Eastern Ridges and Lowlands
Lake Superior Lowland
Words in the text shown in blue are explained in the Glossary.
These pages are excerpted and adapted from Lawrence Martin, The Physical Geography of Wisconsin, published by the University of Wisconsin Press, copyright © 1965 by the Board of Regents of the University of Wisconsin System. Used by permission of the publisher. This work, originally published in 1916, is still available from the University of Wisconsin Press as a reproduction of the second (1932) edition. It is considered a timeless work on its subject and is recommended for the library of anyone interested in the natural history of Wisconsin. To purchase a copy, go to your local bookstore or visit the University of Wisconsin Press web site.
The Eastern Ridges and Lowlands of Wisconsin
The Eastern Ridges and Lowlands
Eastern Wisconsin contains a large proportion of the people of the state. The reasons for this are not simple. The three factors of prime importance are level topography, fertile soil and favorable climate. Topographic features are distinct, but they are low. The dominant thing in eastern Wisconsin is the plain.
Alternate weak and resistant rock layers having a moderate inclination will be carved by streams and weather into a belted plain. This plain will have parallel strips of upland and lowland corresponding to the more important resistant and weak strata. The uplands are called cuestas and the lowlands have sometimes been called vales. A cuesta is a ridge which has a steep escarpment on one side and a long gentle slope on the other.
The topography of the eastern ridges and lowlands is controlled by cuestas. The westernmost ridge is the rather low, narrow cuesta formed by the resistant Lower Magnesian limestone. It is alluded to hereafter as the Magnesian cuesta. The eastern upland is the higher and broader cuesta of Niagara limestone. The intermediate Green Bay- Lake Winnebago- Rock River lowland lies upon the belt of Black River and Galena limestone, with the gentle back slope of the Magnesian cuesta for one wall and the steep escarpment of the Niagara cuesta for the other.
The Lake Michigan lowland, half of which lies in the state of Wisconsin, owes its abnormal depth chiefly to glacial erosion rather than weathering and stream work, while the two cuestas and their intermediate lowland in eastern Wisconsin, though also modified by glaciation, are normal products of weathering and stream work.
The Magnesian Cuesta
The cuesta of Lower Magnesian limestone varies in elevation from 724 feet above mean sea level (MSL) in Marinette County (near Pound) to 1240 feet above MSL in Dane County (at Lutheran Hill), showing a general increase in height from northeast to southwest.
In parts of Marinette, Shawano, Outagamie, Winnebago, Green Lake and Columbia counties, the width of the cuesta is only two to seven miles, in contrast to ten to 20 miles wide north of Madison.
A west and northwest- facing escarpment terminates the Magnesian cuesta. From this crest one overlooks the lowland of the Central plain. This escarpment in eastern Wisconsin is 175 miles long. It is 300 feet high in Dane and Columbia counties. Good places to see the high portions of the escarpment are between Dane and Lodi, and between Arlington and Poynette. The larger part of the escarpment, however, is much lower. In Marinette County the escarpment is only 50 feet high.
The escarpment is unusually simple in outline, although here and there its front projects in great salients. In Shawano County a triangular area projects seven miles. There are similar salients in southwestern Outagamie County and in Winnebago County south of Lake Poygan. The few reentrants are complementary to these, as in Columbia County near Cambria.
The escarpment is likewise abnormal in the absence of great numbers of salients cut off and converted into isolated, flat- topped buttes or mesas. There is a large mass of this sort in Green Lake County surrounded by narrow valleys near Princeton and Green Lake. the northern 160 miles of the escarpment is almost entirely without such outliers. In a small area in Columbia County south of the Baraboo Range there are a few outliers in front of the escarpment, especially in the region between Prairie du Sac and Portage. Gibraltar Rock, 1240 feet high and capped by the St Peter sandstone, is the highest of these. These outliers have been isolated by erosion in preglacial time.
The Black River Escarpment
The western edge of the Galena- Black River limestone is so resistant in places as to form a low escarpment. This escarpment is, variably:
- an inconspicuous ledge, or
- a higher cliff, in several cases exceeding the crest of the Magnesian escarpment in height, or
- entirely wanting, or
- buried beneath the glacial drift.
Near Seymour, the escarpment is a more conspicuous feature than that of the Lower Magnesian limestone. Forty miles south of this, however, in Winnebago County, the Black River escarpment is an inconspicuous feature, seen near the quarries between Oshkosh and Omro. Fifteen miles south of this at Tipon, the black River escarpment is again a conspicuous feature.
Two kinds of valleys indent the edge of the escarpment. One is narrow and occupied by torrential streams, such as Mitchell's Glen and Arcade Glen southwest of Ripon. These are post glacial gorges in which the streams descend by rapids and waterfalls. the other sort of valley slopes in the opposite direction across a low part of the escarpment. These are larger streams, like the Menominee River in Marinette county, the upper Fox River in Winnebago county, and the several headwaters of the Rock River in Columbia and Dane Counties.
The back slope of the Galena- Black River limestone is the floor of the Green Bay- Lake Winnebago- Rock River lowland. The eastern edge of this lowland is lower than the western, and slopes northward so that the Green Bay end is nearly 300 feet lower than the part near the Illinois border. The floor of the lowland may be divided into three parts:
- the submerged part, north of the city of Green Bay,
- the middle area of rather smooth plain, and
- the southern, hilly area.
The Niagara Cuesta
The upland between Lake Michigan and the Green Bay- Lake Winnebago- Rock River lowland is underlain by the Niagara limestone. This upland is unsymmetrical. The eastern border is everywhere lower than the western. The middle portion is more than 300 feet higher than the northern and southern portions.
The Niagara cuesta is an upland seven to 20 miles wide at the north on Washington Island and the Door Peninsula, and 25 to 45 miles wide at the south between Milwaukee and the Illinois border. The limestone is 450 to 800 feet thick and the shale at its base has a thickness of 200 to 500 feet. It forms an upland or ridge in practically all of the 900 miles of its circuitous course from Niagara Falls to Wisconsin. The west- facing escarpment overlooks the Green Bay- Winnebago- Rock River lowland and extends across the state of Wisconsin for more than 230 miles, but is nowhere so conspicuously developed a feature as east of Lake Winnebago where it is known as "The Ledge."
In Door County and Washington Island its rises only 160 to 220 feet above Green Bay (which, however, is 100 to 144 feet deep). At High Cliff, south of Clifton in Calumet County, the Niagara escarpment falls 223 feet (from 970 to 747 feet above MSL) in less than 700 feet horizontally. South of Stockbridge the crest of the escarpment is at an elevation of 1060 feet and is 313 feet higher than the base. It continues southward into Fond du Lac County with about the same altitude. Near Waukesha and Oconomowoc it is inconspicuous as a present- day topographic feature, but well records show that it is still 120 feet high.
In contrast with the Magnesian and Black River escarpments, the Niagara escarpment and cuesta are remarkable for the absence of transverse gaps in their southern 170 miles. The single exception is the Manitowoc River, northeast of Lake Winnebago. The northern portion is breached by several gaps. The widest of these lies between the end of Door Peninsula and the Upper Peninsula of Michigan. This gap of 30 miles is interrupted by Washington Island (8 miles long) and the smaller Rock Island in Wisconsin, and by several islands further north in Michigan. Another gap is at Sturgeon Bay. All these northern gaps are now occupied by the waters of Green Bay and Lake Michigan.
The upland on the back slope of the Niagara cuesta is a region of very moderate relief, with glacial deposits forming the greatest irregularities. The erosion of the largest streams, like the Milwaukee River near its mouth, results in a maximum relief of only 100 to 120 feet by cutting into the glacial drift and the rock. The greatest relief resulting from the glacial deposits lying upon the rock surface is 100 to 200 feet.
The slope of the drift- covered upland from the crest to the wave- cut cliffs of Lake Michigan is an average of about 12 feet to the mile. It descends from 1000 feet at the escarpment near Hartland, Waukesha County, to 700 feet near Lake Michigan. The Fox River of Waukesha, Racine and Kenosha counties and several smaller streams have a longitudinal trend (ie trending north- south along the back slope of the cuesta). The Milwaukee River flows eastward down the dip slope to within seven miles of Lake Michigan, then, at Fredonia, Ozaukee County, it turns abruptly southward and flows parallel to the coast for 32 miles before entering the lake at Milwaukee.
The eastern termination of the Niagara upland is masked by the waters of Lake Michigan.
The Glaciation of Eastern Wisconsin
In southeastern Wisconsin there are more than 1,400 oval hills of glacial drift in an area of 4,200 square miles. There are fully as many of these oval hills in the northeastern part of the state. They are called drumlins and they were made by the continental glacier. Wisconsin is famous in the world outside for two of its geographic features. One of these is the Driftless Area (above), and the other is the drumlins.
These oval drumlins have one peculiarity. Their longer axes are always parallel to the direction of the ice movement. Therefore they tell us the directions in which various parts of the continental glacier moved in eastern Wisconsin.
The ice moved across Wisconsin for long ages. The continental glacier advanced not once, but several times. Each glacial epoch was probably of greater duration than the time since the last ice sheet melted away. The proofs of unusually- effective glacial erosion in eastern Wisconsin are to be found in the following:
- the rock basin character of Lake Michigan,
- the similar form of Green Bay,
- the submerged hanging valley relationship of Green Bay and Lake Michigan,
- the absence of the Richmond shale from the floor of the Green Bay- Lake Winnebago- Rock River lowland,
- the amount of quartzite derived from certain small ledges,
- the simple outlines of the limestone escarpments,
- the absence of residual soil on the surfaces of the cuestas,
- the paucity of caves and sink holes,
- the absence of marked ridges and valleys upon the cuesta surfaces,
- the topographic contrast between the glaciated and driftless portions of Wisconsin, and the gradation from one to the other in the border region.
One part of eastern Wisconsin where a great amount of glacial erosion took place was the basin of Lake Michigan. It has a broad, flat bottom and abrupt walls, descending to a depth of 500 to 800 feet. The weak, Devonian shales underlying Lake Michigan must have formed a lowland in preglacial times. The lowland was doubtless occupied by a master stream flowing southward.
The preglacial stream course in the Lake Michigan basin was near present lake level at the southern boundary of Wisconsin. The bottoms of the preglacial valleys in what are now Lake Michigan and Green Bay were, accordingly, higher than [the current Lake Michigan level of] 581 feet above sea level. As the bottom of the lake is (a) at a level of only five to 80 feet above sea level east of Door Peninsular, (b) 323 feet below sea level in the deepest portion southeast of Sturgeon Bay, and (c) just about at sea level east of Racine in southern Wisconsin, the amount of glacial deepening, vertically, was from 500 to nearly 900 feet.
There are good reasons for supposing that, before the Glacial Period, the site of Green Bay was occupied by a river rather than a lake.
The depth of Green Bay at the junction with Lake Michigan is 100 to 144 feet, and the depth in the straits north of Washington Island is 156 feet. To the east the water deepens rapidly to 576 feet. Junctions of main and side streams are normally even, or accordant, in regions where there have never been glaciers. the junctions of main and side valleys in glaciated regions are almost always discordant, and the side valley hangs above the main valley. This is spoken of as a hanging valley. Such discordance is produced because the larger glacier in the main valley erodes its bed more deeply than the smaller ice tongue in the side valley. Since, in the case of Green Bay and Lake Michigan, this discordant valley junction lies below lake level it is spoken of as a submerged hanging valley.
Scarcity of Caves and Sink Holes
In the Driftless Area, caves and disintegration seem to be abundant down to the limit of ground water. This is ten to 100 feet in some places, and 100 to 300 feet in others. Sink holes in the driftless portion of the state are from five to 20 feet deep. Caves penetrate to a depth of 50 to 75 feet in driftless southwestern Wisconsin. It seems logical to conclude from the relationships of residual soil and of caves that one or two hundred feet of weathered and cavernous rock have been eroded by the ice in eastern Wisconsin.
Surface Features Due to Glacial Deposition
The deposits left by the ice sheet are unassorted till, or boulder clay, and stratified gravel, sand and clay. they contain not only fragments of the local limestone, shale and sandstone, but also igneous and metamorphic rocks imported into the region by the ice sheet.
Extending southwestward from Waterloo are abundant boulders of quartzite scattered by the glacier in the lee of the ledges. This is known as a boulder train. It is recognizable because quartzite is a unique rock in this region of limestone and sandstone. The Waterloo boulder train is more than 60 miles long. It is fan- shaped, increasing in width from a narrow band to 20 miles near Sun Prairie and Lake Mills, and 50 miles near whitewater and Madison. Smaller boulder trains are found in the valley of the Fox River in the Central Plain, and in the Powers Bluff monadnock of the Northern Highland in Wood County.
The drift in eastern Wisconsin contains fragments of native copper from the north. Masses up to 487 pounds in weight have been found in southeastern Wisconsin.
A few diamonds are also found in the glacial drift. Such diamonds have been found near Eagle in Waukesha County, southwest of Oregon in Dane County, near Saukville in Ozaukee county, Burlington in Racine county and Kohlsville in Washington County. The largest of these weighed 15-12/32 carats. Their source is unknown, but is supposed to be somewhere in Canada. As long ago as 1670 the Jesuit fathers related a story of diamonds on some of the islands at the entrance to Green Bay.
The ground moraine which covers nearly all of eastern Wisconsin has the variable, slightly rolling topography of drift- mantled plains. The ground moraine is made up largely of till, but may contain small areas of stratified sand and gravel. The ground moraine covers a much larger area than the terminal moraines, which are in long narrow belts. McGee described the similar ground moraine of Iowa:
"The whole mass (of ice), indeed, must have lain in majestic inactivity until devoured by the hungry sun and thirsty wind. The boulder- dotted surface . . . is its epitaph."
The thickness of the ground moraine in southeastern Wisconsin varies from a few feet on the hilltops to more than 400 feet in the bottoms of the preglacial valleys. The surfaces mantled by the ground moraine have local relief of 50 to 200 feet, except where the topographic forms like terminal moraines and drumlins rise above the ground moraine.
Most of the ground moraine is covered by a rather fertile clay soil, but parts of it are stony. Large areas are too swampy for agriculture, or are covered by lakes.
Drumlins are confined mostly to the limestone belt and lie within five to 35 miles of the outermost terminal moraine. The ice in this belt is thought to have been at least 450 to 1,450 feet thick.
Some of the drumlins rise as much as 140 feet above the adjacent plain. A few are as low as five feet. their average width is about a quarter mile, and their length varies from a few rods to two miles. The material is chiefly unstratified glacial drift. Numerous well sections show that they do not have rock cores.
The Kettle Moraine
Between the Green Bay and Lake Michigan lobes was formed an interlobate deposit of unusual height and irregularity. This is a part of the kettle moraine of Wisconsin, so called because of the deep hollows or "kettles." It rises 200 feet above the region southeast of Whitewater and is especially well seen near Eagle in Waukesha County. The kettles are due to the melting of buried ice blocks, or to the building of irregular morainic ridges which enclose undrained depressions.
Deposits made by streams which issued from the edge of the melting ice are found in many parts of eastern Wisconsin. They are typically developed near Janesville and Beloit in Rock County. Outwash plains consist of low, coalescing, alluvial fans which head up against a moraine. Outwash may be built at the border of any recessional moraine. Near Janesville the outwash plain slopes southward at the rate of nearly 10 feet to the mile. It as a smooth surface with slight irregularities. The thickness of the outwash at Janesville is 450 feet.
Allied to the outwash plains in origin are the eskers, built by glacial streams flowing beneath the ice. These are narrow, winding ridges of stratified gravel. They are not numerous. Eskers as much as six miles long are known in eastern Wisconsin. Conspicuous one are to be seen near Waterloo in Jefferson County, west of Cottage Grove in Dane County, in the southeastern part of Dodge County, the eastern part of Columbia County, and the southeastern part of Marinette County. [Parnell Esker may be hiked via a trail in the Kettle Moraine State Forest Northern Unit, near Dundee in southeastern Fond du Lac County. Ed.]
A Forest Bed
At Two Creeks, between Kewaunee and Manitowoc, the wave- cut cliffs of the lake shore reveal an ancient forest bed, buried beneath red till and resting on stratified red clay. It consists of logs, branches and upright stumps. This forest bed proves that there was a period long enough for forest growth between the retreat of the ice and accumulation of the red clay and the readvance of the ice during which the red till was deposited. Similar vegetable accumulations are found in wells in the Fox River Valley.
[The book's extensive and detailed chapter on The Glaciation of Eastern Wisconsin is followed by a chapter on The Drainage of Eastern Wisconsin. The Wisconsin Coast of Lake Michigan is then discussed in detail in a separate chapter beginning on page 294.]