Redwood County, Minnesota - Chapter 3: Physical Features, 1916

Geologic Eras. During the Geologic Eras, in one of which we are still living, the earth has assumed its present physical aspect. The study of these successive changes, except those which have been brought about by the occupation of modern man, and those which are still taking place and may thus exert an influence on the economic life of mankind, is beyond the scope of this work. A consideration of the physical characteristics and geologic phenomena observed in this county is, however, appropriate.

Topography. The surface of the county is, with the exceptions of the valleys of the streams, a series of broad swells. The highest portions of the adjoining undulations vary from a few* rods to a half mile or more apart; and their elevation is sometimes 5 to 15 feet, and again 20 to 30 feet, or rarely more, above the depressions, to which the descent is usually by very gentle slopes. These hollows have a form that is like that of the swells inverted, being mostly wide, and either in long and often crooked courses of unequal length, variously branched and connected one with another, or in basins from one to one hundred acres or more in extent, which have no outlet but are surrounded by land 5 feet or perhaps 10, 20 or 30 feet higher upon all sides. The small swamps, which often fill the depressions, are called sloughs or marshes, the former name being the most common in this prairie region, while the latter is applied to them in wooded parts of the state.

Many others of these depressions contain bodies of water, which vary from a few rods or a hundred feet to five or ten miles in length. All these are called lakes, and the term pond, which would be applied to them in the northeastern United States, is here restricted to reservoirs made by dams. The lakes of this and surrounding counties usually lie in shallow basins, bounded by gently ascending shores, which, however, are here and there steep to the height of 10 to 15, and rarely 20 to 25 feet. These higher banks are mostly at projecting points of the shore, and they have been formed by the undermining action of the waves. The foot of such banks is plentifully strewn with boulders that had been contained in the till, all the fine parts of which have been thus washed away. Other parts of the lake shore, adjoining tracts of lowland or marsh, are frequently bordered by a flattened ridge of gravel and sand, often with intermixed boulders, heaped up by the action of ice in winters, in its ordinary freezing, thawing, and drifting, when broken up, before the wind. These ice-formed lake-ridges rise only from three to six feet above the line of high water of the lake, and are from two or three to five or six rods wide. They occur most frequently in situations where they separate the lake from a bordering marsh, whose area evidently was at first a part of the lake.

The most notable features of the topography of this region are the valleys or channels that have been 'eroded in its broadly smoothed and approximately flat expanse by creeks and rivers. The smaller streams generally flow 15 to 30 feet below the general level, with valleys from a few rods to a quarter of a mile wide. The valley of the Redwood river is of small depth, 25 to 50 feet, along its course above Redwood Falls. At and below this town, within a distance of one mile, this river descends a hundred feet in a succession of picturesque cascades and rapids, over granite and gneiss, decomposing portions of which form towering cliffs, 100 to 150 feet high, on each side, from an eighth to a quarter of a mile apart. This gorge, extending one and a half miles before it opens into the broader bottomland of the Minnesota river, is quite unique in its grand and beautiful scenery, with dense woods along its bottom through which the river flows, but crowned above by the verge of prairies whose vast expanse, slightly undulating but almost level in this extensive view, stretches away farther than the eye can reach.

In Redwood county the Cottonwood river lies in a depression from a third to a half of a mile wide, composed of level alluvial bottomland, 40 feet below the average surface.

The valley of the Minnesota river on the north side of this and Brown county is from 165 to 180, and in some portions 200 feet deep, having a bottom land of alluvium 5 to 20 feet above low water and from three-fourths of a mile to one and a half miles wide, bordered by steep bluffs which rise to the general level of the country. Within this valley at numerous places are jutting knobs and small ridges of gneiss and granite, exposures of Cretaceous strata, and terraces of modified drift, which are described farther on in treating of geological structure. From the top of the bluffs the vast prairie stretches away beyond the horizon, having a smoothly undulating surface of till, which appears to be in general approximately level, though a considerable ascent, varying in amount from 75 to 150 feet, is made imperceptibly in a distance of twenty to twenty-five miles southwestward across these counties.

Here and there this sheet of unmodified glacial drift or boulder-clay, the direct deposit of the ice-sheet, is sprinkled with knolls, small and short ridges, or mounds, of gravel and sand, which rise sometimes by steep, but again by moderate or gentle slopes, 10 to 15 or 20 feet above the general level. The distribution and origin of these kame-like deposits of modified drift are more fully noticed on a following page.

In the southwest corner of Redwood county, its even contour, which to this distance from the Minnesota river may be called in general a vast plain, is changed; and a gradual rise of 200 or 300 feet takes place within a distance of a few miles, along a massive terrace which extends from northwest to southeast and east-southeast. This line of highland forms the northeastern border and first prominent ascent of the Coteau des Prairies, which farther west rises gradually and at length steeply again, to the much higher watershed between the Mississippi and Missouri rivers. In southwestern Redwood county a gradual rise begins a few miles south from the Cottonwood river, and in six or eight miles southwestward to the corner of this county amounts to about 250 feet, beyond which a slower rate of ascent continues in the same direction to the belt of swelling and somewhat hilly till at the northeast side of lakes Shetek and Sarah, in Murray county. On the Northwestern railroad, which makes this rise obliquely running from east to west, the ascent from Lamberton to Walnut Grove, in ten miles, is 79 feet; and in its next eight miles, to Tracy, is 180 feet.

Elevations. In the early eighties, John E. Blunt, engineer, of Winona, prepared a list of the elevations along the line of the Chicago, Northwestern Railway in this region, selections from which are here given, the miles indicated being the distance from Winona, and the feet given being the elevation above the sea level.

The elevation of the Minnesota river along the north side in this region at its ordinary stage of water, 20 to 25 feet below its high floods, is approximately as follows: At the northwest corner of Redwood county, 845 feet above the sea ; below Patterson's rapids, at the east side of Swede's Forest, 820 feet; at the mouth of the Redwood river, 810 feet ; at the line between Brown and Redwood counties, 789 feet; at Ft. Ridgely, 793 feet; at New Ulm, 784 feet; at the mouth of the Big Cottonwood river, 782 feet.

The Redwood river enters Redwood county at a height of nearly 1,100 feet above the sea, and its descent in twenty-four miles to Redwood Falls is some 150 feet. Thence to its mouth, in three miles, it falls about 140 feet, the greater part of this descent being in less than a half mile at Redwood Falls.

At the west line of Redwood county the Cottonwood river is about 1,120 feet above the sea, and it leaves this county and enters Brown county at an elevation of about 1,030 feet. Its height at Iberia is estimated to be 900 feet, and at its mouth, as already stated, approximately 782 feet.

The highest land of Redwood county is the southwest part of Springdale, its most southwestern township, about 1,400 feet above the sea, being some 300 feet above the Cottonwood river, ten miles distance to the north, and about 600 feet above the lowest land of this county, the shore of the Minnesota river at its northeast corner. Estimates of the mean elevation of its townships are as follows: Sherman, 990 feet; Morgan, 1,030; Brookville, 1,040; Honner, 900; Paxton, 1,025; Three Lakes, 1,060 ; Sundown, 1,070 ; Delhi, 1,000 ; Redwood Falls, 1,050 ; New Avon, 1,080; Willow Lake, 1,100; Charlestown, 1,120; Swede's Forest, 940; Kintire, 1,050; Sheridan, 1,070; Vail, 1,100; Waterbury, 1,125; Lamberton, 1,140; Vesta, 1,080; Granite Rock, 1,120; Johnsonville, 1,125 ; North Hero, 1,175 ; Underwood, 1,120 ; Westline, 1,150; Gales, 1,175; Springdale, 1,275. The mean elevation of Redwood county, derived from these figures, is 1,090 feet above the sea.

Soil. The black soil, everywhere from one to two feet thick, and often reaching to a depth of three or four feet in the depressions, forms the surface, being glacial drift or till, colored by a small proportion of humic acid derived from the decaying vegetation. This drift is principally clay, with which is an intermixture of sand and gravel, with occasional but not frequent boulders. The composition of this clay makes it quite unfit for brick-making, but gives it a porous character, so that rain and the water from snow melting are, to a certain extent, absorbed by it, excepting the large part which is drained away by the gentle slopes and the numerous water-courses, and some which stands in the swamps and lowlands. Below the soil cellars and wells find a continuation of this till, yellow in color and commonly soft enough to be dug with a spade, to a depth of ten to twenty feet or sometimes more, and then dark bluish and usually harder to a great depth beyond, which is seldom passed through.

The valley of the Minnesota river, 160 to 200 feet deep, has cut through this mantle of till. Along this valley, and in the last two miles of the Redwood valley before it joins the Minnesota, irregular knobs and ridges of gneiss and granite are exposed to view; and in some places these occupy nearly the whole width between the bluffs of the Minnesota river. Generally, however, the bottomland of the Minnesota river, as also of its large tributaries, are flat tracts of very fertile fine alluvium, or interbedded sand and gravel, covered by a rich soil of fine silt. These bottoms, which would be called intervals in New England, are elevated five to fifteen feet above the streams, being thus mostly within the reach of their highest floods in spring, but are very rarely overflowed during the season of growing crops.

Redwood county was originally mainly prairie or natural grass land, without tree or shrub, consisting of a continuous green sweep, often reaching in gentle undulations and swells, five to twenty feet high, as far as the view extended.

Timber. A nearly continuous though often very narrow strip of timber is found immediately bordering the Minnesota river through almost its entire course ; but generally much of the bottomland is treeless. The bluffs on the northeast side of the Minnesota have, for the most part, only thin and scanty groves. The southwestern bluffs are, for the most part, heavily wooded. The greater abundance of timber on the southern bluffs of this and other rivers in this region appears to be due to their being less exposed to the sun, and therefore more moist than the bluffs on the opposite side.

Along the Redwood river, and the Cottonwood river through Redwood county and in western Brown county, and along the upper part of the Little Cottonwood river, the width of woodland, excepting occasional interruptions, usually varies from a few rods to an eighth of a mile ; but along the last twenty miles of the. Cottonwod river and the last eight miles of the Little Cottonwood, the timber generally fills their valleys, from a fourth of a mile to one mile wide.

In northwestern Redwood county, Malcom McNiven has enumerated the following species of trees and shrubs occurring at Swan Lake, on the west line of Underwood : white elm, white ash, box-elder, cottonwood, wild plum, willows, Virginia creeper, climbing bitter-sweet, frost grape, prickly ash, choke-cherry, black currant, and prickly and smooth wild gooseberries, and wild rose, less frequent. Species not found at Swan Lake, but common or frequently on the Redwood river, are bass, red or slippery elm, iron-wood and sugar maple. Red cedars grow on the cliffs of this river at Redwood Falls, and from them has arisen one of the traditions of the name of this river and thence of the county.

The Cottonwood river is said to have its name, which also has been given to a county, from a very large, lone cottonwood, beside this stream, in the south part of Redwood county, about seven miles northwest of Lamberton ; but thjis tree has also a luxuriant growth throughout the timbered bottomlands of this river.

The northern limit of the black walnut appears to be at the Walnut Grove, of about a hundred acres, from which comes the name of the neighboring station and village on the railroad, the grove itself being on Plum creek in sections 25 and 36, Springdale, close to the south line of Redwood county, and one to two miles southwest from Walnut Grove village.

Geological Structure. The foundation of Brown and Redwood counties, northwest from New Ulm, consists of metamorphic gneiss and granite, belonging to the great series denominated Eozoic or Archaean, which embraces the most ancient rocks known to geology. This is overlain by various shales, sandstones, limestones and clays, the latter sometimes holding beds of lignite, which are regarded together as of Cretaceous age. Cretateous strata, including lignite, outcrop in the bluffs of the Redwood river close north of Redwood Falls; in the bluffs of Fort Creek near Fort Ridgely, in the west extremity of Nicollet county and close to the Minnesota valley, about sixteen miles below the last, and on the Cottonwod river in western Brown county.

Fossiliferous and sometimes lignitic clays of Cretaceous age are occasionally encountered in the wells through this region, especially at Walnut Grove and northward in western Redwood county, and in Lyon county, adjoining this on the west. The sheet of drift which forms the surface is thus often separated by unconsolidated Cretaceous beds from the underlying floor of crystalline rocks. Within the area here reported this gneissie and granitic floor outcrops, away from the valley of the Minnesota river and Redwood, at only one or two points, which are in Granite Rock township. These formations will be described in the order of their age, beginning with the oldest.

Gneiss and Granite. These rocks have the same composition, being made up of quartz, feldspar and mica. Gneiss differs from granite in having these minerals laminated, or arranged more or less distinctly in layers. Nearly all of the metamorphic rocks to be described here are varieties of gneiss, with which masses of granite, syenite and mica and hornblendeschists occur rarely.

In the N. E. % of Section 12, Granite Rock, an exposure of rock extends ten rods in length, from northwest to southeast, with half as great a width, rising five to ten feet above the surface of the undulating prairie. It is light grain gneiss, much contorted, with its strike and dip obscure ; intersected by few joints, which in some portions are absent across an extent of three or four rods, enclosing in the southeast two or three masses of nearly black mica schist, each two or three feet long.

About five miles further west, in N. E. 14 of the S. E. % of section 6, in the same township, is said to have an exposure of the same rock about three rods in extent, with a larger space around it where the rock lies only a few feet beneath the surface.

The depth of these rocks in this region is generally from 100 to 200 feet or more, so that they are not reached by wells nor by the channels of most of the rivers. Their only other outcrops in Redwood and Brown counties are within the Minnesota valley and are in the gorge of the Redwood river at and below Redwood Falls.

, The Minnesota valley, in the northwest corner of Swedes Forest and in the edge of Yellow Medicine county, contains abundant ledges for two miles, reaching 40 to 75 feet above the river. A lone school house is situated among them, about a mile east of the county line. Half a mile west from this school house the rock is reddish gray gneiss, dipping 15 N. N. W. A third of a mile west from this school house are massive granite cliffs, probably rising 75 feet above the river, divided by joints into nearly square blocks ten to fifteen feet in dimension. An eighth of a mile east from the last it is obscurely laminated gneiss, much intersected by joints, the principal system of which dips 15 S. At the east side of the school house it is also gneiss, somewhat water-worn, dipping about 5 S.

Within the next few miles following down the river, similar ledges are seen on its northeast side, in the N. E. ^4 of section 16, in Sacred Heart, Renville county, rising about 50 feet above the river; in the southeast part of section 17, Swedes Forest, rising at several points 25 to 40 feet ; at south side of Big Spring creek, in section 20 and the west edge of section 21, Swedes Forest, about 50 feet above the river, and near the north line of section 27, small in area and only about 20 feet high.

From the small creek a mile farther east in section 26, Swedes Forest, ledges of gneiss and granite abound in this valleythrough a distance of twelve miles, to the mouth of Redwood river and Beaver creek. They often quite fill the bottomland, occurring on each side of the river and rising from 50 to 125 feet above it. Between Redwood river and Beaver creek frequent small ledges rise along the bottom of the Minnesota valley, in knobs 40 to 60 feet above the river, but yet leave much open tillable land. Between Beaver and Birch Cooley creeks outcrops are mainly on the north side of the river, rising 100 feet in their highest portions. Below the mouth of Birch Cooley they are mostly on the south side, occurring in great abundance for two miles above and three miles below the mouth of Wabashaw creek. The highest of these are a mile above this creek, rising 75 to 125 or perhaps 140 feet above the river.

It will be remembered that the bluffs along this part of the valley are about 175 feet high, so that none of these ledges were visible until the surface of the drift-sheet had been considerably channeled.

On the Redwood river where it enters the Minnesota valley, one and a half miles northeast of Redwood Falls, the rock is greenish, being apparently a "talcose quartzite," or protogine gneiss, dipping 25 S. E. It forms cliffs 50 to 75 feet high, which are continuous on the west side of the river a quarter of a mile more. The picturesque gorge of the Redwood river at and below Redwood Falls is principally cut through a similar gneiss, partly decomposed, and sometimes almost completely kaolinized, overlain by Cretaceous strata, which in turn are capped with glacial drift. The largest cascade, having a fall of about 25 feet, is over a ledge of this protogine gneiss, much contorted and jointed, often obscure in its lamination.

The dip of the principal system of joints, which appears to coincide nearly with the lamination, is 20 to 30 N. At a cut which has been made through the rock two rods east of this cascade, it contains a nearly vertical trap dike, seen along an extent of some thirty or forty feet, bearing N. 40 E., about two feet wide, composed of dark greenish, compact rock, which weathers to a reddish color, much joined in planes parallel with its walls. Ten feet above the bottom of this cut, and higher, the cliff of gneiss is much decayed and changed to impure kaolin.

Decomposed Gneiss and Granite. Very remarkable chemical changes have taken place in the upper portions of many of the exposures of gneiss and granite near Redwood Falls. The rock is transformed to a soft, earthy or clayey mass, resembling kaolin. It has a blue or greenish color, when freshly exposed; but when weathered, assumes a yellowish ash color, and finally becomes white and glistening. Laminae of quartz are generally contained in this material, and have the same arrangement as in gneiss, so that the dip can he distinctly seen. Veins of quartz or feldspar, the latter completely decomposed, and the lines of joints, are also noticeable, just as in granite or gneiss ; making it evident that this substance is the result of a decay of rocks in their original place.

Because of the enclosed quartzose laminae, grains and particles of more or less gritty character, throughout these kaolinlike rocks, they appear to be unsuited for the manufacture of porcelain or any kind of ware. So far as can be judged from stream channels and other exposures, this decomposition reaches in some places to a depth of 20 or 30 feet, perhaps more. All grades of change may be found, from ledges where only here and there a few spots have been attacked and slightly decomposed, to portions where nearly every indication of the original structure has been obliterated.

Of these decomposed rocks on the Redwood river, Prof. N. H. "Winchell wrote in the second annual report of the Geological and Natural History Survey of Minnesota: "At Redwood Falls the granite is overlain by the kaolin, which has been mentioned, presenting, in connection with this substance, a very interesting series of exposures, suggesting very interesting questions both economical and scientific. About a mile below the village, on the left bank of the river and at the northwest of the bend, is a conspicuous white bluff (probably that seen by Keating, and pronounced white sandstone), composed of white kaolin clay. Near the top of this bluff, where the rains wash it, it is silvery white, and that color is spread over much of the lower portions, though the mass of the lower part is more stained with iron, having also a dull greenish tinge.

The white glossy coating which appears like the result of washing by rains is spread over the perpendicular sides. On breaking off this glossy coating, which is sometimes half an inch thick, the mass appears indistinctly bedded horizontally, but contains hard lumps and irony deposits. Further down, the iron becomes more frequent, and gritty particles like quartz impede the edge of a knife. The bedding is also lost, and the closest inspection reveals no bedding. Yet there is, even then, a sloping striation of arrangement of lines visible in some places on the fresh surface that corresponds in direction with the direction of the principal cleavage plane of the talcose and quartzitic slate already described. In other places this arrangement is not seen, but the mass crumbles out in angular pieces which are superficially stained with iron.

The profile of the bluffs here presents a singular isolated knob or buttress that rises boldly almost from the river. On either side of this bold promontory are retreating angles in the bluff.

A careful inspection of these ravines and of the adjoining bluffs affords indubitable proof that this material, white and impalpable as it is, results from a change in the underlying granite rocks.

"Just above this point is another exposure. It here supplies what is locally known as the 'paint rock,' from an enterprise started several years ago in the manufacture of mineral paint from this material. The decomposed granite here has very much the same appearance as the kaolin at Birch Cooley, but contains more quartz, and is more stained with iron. It is a rusty brown color, but within might be green or blue. It passes upward into the greenish, and then white, kaolin clay already described, but it stands out in a crumbling rusty buttress, exposed to the weather, and has quartzitic grains and concretions, iron-coated, and often an impure iron ore in considerable quantities. It shows silvery or shining talcose flakes, the same as seen in the so-called building rock, near the point where the railroad bridge crosses the Redwood river at North Redwood.

"A short distance above this, nearly opposite Redwood Falls, is situated the rock which was quarried for the manufacture of paint. This has in every respect the same character and composition as that last described. It consists of a perpendicular bluff or point, standing out from a lower talus that rises about 75 feet above the river, to the hight of 75 feet more. On the top of this is the drift-clay hardpan, covered by four or five feet of sand and gravel, the whole bluff being about 150 feet above the river. This bold bluff, or promontory, stands between re-entrant angles, its face falling down sheer thirty or forty feet. There is here visible an irregular slatey or cleavage structure in the rock, that at a distance has the appearance of dip toward the S. E. 30.

"This also contains quartz veins and deposits, accompanied by iron, in some places too abundantly to allow of being cut with a knife, though very much of it can be easily shaped with a knife. It shows ' slickensides, ' or surfaces that seem to have been rubbed violently against each other, causing a scratched and smoothed appearance, even within the body of the bluff. These surfaces are concave or curving, like putty hardened after being pressed through a crevice."

Before the extensive denudation of the glacial period, it is probable that all the granite and gneiss of this region were covered by a similarly decayed surface. Upon the areas where decomposed rocks still exist, the glacial plowing was shallower than elsewhere. These kaolinized strata are exposed in a ravine north of the Minnesota river, opposite to Minnesota Falls; in the gorge of the Redwood river, below Redwood Falls; in many of the ledges of the Minnesota valley for several miles next below, especially in excavations made by roads at the foot of the bluffs; in the valley of Birch Cooley near its mouth; and occasionally for eight or ten miles farther southeast. They have been found also in well-digging at considerable distance from the Minnesota valley.

Cretaceous Beds. In western Redwood county wells occasionally have gone through the drift and passed into clay or shale below, apparently of cretaceous age, and sometimes proved so by enclosed fossils. Such sections are reported at Walnut Grove in North Hero township, and in Granite Rock.

Cretaceous strata doubtless lie next below the drift upon the greater part of this district; but their only outcrops, excepting within the Minnesota valley and the gorge of the Redwood river, occur on the Cottonwood river in Brown county.

In Sherman, in Redwood county, Prof. Winchell records an exposure of cretaceous beds of sandy marl, horizontally stratified, seen in the road that descends from the Lower Sioux Agency to the old ferry. At this place in 1860 Prof. A. W. Williamson found in a cut for the road about thirty feet above the Minnesota river a large coiled shell, since lost, which agreed nearly with the figure of Ammonites monilis seen in an English textbook of geology.

Lignite. About four miles farther northwest, or half way from the Lower Sioux Agency to Redwood Falls, a cretaceous outcrop, including a thin layer of lignite, occurs in the south bluff of the Minnesota valley, above Tiger lake, being in the southwest corner of section 35, Honner, some three-quarters of a mile west from the mouth of Crow creek. Mining for the exploration of the lignite, which is an imperfectly formed coal, of inferior quality, yet valuable for fuel, was undertaken here, on the land of George Johnson, in 1871, by William H. Grant and others, a horizontal drift, or adit, being excavated into the bluff to a distance of about 260 feet from its face southward. This followed the same lignite, which, or at least, a black lignite shale, was found continuous along all this distance, being level in the direction of the adit, but dipping to the west about three degrees, or five feet in a hundred.

The adit is about a third of the way up from the foot to the top of the bluff, or some sixty feet above the river. Several tons of coal, sometimes quite clear for a thickness of six to nine inches, were obtained from the mine, and were used as fuel. The cost of the work, however, was about $2,000, without discovering any portion of the bed that could be profitably mined.

Prof. Winchell describes the formation here explored, and the similar lignite layer in the bluffs of the Redwood river, as follows: "This coal is from one of those layers in the Cretaceous that are usually known as lignites. It is earthy, passing sometimes into a good eannel coal, or into a bituminous clay. The compact cannal coal is in detached lumps, and occurs throughout a band of about four feet in thickness. This lignite band was followed in drifting into the bank at Crow creek, and was found to divide by interstratification with black clay, showing some leafy impressions and pieces of charcoal.

"The 'coal' here is said to overlie a bed of lumpy marl. . . . In some of the concretions are small shining balls of pyrites. . . . Over the 'coal' is a blue clay, requiring a timbered roof in the tunnel. This clay is likewise Cretaceous. The underlying lumpy or concretionary white marl becomes siliceous, or even arenaceous, the concretions appearing more like chert. Some of it is also pebbly, showing the action of water currents.

The same lignite coal also occurs elsewhere in the same region, the exposures being kept fresh by the freshet waters. More or less exploring and drilling, besides that done by Mr. Grant, has been engaged in, in this vicinity, but never with any better

"Near Redwood Falls, on land of Birney Flynn, is another outcrop of carbonaceous deposit in the Cretaceous. This is seen in the left bank of the Redwood river. It is in the form of a back bedded clay or shale, five or six feet thick, more or less mingled with charcoal and ashes, the whole passing below into charcoal fragments mixed with the same ash-like substance. In the latter are sometimes large pieces of fine, black, very compact coal, the same as that already spoken of at Crow creek as eannel coal. These masses show sometimes what appears to the eye to be fine woody fiber, as if they, too, were simply charred wood. Further examination will be needed to determine their origin and nature. They constitute the only really valuable portions of the bed, the light charcoal, which everywhere shows the distinct woody fiber, being generally mixed with the light ashy substance, and in a state of fine subdivision.

"A short distance above Mr. Flynn 's land is that of George Houghton, where the Redwood Falls' coal mine was opened. This mine consists of a drift into the bluff, forty feet, following a lignite, or charcoal bed in the Cretaceous. The bed here is seven feet thick, the greater part of it being made up of black, bedded shale or clay, though Mr. Flynn is authority for the statement that it showed a great deal more of the real charcoal than any other point discovered. Some fragments that lay near the opening, contained about nine parts of charcoal to one of ash, the whole very slightly cemented, and so frail as to hardly endure transportation. In this drift were also numerous pieces of what is described by the owners both here and at Crow creek, as 'stone coal.' It is the same as that mentioned as probably a cannel coal, occurring at Crow creek. It is these harder lumps that are found scattered in the drift throughout the southwestern part of the state."

This mining was done in 1868 or 1869, on the northwest or left side of the Redwood river, about one and a quarter miles north from Redwood Falls, on the south part of the S. W. %, of section 30, Honner, the height of the drift being some 75 feet above the river, and about the same amount below the top of the bluffs and general surface of the country. The lignitic bed is reported to dip slightly toward the southwest, and to be overlain conformably by shale, above which the upper part of the bluff is till. Next below the black coaly layer is said to have been a marl, varying from reddish to white, six inches to two feet in thickness, underlain by yellow and blue clay. No exposure of gneiss or granite is visible at this locality.

It appears nearly certain that no workable deposits of coal exist in this region. Prof. Winchell summarizes his observations and conclusions upon this subject as follows:

"First. The rocks that have been explored for coal, on the Cottonwood and Redwood rivers, belong to the Cretaceous system, and do not promise to be productive of coal in valuable quantities.

"Second. The coal there taken out is of an inferior grade, though varying from cannal coal to charcoal." . . . The charcoal, "while it is the more abundant, is of less value for use as fuel. It is light, and quickly ignites. ... It lies in irregular sheets, generally not more than half an inch thick when pure, but may be disseminated through a thickness of six or eight feet. It is very fragile, hardly bearing transportation."

The cannel coal "is black, or brown black, lustrous, compact, rather hard, and presents every aspect of a valuable coal. It occurs in isolated lumps or pockets, in the same beds as the charcoal, but less abundantly. It readily burns, making a hot fire. In the air, when it has become dry, it cracks and crumbles something like quicklime, but not to a powder."

"Third. As the rocks of the Cretaceous period are believed to have existed throughout the most of this state, the only probable exception being in the southeastern portion, including half a dozen counties, such coal is likely to occur at a great many places.

"Fourth. The 'float' coal which has so often attracted the attention of the people, is derived, so far as yet known, from the disruption of the Cretaceous rocks by the glaciers of the ice period. It is scattered through the drift, and is met with in wells and other excavations, and may be often picked up along the beds of streams."

The surface of Redwood county is principally till, or the mixture of clay with smaller proportions of sand and gravel and occasional enclosed boulders, which was thus deposited in a mingled unstratified mass by the ice sheets of the glacial period. Its thickness in this county is generally from 100 to 200 feet. Within the till are found occasional layers of sand or gravel, which often yield large supplies of water in wells. Many of these veins of modified drift were probably formed by small glacial streams, and they ean not be regarded as marking important divisions of the ice age. It is shown, however, by shells, remains of vegetation and trees, found evidently in the place where they were living, underlain and overlain by till, that this very cold period was not one unbroken reign of ice, but that this re-treated and re-advanced, or possibly at sometimes was nearly all melted and then accumulated anew.

Two principal glacial epochs can be distinguished, in the first of which all of Minnesota except its southeast corner was deeply covered by the continental ice sheet, and its border was several hundred miles south of this district, in Nebraska, Kansas, Missouri and southern Illinois; whereas in the later very severely cold epoch, the ice fields were of less extent, and terminated from 50 to 300 miles within their earlier limit, covering all the basin of the Minnesota river, but not enveloping a large tract in the southwest corner of Minnesota and leaving uncovered a much larger area than before in the southeast part of the state. Between these glacial epochs the ice sheet was melted away within the basins of the Minnesota and Red rivers, and probably from the entire state.

The greater part of the till appears to have been deposited by this earlier ice sheet; and during the retreat of the ice this till was overspread in some places, especially along the avenues of drainage, by the beds of modified drift, or stratified gravel, sand and clay, washed from the material which had been contained in the ice and snow and now became exposed upon its surface to the multitude of rills, rivulets and rivers that were formed by its melting.

In the ensuing interglacial epoch, this drift sheet was channeled by water-courses till its valleys were apparently as numerous and deep as those of our present streams. The interglacial drainage sometimes went in a different direction from that now taken by the creeks and rivers; and the valleys then excavated in the drift, though partly refilled with till during the last glacial epoch, are still, in some instances, clearly marked by series of lakes. More commonly the interglacial water-courses must have occupied nearly the same place with the valleys of the present time; and there seems to be conclusive proof that this was true of the valley of the Minnesota river.

A long period intervened between the great glacial epochs; the earlier ice sheet gradually retreated northward; a lake was formed in the Red river valley by the receding ice barrier on the north; the outflow from this lake, and the drainage of the Minnesota basin itself, appear to have excavated the valley of the Minnesota river nearly as it now is; and the further recession of the ice sheet probably even allowed the drainage of the Red river basin to take its course northward, as now, to Hudson bay, this being indicated by fossiliferous beds enclosed between deposits of till within the area that had been covered by this interglacial lake and was afterward occupied by lake Agassiz at the close of the last glacial epoch.

Again a severely cold climate prevailed, accumulating a vast sheet of ice upon British America and the greater part of Minnesota. By this glacial sheet the valley of the Minnesota river was partly refilled with till, but it evidently remained an important feature in the contour of the land surface. During the final melting of this ice sheet, its waters, discharged in this channel, quickly removed whatever obstructing deposits of drift it had received, and undermined its bluffs, giving them again the steep slopes produced by fluvial erosion. This partial re-excavation and sculpture were then followed immediately, during the retreat of the ice sheet, by the deposition of the stratified gravel, sand and clay, 75 to 150 feet deep, remnants of which occur as terraces on the sides of this valley, from its mouth to New Ulm, and less distinctly beyond.

Had not the great valley existed nearly in its present form through the last glacial epoch, it could not have become filled with this modified drift, which must belong to the era of melting of the last ice sheet. After the departure of the ice, the supply of both water and sediment was so diminished that the river could no longer overspread the former flood plain of modified drift and add to its depth, but has been occupied mainly in slow excavation and removal of these deposits, leaving remnants of them as elevated plains or terraces.

Terminal Moraines. In Redwood county the morainic tract is not prominent, and its course, which is believed to coincide approximately with that of the Cottonwood river, has not been traced. Close south of the valley of this river in the N. W. % of section 14, Gales, numerous small hillocks and ridges, ten to twenty feet high, rough with abundant boulders, were observed to occupy a width from a few rods to an eighth of a mile or more, reaching a half a mile or more in length from east to west ; and from a bridge in section 10, Gales, a noteworthy hill, perhaps sixty feet high, is seen in the view westward, situated not far from where the Cottonwood river crosses the county line. Farther northwest, this moranic belt is clearly traced across Yellow Medicine and Lac Qui Parle counties, its most conspicuous accumulations being the Antelope hills.

During the later stages in the recession of this ice sheet, when the fourth and fifth terminal moraines of its Minnesota lobe were formed, its southern extremity was successively at Kiester in Faribault county and at Elysian in Le Sueur county, and its southwest boundary doubtless crossed Brown and Redwood counties, but the marginal accumulations of drift belonging to these stages have not been traced here. A shallow lake extended along the edge of the ice sheet across these counties and acted to partially level down and smooth the morainic deposits. It seems likely, however, that they are still recognizable, and by careful observation might be mapped approximately. At the time of the fourth or Kiester moraine, the ice margin probably extended through the central part of Brown and Redwood counties; and the kame-like deposits near Sleepy Eye and in Granite Rock and the northwest part of Vesta, may in part represent this moraine. The fifth or Elysian moraine is probably indicated similarly in section 33, Swedes Forest.

Modified Drift of the Last Glacial Epoch. Upon the sheet of till which covers Redwood county are frequently noticed mounds and knolls or short ridges of gravel and sand, 10 to 20 feet, or rarely 30 feet or more, in height, which in any excavation are seen to be irregularly interstratified and obliquely bedded. These deposits appear to have been formed by streams that flowed from the drift-strown surface of the departing ice fields of the last glacial epoch ; having a similar origin with the eskers or kames, which form prolonged ridges, or series of interlocking ridges and mounds, in Ireland and Scotland, in Sweden, and in New England. Conspicuous kame-like deposits of modified drift in Redwood county were observed in the N. E. 14 of section 33, Swedes Forest, where a mound of this class rises some 30 feet above the general level; in the northwest part of Vesta, which has numerous hillocks and short ridges of gravel and sand, 10 to 40 feet in height, trending from north to south more commonly than in other directions; and in Granite Rock and thence southwestward to the Cottonwood river.

Authority. "The Geology of Brown and Redwood Counties," by Warren Upham, contained in pages 562-558 of "The Geology of Minnesota," published in 1884, the whole volume being Vol. I, of the Final Report of the Geological and Natural History Survey of Minnesota, 1872-1882.