USA > Minnesota > Brown County > History of Brown County, Minnesota: Its People, Industries and Institutions (Volume 1) > Part 6
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the lowest of the Cretaceous series, in Nebraska and Kansas, and two in the same group in Colorado.
Clay and an underlying more sandy deposit, which have been used together for the manufacture of fire-bricks, occur in the base of the north bluff of the Cottonwood river south of New Ulm. The entire section of this bluff is given by Professor Winchell in the second annual report, in a classi- fication of a section of the Cottonwood river south of New Ulm: "1. Hardpan drift, made up of clay and stones, seen about thirty feet. 2. White sand, the age of which is un- certain, containing irony concretions and deposits. It is somewhat indistinctly stratified obliquely, like drift sand, and has some coarse grains. Its position in reference to the overlying hardpan drift, together with its thickness and purely white color, indicates its age to be Cretaceous, one hundred feet. 3. Blue clay, containing some siliceo-calcare- ous, irony lumps; said by Mr. Dauffenbach to hold some coal; mixed with No. 4 for making fire-block, four feet. 4. Fine, somewhat gritty clay, largely aluminous. This is white, and when long submerged, soft and fluid-like, but when dry has to be quarried by blasting. This mixed at the rate of two-thirds with one-third of No. 3 makes a fine, white fire-brick, seen, twelve feet. Total height of bluffs, one hun- dred and forty-six feet."
"The above section varies in short intervals. About half a mile further up the river a sandstone outcrop was encountered. It rises in a bluff immediately from the water, on the opposite side of the river. In this sandstone, which here appears firm and massive, and which is probably equiv- alent to No. 2, of the foregoing section, are many irony mud balls, or concretions, having a fancied resemblance to plums
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or bananas. They vary in shape and size. They have been gathered as fossil 'fruits,' and sent east as rare curiosities."
The valley of the Minnesota river was explored by Pro- fessor Winchell in 1873, and the greater part of the descrip- tions of the Cretaceous strata, as here presented, is from his report for that year. Some additional observations and information were gathered by the writer in 1879 and 1880.
In section 2, Cottonwood township, Brown county, near its east line, a bluff on the south side of the Minnesota river, situated on the land of John Gruebel, four miles below New Ulm, is described by Professor Winchell, as follows: "1. Black alluvium, two feet. 2. Clayey alluvium, of a light brown color, four and one-half feet. 3. Red clay, con- taining some sandstone in masses; stratified, two and one- half feet. 4. Belt of greenish sandy clay, one foot. 5. Sandy clay, of a light umber color, one and one-half feet. 6. Bedded sandy clay, of an earth color, two feet. 7. Green- ish sand, the color coming from the mixture of green shale with the sand, the grains of sand being white quartz, two inches. 8. White sandstone in one bed, or weathering into beds of two inches, one foot. 9. Green bedded shale, or clay, with some fine sand grains, and some laminations or thick beds that are all white sand, but generally maintaining a green color, seen, eighteen feet. 10. Slope and talus, ten feet.
"The bedding seen in the foregoing section is horizon- tal, and shows no fossils. Although there is no opportunity at this place to determine whether this series of shales lies above or below the sandstone at a place four miles southeast, on the north side of the Minnesota river, by an observation made in the bank of the road at the crossing of the Cotton-
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wood river, it is believed to overlie that sandstone, but to underlie a series of calcareous beds that appear in the right bank of the river, about a mile below the mouth of the Cot- tonwood. The colors near the top of the foregoing section exchange places a little in following the bluff along, drift boulders and gravel occupying the place of clay in No. 3. In some places the red irony stain passes down lower. It is likely that the red, brown and ochery colors are due to ferriferous waters, since the deposit of the Cretaceous, and to oxygen in the air. Hence it is not certain that the drift extends through the whole of No. 3, although drift boulders are mixed with it, or replace it, in some places. When evenly bedded and free from boulders, it undoubtedly be- longs to the Cretaceous, the drift stopping with No. 2. When it is replaced by boulders, the Cretaceous is only so much more worn away, the color prevading them, as passing down to lower beds."
Professor Winchell continues: "From the mouth of the Cottonwood river going down the right bank of the Min- nesota, a regular terrace is seen to rise several feet above the flood plain. About a mile down, this terrace shows its origin and composition in the banks of the ravine which cuts it. Before reaching that point, however, an outcrop of 'gray concretionary limestone' is seen on the top of the ter- race plateau. This limestone here is overlain by a couple of feet of water-washed limestone, gravel and cobble-stones, mixed toward the top with the usual black alluvium. The appearance of the quarried stone is like drift pieces, and the bed from which it is taken is intersected variously with divisional planes, cutting the mass into irregular fragments, which, on being taken out, appear weathered. Yet there are
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crystal-lined cavities, some parts of it being mostly made up of calc spar. Since the formation of the crystals, cal- careous water has again deposited lime on the edges of the crystals, which, having first been of the thin (axe-shaped) variety, have now the appearance of separate but crowded cock's combs, the little beaded accretions of lime being ar- ranged on their edges. There is also a considerable quan- tity of uncrystallized lime on other surfaces. The interior of the stone is of a light gray or drab color, and when com- pact and free from crystals is very fine grained. It is said to make a white, strong quicklime, of which there can be no doubt. This limestone outcrop, which shows only about sixteen inches, is within a mile of the red quartzite outcrop near New Ulm, the bare, bald surfaces of which are visible from this point, on the other side of the Minnesota.
"A little below the last described exposure, is the old Winkelmann lime-kiln and quarry, in section 2, Cotton- wood. The limestone is much mixed, confusedly, with shale, but the following general section can be made out, in which no fossils were seen: 1. Alluvium and boulders, two feet. 2. Green shale, interstratified with belts and irregular no- dules or masses of gray limestone, fifteen feet. 3. Green shale, one foot. 4. White sand, varying to green shale, one and one-half feet. 5. Green clay, two feet. 6. Calcareous shale, or marl, with some argillaceous matter, five feet. 7. Green shale, or clay, with blotches of red, seen, one foot. Total, twenty-five and one-half feet.
"The same kind of greenish marl is exposed up the Cottonwood, the immediate bluffs being somewhat wrought in it, to a point just back of New Ulm."
In a later examination of the strata at the Winkelmann
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quarry, Professor Winchell has noted about forty feet of the green shale, with thin layers of concretionary limestone ; underlain by red shale, of which a thickness of about five feet was seen, but it may extend below the river-level, which is some five feet lower than the base of the section exposed. Occasional layers of red shale were seen somewhat above its general mass, separated from it by green shale. There seems to be a very slight dip toward the south.
Prof. James Hall mentions ferruginous sandstone, containing plant remains, interbedded with red marls, lying below the green shale and concretionary limestone in the vicinity of the Winkelmann lime-kiln. Four species of fos- sil leaves, collected in these beds by Hall, and found also in other states on the west and south, are described by Les- quereux, who regards them as proof that the formation belongs to the Dakota group at the base of the Cretaceous series. The green shale and nodular limestone may belong to a later formation, and Professor Winchell refers them provisionally to the Niobrara group. The highest divisions of the Cretaceous series seem also to be represented in these counties, at least by fossils derived from them, found in the drift.
Of the Cretaceous strata seen at New Ulm, Professor Winchell writes: "The flat on which New Ulm stands seems to be made up by a terrace wrought in Cretaceous. The surface of this flat is strewn with boulders. The gen- eral section of the Cretaceous at New Ulm is as follows: 1. Drift, gravel and boulders, with a surface-loam in some places, or largely made up of sand, ten to twenty feet. 2. Fine clay, blue, bedded, weathering white, used for pot- tery or brick, four to ten feet. 3. Sand or fine gravel, not
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cemented, readily crumbling, containing magnesian balls, or rounded lumps made up of a fine white powder, seen, twenty to thirty feet.
"The conspicuous Cretaceous terrace that occurs along the Minnesota at New Ulm, is due to this fine sand, overlain by a more tenacious clay or shale. The varying composition of the Cretaceous makes it difficult to establish the hori- zontally of different outcrops, but there cannot be much doubt that No. 3 above is equivalent to No. 2 of the section on the Cottonwood."
The terrace at New Ulm thus formed of Cretaceous beds, overlain by drift, is more than a mile long, parallel with the river, and varies in width from twenty-five to fifty rods or more. Minnesota street, the principal business ave- nue, is on this terrace, sections of which, agreeing well with that just quoted, are exposed, especially near its south end. by ravines and gullies at its margin. Its height is about ninety feet above the bottomland and river, and forty feet above the depot, which is on an intermediate terrace. The west part of New Ulm, including State street, several churches and the county buildings, occupies a higher terrace or plateau of modified drift, which is elevated some twenty- five to thirty-five feet above Minnesota street, or 115 to 125 feet, approximately, above the river. Further details re- specting the topography and geology of the Minnesota val- ley in this vicinity will be brought out in treating of the glacial and modified drift.
In the north part of New Ulm the grading of North Third street close northeast of the railroad, express Creta- ceous clays. This cut is fourteen feet deep and 200 feet long, with its top about forty-five feet above the river. Its upper
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four feet are soil and drift, containing and overspread with boulders of granite, gneiss and schists, up to six feet in diameter. The remaining ten feet are curved, contorted, and irregularly interstratified, red, yellow, green and gray clays. They are free from gravel, but contain flat, limey concretions, in some portions abundant up to one inch in diameter and elsewhere joined in sheets a foot or less in length and one-half inch or less in thickness, conforming with the stratification. These strata are eroded and cov- ered unconformably by the drift.
Glacial and modified drift. Glacial striae are plainly seen on the southwest part of the outcrop of quartzite that forms the waterfall in section 31, Stately, having a course south fifty degrees to fifty-five degrees east, with reference to the true meridian; and upon the ledge of gneiss in sec- tion 12, township 111, range 38, bearing south 50 degrees to 60 degrees east.
The surface of Brown 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 gla- cial period. Its thickness in these counties 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 cannot 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 retreated
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and re-advanced, or possibly at some times 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 cor- ner 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; where- as, in the later very severely cold epoch, the ice-fields were of less extent, and terminated from fifty to 300 miles within their earlier limit, covering all the basin of the Minnesota river, but not enveloping a large tract in the southwest cor- ner 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 beds of modi- fied drift, or stratified gravel, sand and clay, washed from the material that had been contained in the ice 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 direc- tion 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 com-
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monly the interglacial water-course 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 inter- vened 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 Minne- sota basin itself, appear to have excavated the valley of the Minnesota river nearly as it now is; and the further reces- sion 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 en- closed between deposits of till within the area that has been covered by this interglacial lake and was afterward occu- pied 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 evi- dently 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 what- ever obstructing deposits of drift it had received, and un- dermined its bluffs, giving them again the steep slopes pro- duced by fluvial erosion. This partial re-excavation and sculpture were then followed immediately, during the re- treat of the ice-sheet, by the deposition of the stratified gravel, sand and clay, seventy-five to 150 feet deep, rem- nants of which occur as terraces on the sides of this valley,
(7)
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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 dimin- ished 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. The morainic tract in Stately is probably a portion of the third terminal moraine, formed at the boundary of the ice of the last glacial epoch during a pause in its recession. This moraine is well exhibited in Martin county and thence to Forest City and Pilot mound in Hancock county, Iowa.
The valley of Mount creek, across the morainic area in Stately, has a level bottom from 500 to 1,000 feet wide, and appears as if in some former time, which was doubtless the epoch of melting of the last ice-sheet, it had been the water- course of floods pouring southeastward from the upper part of the basin of the Big Cottonwood river into the Little Cottonwood valley.
Modified drift of the earlier glacial epoch. Thick de- posits of stratified sand and gravel, found enclosed in the till near New Ulm, are believed to be portions of the modi- fied drift which was deposited at the close of the earlier glacial period, as explained in the foregoing brief history of the ice age. The locality first mentioned is on the exten- sion of Center street, one-half mile west of New Ulm, where
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it rises to the top of the bluff, 180 feet above the river, but only some 100 feet above its old channel which lies between New Ulm and this bluff. The height here reached is the general level of the vast prairie of gently undulating till, through which the Minnesota valley is excavated. The grade cuts to a depth of about forty feet at the edge of the bluff and thence ascends, with decreasing depth of cut, along a distance of some twenty-five rods, to the surface of the drift-sheet. This section exhibits two beds of true till, sepa- rated by modified drift which is probably an interglacial formation, supplied, as already stated, at the time of final melting of the earlier ice-sheet and spread beyond its reced- ing margin upon the unchanneled surface of the till that had been formed during that earlier part of the ice age. The upper bed of till, apparently representing the total thickness of the drift deposited here in the last glacial epoch, is sixteen to eighteen feet thick, and is an entirely unstratified yellowish clay, containing occasional rock-frag- ments up to six or eight inches in diameter, but showing only two or three of larger size, these being two or three feet in diameter. Portions of this till, within six to eight or ten feet below the top, are gray, with limey concretions and limey layers that have been gathered by percolating waters. The bottom of this upper till, seen clearly exposed along a distance of about 250 feet, is an almost exactly level line. Next below is the earlier modified drift. Its thickness is also sixteen to eighteen feet, levelly stratified throughout, but having the horizontal layers often obliquely laminated. The dip of this lamination, which marks the direction of the cur- rent of water that brought this sediment, is to the east or northeast, toward the Minnesota river, and varies in amount
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from two or three to fifteen or twenty degrees. Floods pro- duced by glacial melting, and carrying gravel, sand and clay that had been contained in the ice-sheet, appear to have taken their course along the central depression of the Min- nesota basin, coming from ice-fields which still covered its upper portion, with their retreating border probably only a few miles distant at the time when this stratum was depos- ited. Its largest pebbles are six to eight inches in diameter. The underlying till was seen along an extent of 100 feet, the greatest depth cut into it being about eight feet. Its upper line, separating it from the modified drift is approximately level but undulating, with its highest points two or three feet above the lowest. This till, like the upper bed, bears no marks of stratification; and neither shows any inter- bedding or transition, but both are bounded by definite lines, at their junction with the intervening gravel and sand. The lower bed of till is dark bluish, excepting for about twenty feet from the face of the bluff inward, where weathering has changed it to the same yellow color that characterizes the modified drift and upper till.
Modified drift of the last glacial epoch. Upon the sheet of till which covers these counties are frequently noticed mounds and knolls or short ridges of gravel and sand, ten to twenty feet, or rarely thirty feet or more in height, which in any excavation are seen to be irregularly interstratified and obliquely beaded. In Brown county a notable series of kames, or short ridges and knolls of gravel and sand, twenty- five to forty feet high, occurs about a mile east and south- east of Sleepy Eye, extending from north to south through the southwest quarter of section 28, and in the west half of section 33, in the south part of Home.
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The modified drift which was deposited in the Minne- sota valley is represented at New Ulm by the plateau of gravel and sand, a mile long and about an eighth of a mile wide, on which the west and highest part of the city is built. A hollow, about forty feet lower and a quarter of a mile wide, lying between this plateau and the bluff, was formerly a channel of the river, since which time the valley has been cut eighty feet below it. Other remains of the valley drift are seen on the southwest side of the river for two or three miles northwest from New Ulm; and on the northeast side it forms long and wide terraces in Courtland.
Below the modified drift, New Ulm is underlain by Cre- taceous beds which have been already described. These dif- fer in hardness and ability to withstand the river's erosion in cutting its valley, which characters have been elements in determining the position and outlines of the lower terraces of this city, as that of Minnesota street, about ninety feet above the river, and that of the depot and brick yard, fifty to forty feet above the river, and of the continuation of the latter, about forty feet in height, along the valley some three miles below New Ulm, reaching beyond the Cotton- wood river, as also of a terrace at nearly the same elevation on the opposite side of the Minnesota river. A considerable thickness of modified drift forms the surface of these ter- races, but their lower portions are Cretaceous beds, from which pottery clay has been taken near the southeast end of Minnesota street, while the terraces about forty feet high, at each side of the Minnesota river contain beds of nodular gray limestone, much of which has been burned for lime, interstratified with green and red clay and shale. The cut in Cretaceous clays upon North Third street in New Ulm
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is at nearly the same horizon, but in that vicinity it forms no well marked terrace.
Alluvium. The bottom land at New Ulm and gener- ally along the Minnesota valley at the north side of these counties, is from one-half mile to a mile wide. It is com- posed of recent alluvium, mostly sand and fine silt, having a height from five to fifteen feet, and sometimes more, above the river, which meanders through this lowland, here and there sweeping quite to its border. The highest floods, formed by snow-melting in spring or by heavy rains, cover the greater part of this bottom or flood-plain and at each inundation add slightly to it by their sediment.
MATERIAL RESOURCES.
The excellence of this county for agriculture, and its area of woodland and prairie, the latter far exceeding the former, have been noticed in treating of its soil and timber. Besides the fertility of the land, this region possesses an invigorating, healthful climate, and almost invariably good water in its wells and springs. The material resources which remain to be mentioned are water-powers, building stone, lime, bricks, pottery and mineral paint. Explora- tions made for coal, its mode of occurrence, and the improb- ability that it exists here in any valuable amount, have been spoken of in the account of the Cretaceous strata. No ores of any practical importance have been found. The princi- pal resources of this part of the state are the products of its rich soil, and the waterpowers afforded by many of its streams.
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