Grant County, Wisconsin - Chapter 1: Geological History of Wisconsin, 1900

Chapter 1: Geological History of Wisconsin

Paleozoic Age - The Potsdam Period - The Lower Magnesian Limestone - The Trenton and Galena Limestones - The Hudson Shales and Niagara Limestone - Wisconsin during the Paleozoic Age - The Carboniferous Age - Natural Gas and Petroleum - The Mesozoic Age - The Glacial Epochs - Relations of Geology to Political Economy.

A knowledge of the geological history of the region of which Grant County is a part is necessary to a good understanding of the mineral resources of the county, and the geological history also has an important bearing on the political and commercial history of the county, which it is interesting to observe. These considerations induce me to note a few brief points in the long historj' of the "Isle Wiscon¬ sin for geological changes and formations are not confined to so small areas as counties. I shall try to do so, not in the technical jargon of the geologist, but in language which the school-boy and the working-man can understand.

This history has been given at a considerable length in a masterly manner by Prof. Chamberlin in the first volume of the Geology of Wisconsin ; but that was nearly twenty years ago, and since then the investigations of a dozen eminent geologists have added much to and taken something away from what is given in the volume cited.

Original Land

Many million years ago (how many no man can say, for in those geologic times ten thousand years are as one day and a thousand years as a watch in the night) this mundane sphere, before a ball of liquid fire, had become cooled down so that its oxygen and hydro¬ gen gases became combined as vapor and then as liquid water, which descending, covered the whole face of the earth in one shoreless, unbroken sea.

But the earth cooled still more, and as it cooled it shrank and wrinkled, just as a potato or an apple does when it shrinks by its internal juice drying up. These wrinkles appeared above the water as the pristine land. One great mass of it lay, shaped like a V, its arms extending on each side of where Hudson Bay now is, its point lying just north of Lake Superior. Another formed the beginning of what since became the now long-lost continent of Atlantis, famed in classic fable. A third formed the " Isle Wisconsin," a little south of the present site of Lake Superior.

This pristine land was of immense height, perhaps twelve miles, for a single formation from its ruins (the Laurentian) is known to have a thickness of 30,000 feet, nearly six miles. Even that vast height would not be a two-thousandth part of the circumference of the earth, less comparatively in size than the wrinkle upon a shriveled apple. This Isle Wisconsin must have had mountain cliffs beside which those of the Rockies or the Andes would be pigmies indeed. They were of the most primitive rock, just what cannot be told, for no geologist has ever seen their like in its primitive state. They were not granite nor gneiss, but were probably harder than either.

But hard and high as they were, they were all finally torn down by seas and storms - and such seas and storms! The earth's crust was then hot and the sun shone with terrific heat compared with to-day. This caused enormous evaporation ; evaporation begets both electricity and clouds, which unite to form storms. The earth then revolved upon its axis in twelve or fifteen hours and the rapid alternations of day and night added to the disturbances of its elements. Travelers have exhausted the powers of language in describing tropic thunder storms and newspaper reporters in writing up western cyclones, but they are tame indeed compared with the storms that beat upon the lofty mountain brows of the new-born Isle Wisconsin. I had almost said that these storms were appalling ; but there was no living thing on all the globe to be appalled. On the raw, rough rocks of the dizzy cliffs there was not even the humblest moss to be tempest-torn ; in the acid waters of the raging ocean there was not the lowest protoplasm or slime-life. It was the Azoic or Lifeless Age. So, too, that tremendous evaporation must have pro¬ duced storm-clouds of exceeding density and immense extent and depth. Those storms must have raged through a plutoni^n darkness that could hardly be illuminated by the -sheets of awfully vivid light- ening that flashed through it almost incessantly. We think the climate of Wisconsin is now bad and blustery for a great part of the year, but compared with what it was in the Azoic Age it is the changeless, calm and smiling, perfect peace of Paradise.

With what inconceivable fury those mountain torrents, age after age, must have torn down those great cliffs, crunched the fragments together and hurled them down into the boiling sea! And the sea, too, battered ever upon the shores of the new land with a force of which we cannot now conceive. Its waters were also hot and acid and they not only tore down the cliffs of the shore, but dissolved their alkaline rocks as vinegar does limerock. The coarse fragments of the wasted cliffs were piled about the shore and the dissolved parts were carried farther out and deposited as fine sediment. And thus the land ever grew lower and broader.

Ages passed and the shrinking earth again wrinkled. This time the Isle Wisconsin, it seems, fell into a depression of a wrinkle instead of a ridge, and it sank far beneath the waves and lay there for centuries while the waters dropped slowly and silently upon it the sediments they had dissolved from the shores of other lands.

The Laurentian Period

Another shrinking of the cooling globe gave the Isle Wisconsin a second birth, but not at first as an island. It was probably a penin¬ sula of the great Labradorian continent until the advancing sea ate through the channel where n6w lie the Great Lakes (as it has done several times since), and made Wisconsin again an island.

It is probable that this elevation never attained any great height. The land rose very slowly through thousands of years and the heavy rains of that age probably cut away the land almost as fast as it rose. Then it sank again beneath the sea and remained thus for centuries in shallow water which dropped sediments upon it until they accumu¬ lated miles in depth.

This period of rising and subsequent sedimentation is called by geologists the Laurentian Period or age. That portion of the Laurentian formation which still remains is known to be 30,000 feet thick, and probably many thousand feet were washed away, when it rose again, by the rains of the Paleozoic Age. It may be asked : How can the thickness of this formation be known? The earth has never been penetrated to the depth of six miles. When this formation was the second time heaved up it was very much crumpled and wrinkled and in some places, notably in Canada, the broken edges were turned up to the surface, and it is easy to measure across these upturned edges the thickness of the strata.

The Huronian Period

At the close of the Laurentian sedimentation the Wisconsin land again began to rise and there followed another long period of rising, erosion, sinking and sedimentation, called the Huronian Period. While the Laurentian strata were under the water they became by pressure and heat solid rocks, but not brittle ; they bent like half-melted glass. When they were thrown up again it was by the wrinkling of the earth's crust, and consequently they were very much folded and twisted. The Huronian formation is also, but in much less degree than the Laurentian. After the Huronian formation was formed, sank and was again upheaved, the earth ceased to wrinkle and all the subsequent formations lie in comparatively flat, un wrinkled strata.

The commercial and political development of the Wisconsin of to¬ day is connected in one important respect with this Huronian forma¬ tion of millions of years ago. It was during this period that the great Gogebic-Penokee iron deposits were laid down. The Gogebic region was then a low swamp covered by the high tides of the Superior Sea, which were heavily charged with iron in solution. These swamps must have been filled with a kind of vegetation which took up the iron dissolved in the water and deposited it with their dead remains.

It is noticeable that all great iron deposits (in the Appalachian range from Pennsylvania to Alabama, in the Ozark region, in the iron¬ bearing ranges of Colorado and New Mexico) were made in lands which were just above sea-level during the Huronian Period. South¬ ern Wisconsin was then all under water, and it has no iron worth mentioning.

The Isle Wisconsin In The Paleozoic Age

The Paleozoic Age signifies the age of ancient or primitive life. When the Huronian sedimentation ceased the land in the northern part of Wisconsin was about the level of the water. Then occurred a most remarkable era. Along the southern shore of the Superior Sea (then become a shallow lake) and far across the Labrador continent, great fissures opened in the rock and lava flowed forth, not in rivers as from the crater of a volcano, but in vast lakes from abyssmal chasms a hundred miles in length.

The flows of fiery rock followed each other at first in quick succession, heaping layer upon layer in immense thickness. Then they become slower and between each eruption the land sank beneath the sea and a layer of silt, sand, and pebbles was spread over each layer of lava. The thickness of these combined accumulations seems to have been not less than 40,000 feet, about one-fourth of which was watery sediment and the rest lavas. This eruptive era is called the Keweenawan Period.

These Keweenawan rocks are important as being the formation in which the Lake Superior copper is found. It is thought that the copper was brought up from the interior of the earth by these eruptions. It was probably first dissolved by the acid water and then precipitated and concentrated by contact with the iron which was deposited in this region during the Huronian Period. How this may be you can see by placing a piece of iron in a solution of blue vitriol, when the iron will be covered with a coat of metallic copper. Although the copper was probably brought up by the Keweenawan eruptions, its solution by the water and subsequent pre¬ cipitation and concentration were probably the work of a long time afterward.

The formations I have described are grouped together by geolo¬ gists under the name of Archaean, that is, ancient. The highest parts of this- Archaean, never, after the Keweenawan Period, sank entirely under the sea, but formed a core about which the later formations, the sandstones and limestones I am about to mention, were wrapped, never completely covering it as a blanket, but encircling it like skirts, their inner edges lapping far upon it and their outer parts extending far out under the sea. This Archaean core corresponds to the locality of the pineries of Wisconsin, Michigan and Minnesota.

The Potsdam Period

Again the sea advanced upon the land until the shore line of the Southern Sea was considerably north of central Wisconsin and that of Superior some fifty miles south of the present shore of Lake Superior. Some knobs of the ancient rocks of especial hardness resisted the teeth of the ocean and stood as little islets and still stand in central Wisconsin.

But the sea was verv shallow and its surf and breakers ground up the fragments of the Archaean rocks that were dug out of the shore or borne into the sea by the torrents from the land. The waters of the ocean were still acid and from the ground-up fragments of the granites and gneisses they dissolved out the lime, potash, soda and clays, and carried them far away into the deep water. But the silica was insoluble and it remained behind in the form of grains of quartz or sand, which sank to the bottom of the shallow sea and in time hardened into sandstone.

This deposit is of great extent and in places 1,000 feet thick. It is called the Potsdam Sandstone. It is a common outcrop in central Wisconsin, but is too low to appear in Grant County, except in the northeastern corner, where it forms the base of the bluffs of the Wisconsin River. The deposit of the Southern Sea was generally white or yellow, but on the Superior side it was stained red or brown by the iron and various shades of green by the copper, forming the " Pictured Rocks" of Lake Superior.

During the Potsdam Period occurred a deposit in central Wiscon¬ sin that may in the near future have an important influence on the commercial and political history of the State. It was the Potsdam iron deposit,, found in Sauk, Vernon, and northern Richland, and Crawford Counties. It is not so rich as the deposits of the Huronian Period in the northern part of the State, but may yet be valuable. It shows that at the close of the Potsdam Period the region where this deposit occurs became a marsh with vegetation capable of precip¬ itating iron from the currents that crept through it.

The Lower Magnesian Limestone

At the end of the Potsdam Period the sea on the southern shore of the Isle Wisconsin suddenly became deep. The isle had become low; its rivers were cut off and no longer bore the debris of the Archaean rocks into the sea, and such as the sea broke off from the shore sank into deep water and were not ground up. and dissolved. So the sand deposits ceased.

The deep waters became clear and fitted for marine life. In the Huronian Age life began and consisted at first of a low order of vegetation in the shore marshes and zoophytes or plant-like animals, such as sponges, in the sea. At the end of the Potsdam Period life had developed into mollusks or shell-fish, at first very minute, with shells no larger than a grain of sand, or coral-like insects. These had the power to extract lime from the sea water to make their shells. These shells and corals accumulated upon the still bottom of the deep water forming a limestone deposit, called the Lower Magnesian Limestone. What innumerable billions of these little animals there must have been and how many thousands of years they must have worked to make the 250 feet thick of this limestone that still exists in some places !

This limestone forms the bulk of the bluffs at Boscobel, but its surface is the floor of the Wisconsin River at its mouth, while at Glen Haven its upper surface is below the river, showing that the bed of the sea during this formation sloped sharply to the southwest. Near the shore of Lake Michigan, in Wisconsin, the top of this lime¬ stone lies about 1,150 feet below the surface, showing a southeast slope on that side of the State.

This formation was laid down upon a smooth surface of sand¬ stone, but its upper surface is rough and billowy. This shows that at its close the sea suddenly retreated, leaving the land exposed to the channeling and eroding rains of centuries.

Again the sea covered the southern part of Wisconsin, but the water was shallow and laid down only sand. This formation is called the St. Peter Sandstone. It formed only a narrow fringe about the Isle of Wisconsin and has not much thickness or continuity north of the Wisconsin River. In Grant County it is the only sandstone we see, except in the extreme northeastern corner. It comes to the sur¬ face in places near the Military Ridge, but slopes so much to the south¬ west, that in the central parts of the county it is seen only in the deep valleys, fits most southern outcrop is on the Mississippi about two miles below the mouth of the Platte.

The Trenton And Galena Limestones

Again deep water prevailed over southern Wisconsin and the ma¬ rine animalcules and mollusks laid down a thick formation of lime¬ stone called the Trenton. Then the water began to shoal and the limestone that was formed was somewhat impure and coarse-grained and is called the Galena Limestone.

These two formations, more especially the Galena, are important on account of being the lead and zinc-bearing strata. The source of these metals and the manner of their deposition have been a subject of much speculation and many theories. The best authorities at present conclude that they were brought by oceanic currents and pre¬ cipitated by decaying animal matter in the waters, furnishing sul- phuretted gases, and thus forming sulphurets of lead and zinc. It is obvious that the currents and the sources of the sulphuretted gases must have been unusually favorable in the Lead Region.

The zinc deposits are mostly in the Trenton, consequently they are deep in southwestern Grant County, but as the strata slope upward toward the Military Ridge, the zinc deposits come almost to the sur¬ face near Mont fort.

The Hudson Shales And The Niagara Limestone

At the close of the Galena Period occurred a long period of deposi¬ tion of varied matters washed down from the land - limestones, sand¬ stones, clays, and slates intermingled - called the Hudson Shales. Thick as this deposit was, it was very soft and was all worn away in the long ages that southwestern Wisconsin has since lain above the sea. That underlying the "Mounds" is about all of it that is left in Grant County.

Yet once again the sea encroached upon the land in southern, east¬ ern, and western Wisconsin, and there was deposited a formation, in places 250 feet thick, of hard, siliceous (sandy) limestone, called the Niagara. Then the sea retired again and has never since rolled over southwestern Wisconsin and in the long ages that followed the Niag¬ ara, hard and thick as it was, was almost wholly eroded in this re¬ gion, being disintegrated by the water, air, and frost and washed away by the rain. In northeastern Iowa, where the land was long afterward submerged and other deposits, both marine and glacial (which I shall mention hereafter), were piled upon the Niagara, that rock is well preserved, as are also the shales below, there called the Maquoketa Shales.

Wisconsin During The Paleozoic Age

The time during which mollusks were the highest type of life is called the Silurian time or age. To these mollusks belong snails, which were the first animal inhabitants of Wisconsin land. Then came a higher type - the vertebrates or animals with backbones. Man is the highest form of the vertebrates, but the lowest form, the fish, was the first to come into existence. There is no record in the rock tablets that fish inhabited Wisconsin seas for many centuries after their existence elsewhere, even as near as Ohio. Why the fish didn't "go West" sooner I have never seen explained. The time when fish were the highest type of life is called the Devonian Age. Both the Devonian and the Silurian are parts of the Paleozoic Age.

The Silurian Age was for southern Wisconsin on the whole one of deposition, formation, and construction. The following Devonian Age was, on the contrary, one of constant erosion and destruction of the land surface, which, during all that age and all the succeeding ages, lay entirely out of the water. This period of erosion has been enormously, inconceivably long. Although during the greater part of that period southern Wisconsin lay low and flat and little subject to wash, and during the latter part of the period the surface was pro¬ tected by a dense vegetation, yet the effect of the erosion was pro¬ digious. The whole of the great, hard, thick Niagara Limestone and the Hudson Shales, with an aggregate depth of about 700 feet, were totally carried away. All that is left of them in Grant County is Sinsinawa Mound, the capping of which is Niagara and the body Hud¬ son. It owes its preservation to the especial hardness of its cap of Niagara and to the fact that it stood on an ancient watershed. On the highest parts of the Military Ridge and other elevations even the great thickness of the Galena and Trenton Limestones were worn away, exposing in some spots the sandstone beneath, and the same is the case in the large stream-courses.

The northern part of the State, the old Archaean core, must have been rising all this time, as places where the earth's crust was first broken formed "lines of ancient weakness" where the crust continued to heave up as the earth cooled and shrank during the succeeding ages. But this rising was probably intermittent and very slow, slower even than the erosion which it suffered, so that this land is now only a low watershed about 1,500 feet above the sea.

The Devonian Age was for many parts of America an age of ac¬ tive creative history, but of this history-making Wisconsin was a pas¬ sive spectator. She was a grass-widow divorced from the Sea King and living in retirement, living on through innumerable centuries till her face was deeply furrowed with the wrinkles of age. The Sea King was a donor of many and rich gifts, and how many of these (coal, petroleum, natural gas. phosphates, etc.) Wisconsin lost bv being di¬ vorced thus earl\ and forever I shall tell hereafter.

The Carboniferous Age

During most of the Devonian and all the preceeding ages plant life was of a low order and not very great in quantity. But toward the close of the Devonian some cosmic developments set free an enormous amount of carbonic acid gas, which is the bread of plant life, and this.

together with other favorable conditions, caused an immense increase in vegetable growth. The climate of the globe was still of more than tropical warmth, and great humidity still prevailed, and so vegeta¬ tion was still of a low order, without flowers, fruit, or seed, for the higher orders of plant life require bright sunshine, dry soil, changes of temperature, and other conditions which were not found at the time of which I speak.

The plants that throve in the hot climate and eternal mists of the Carboniferous Age were of the class called acrogens - furns, rushes, etc. - but they grew to enormous size. In the great coal beds of to¬ day are found the carbonized remains of ferns that were 80 feet tall and rushes 30 feet high and two feet in diameter.

A large portion of what is now the United States, a belt beginning at Rhode Island and sweeping through the whole Appalachian region and southern Ohio, Indiana, and Illinois, and a large belt about the Ozark region of Missouri and Arkansas, lay, dhring the Carboniferous Age, about the level of the sea, sometimes above and sometimes below the surface of the water. Thus there were immense marshes filled with the giant plants I have just mentioned and doubtless an immensity of humbler grassy or moss-like vegetation. The roots of these plants and the bodies of the mosses and grasses filled the swamps with vege¬ table matter, to which were added the leaves shed from the great fern forest and the dead bodies of these giants themselves, all preserved from decay by falling into the salt water of the marshes in w'hich they grew. The flatness of the country and its dense vegetation prevented for the most part the inwashing of mud and sand, so that the accumu¬ lation was almost entirely vegetal.

After an immense deposit of vegetal matter had thus been formed the land sank far enough under the sea to be covered with a deposit of mud and silt which in time hardened into slates and shales; or, if the water was deeper, sandstones or even limestones formed, and the layer of vegetal matter thus lying between the much thicker strata of earthy sediment was compressed and underwent slow chemical changes and became bituminous coal. In some parts of the Alleghany region still greater pressure and great heat still further decomposed the vegetal matter into anthracite or stone coal.

The land thus oscillated, first just above and then below the sea, until several of these coal beds had been formed and between them strata of slates, shales, sandstones, and limestones, in some places

But during all this time Wisconsin stood entirely out of the water, the Carboniferous sea not reaching its southern line by a hundred miles ; consequently Wisconsin has no coal beds worth mentioning, nor has northern Illinois.

At a still later time called the Cretaceous Period most of what is now Iowa, Nebraska, Kansas, eastern Colorado and New Mexico, and western Texas, was at or* just below the level of the sea and there were formed other coal beds called the Cretaceous Coal Meas¬ ures. But the Cretaceous sea did not encroach upon Wisconsin. Indeed, during the whole Devonian Period the coast of the " Minnesota Gulf," it is thought, coincided with the present course of the upper Mississippi.

The conditions which caused the formation of the Coal Measures were also favorable to the formation of iron deposits, in the manner mentioned in connection with the Huronian Period, and thus we find in many of the coal localities heavy deposits of iron made during the Carboniferous Period. It was a very fortunate combination, and has done much for the prosperity of the regions where such com¬ bined deposits have been found and developed.

Natural Gas And Petroleum

It is the popular supposition that both petroleum and natural gas are the products of coal ; but it is the present opinion of scientists that they are both usually of origin independent of coal. Indeed, natural gas is often found in regions where there are no coal deposits. It is also the present opinion of the best authorities that natural gas and petroleum, especially the former, are not always, nor even gener¬ ally, of vegetable origin, as coal is. The fact that these products, especially gas, contain considerable nitrogen is one of the several reasons for considering them of animal origin.

The great formations of limestone and chalk, as I have before said, are the remains of the shells of mollusks and corals and the bones of fishes. By far the greater number of the animals (or rather animalcules) were exceedingly minute, and their number in each generation was so great that no combination of figures can express it nor no mind conceive it, nor the number of generations that have lived and died. The surface of the globe, on land and under sea, is a charnel house on a scale inconceivably vast. While the shells and bones of these little beings were mostly of lime, their bodies were com¬ pounds of nitrogen with hydrocarbons. When their bodies were buried in the strata formed by their shells and slowly decomposed, most of the nitrogen escaped and the remaining hydrocarbons were distilled into petroleum and gas. Thus all the limestones, chalks and shales, all the formations (except the sandstones) that have been formed since life became prolific on the globe, are the abundant source of these hydrocarbons.

The greatest source and reservoir of natural gas is the Trenton Limestone, in which the gas is not only formed but stored in its cavities and its porous upper portion, like water in a sponge. But in most localities the gas thus formed escaped as fast as it was formed. To retain it there must be an overlying stratum of impervious material. In the gas region of Indiana and Ohio this impervious cover is the" Utica Shales." In order that any great quantity may be collected this cover must have the form of an inverted bowl or trough. Such a formation is the great "Cincinnati Arch" and several parallel smaller arches in Ohio, Indiana and Illinois, and numerous still smaller ones in Pennsylvania and West Virginia. Such an arch there is also in Wisconsin, extending from north to south through the central part of the state with a southwestern offshoot, the Military Ridge. The State has in its southern part a great thickness of Trenton and Galena Limestones. Then why has it no natural gas or petroleum ? Simply because the Hudson Shales, which might have formed the necessary cover to retain the gases,, were all washed away, and although the gas has been forming for countless centuries since the Trenton and Galena were laid down, it has all escaped into the air. The northern part of the State never had either the gasforming limestones or the covering shales.

An old proverb characterizes the unlucky man as the one whose platter is always bottom side up when it rains porridge. Grant County's platter was all right when it rained lead and zinc, but all wrong when it rained iron and coal. Her platter was right side up (which was bottom side up) to catch gas and oil, but unfortunate^' for her to-day, it has been there exposed to the weather so long that the bottom is all worn out and the gas and oil have all escaped.

The Mesozoic Age

In ancient fable Atlas bore the earth upon his shoulders and on one occasion let it down to go and gather the golden apple of Hesperides. As we have seen, Atlas let down his burden many times - several times during the Carboniferous Period. But now he rose refreshed and reared the whole Appalachian region not only out of the water but high in the air. The Sierra Nevada and Cordilleran ranges were also raised. Most of the region between the Alleghanies and the Missis¬ sippi was raised permanently out of the water Defeated Neptune, driven back from the last of his many conquests of this continent, fell upon the enfeebled ancient continent in the rear, and Atlantis was no more forever.

Let it not be thought that this change took place with the sudden¬ ness of an earthquake. It was a slow and measured flexure of the strata by a pressure steady and powerful, but not violent, working through very long time.

This increase of land surface and these mountain ranges thrown athwart thecurrentsof air and ocean caused marked climatic changes. Also, after the enormous vegetation of the Carboniferous Period had cleared the air of its excess of carbonic acid the conditions of both air and earth became more favorable for life on land and amphibious life than it had ever before been. These favorable conditions caused the sudden and enormous development of a new kind of animal life, the reptilian. This development was sudden in the geologic sense, although it may have been thousands of years in occurring.

The Glacial Epochs

We come now to a very modern time in geological history, al¬ though it was probably nearly two thousand centuries ago. The gigantic race of reptiles had disappeared, leaving behind them only comparatively small and feeble descendants. But a gigantic race of mammals had developed and were now lords of the land. In the great forests of oak, elm, and birch (modern trees, you see) that covered the tipper Mississippi region roved the mastodon, mammoth, and the giant elk. The tropical climate of the Mesozoic Age had passed away in Wisconsin, and was soon to change to more than arctic cold.

Although there is abundant evidence that there were two great ice invasions, separated by a long period of time, geologists have no means of knowing how long ago in years they occurred, nor what could have caused this extraordinarily great cold and snow-fall. But the astronomers have come to the aid of the geologists in this matter.

It has been calculated that the earth's orbit has periods of great eccen¬ tricity, during which the northern hemisphere is subject to just such intense cold and great snow-fall as would be required to make the vast continental glaciers' to which I have just referred. One such period of great eccentricity occurred something more than two hun¬ dred thousand years ago and another not quite so great, a little less than one hundred thousand years ago. Such a period will return upon the earth in about ten thousand years. Although this is a very short time in the geologic ages, it is so vast a time in the history of human life that we need not worry about the time when the sea of ice shall flow over the cities and prairies, the farms and factories of the great Northwest.

The first ice invasion was much the greatest. It has left its record up among the mountain peaks, telling that it had a depth of more than four thousand feet. The weight of this enormous mass of ice actually caused the crust of the earth to sink somewhat.

We are accustomed to think of ice as an unyielding solid, so that to speak of its "flow" seems nonsense; and yet the glaciers of to-day show ice flowing in real rivers, though very slowly.

This great sea of ice moved on over the land across the whole con¬ tinent till its southern border reached about the lower part of the Ohio River on the east and the Missouri River on the west. But, curiously enough, there was a small area which this glacial sea did not cover. This area includes Jo Daviess County in Illinois, the whole of Grant, LaFayette, Iowa, Richland, Crawford, Vernon, Juneau, Monroe, La Crosse, Trempealeau, Buffalo, and parts ofGreen, Dane, Sauk, Wood, and Jackson Counties in Wisconsin, with a narrow strip west of the Mississippi in Iowa and Minnesota. This is called the Driftless Area and is a region of intense interest to geologists, as it enables them, by the sharp contrast it affords with the region covered by the glaciers, to see what effect the glacial epoch had upon the land.

The causes of this split in the glacial flow, that left southwestern Wisconsin an island in a sea of ice, are rather obscure, and the more curious because the Driftless Area was then, as now, considerably lower than much of the region which was overwhelmed by the ice. It is probable, however, that, although the ice-flow climbed the Archaean highland of northern Wisconsin and descended its south¬ ern slope, it was by doing this so much retarded and weakened that before it could get farther on its course the cold period passed away.

As it was, the great glacier from Superior and the one from Michigan came together down about Clinton, Iowa, and dammed up the Missis¬ sippi River, so that the waters backed up over most of the Driftless Area till they found a new way over the low plains of Iowa into the Missouri. Meanwhile the Michigan glacier discharged its waters in a broad sheet over the still lower and more level plains of Illinois.

The ice invasion found the country covered with a great forest inhabited by mammoth beasts. The great trees were covered deep by the debris borne along by the ice, and their remains still exist in a thick stratum called " the forest bed."

The ice invasions found the country drained by valleys cut deep into the ancient formations, very much as you now see them in Grant and Crawford Counties, and elsewhere in the Driftless Area.

Stand on one of those high divides in Grant County, and contem¬ plate the intricate and yet regular and complete system of drainage which characterizes that region. Notice how the smallest " hollows," each starting up near the crest of the ridge in a faint depression, gradually increases in size as it descends until it unites with one like itself to form a larger "hollow," or embouches into a larger one, and this larger one goes on down increasing in size and uniting with others till it embouches into a creek valley, and this into a small river valley, and this into the valley of the great river. All is regular, systematic and perfect. I once thought all the world was drained just that way, little knowing that outside of this narrow Driftless Area this perfect drainage system has been all destroyed.

But as the mighty glaciers crept over the surface of the land they wiped out all this perfect work of innumerable thousands of years, this "dendritic" system of drainage. The deep valleys were all filled by the tremendous loads of debris that the glaciers plowed up from their beds and bore along with them. When they began to melt, about their southern ends great lakes were formed and the mud from the melting ice borne into these lakes formed thick deposits of clays, especially the "gumbo" clay of southern Iowa and northern Missouri. When the glaciers finally retreated they left the debris they had borne either piled up at their termini in heaps or long ridges called "moraines," or spread and scattered over the plain formed above the filled-up valleys of the ante-glacial time. Much of this debris was rock torn from the Archaean ledges of the far North and deposited on these more southern plains, in fragments of all sizes, from boulders like haystacks and houses to mindte pebbles, but all worn smooth and rounded by the friction they encountered in their long and very slow journey.

I have spoken of the ice retreating at the end of this glacial epoch, but it is not to be supposed that it actually flowed back northward. It still kept on its southward flow, but its extremeties melted more rapidly than it came down, and so in fact it retreated northward.

As I have said before, there were two of these ice invasions, sepa¬ rated by a long period of time. During this time the country again became covered with forests inhabited by animals.

The second ice flow was far lighter and of somewhat less extent than the first. It covered only a small corner of Illinois, about half of Iowa and three-fourths of Wisconsin. Its depth was only a few hun¬ dred feet, while that of the first was more than four thousand feet.

When the sea of ice retreated from the land it left a vast plain half covered with numerous lakes, many of them caused by morainic dams, in northern Wisconsin, Michigan and Minnesota, and a part of these lakes remain to this day, for the many thousand years since the re¬ treat of the ice have not been sufficient for the cutting of a new and perfect drainage system like that of the Driftless Area or of the whole country before the the glacial epochs.

There is comparatively little of the geological history of Wisconsin after the last glacial epoch, for, although the time since then covers nearly the whole period of human existence on the globe, in geology it is a matter of only a few uneventful days. It remains only to point out some of the bearings which the facts of geological history I have mentioned have upon the political history and economy of Wisconsin and particularly Grant County.

Relations Of Geology To Political Economy

Let us see if we can trace any connection between the geological history outlined in the preceding chapters and the political history of Wisconsin. That this history is somewhat peculiar is shown by the fact that in the legislature of 1838 Grant County had four of the twenty-five members of the assembly, or one-sixth of the whole, while in the present legislature she has two out of one hundred, or onefiftieth of the whole. On the population map of the State published by the census bureau in 1890 the counties of Grant, LaFayette, and Iowa (including the Lead Region) are colored yellow to indicate de¬ crease of population, while the State as a whole has considerably in- creased in population and many other States have increased much more than Wisconsin. This decrease of population in the southwest¬ ern part of Wisconsin has been going on for the last three decades up to 1890.

What is the matter ? Can geology tell and can it give any hope for the future of this region ? It is not a bad part of our great and glorious country. I have traveled through more than half of the States of the Union and four or five Mexican States, and I have found that in many natural advantages and attractions the Lead Region of Wis¬ consin is incomparable. Two of these advantages, which no doubt had much to do with attracting settlers here in an early day, are its beautiful scenery and excellent and abundant running water. The rain which falls upon it soon sinks to a stratum of limestone impervi¬ ous to water and which slopes downward and outcrops in some little valley, and the water is poured out in the form of a spring of cold, clear water, and these springs unite into rills and creeks. It is not so where the glacial drift covered the sloping strata deep beneath its debris, for although in those regions there may be many lakes (owing to the imperfect drainage mentioned on page 206) there is little running water. And the same may be said of the level prairies and alluvial plains farther south and west that were not covered with the glacial drift. Also, in the drift region much of the well water is im¬ pure and unpleasant from the decayed wood of the "forest bed."

Then, a soil formed from decomposed limestones is much more favorable for grass and foliage than a soil formed from outcropping sandstones, or the Archaean dgbris of the glacial drift ; consequently, nowhere else have I ever seen such viyid verdure as glorifies the woods and fields, the hills and vales of the Lead Region of Wisconsin in the prime of summer. But greenbacks are better than green leaves and green grass, and so many thousands of the former citizens of this verdant region have gone at the call of the almighty dollar to work out prosperity for other regions.

The four great factors which have contributed to Wisconsin's growth have been lead, lumber, iron, and agricultural products. Of the mineral products, we have seen that the deposit first laid down (the iron of the Huronian Period) has been the last to be developed, while the lead, laid down at a much more recent period (the Galena ), was the very first to be developed. This was owing to geological con¬ ditions. If the Lead Region had been covered deep by the glacial drift it would probably not yet have been known as a lead region. But it was exposed for such immense periods to erosion that the overlying strata were worn away and deep valleys cut into the lead-bearing limestones, so that the mineral outcropped in scores of little ravines, to be found by the most careless and ignorant prospector. It was easily accessible, so that the poorest man who could procure a pick and shovel could find it in paying quantities, and its value per pound was so much greater and the cost of reducing it so much less than that of iron ore that it is no wonder the Lead Region was so early and quickly developed, while the iron region waited for railroads, a large population and great capital. Thus the Lead Region became early the seat of political power in the State, while the eastern part of the State had for its only advantage its nearness to water transportation to the East, which caused the early development of agriculture in that region.

We have seen that the Pineries correspond roughly to the old Archaean core of the State, and they were the next important natural resource to be developed ; and for thirty years they have been transfer¬ ring the balance of political power from the southwestern to the north¬ ern and northwestern part of the State. However, the pine woods are not inexhaustible and the time will soon come when this region, stripped of its magnificient pine trees, its silica soil poor for either grain or grazing, will begin to fall behind in the race of progress, and need a yellower coloring on the census map than has the Lead Region in 1890.

One thing that enabled Grant County to hold her own in some measure for ten years after the lead interest began to lose its impor¬ tance was the agriculture of her remarkable prairies. During the fifties the price of wheat ruled high, owing to European wars and other causes, and the prairies of Old Grant were found to produce enormous quantities of that wonderful "Canada club" wheat, and they quickly became almost solid wheat fields.

These prairies are peculiar, unlike those of any other region, which leads me to give my theory of their formation. It will be observed that they correspond to the divides or watersheds of the county. This shows that they were in ancient times upland swamps, before the little valleys which now drain them so perfectly had cut their way up from the river valleys, then not nearly so deep as now. To the young reader who has never been out of the Driftless Area and never.seen a swamp except upon a low river bottom, the term "upland swamp" may seem a paradox; but such swamps are not unknown in other parts of the world, where the drainage system is not so old and perfect as that of the Driftless Area. The acids formed from decaying vegetable matter ate deep into the limestone rocks and the basins thus formed became swamps which gradually filled up with vegetable deposits and the soil is now deep and rich in proportion to the depth of those deposits. The western edge of such an upland swamp may now be traced near the western edge of the city of Lancaster. But even the deep, rich soil of these prairies seemed unable to stand more than ten years of our reckless wheat culture, and Grant County now imports much of her bread from Minnesota.

One thing that has hindered the prosperity of Grant County has been its long-time lack of railroads, leaving it a sort of dead eddy around which ran the tides of commerce. This was the direct result of its being in the Driftless Area, with its deeply cut drainage system interposing its high ridges and deep valleys athwart the ways of commerce from the populous East with its ocean ports-to the great and growing West. Thus the great trunk railroads avoided Grant County and crossed the drift plains to the south and north of her.

One serious drawback to the Driftless Area and much of the country to the south that was never covered with the drift is the extreme liability of the clay soils of its steep slopes to wash. To-day hundreds of thousands of acres of the old fields of the Southern States are miniature "Bad Lands" or small copies of the great deserts of the far Southwest. There are now in Grant 'County a few fields some¬ thing like but not nearly so bad as those old southern fields, but there will be hundreds of them in years to come if corn culture is persisted in too long and too continuously. This fact and the remarkable adapta¬ bility of the soil for grass and foliage points to dairying as the propci great industry of the region.

But a dairy region cannot, in the nature of things, be a region of dense population and great wealth ; only extensive manufactures and the incident commerce give these. But without coal, iron, petroleum, or natural gas, extensive manufactures cannot be maintained. Even the Gogebic region, with its rich deposits of iron, cannot very success¬ fully compete with the regions which have coal and iron together, as the Appalachian region from Pennsylvania to Alabama, the Ozark region, and the Raton region of eastern Colorado and New Mexico.

To conclude, then, the capitalists of the Driftless Area, if they de¬ sire for their section that wealth, population, and political supremacy which can come only from manufactures and commerce, ought to pray (or rather, pay) for the invention which will dethrone King Coal, with his principal ministers, Pretroleum and Gas, and the invention which will usher in the Aluminum Age (when the clay hills of Old Grant will be mines of wealth), to take the place of the Iron Age, which has prevailed upon the earth since Tubal-cain.first taught man¬ kind the secrets of the furnace and the forge.