BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 23, pp. 277-296, PL. 11 JUNE 27, 1912 



POSTGLACIAL EROSION AND OXIDATION ^ 



BY GEORGE EEEDEEICK WRIGHT 



{Presented before the Society December 29, IVll) 



CONTENTS 



I'age 



Erosion in the valley of the Great Lakes 277 



Stream erosion south of the Saint Lawrence-Mississii)!)! watershed 280 



Significance of esker terraces 285 



Postglacial oxidation 280 



Conclusion 204 



Discussion • • • • ^^ 



Erosion in the Valley of the Great Lakes 



Northern Ohio furnishes unrivaled opportunities for estimating the 

 amount and rate of erosion since the final withdrawal of Wisconsin ice 

 from that region. The watershed hetween the hasin of the Great Lakes 

 and that of the Mississippi Valley is nowhere more than 100 miles south 

 of Lake Erie, averaging not more than 50 miles. The elevation of the 

 cols through which the drainage passed into the Mississippi A^alley, as 

 the ice retreated northward from the watershed, ranges from about 300 

 feet above Lake Erie, at Warren, Ohio, and Lodi, to 200 feet at Fort 

 Wayne, Indiana. Of these, the col at Fort Wayne is most important in 

 regulating the level of the temporary glacial lake which was formed north 

 of the watershed. The occupation of this col by the drainage stream was 

 so long that a well-defined shoreline, 200 feet above Lake Erie, can be 

 traced across Ohio for hundreds of miles. This affords an excellent 

 starting point for forming estimates of post-Glacial erosion; for, while 

 south of the watershed the problems are complicated by the effect of the 

 streams during all the period which elapsied while the ice was retreating 

 from the southern boundary to the watershed, north of this watershed 

 there is no such complication. The entire amount of- work accomplished 

 since the opening of the channel at Fort Wayne and the formation of 

 the 200-foot shoreline south of Lake Erie, is every wliere open to iiispec- 



1 Manuscript received by the Secretary of the Society January U, lOli,*. (277) 



