Rensselaer Republican, Volume 27, Number 21, Rensselaer, Jasper County, 17 January 1895 — Observations on the Glacial Drift of Jasper County. [ARTICLE]

Observations on the Glacial Drift of Jasper County.

Note: The following is a paper by Prof A. H. Purdue, principal of the Rensselaer High School,read before the Indiana Academy of Sciences, at Indianapolis, Dec. 27, 1894. Ed. Republican. Jasper county is situated [in the northwestern part of the state, with Porter county intervening between it and Lake Michigan, and is separated from the state of Illinois by Newton county. It is therefore in one of the most active fields of all the glacial epochs. Mr. Collett claims (Twelfth An. Report Geol <t Nat. Hist. Ind. page 66.) that glacial erosion bas removed from fifty to two hundred feet of rock from the entire surface of the county. This great erosion, and subsequent glacial action have left it practically level, with poor drainage, so that numerous peat marshes abound in all parts of the county, varying in size from a half acre and less to several thousand acres. Notably among the larger ones are “Gifford’s marsh/’ a swamp of 12,000 or 15,000 acres lying 12 miles north-east of Rensselaer, and the “Blue Sea,” a similar marsh ly-

ing in the southeastern part of the county. Only the former of these has been visited by the writer, It is an old glacial lake filled up with peat and muck, varying in depth from three to fifteen feet, the monotony of which is broken by numerous accumulations of sand, which in form simulate drumlins. Many wells have been drilled in all parts of the county, but no com-

pilation of the data furnished by them has been made, so that nothing is'known of the subglacial topography. It might be stated, however, that the drift varies in depth from a few feet, as at Rensselaer, to two hundred feet The latter extreme depth has been found nowhere, so far as I have learned, except on the moraine which extends in a northeasterly direction across the county, passing one and one-half miles north of Rensselaer.

This moraine is possibly the most marked topographic feature of the county. In width it averages probably a mile and in height it varies from twenty to eighty feet. It is said by Mr. Leverett of the U. S. Geological Survey to extend north-eastward into Pulaski county and south-westward through Newton county into Illinois, and is thought by him to possibly be interlobate between the Saginaw-Erie lobe froWthih north-east, and the Lake Michigan lobe from the north. One of the first things to attract attention in the study of this locality is the great number of sandy ridges everywhere prevailing. With reference to direction, it appears that there are two classes of these. One class extends almost parallel with the above mentioned moraine. I have observed them in Pulaski and Jasper counties northwest of Monon, and in passing over the Monon Ry. from one and a half miles north-west of Rensselaer to Parr. The other class, which I have observed only south of the moraine, have an average course of about S. 30 deg. East and consequently run in a direction almost at right angles to it. It is the latter class to which we wish to invite attention. These ridges are of two types, each frequently passing into the other. FOr convenience, we will speak of them as the symmetrical and the unsymmetrical. The most common form is the symmetrical. These are low, broad symmetrical ridges. They vary in width from forty yards to an eight of a mile. Though frequently running into each other, they are in the main parallel and often are crowded so close together as to give the surface a billowy appearance. The troughs between them always contain rich, black soil, formed from the decay of peaty matter, and indicating former shallow lakes. An excellent view of this type is presented along the “Range Line Road” from Rensselaer to Remington for a distance of five miles south of the former place. The view along this road shows them to ran east and west, but a short distance to the east they swing to the south and southeast AU the ridges of this class are composed largely of sand, though they contain enough vegetable mould to prevent shifting by winds and permit of an excellent yield to the fanner. I have never noticed any gravel in them except north of the Iroquois in the vicinity of the large moraine. Bowlders are sometimes seen along and near their bases, bat seldom on the swell of the ridge except also in the vicinity of the large moraine. The unsymmetrical type differs from the symmetrical in size and shape, in being composed more largely of sand, and in not being so numerous. They are much larger than the symmetrical, varying in height from five to twen-ty-five ‘ feet above the general level. The average is probably about ten feet. The south and west slopes are gradual and more or less broken, while the north and east slopes are steep and even. Horizontally these slopes are very sinuous, resembling the banksofa winding stream;but the fact that at their bases, often stretching to the north and, east for a mile or more, are level expanses

frequently covered with peat and forcing upon even the unobserving the recognition of old lake beds, dispels the idea of their being such. At the same time the winding course of the ridges prohibits the idea of their having been thrown up by wave action from the lakes. In many places these ridges are too sandy to be cultivated with profit, in others the soil is good, and at a few points to be mentioned later, gravel has been found. They are frequently cut through by what apparently were escapes for the water confined by them. In these cuts, which usually reach to or near the base of the ridge, bowlders can pretty confidently be searched for. Bowlders are also occasionally found along their bases. Only in the graved pits above referred to has the writer seen any indication of jtratification. Two of these pits are situated a mile and a quarter west of Rensselaer near the Iroquois river. There are three others a mile and a half south of Rensselaer. Places in these show attempts at sorting by rapid and changeable currents, but the greater part of the material is unsorted, and it would seem that their deposition was affected almost wholly by direct glacial action. Let it be repeated that the two

types often grade into each other. A ridge that in places presents the most rugged aspect of the unsymmetrical, may, in the course of a mile, grade into the most feeble of the symmetrical type; and at a point about three miles north of Remington an unsymmetrical ridge grades into a low,

flat ridge covered with numerous bowlders, and evidently a moraine. Of course the thing of interest in connection with these ridges is the question of their origin. It has been claimed (Twelfth An. Rep. Geol. & Hist of Ind., page 66.) that they are dunes formed along the north-east

and east shores of former lakes, and were produced by south-westerly winds. While the examination of numerous cuts has not disclosed the least sign of lamination by either wind or water, there seems to be no doubt that the unsymmetrical ridges are due very largely to aeolian [wind] action; but it does not seem that the low, flat, symmetrical ridges, so frequently connected, or passing Into each other, and forming the rims of ponds could have been produced in this way. The fact that the two types grade into each other indicates a common origin at least of their basal portion. Also the fact that bowlders are more numerous along and: near the bases of these ri ggs, especially the symmetrical type, than elsewhere, together with the fact that bowlders are liable to be found in the cuts through the large ridges is considered significant. It would also seem that the parallelism and continuity of the ridges of both types are greater than could be expected of deposits determined alone by wind. In the gravel pits south of Rensselaer there is nothing to indicate that the adjoining portions of the ridges were formed in a manner different from those portions where gravel is found. The above facts suggest the possibility of the symmetrical ridges having been formed directly by glacial action along the margin of the glacier as it receded to the north-east; and in some cases they have served as lodgment tracts for the accumulation of wind-blown sand, in that way largely determining the course and extent of the unsymmetrical or dune type. But more field work is necessary before considering this beyond a hypothesis. There are at least two bowlder belts in the county but because of limited time I have not been able to follow them out One of these is north of Remington and the other is east and southeast of Rensselaer. The latter I have have traced from the junction of the Iroquois and Pinkamink rivers southeastward for a distance of three miles. It will probably be found to extend south-eastward and eastward into White forming the southern border of the old lake through the bed of which the Monon railway passes from Lee to Pleasant Ridge. The careful location of these bowlder belts will probably throw light on the glacial phenomena of the locality.

A. H. PURDUE.