USA > Wisconsin > Lafayette County > History of Lafayette county, Wisconsin > Part 51
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In his discussion of the glacial drift, Mr. Irving reaches certain conclusions, which are here reproduced only so far as they relate positively to the area devoid of drift. The negative arguments, or those that go to prove the absence of drift, because the region is not like the vast majority of the country, and of the Northern Hemisphere of the globe, are recited in brief :
"1. The drift of Central Wisconsin is true glacier drift. [See Report 1877, p. 630.] "2. The Kettle Range of Central Wisconsin is a continuous terminal and lateral moraine. The mere fact of the existence of such a distinct and continuous belt of unstratified and mo- raine-like drift, which, in much of its course, lies along the edge of the driftless area. or, in other words, along the line on which the western foot of a glacier must long have stood, would go far toward proving the truth of the proposition [that this is true glacial drift], of which, however, a complete demonstration is at hand. In all the country just inside the Kettle Range, we find that glacial striæ-channels-lines of glacial erosion, and lines of travel of erratics- bowlders, or minerals foreign to the locality where found-preserve a position at right angles to the course of the range, although that course veers in the southern part of the district from west to north. East of the Central Wisconsin district, the Kettle Range extends eastward and northeastward to the dividing ridge between the valley of Lake Michigan and the valley in which lie Green Bay, Lake Winnebago, and the head-waters of Rock River, and along this ridge northward, into Green Bay Peninsula. All along this part of its course, Prof. Chamber- lin has found the glacial striæe pointing east of south, and toward the Kettle Range, whilst along the middle of the Green Bay Valley he finds the striæe directions parallel to the main axis of the valley, or a little west of south. On the west side of this great valley, and along the eastern border of the Central Wisconsin district, the stria trend about southwest, whilst still
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further west, they gradually trend further to the west, becoming at last nearly due west, or at right angles to the western Kettle Range.
" We have then a most beautiful proof that at one time the Green Bay Valley was occupied by a glacier, which was not merely a part of a universal ice sheet, but a distinctly separate tongue from the great northern mass. The end of this glacier was long in northern Rock County, its eastern foot on the East Wisconsin divide, and its western on the summit of the divide between the Fox and Wisconsin River systems, as far south as southern Adams County, after which it crossed into the valley of the Wisconsin, and from that into the head-waters of the Catfish branch of Rock River, in the Dane County region. Whilst the main movement of the glacier coincides in direction with the valley which it followed, it spread out on both sides in fan shape, creating immense lateral moraines. Peculiar circumstances caused the restriction of the eastern moraine or narrow area, whilst that on the west, having no such restriction, spread out over a considera- ble width of country, the breadth of the moraine reaching in Waushara County as far as twenty- five miles. This width of moraine must have been due to the alternate advance and retreat of the glacier foot. Such an advance and retreat appears, moreover, to be recorded in the long. lines of narrow sinuous ridges, each marking, perhaps, the position of the glacier foot, or a por- tion of it, during a certain length of time. The intersecting of these winding ridges, which have no parallelism at all with one another, appears to me to have been the main cause of the formation of the kettle depressions. Col. Whittlesey [Smithsonian Contributions to Knowledge], has supposed that these owe their origin to the melting of ice masses included within the moraine materials, and this may possibly be true with regard to more regularly circular kettles. The thickness of the great glacier we can only conjecture. It is easy to see, however, that it was at least a thou- sand feet, for it was able to accommodate itself to variations in altitude of many hundred feet. Morainic drift occurs on the summit of the Baraboo ranges over 900 feet above Lake Michigan, and on the immediately adjacent low ground, 700 below.
" 3. The driftless region of Wisconsin owes its existence, not to superior altitude, but to the fact the glaciers were deflected from it by the influence of the valleys of Green Bay and Lake Superior. Some writers have thrown out the idea that thic driftless area is one of present great altitude compared with the regions around it, and that, by virtue of this altitude during the Glacial period, it caused a splitting of the general ice sheet, itself escaping glaciation. This idea may have arisen from the fact that, in the southern part of the area, the district known as the ' lead region,' has a considerable elevation ; but the facts hitherto given have shown that, in reality, the driftless area is for the most part lower than the drift-covered country immediately around ; the greatest development, for instance, of the western lateral moraine of the glacier of the Green Bay Valley, having been on the very crown of the water-shed between the Lake Mich- gan and Mississippi River slopes, whilst the driftless region is altogether on the last-named slope. Moreover, to the north, toward Lake Superior, and in Minnesota, the whole country covered with drift materials lies at a much greater altitude. J. D. Whitney, in his report on the lead region of Wisconsin, favors the idea that the driftless district stood, during the glacial times, at a much greater relative altitude than now, and so escaped glaciation. But it is evident that, in order that this could have been the case, either (1) a break or bend in the strata must have taken place along the line of junction between driftless or drift-bearing regions, or else (2) the drift- less region has since received relatively a much greater amount of denudation than the drift- bearing.
" That no break or bend ever took place along the line indicated, is abundantly proven by the present perfect continuity of the strata on both sides of the line, the whole region in Central Wisconsin being in fact one in which faults of any kind are things absolutely unknown. That no sensible denudation has taken place in Wisconsin since the glacial times, in either drift-bear- ing or driftless areas, is well proven by the intimate connection with one another of the systems of erosion of the two regions. The valley of Sugar River, for instance, with its branches, is throughout its course worn deeply into the underlying rocks; on its east side it contains moraine drift, proving that it was worn out before the Glacial period, whilst on the west it
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extends into the driftless regions. We are thus compelled to believe that, during the Glacial period, the region destitute of drift had the same altitude relatively to the surrounding country as at present. Before the Glacial period, portions of the drift-bearing region may indeed have been somewhat higher, for in it a considerable amount of material must have been removed from one place to another by the glacial forces. The only satisfactory explanation remaining, then, for the existence of the driftless region, is the one I have proposed. We have already seen that the extent of this region to the eastward was marked out by the western foot of the glacier which followed the valley of Green Bay. That it was not invaded from the north, is evidently due to the fact that the glacier or glaciers of that region were deflected to the westward by the influence of the valley of Lake Superior. The details of the movement for this northern coun- try have not been worked out, but it is well known that what is probably the most remarkable and best-preserved development of morainic drift in the United States, exists on the water-shed south of Lake Superior. Here the drift attains a very great thickness, and the kettle depres- sions and small lakes without outlet are even more numerous and characteristic than in other parts of the State. The water-shed proper lies some thirty or forty miles south of the lake, and 800 to 1,200 feet above it, but the morainic drift extends twenty-five to fifty miles further south- ward. On the east side of the State, the drift of Lake Superior merges with that of Central and Eastern Wisconsin, while west of the western moraine of the Green Bay glacier, it dies out somewhat gradually, until 125 to 150 miles south of the lake the drift limit is reached. Much of the country twenty-five to seventy-five miles north of the driftless region, though showing numerous erratics, is quite without any marked signs of glaciation, as, for instance, along the valley of the Wisconsin, from Grand Rapids north to Wausau. Further west, the drift extends more to the southward. The course of the Lake Superior glaciers conveyed them further and further southward as they moved westward.
" Future investigations will undoubtedly bring out a close connection between the structure of the Lake Superior Valley and the glacial movements south of it. Even the facts now at hand seem to point toward some interesting conclusions. Projecting from the south shore of Lake Superior, we find two great promontories, Keweenaw Point and the Bayfield Peninsula. Both of the projections have a course somewhat transverse to the general trend of the lake, bear- ing some thirty degrees south of west. Both have high central ridges or backbones, which rise 1,000 to 1,500 feet above the adjacent lake, and are made up of bedded igneous rocks, sand- stones, and conglomerates of the copper series. Both of these ridges continue far westward on the mainland, having between them a valley, partly occupied by the lake, which is a true syn- clinal trough ; the rocks of the two ridges dipping toward one another. North of the Bayfield Peninsula, and again south of Keweenaw Point, we find two other valleys running in from the lake shore in the same direction. In all probability each one of these valleys has given direc- tion to a glacier tongue. An inspection of a good map of the northern part of Wisconsin, Min- nesota and Michigan, will serve to show that the almost innumerable small lakes (which are far more numerous than are shown in the best maps) of these regions, are concentrated into three main groups, each group corresponding to a great development of morainic drift, and lying in the line of one of the three valleys just indicated. I suppose that each of the lake groups is a moraine of the glacier which occupied the valley in whose line it lies. The main ice-sheet com- ing from the north met, in the great trough of Lake Superior, over 2,000 feet in depth, an obstacle which it was never able to entirely overcome, and so reached southward in small tongues composed perhaps of only the upper portions of the ice. These tongues being deflected westward by the rock structure of the country, and having their force mainly spent on climbing over the water- shed, left the region further south untouched. The eastern part of the Lake Superior trough is not nearly so deep as the western, and the divide between Lake Superior and the two lakes south of it, never attains any great altitude, so that here the ice mass, having at the same time perhaps a greater force on account of its nearness to the head of the ice movement on the Lau- rentian highlands of Canada, was able to extend southward on a large scale, producing the glaciers of the Green Bay Valley, and of Lake Michigan.
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" Although quite crude in its details, I am convinced that the main points of the explana- tion thus offered for the existence of the driftless region in the northwest will prove to be cor- rect. To obtain a full elucidation of the subject, much must be done in the way of investigation, not only in Wisconsin, but over all of Minnesota and the States south, in order that the details of the ice-movement for the whole northwest may be fully understood.
"4. The stratified drift of the valleys (in the drift-covered regions) owes its structure and distribution to the water of the swollen streams and lakes that marked the time of melting of the glaciers.
" 5. The depth below the present surface of the rock valleys appears to indicate a greater altitude of this part of the continent during the Glacial period than at the present time."
TOPOGRAPHY AND SURFACE GEOLOGY OF THE LEAD REGION.
Mr. Moses Strong, in his report of 1877, says : " Unlike most regions which nature has selected for the reception of metallic ores and useful minerals, the lead region bears no evidence of any sudden disturbances or violent action of physical forces. The effects produced by igneous and eruptive agencies are wanting. Faults and dislocations of strata are nowhere found. The only irregularities are slight upheavals or bending of the strata (and these never of great extent), producing changes of but a few feet from the normal dip. Between the geological condition and the general surface contour of the country, there is no direct correlation. The existence of a hill or a valley on the surface is not due to a subterranean elevation or depression of surface, as is by many supposed, and whatever irregularities exist must be chiefly attributed to the milder natural agencies now constantly at work, such as running water, frost, winds, etc., acting through an immensely long period of time.
" Drainage .- The most marked and persistent feature of the lead region is the long divid- ing ridge, or water-shed, which, commencing near Madison, continues almost directly west to the Blue Mounds, a distance of about twenty miles. Here it takes a slight bend to the south- west for fifteen miles until it reaches Dodgeville, where it resumes its westerly course until it terminates in the bluffs at the confluence of the Wisconsin and Mississippi Rivers. Its total length is about eighty-five miles. Two points are noticeable-one is its general uniform direct- ness of outline (it being subject to but few and unimportant flexures), and the other is its paral- lelism with Wisconsin River so long as the latter holds an approximately westerly course, the summit of the ridge being always about fifteen miles from the river. The divide maintains an average elevation of about six hundred feet above Lake Michigan, and is seldom less than five hundred or more than seven hundred, except at the Blue Mounds, where it gradually rises east and west for several miles until it attains an elevation at the west mound of one thousand one hundred and fifty-one feet. This, however, is an extreme case, and, in fact, the only marked exception to the general level. In the town of Mount Hope, a slight decrease of elevation is about four hundred and thirty feet at a point within a mile of both the Mississippi and Wiscon- sin Rivers. There are also two main branches or subdivisions of the water-shed. Of these, the western is the ridge which separates the waters that flow into the Platte and Fever Rivers from those which flow into the Pecatonica. It leaves the main divide in the town of Wingville, and, passing through the townships of Bellmont and Shullsburg in a southeasterly direction, passes out of the State in the town of Monticello. The ridge is not so conspicuous as the main water- shed, either for the directness of its course or the uniformity of its elevation. The most con- spicuous points on it are the Platte Mounds, which appear from a distance to be very high, but their height is only relative, their actual elevation being about seven hundred feet above Lake Michigan. The ridge appears to slope somewhat in its approach to Illinois, its average eleva- tion there being about five hundred feet.
" The easterly subdivision is that which separates the waters of the Pecatonica and Sugar Rivers. It may be said to begin at the Blue Mounds or a couple of miles east of them, and, pursuing quite a devious course through the townships of Primrose, Washington and Monroe, it crosses the State line in the town of Jefferson. "This ridge is characterized by a much greater
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want of uniformity in its general course and its very irregular elevation. It is much narrower than either of the others, more abrupt in its slopes, and contains quite a number of hills and low places. These are the principal elevations of the country affecting the drainage. There are, of course, many minor ones.
" Streams .- The present situation of the streams was probably never modified nor influenced by drift or glacial agencies. Premising this, it follows that the location of the streams must have depended upon the natural configuration of the country and the superior advantages of cer- tain strata in certain positions predisposing them to become the beds of streams. Other things being equal, surface waters would naturally form a channel first in the more soft and easily eros- ible strata lying along the line of strike of some soft formation, and would cause a river to con- form its first channel to its outcropping edge. Simultaneously, its tributaries would shape their channels approximately at right angles to the river, under the following conditions: When the gen- eral slope or drainage of the country is not contrary to the geological dip of the formations, which, in the lead region, does not appear to have been the case, the tributaries on one side of the river thus formed would conform themselves to the natural dip of the underlying strata, sloping toward the main river, and would be found wherever there were depressions or irregularities in the surface suitable to their formation. These would, at their inception, approximate to their final length and course, and future changes in them would be confined to the deeper erosion of their beds and widening of their valleys, the formation of lateral branches, the division of the head of the stream into several smaller sources, and, finally, the gradual recession of all the sub- ordinate parts.
" With the tributaries on the other side of the principal river, a different order would pre- vail as regards their position and growth. They would at first be the merest rivulets, and increase only from erosion, and their beds would lie across the edges of the strata. There would be only a very limited extent of country tributary to the river on this side, the great volume of its water being derived from the tributaries of the other side. The dividing ridge would thus be very near the river, and a second set of long streams tributary to some other river would here take their rise and flow away.
"In the process of time the main river would slowly cut its way through the soft formation, in which it had its original bed, into and through those which underlaid it. This might, at first, be accompanied by a slight recession parallel to the line of strike. Such a movement, however, could not be of long duration, but would become less as the valley became deeper, because any such recession would necessitate the removal of all the overlying formations. Finally, the small streams flowing across the strata would cut their valley back from the river, the dividing ridge would recede, and their sources would, from the position of the strata, be in steep and pre- cipitous ravines. Such, in brief, is the theory of the formation of the streams in the lead region.
" The Wisconsin River, from the eastern limit of Iowa County to its mouth, is a conspicu- ous example and illustration of the foregoing theory.
"Although the surface of the country, in its present condition, does not permit the accurate delineation of the former lines of outcrop of the paleozoic formations, yet a sufficient number of others remain to show that they must once have covered the country far north of where they are at present found. The existence of Niagara limestone in a thickness of about one hundred and forty feet at the Platte Mounds, and probably the full thickness of the formation at the Blue Mounds, warrants us in supposing that the former outcrop of the underlying Cincinnati group was at least as far north as the present bed of the Wisconsin River.
" The valley now occupied by the river, from Mazomanie to Blue River, is very nearly that of the present line of strike of the Lower Silurian formation, and, although from there the strike of the lower members (of which outliers still remain) appears to bear rather more to the northward, yet observations on the dip of the Cincinnati group, in such occasional outliers as remain, lead us to believe that its original strike was approximately in a southwesterly direction, from Blue River to the Mississippi.
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" Assuming, then, that the Cincinnati group once had its northern outcrop where the river now runs, or in a line parallel to it in that vicinity, the surface waters would easily erode a channel in the soft and friable shales which, to a great extent, compose this formation.
"In fine, the whole process of formation previously described would take place. On the north side it had, as now its principal tributary streams, the Kickapoo, Knapp, Eagle, Pine and Bear, in their present localities, and approximately their present length. On the south side of the river, however, the principal water-shed already referred to was probably quite near the river, from which position it has receded to the place it now occupies. The Green and Blue Rivers and Otter, Mill and Blue Mound Creeks were small and insignificant streams, which, by the gradual process of erosion, have increased to their present size and length; but even now are small when compared to the northern tributaries.
"A further effect was to shorten the Grant, Platte and Pecatonica Rivers by the gradual southwesterly recession of the water-shed and the lowering of the latter by the denudation of the Niagara limestone and Cincinnati groups ; except in such localities as were protected by a superior hardness of some part of the formation, as in the case of the Blue Mounds.
"The result of the denudation has been to divide the country into two parts, each differing widely from the other in its topographical features. The streams flowing southward from the water-shed have eroded the country into gently undulating slopes. This is probably due to the direction of the streams conforming in a measure to the dip of the strata. Abrupt cliffs and steep ravines are the exception, and not the rule, never being found in the immediate neighbor- hood of the water-shed, but rather confined to the small lateral branches. On the other hand, to the north of the water-shed the panorama of bluffs and precipitous ravines is almost moun- tainous in its aspect. In fact, nothing can be more striking than the contrast which presents itself from certain points on the divide in looking from north to south. In nearly all of the ravines leading northward the fall of the first quarter of a mile is not less than one hundred feet; and, in general, it is true of the streams running northward that three-quarters of the fall takes place in the first quarter of the distance from their sources to their mouths.
" It seems not improbable that these sudden declivities are due to the streams flowing over the edges of the strata, rather than lengthwise, along their dip. Again, the streams flowing to the southward become comparatively sluggish in their course as soon as they cease to be brooks. They have usually a soft, muddy bottom, while those tributary to the Wisconsin are clear, rapid streams, flowing over a sandy or gravelly bottom, their valleys being narrow and their sides very steep.
" The streams tributary to the Platte, Grant and Pecatonica Rivers do not exhibit any marked characteristics on one side that are not shared equally by the other. It may be re- marked, however, that the short streams which flow into the Mississippi River present very much the same topographical characteristics as are seen in the southern tributaries of the Wis- consin, narrow and deep ravines and valleys being apparently the rule in Grant County.
" It is remarked that there has been a gradual diminution of water in the lead region since the early mining days. The larger streams contain much less water than hereto- fore, within the memory of living men. It is probable that cultivation of the land is the chief cause of this decrease, as a much greater amount of surface is thus exposed, and evaporation takes place more rapidly and in larger quantities. Removal of the timber is, without doubt, another cause of this decrease. The soil of the timbered land contains more moisture than that of the prairie ; and in all countries the removal of the timber has always been followed by a marked decrease of the water supply.
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