THE BLOOMINGTON MORAINIC SYSTEM. 281 



eastern Bureau counties, shows a marked descent from northwest to south- 

 east and a less marked descent from northeast to southwest. Its altitude 

 along- the border of the moraine declines from about 800 feet at. the north- 

 east to 700 feet at the southwest, or 100 feet in a distance of 50 miles. It 

 declines an equal amount in scarcely 25 miles in passing from the border 

 of the moraine southeastward to the bluff of Fox River. The altitude 

 along the bluff of this river ranges from about 700 feet at the north to 620 

 feet at the south. Aside from the narrow morainic belt already discussed, 

 which traverses this plain from Utica northward to Earlville, the surface is 

 as a rule only slightly undulatory. There are, however, a few short eskers 

 with associated chains of gravelly knolls — discussed below— and also scat- 

 tering knolls 10 or 20 feet in height, all of which rise somewhat abruptly 

 above bordering plains. 



South from the great bend of the Illinois River the features are more 

 varied than in the district just touched upon. The narrow strip on the 

 west of the Illinois Valley descends rapidly from the moraine to the river 

 bluff. It has a gently undulating surface, with a tendency to north-south 

 ridging. East from the Illinois Valley there are nearly plane tracts inter- 

 rupted by small areas with undulatory surface, which in places bear strong 

 resemblance to the morainic belts. These undulatory tracts are most abun- 

 dant in a belt a few miles in width that leads southward from the bend of the 

 Illinois through eastern Putnam, eastern Marshall, and east-central Wood- 

 ford counties, its eastern edge being near the divide between tributaries of 

 the Vermilion and streams that flow westward to the Illinois. From this 

 divide eastward to the Vermilion River the surface shows very little undu- 

 lation. There is, however, a marked descent, the altitude of the divide 

 being 700 to 750 feet, while the immediate borders of the Vermilion north 

 from Pontiac stand but 620 to 640 feet above tide. The descent from this 

 divide westward to the Illinois is very slight; indeed, in places east-west 

 lines are nearly level from this divide to the border of the river valley. 



There is a small tract south of Ottawa, occupying the interval between 

 the inner ridge of the Bloomington system (Farm Ridge) and the Mar- 

 seilles moraine, which has a nearly plane surface. It is crossed in an east- 

 west direction by a sand ridge, discussed below. Another sand ridge 

 follows the south bluff of the Illinois part way across this plain. Both 



