UIHistories Project: A History of the University of Illinois by Kalev Leetaru
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Repository: UIHistories Project: Board of Trustees Minutes - 1871 [PAGE 196]

Caption: Board of Trustees Minutes - 1871
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188 that produced the plane with its grooves. Perhaps the most reasonable explanation is that the stream under a glacier produced the oval form, while the ice in which the pebble was afterwards entrapped and forced along, produced the plane with its different sets of grooves. Another fact of importance in this connection is, that not only pebbles and small bowlders, two or three feet in diameter, occur in the prairie deposits, but huge blocks of several tons weight, which must have required large masses of ice, either in the form of a glacier or of icebergs, to bring them hither. At Chatsworth, a bowlder of magnesian limestone, weighing some ten tons, and having its surface grooved, was found only one or two feet below the surface, and lying, if we mistake not, on a stratum of earth. It seems scarcely possible to account for this in any other way than by an iceberg. All these facts are extremely important and interesting, since, when correctly interpreted, a pebble is not only made to tell its own individual history, but to throw light on those mighty forces which prepared for us our soils. Passing through the red clay we reach at a depth of seventy-six feet a layer of black, peaty material, rich in ammonia and other nutritious matter, with occasional fragments of wood, and filled with the remains of several species of fresh water shells. It is evidently an old soil, and in this particular instance, probably a marsh. It is without doubt a Continuation of the same soil that was struck in two places at Bloomington, at a depth of 118 feet, where logs were found scattered promiscuously about, and the stump of a conifer still standing where it grew At Jacksonville the same soil with trunks of trees (cedar) was struck at about the same depth, and at Crawfordsville, Indiana, it was found at a depth of ninety feet, also with trunks of trees. It has been traced as far north as Beloit, "Wisconsin, and several other places, but with no animal remains, so far as known, except in this instance. Here then we have the old surface soil of this valley covered with dense ferests at the close of the tertiary and the beginning of the glacial epochs; for on this soil lies the drift. It will be seen that this old soil has a direct bearing on the question whether a glacier extended over all this valley to the gulf during the glacial period, and by melting left its debris in the form of drift. "Whatever glaciers may have existed in ages previous to that of the drift, is a distinct question by itself; but that a mass of ice several thousand, or even one thousand feet deep, could have moved from the north over this valley to the gulf during the glacial period, without having obliterated every trace of this old soil, is certainly very difficult to understand. And yet the materials of the prairie deposits do plainly