http://SaturnianCosmology.Org/ mirrored file For complete access to all the files of this collection see http://SaturnianCosmology.org/search.php ========================================================== It is also probable that the basin of Lake Michigan is very largely excavated in deposits of Devonian age. So it is not at all surprising that Devonian deposits should have extended over the region about Chicago. "Description of the Chicago District" by William C. Alden. 1902 No indurated rock formations later than the Niagara limestone and the slight remnant of Devonian rock are known within the district. Upon these formations lies the heavy mantle of unconsolidated material referred to as drift (figs. 2 and 3). This drift not only overlies the rock formations here represented, but, extending out over the greater part of Illinois, and in fact over a large part of northern United States and Canada, it overlies rock formations of all ages, even the most recent; whence it is evident that the drift is the latest of all the great geologic formations of North America. It was deposited in the Pleistocene, the era immediately preceding our own. There may have been intervals during which the sea waters again encroached upon this land, but no evidence other than that noted on page 10 of this folio has been found. The work of geological agents did not, however, cease in this region during this great interval. Up to this time the area of northeastern Illinois had been receiving contributions principally from the Wisconsin land to the north; during this interval the rock beds of this area were subjected to erosion and the material thus obtained was carried off southward by the streams, to help in the formation of other rock beds in the sea. So great was this interval of rock disintegration and erosion that the Devonian beds and whatever subsequent rock formations may have been present in this area were entirely removed. More or less of the Niagara limestone was also cut away at this time. As the rock disintegrated into soils vegetation developed and faunas of the air and land appeared, yet no traces of these faunas and floras here remain. The only evidence here is of destruction; one must go elsewhere to find the results of constructive work of post-Devonian and pre-Pleistocene time. With the deposition of the drift the process of rock destruction in this area practically ceased. An examination of the drift at these exposures shows that while stratified deposits of sands, gravels, and clays are of frequent occurrence, the drift as a whole is unassorted. It consists generally of a matrix of bluish clay in which is embedded rock material of all shapes, sizes, and lithologic characters (fig. 17). The clay is highly calcareous and is evidently largely the result of abrasion of beds of limestone and calcareous shale. The stony material embedded in this clay matrix ranges in size from fine gravel to bowlders several tons in weight. For the most part these pieces of rock are less than 1 foot in diameter, but frequently bowlders 2 to 3 feet in diameter occur, and rarely blocks 5 to 10 feet in diameter are seen. These bowlders are of such size that they could not be transported by water currents of ordinary strength unless they were frozen in floating blocks of ice. The arrangement of the drift is most heterogenous, fine and coarse, clay and stones being intimately mixed. This is in striking contrast with the assorted and stratified beds of water deposited material. Yet, from the frequent occurrence of stratified beds at some points, it is evident that considerable water must have aided in the deposition. figure 18The shape of the pebbles and bowlders of the unstratified drift is not that of streams or shore pebbles. Instead of smoothly rounded forms, the pebbles and bowlders of the drift are partly angular and partly somewhat rounded, but largely subangular with numerous flat faces, or facets. The facets usually show polishing, parallel grooving, and scratching, or though smoothed and striated while being held firmly in one position and moved over a hard surface (fig. 18). This, however, is not the character of the rock surface where exposed by the removal of drift. Here the line between the drift above and the rock beneath is sharp (fig. 5). Unless the upper rock beds be thin and shelving it is usual to find a smoothed and polished surface marked with parallel grooves and scratches, similar to those upon the pebbles and bowlders of the drift. If the rock surface has not been long exposed the striations are usually sharp and distinct. Sometimes they are continuous for several yards. usually they are shorter. They are sometimes almost perfectly straight, sometimes curved, broken, or jagged. They are usually nearly parallel at any given place, or they cross at low angles. It is also found that where there are slight inequalities of the surface, as protruding knobs or jutting ledges, one side - in this district the east and northeast - is smoothed, polished, and scratched, while the opposite side is rougher and more or less unmodified. With small, sharp depressions the east and northeast sides are rough, while the west and southwest sides have been smoothed. These different phenomena are will exhibited by the rock surface at Stony Island. These various phenomena give indisputable evidence that these features are not the results of weathering or of water erosion, but that over the rock surfaced has moved some great mass with abrasive material at its bottom, smoothing, polishing, and scratching as it went; that this body was more or less plastic in its nature, so that it conformed in a measure to the inequalities of the rock bed, and that the movement was in the direction of the striations and against the abraded sides of surface inequalities. The fine and coarse material of the drift overlying the rock would furnish the abrasive material, the polishing powder, and the graving tools to a moving mass of the right kind. These various phenomena of the drift and the underlying rock surface give unmistakable evidence of the agency which produced them. The drift is identical in kind with the deposits now being made by glaciers in varous parts of the world (see fig. 19 and compare fig. 17), and the characteristics of the surface of the rock beneath the drift are identical with those of the surface of the rock over which glacier ice is known to have recently passed (fig. 20). Hence it is evident that the drift is really a glacial deposit. too bad