Physical features of the Des Plaines Valley . erof the ice was on the Valparaiso moraine to the east, and which at length 40 THE DES PLATNES VALLEY. [BULL. NO. 11 melted away, allowing the gravels iu contact with it to slip down, form-ing a steep slope. The form of the ridge varies greatly as it runssouth, gaining at times a steep slope on hoth sides. In places, however,the steepness of the slopes seems clearly due to lateral erosion of Hickorycreek on the one side or of the old outlet on the other; for the DesPlaines valley for a time was occupied by a large river which dischargedfrom Lake Ch
Physical features of the Des Plaines Valley . erof the ice was on the Valparaiso moraine to the east, and which at length 40 THE DES PLATNES VALLEY. [BULL. NO. 11 melted away, allowing the gravels iu contact with it to slip down, form-ing a steep slope. The form of the ridge varies greatly as it runssouth, gaining at times a steep slope on hoth sides. In places, however,the steepness of the slopes seems clearly due to lateral erosion of Hickorycreek on the one side or of the old outlet on the other; for the DesPlaines valley for a time was occupied by a large river which dischargedfrom Lake Chicago. It may be that all these steep slopes are to be ac-counted for thus, by erosion, rather than by previous contact with theice edge and the removal of that support. At Overholsers pit, near Linden heights, is a fresh forty foot-sec-tion of cross-bedded sands and gravels, which here form the outer borderof the main Valparaiso moraine. The cross-bedded layers (as seenin Plate 4, A) show a rather persistent dip towards the west, indicating. Fig. S. Diagram showing the border of the ice resting against the outermorainic ridge of the Valparaiso system, near Joliet, Lockport, and Romeo. Fourtransverse passages are occupied by glacier-fed streams, and are being aggradedwith gravel. The passage nearest the foreground later became the course of theChicago outlet, and finally of the Des Plaines river. The one next to the left isthe big slough north of Joliet. that the growtk of the deposit was tothe westward. The relations tothe A^alparaiso moraine suggest that this is part of a smooth fan-likedeposit or frontal apron, washed forward from the ice while it lavagainst tlic inorainc. The plain which separates the main ridge from tlu,wist ridge of the Valparaiso morainic system south of Joliet may be thesurface of a part of the same frontal apron. The deposit is of specialinterest liecause it resembles in structure a much older, gravel deposit,the Joliet conglomerate described later. ST
Size: 1953px × 1279px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, bookcentury1900, bookdecade1900, bookidphysicalfeatures00gold
