THE CHESTER SERIES IN ILLINOIS 413 



a source. The sand of these formations may have been derived 

 from the Appalachian land, still farther to the east. The Palestine 

 and Degonia sandtones, which are almost equally thick clear 

 across Illinois, belong in still another category. The Waltersburg 

 sandstone differs in distribution from all of the others, being 

 essentially restricted to an area about forty miles in width east 

 and west, with an unknown extent in a north-south direction. 

 This may be an accumulation in the form of a delta at the mouth 

 of some stream from the north, which emptied into the Illinois 

 basin, perhaps bringing the sand from some far-distant region. 

 The origin of such sands as the Palestine and Degonia, which are 

 more uniformly developed across the entire basin, and even some 

 of the others which are less uniformly developed, may have been 

 from more than one source. 



The lateral distribution of the sands of the Chester series in the 

 Illinois basin was doubtless through the agency of wave action 

 along the shore line. During the stages of withdrawal of the waters 

 in the basin, those shore sands, left high and dry, would be sub- 

 jected to erosion and to transportation southward and redeposi- 

 tion, and to re- working in the next following advance of the waters. 

 In this manner the same sand may have been worked over and 

 over again in the shore deposits of the basin, a condition which 

 may account in part at least for the great similarity between the 

 several sandstone formations of the series. 



The areal distribution of the Chester formations is very dif- 

 ferent from that of the Lower Mississippian. The northernmost 

 exposures of the Chester is in the Mississippi River bluff in St. 

 Clair County, Illinois, about one-half mile north of the St. Clair- 

 Monroe County boundary line, opposite Bixby. Beyond this 

 point the Chester formations are covered by the Pennsylvanian, 

 but well records indicate that they swing off to the northeast from 

 the last exposure to the vicinity of Decatur, Illinois, and from 

 there continue in a southeasterly direction, passing into Indiana. 

 These formations, therefore, were deposited in a basin lying between 

 Ozarkia on the west and Cincinnatia on the east, with its northern- 

 most extremity near the center of Illinois. This basin had a 

 very different outline from that in which the Lower Mississippian 



