THE BLOOMINGTON MOEAINIC SYSTEM. 275 



On the Illinois River Valley there are extensive gravel deposits forming 

 a broad terrace which occupies a gap in the Shelbyville moraine just below 

 the outer border of the Bloomington moraine, a gap through which the 

 river passes. The north part of the city of Peoria stands on this terrace 

 and is commonly referred to as the bluff or upland portion, since it stands 

 about 170 feet above the Illinois River. These deposits may prove to date 

 from the Shelbyville substage of glaciation, though from their coarseness 

 and general relations it seems more probable that they were connected with 

 the Bloomington and represent the height of valley filling on the outer 

 border of that morainic system. Their freshness certainly places them in 

 the Wisconsin series. The following reasons for referring them to the 

 Bloomington rather than the Shelbyville substage may be mentioned: 

 (1) The terrace corresponds closely in elevation with the gravel terrace 

 on Farm Creek just described, which connects with the Bloomington 

 morainic system east of the Illinois River; (2) the terrace on the Illinois 

 occupies a shallow valley cut into the Shelbyville till sheet ; (3) the vigor of 

 drainage corresponds to that of the Bloomington and is greater than seems 

 elsewhere to characterize the Shelbyville substage of glaciation. A view 

 in a gravel pit on this terrace appears in PI. XIII. The gravel wherever 

 exposed on this terrace is composed largely of limestone pebbles. The 

 local sandstone and shale pebbles and the Canadian crystallines constitute 

 only a small percentage of the coarse rock material. The sand and fine 

 material found associated with the gravel are also calcareous. In places 

 the gravel is cemented with lime. It is probable that the large percentage 

 of limestone pebbles is due to the great number of such pebbles in the till 

 of the Wisconsin sheet in that vicinity. 



The highest well-defined terrace noted on the Illinois above Peoria, 

 which seems referable to the Bloomington substage of glaciation, is found 

 near the inner border of the moraine at and below the village of Chillicothe. 

 It stands only 550 to 560 feet above tide, or 40 to 50 feet lower than the 

 tei-race on the outer border at Peoria. This difference is probably referable 

 in part, if not entirely, to a reduction from the original height of valley 

 filling, for a well-defined bank separates the top of the terrace from the 

 portions of the moraine bordering it. The terrace in the vicinity of Chilli- 

 cothe contains much coarser material than at points above or below. The 

 extensive excavations for railway ballast reveal a mass of cobble and 



