Page:Popular Science Monthly Volume 46.djvu/239

Rh defined than before, chiefly because of the smaller depth to which it could be cut in the lower ground. The bluffs are only about fifty feet high at Joliet, while at Morris, eight miles below the entrance of the Kankakee, they are hardly perceptible. Through this district the floor of the old channel is generally rocky, and in the floor the Desplaines River—or the Illinois, as it is called below the entrance of the Kankakee has cut a narrow and shallow trench. Occasionally heavy gravel beds were seen, but their origin could not be determined in our rapid excursion.

A peculiar feature of the northeastern part of this district is the subdivision of the old channel into several courses, as if a number of almost equally good lines of escape had been originally offered to the lake overflow, along all of which the waters ran for a time, but into one of which they were gradually collected, that one being the channel now followed by the Desplaines past Joliet. Two of these temporary branching channels are represented on the Joliet sheet, a short distance above that city, in the form of swampy passages connecting the Desplaines with the Dupage River. A third is seen southwest of Joliet, and is now utilized by the Illinois and Michigan Canal.

The second belt of higher ground again reaches a level of seven hundred and fifty feet north and south of the town of Marseilles, after which it may be named; and through this belt the old channel again appears as a depressed linear plain, now about a mile and a half wide at an altitude near four hundred and ninety feet. It is inclosed by steep bluff's, a hundred or more feet in height. Back from the bluffs, narrow and steep-sided ravines dissect the rolling upland for a distance of from two to four miles. There are flat alluvial fans in front of some of these ravines, and it may be for this reason that several small lateral streams in the neighborhood of Marseilles enter the river by direct courses instead of first running a distance down the valley, as is so often the habit of side streams while traversing the flood plain of their master. The contour lines of the maps do not indicate the occurrence of any fans, the lines being concave toward the mouth of the streams; but I think some of them should be slightly convex in that direction. It is possible that small matters of this kind may have escaped the attention of the topographers, although the scale of the maps is large enough to show them clearly if they really exist. As in the Morris basin, the present river about Marseilles is sunk in a narrow trench, twenty or thirty feet below the broad plain of the old channel bottom.

West of the Marseilles morainic belt—the second belt of higher ground—there is a broad stretch of even country at a height of about six hundred and fifty feet. The city of Ottawa is located in the old channel where it traverses this even upland; the