USA > Minnesota > Houston County > History of Houston County, Including Explorers and Pioneers of Minnesota > Part 48
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In this state of the question concerning these Bandstones it seems justifiable to retain for the present the term St. Croix, inasmuch as there can
be no misunderstanding of the horizon under con- sideration. It is perfectly legitimate, in the fur- ther investigation of this question, for the geolo- gists of States further east to inquire which of the sandstones lying below these beds may be the equivalent of the New York Potsdam, for it seems as if on ascertained stratigraphical evidence, as well as on lithological and palæontological facts that are undisputed, these beds occupy a much higher horizon. They seem rather to be embraced in the great calciferous or Canadian epoch.
Although these sandstone beds occupy the river bluffs along the Mississippi and the Root River throughout the county, they afford but very few opportunities for satisfactory examination. They are in the lowest part of the bluffs, and are gener- ally hid by a sloping talus that is usually turfed over. The only point at which a useful section of their composition could be had was at Hokah. The general section at this place, as nearly as it could be made out, is as follows, in descending order:
GENERAL SECTION AT HOKAH.
Feet.
St. Lawrence limestone, of the Lower Magnesian,
about. 200 Slope, unseen. 30
Sandstone, line of constant exposure .. 90 Slope, rock unseen .. 30
Whitman's quarry, made up as follows:
1. Broken, shaly, and sandy, crumbling and frag- mentary. 10
2. Shale bed, greenish, with remains of trilobites 1
3. Tough, persistent layers, like an indurated, are- naceous shale, with green sand, in thin layers .... 12 4. Crumbling sand, in oblique stratification. 3 Rock very similar to No. 8 extends downward, cover- ing the horizon of an old quarry east of Hokah, now abandoned as worthless embracing a thickness, that is generally a turfed slope, of about .. 150
Rusty, coarsely arenaceous sandrock with Lingulepis (Lingula) 10
Crumbling, white sandrock, massive. 25
Variegated, arenaceous quartzyte, purple and white, hard and persistent, level with the top of the dam .. 2
Massive, white sandrock 20
Total rock, about. 523
The height of Mount Tom at Hokah, by aneroid, above the flood plain, was found to be 530 feet.
At an old quarry east of Hokah, and across Thompson's Creek, now abandoned because the rock is worthless for all purposes, the general as- pect of the layers is much like that at Whitman's quarry, but the sand is less frmly cemented, mak- ing a stone not so good. It is a shaly and arena- ceous sandstone, of course and fine grain, marked
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with fucoids and abundant greensand, and is be low the stratigraphical level of Whitman's. In the same bluff, about twenty-five feet higher, is a blind shoulder or terrace, which is more likely to contain the layers of Whitman's quarry. This stone is taken from Whitman's quarry, although very shaly, becomes firm and enduring on ex- posure.
At Houston, the bluffs north of the village are 520 feet in height, and of this the lower 420 feet at least belong to the St. Croix sandstone. They probably contain the St. Croix twenty feet fur- ther up, shown by the toppling over of huge blocks of St. Lawrence limestone, from the crumbling out of friable sandrock along the salient angles of the bluffs. The intervals of the sandstone layers is mainly turfed over so as to render an inspection of their contents imposible, except at points near the top and near the bottom. There is a line of nearly constant exposure about forty feet below the top of the St. Croix, occupying an interval of thirty or forty feet, which is particularly noticeable along the north side of the river. There is another exposure of these beds near the level of the river at the dam at Houston. The former con- sists of a hard, firm sandrock, and the latter is soft and crumbling, with cross stratification. Above the line of constant exposure, about twenty- five feet, is a blind terrace which occasionally reveals the rock which causes it. It is a sandstone, and is included in the foregoing thickness of 420 feet.
At one mile north of Sheldon there is an ap- parent dip in the outcropping upper edge of the St. Croix, as it strikes across the bluffs. Its di- rection is perhaps a little west of south, and amounts to two or three .degrees. It is entirely local, and the corresponding upward dip in the opposite direction is invisible. The bluffs south and north have their usual height. * No such dip was noticed in any other part of Houston county, but it is very likely this is on the strike of the noticeable dip in these formations which has been mentioned by Dr. Owen, and by the geologists of Iowa as occurring in the bluffs of the Mississippi River at McGregor and Lansing, in the state of Iowa.
In Caledonia township, section two, the follow- ing section was taken:
* Compare Geology of Iowa, Hall & Whitney, 1858, part II. p. 51.
SEOTION COVERING THE JUNCTION BETWEEN THE
ST. CROIX AND THE ST. LAWRENCE.
Feet.
Slope, covered with large blocks of sandstone .... 200-300 Even layers of limestone quarried 12 Hid. Mainly limestone, like the next 40 Limestone, broken and curling bedding, Cherty, arenaceous or massive with some green sand .. 25 Lime and sand, lumpy with irregular concretions, mainly massive. 15-20
Soft sand, with cemented or quarzitic lenticular lumps
10 Soft. massive sand. (Causes the blind terrace at Houston). 25
The line of constant exposure mentioned as oc- curring at Houston, near the top of the St. Croix sandstone, lies below this section. This line is more evident in the north than on the south bluffs -due, probably, to the erosive action of the pre- vailing winds, which are from the southwest, and to the greater scarcity of timber on the north bluffs, as already noted under the head of Soil and Timber.
The fossils that have been gathered from this formation consists very largely of trilobite remains.
On section eleven, Union township, the sand- stone which has been mentioned as having a nearly constant line of exposure, is sculptured, along the north bluffs, into isolated columns and tables, with some rounded buttresses which present a very conspicuous and highly interesting in- stance of atmospheric erosion. There can be no doubt that the bluffs themselves are the result of the erosion of the valley by water by a process that began thousands of years before the glacial epoch, but the present condition of most of the curious forms, like that of the "sculptured bluffs," is certainly due to the effect of wind in conjunc- tion with moisture and frost. There are also cavi- ties and sheltered nooks, and deep, crooked pas- sages and sharp niches in which the wind could barely enter, and from which there could not have been any wind exit sufficient to have maintained a current capable of producing the most of this sculpture, which, moreover, are lichen-covered, and bear an aspect of age and roughness that forbids their reference to any present atmos- pheric forces. These can be explained only by the solvent action of water in agitation, and are com- parable to the purgatories that are often seen about the rocky shores of lakes or of the ocean. But when the rock shows a recent, fresh erosion, and is soft and crumbling, the present forms are due to
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GEOLOGICAL.
more recent causes, and can only be assigned to wind and frost.
THE DRIFT.
The true northern drift is not spread over this county. It contains no drift clay, nor boulders of foreign origin. There is a thin deposit of for- eign gravel at Riceford, in the extreme south western part of the county, and there is a terrace along the Mississippi River that is made up of gravel and sand of northern origin, but this county wholly escaped the operation of those forces which spread the well-known drift clay and boulders over the most of the State. Whether any former glacial era caused it to be covered with the ice of the northern glaciers cannot be determined, since the materials left by that era, if any there were, may have been decomposed, and may have entered into the stratified clays and the soils of the Mississippi valley further south under the combined influence of time, and the intense activity of the destruc- tive forces of the latest glacial era.
There is to be seen occasionally a local drift, or debris, derived from the rock of the country round about, and this sometimes has a deceitful resem- blance to true northern drift, yet it can always be distinguished from it on examination. On the northwest quarter of section twenty-five, Cale- donia, along the road, near the brow of the Sha- kopee limestone, there is a bank of such loose ma- terial. There is a cut of about three feet which consists mainly of rusty loam, rather sandy, em- bracing large masses of black quartzite, which also vary to a lighter color but show very little, if any, lime. Other lumps consist of pyrite crystals, now converted to limonite, and of rusty, hardened sand- stone, perhaps from the St. Peter. These last, in- deed, comprise, perhaps a majority of the stony masses. There are also large quantities of ordi- nary chert, and an occasional piece of water-worn limestone. The bank shows no stratification, but consists of these materials simply mingled with the loam. The whole appears red and rusty, but discloses not a single piece but can be referred to the Lower Magnesian formation.
As to the cause of this exemption of a part of southwestern Minnesota, and portions of Wiscon- sin, Iowa, and Illinois adjacent, from the forces of the northern drift epoch, there has been but one opinion advanced, so far as the writer is aware. It is that of Prof. J. D. Whitney, who attributes it
to the non-submergence of this region since the de- posit of the Silurian rocks and their elovation above the ocean. If it were demonstrated or gen- erally believed that the prevalence of the drift in other parts of the Northwest in the same latitude, is due to the submergence of the continent be- neath the ocean since the Tertiary age, this as- sumed cause would be apropos. But, on the con- trary, it is pretty generally agreed by geologists both in America and Europe, that the drift is due to the former existence of glaciers that covered the surface of the country, and, moving generally southward, not only brought from the northern regions the foreign substances that constitute the drift, but required, for their existence, that the land surface should be raised several hundred feet at least above the ocean during their prevalence .* Again there is every reason to suppose this region has been submerged since the age of the Silurian. It is difficult to conceive what could have pro- duced the horizontal lamination of the loess loam, unless it be attributed to the action of standing or slightly agitated water. This loam not only ex- ists along the immediate river valley, but is spread widely over the highlands of the whole district. It is true there is no evidence of its having been the product of marine depositions, on the contra- ary it is evidently of fresh water origin; but that the country has been deeply submerged and re- mained so for a long period within recent geolog- ical time can hardly be questioned. There is also reason to believe that some portions of it were buried beneath the waters of the Cretaceous ocean.
In the light af the more recent investigations of geologists, it is safe to take for granted the fol- lowing conclusions respecting the drift, so far as they bear on this question.
1st. That the earth suffers such changes of climate that, after the lapse of long periods, the temperate latitudes become frigid, and are covered with continental ice-fields or glaciers, which have a slow movement southward.
2d. That between these periods conditions of more genial climate prevail, when vegetation and animal life return slowly to inhabit the countries from which they had been driven by the rigors of the previous cold.
*Those interested in this subject will find it exhaustively treated in James Geikie's Great Ice Age, and its relation to the antiquity of Man. Second Edition, 1877.
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HISTORY OF HOUSTON COUNTY.
3d. That the severity of the cold during the successive glacial epochs is not always the same; but that the ice-fields are more extensive during some than during others.
These continental ice-fields, while conforming in general to the laws and conditions of a solid, yet exhibited, as glaciers do now, many of the charac- teristics of a plastic body, warped and moved by the force of gravity, and hence exemplified many of the principles of running water. The tendency for them was to seek the low lands, and avoid the natural obstructions presented by mountains or by hills.
In examining the topography and the geologi- cal structure of the country lying to the north of this so-called driftless tract, it is evident that the great valley of the Lake Superior region, once oc- cupied by glacial ice, would overflow, both first and last, along the lines of the lowest outlet, and that perhaps the higher and less passable parts along its southern barrier-shore would never be entirely surmounted. The continental glacier, in this region, would flow toward the southwest or south, guided by the main topographical features. In north-central Wisconsin is an isolated area of granitic and metamorphic rock, which not only extends to the shore of Lake Superior, but wedges out northeastwardly in the form of a long, high, and persistent point or spur, in the southern part of Lake Superior, known as Kewenaw Point, in the state of Michigan. It is plain to see that this point would act on a crowding but somewhat flex- ible mass of ice as an entering wedge to split it into two main masses, and that the widening of the wedge, in the granitic region of northern Wiscon- sin, would perpetuate the division so as to cause, if other topography were favorable, a constant flow along the northwest side, and another in a more southerly direction, that would spread over northern Michigan and find its easiest exit through the valleys of Lakes Michigan and Huron. Ac- cording to Prof. R, Irving and Messrs. Foster & Whitney,* the western end of Lake Superior lies in an Archaean synclinal trough running south- westerly. This again would divert the flowing ice over the northeastern portions of Minnesota to the expense of northern Wisconsin. Glacial scratches on the rocks of Duluth, at the western
* American Journal of Science, 3d Series, Vol. VIII. p. 54. Report on the Geology of the Lake Superior Land District.
extremity of the lake, have a west-south westerly direction.
Now it is a striking coincidence that this drift- less tract lies nearly south and in the lee of this wedge-like area of metamorphic rock, and would be protected from the ice-flow by it. It is hence reasonable to infer that the absence of the drift in this region is due to the existence of this protect- ing barrier lying to the north of it in Wisconsin, while further to the south the two main branches of the ice-flow again united and spread, before their final retirement, a continuous sheet of drift over central Illinois and southern Iowa.
It is very evident, from the fact that the remains of an older drift sheet are found under the loam in some of the western parts of this tract, while the latest drift sheet does not spread so far nor so wide, that the last period of cold was far less in- tense than some former one had been. This last drift sheet is spread over the ancient soil, contain- ing vegetation in a nearly continuous layer, the remains of a forest which flourished between the two glacial periods, along the margin of the last ice-field. This belt, characterized by buried soils and wood, crosses Fillmore and Olmsted counties, and it is probably true, that wherever such re- mains are found, in a flat country like southern Minnesota, lying under glacial drift, they mark the point where glacial ice ceased to act power- fully enough to disrupt the old soils. Such an- cient soils may have existed on the top of older glacial drift, or on any other surface. It is prob- able that it was during the prevalence of the last glacial period, or just as the ice began to recede so as to produce copious waters, that the loess loam of the Mississippi valley was deposited over this region, and that at the same time the waters of the Minnesota were augmented by the drainage of the entire Winnepeg and Red River valleys through its channel, some of them at first reach- ing the Mississippi and through the Cannon and the Vermillion River valleys. At first these waters spread irregularly and widely, fluctuating with the seasons, so as to leave no recognizable beach lines; but at length, when the most of the State had been left by the retreating glacier, they became more uniform in their volume and were confined to the actual river gorge. They seem to have maintained, for a long period, a pretty uniform stage at this point, for when, on the drainage of the Winnepeg basin toward the north, consequent
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GEOLOGICAL.
on the final retreat of the ice beyond the mouth of the Nelson River, in British America, the Min- nesota was reduced to about its present dimen- sions, a high terrace was left along the Mississippi, through all this driftless region and also further south. The high water in the Mississippi as- cended the gorges of the tributary streams, re- tarding their flow and causing similar terraces along their lower reaches.
ALLUVIAL TERRACES.
There is a marked alluvial terrace that accom- panies the Mississippi and Root Rivers, and ascends their lower tributaries, but it does not seem to be true that all the streams are terraced before reach- ing the level of this terrace. This indicates that the high water which produced that terrace was due to backing up from the Mississippi, and that possibly the country, itself in general was not more wet than at present; in other words, that the amount of surface drainage that passed down the valleys was no greater than now. Root River was simply wider and deeper, with a sluggish cur- rent, due to the greater volume of the Mississippi. The highest point at which the terraced condition of the Root River has been observed is Preston, in Fillmore county, but it must certainly extend sev- eral miles further up that valley. By aneroid measurements, united with the levels of the Southern Minnesota railroad, the height of this terrace at Preston is found to be about 300 feet above the Grand Crossing of the Southern Min- nesota railroad near the mouth of Root River, while the same terrace at Hokah, likewise near the mouth of Root River, is only about 100 feet above the flood plain. It is also probable that the loam terrace, as seen at La Crescent, is the same contin- ned to and coalescent with the Mississippi terrace; and there it is ninety feet above the Mississippi flood plian. This would necessitate a fall of about 200 feet in the Root River at its highest stage, in a distance of fifty miles in a right line. If this fall can be explained consistently with the assumed back-water condition of the Root River, at that time, it will further confirm the hypothesis that the Mississippi then drained the Red River and Winnipeg regions, receiving their waters from the Minnesota. It seems further that this explanation is necessary to the maintenance of that hypothesis; for if the Root River was maintained at that high level by the demands of its own drainage area, then much more the Mississippi could also have
been kept there without the aid of the Winnipeg waters. Root River valley, between the rock bluffs, has an average width, through Houston county of about two miles, and that would have been the width of the stream, with a depth of over 100 feet.
There is, besides this high, loam-terrace, a sec- ond terrace level, visible specially at La Crescent, on the Mississippi, which there rises fifty feet above the flood plain of the river and spreads out in a pleant platean on which the village has been lo- cated. This terrace is made of gravel and pebbles of northern origin and was identified only along the Mississipi. The largest stones it contains are three inches in longest diameter. It is passed through in wells and seems to be entirely pervious to water, as all wells on it get water at about the level of the flood plain of the river. This material is used for grading and road-bed, on the Chicago, Dubuque & Minnesota railroad and elsewhere. It consists entirely of rounded waterworn materials, the main part being the usual parti-colored quartzite peb- bles, granitic, hornblendic, amyglaloidal, and lamellar, as well as nniform and massive. A great many of them have a red color, or some shade varying from red. The coarsest pieces are rare, found only in the upper portions of the debris of alluvial fans.
The following more special observations were made on these terraces in Houston county. At Sheldon, six miles from Root River, in the valley of Beaver Creek, the terrace on which the Newberry House stands is thirty feet above the water of the creek below the dam. The materials of the terrace at this place are sandy loam, horizontally stratified, with more clay near the top, and less evident stratification.
At Houston the only observable terrace, meas- ured about a mile west of the city, is sixty five feet above the flood plain. The track of the rail- road is about one foot above the flood plain of the river, which is eighteen feet higher than the water below the mill-dam.
At Money Creek the terrace rises thirty feet above the flood plain which is twenty feet above low water below the mill-dam. The contents of the terrace are stratified. On section thirty in this town the contents of the Root River terrace, and their arrangement are as follows:
Mixed and broken stratifications, roots, soil, etc., 2-4 feet.
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HISTORY OF HOUSTON COUNTY.
Loam and sandy loam, 3-6 feet. Oblique strata of light sand. Loam and light sand. One layer of sand-blown out 8 inches. Oblique layers of sand. Horizontal strata of fine sand. Strata of fine sand, or clay. Sloping clay layers, damp rusty. Dry, blowing sand. Wet clay, with rusty lumps. Contorted, curling, or massive strata. Hid from view by debris.
The full height of the bank is about twenty feet where the section is taken. At a point further to the right a couple of bones were found, but in the confused and broken uppermost layer. They were where that layer comes down to the river, and about three feet below the surface, or five feet above the water of the dam, the surface of the bank sloping about 45 °.
At Hokah, the village is on a terrace sixty-five feet above the flood-plain of Root River, and there is a distribution of loam about the bluffs at a higher level, (as well as at many other points along Root River valley ) reaching to a hundred feet, or a little more, above the flood-plain. This loam appears in indistinct benches or terrace-levels or patches of terrace, rising often with a slope, far up the rock-bluffs. It very rarely appears level, as a well-marked terrace. It suggests rather a worn-out terrace-level, the upper surface of which has suffered erosion by being gullied out and smoothed off toward the river. It is generally cultivated for farms, and has good wheat fields, consisting of the same materials as the lower ter- race. Its actual height is difficult to ascertain.
Southwest quarter of section twenty-two, La Crescent. By the roadside appears a terrace ris- ing about fifty feet, which at the top consists of the fine loam of which the foregoing terrace is composed, showing at least eight feet of such ma- terial, while its lower twenty feet are of drift- gravel, which is course and obliquely stratified, the coarsest pebbles being one or two inches in di- ameter. This occurs on the rounded point of the rock-bluff which faces both valleys.
The village of La Crescent stands on a beauti- terrace of drift-gravel, generously laid out, with wide streets and alleys, fifty feet above the flood-plain of the Mississippi. This terrace slopes gradually toward the high rock-bluffs. It is sur-
mounted along the bluffs by another terrace, rising forty feet higher, which consists of loam.
This drift-gravel must be attributed to the agency of the river. It has every feature of a water-worn alluvial deposit. It is not found in Houston county in any of the valleys of the other streams, back from the Mississippi. It ante-dates the loess loam, as that is terraced above it, and probably bears the same relation to an earlier glac- ier epoch as the terraced loam does to the last.
At Brownsville, the loam-terrace is eighty feet above the flood-plain of the Mississippi.
At Yucatan, the terrace flat is forty feet above the present flood-plain of the South Fork of Root River. The flood-plain is six feet above low water.
At Freeburg, the terrace is twenty feet above the flood-plain of Crooked Creek, which is five feet above the water of the creek.
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