70 PROCEEDINGS OF THE PHILADELPHIA MEETING 



The same general comparison holds for the Nipissing-post-Niplssing series 

 of beaches at the south and north ends of the island, the more ninnerons 

 series at the north having been built by much less powerful waves than those 

 at the south. It does not seem possible in this case to account for the indi- 

 vidual ridges by pauses in uplift. Rather do they seem determined by the 

 amplitude of the waves, the breadth and character of the subaqueous slope, 

 the supply of beach-making material, and by other factors. The beaches and 

 I>arren intervals of the Battlefield and Fort Brady groups seem more clearly 

 related to variations in the rate of uplift. It seems certain, for example, that 

 the strongest ridge of the Battlefield group marks a well defined pause, and 

 it is even more certain that the strongly marked barren intervals do not 

 record pauses. 



Presenter] in abstract from notes. 



SOME PECULIARITIES OF GLACIAL EROSION NEAR THE MARGIN OF THE 

 CONTINENTAL GLACIER IN CENTRAL ILLINOIS 



BY JOHN L. RICH 



(Ahstract) 



Few specific observations ai'e on record of the amount of erosion which the 

 continental glacier accomplished on the plains of central United States, in the 

 zone of predominant deposition near its margin, though the statement is often 

 made that the amount was slight.^ 



The opening of an extensive limestone quarry at Fairmont, Vei'milion 

 County, Illinois, has brought to light definite evidence on this point and on 

 the nature of the ice-movement here, 30 miles within the extreme limits of the 

 early Wisconsin glacier (figure 1). 



The quarry is in a bed of limestone about 20 feet thick, which appears to 

 be a local lens in the midst of horizontal Pennsylvanian shales. Its site stands 

 about 15 to 20 feet above the level of the surrounding plains; hence must have 

 been, on the whole, more exposed to glacial erosion than were its surroimdings. 

 The limestone at the quarry is overlain by 8 to 15 feet of drift. Extensive 

 stripping operations have revealed the surface of the rock round an elliptical 

 area roughly i/£. mile by % mile in extent, giving most excellent opportunities 

 for a study of glacial action. 



The effects of underground water on the limestone are conspicuous. .Toints 

 have been enlarged by solution, and locally, at their intersections, caverns 3 

 or 4 feet in diameter have been developed. 



1 The following papers bear more or less directly on the problems under discussion : 



W. H. Norton : Glaciated rock surfaces near Linn and near Quarry, Iowa. Proc. 

 Iowa Acad. Sci„ vol. 18, 1911, pp. 79-83. 



Frank Carney : Glacial erosion on Kellys Island. Ohio. Bull. Geol. Soc. Am., vol. 20, 

 1910, pp. 640-645. 



William H. Sherzer : Ice worlj in southeastern Michigan. .Tour. Geol., vol. 10, 1902, 

 pp. 194-216. 



H. L. Fairchild : Ice-ero.sion theory a fallacy. Bull. Geol. Soc. Am., vol. 10, 190.5, 

 pp. 1.3-74. 



Frank Levereft: The Illinois glacial lobe. Mon. U. S. Geol. Survey, vol. .S8, 1S99, 

 pp. 8.5-87. 



T. C. Chamberlin : Seventh Ann. Rept. U. S. Geol. Survey, especially page 187. 



