produced with extreme slowness.
"When was the ridge raised-before the glacial epoch ? Wm. H. Canfield, of Baraboo, has found abundant proofs of the movement of glaciers over the rock since it has been metamorphosed. In many places on the elevated portions, smoothly polished surfaces of quartz of great extent have been exposed by removing the soil. Before the glacial epoch there seem to be no data for fixing the time of the ele- vating and metamorphic action. There has therefore been ample time for metamorphic action of the most extreme slowness.
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