182 G. F. Wright — Continuity of the Glacial Period. 



In proof of the same calculation Mr. Leverett also adduces the 

 fact that in Southern Ohio the till is oxidized to a yellow color 

 to a depth of about twenty feet, below which it is unoxidized 

 and blue.* 



These moderate conclusions of the date of the period of 

 maximum glaciation are so strikingly in contrast with those 

 which have been adduced from Mr. Croll's astronomical theory, 

 and with those which would be necessary if Professor Cham- 

 berlin's theory of the interglacial origin of the rock gorge of 

 the Ohio River had been true, that it is hardly worth while to 

 make any issue with regard to them. At the same time it is 

 proper to note, first, that, in streams which are flowing out- 

 ward from the glaciated area, there is considerable danger of 

 confounding preglacial with postglacial erosion ; and in the 

 second place, that we are bound to keep in mind that when 

 these streams w T ere first pushed out of their original channels 

 by the ice the present channels probably became lines of Gla- 

 cial drainage, in which the supply of watei* and other conditions 

 may have favored very rapid work. And, thirdly, apropos of 

 Mr. Leverett's observation upon the oxidation of the till in 

 Southern Ohio, I would say that certain facts which have come 

 under my own observation during the past summer would seem 

 to indicate that local considerations which we do not fully 

 understand may so far control the rate of oxidation as seri- 

 ously to interfere with calculations from that factor alone. 



Oberlin lies in the watershed of Lake Erie in the area of 

 later glaciation north of Mr. Leverett's twelfth moraine. Dur- 

 ing the past season miles of trenches have been dug in provid- 

 ing sewerage for the town, and the facts have been carefully 

 collected by Mr. Lynde Jones, and have been under constant 

 observation by Professor A. A. Wright and myself. Mr. 

 Jones will soon publish his results. But one fact only is neces- 

 sary for my present purpose. Everywhere the yellow till 

 extends down to a depth of several feet, ranging from six to 

 fourteen, where it is underlaid by blue till. It would thus 

 appear that in the compact deposit in the northern part of 

 Ohio, in one place at least, the oxidation is from one-third to 

 two-thirds as deep as that which is reported by Mr. Leverett in 

 the oldest drift in the southern part of the State. 



Mr. Mc Gee's latest Vieics. 



During the year, also, Mr. W. J. McGee, formerly of the 

 LTnited States Geological Survey, has published a highly illus- 

 trated and elaborate report upon " The Pleistocene History of 

 Northeastern Iowa, " which brings to light many suggestive 



*See the Glacial Succession in Ohio, Journ. Geol., vol. i, p. 132. 



