GLACIAL SUCCESSION IN OHIO. 1 43 



supplied. In this respect this morainic system contrasts with all 

 other moraines of Ohio, and especially with the later moraines, 

 there being but few bowlders on their surfaces. In eastern Ohio 

 bowlders are a less conspicuous though not a rare feature. The 

 cause of this unusual abundance of bowlders is an interesting 

 problem and one perhaps not easily solved. It has been 

 suggested by some one, I think it was Mr. McGee, that an 

 unusual abundance of bowlders on the later drift sheets may be 

 an indication that the ice invasion which brought them in was 

 preceded by a long deglaciation interval in the gathering ground, 

 and that the Canadian highlands were scoured afresh after the 

 lapse of sufficient time for ledges to have been seamed and 

 broken under atmospheric influence. The suggestion seems 

 worthy of careful consideration. 



The drainage from the ice -sheet was especially vigorous at 

 this time throughout the entire width of the state and as far 

 to the east and west as this morainic system has been identified. 

 The altitude could not well have been less than at present, and 

 may have been somewhat greater. 



The later moraines. Between this morainic system and the 

 western end of Lake Erie six more or less distinct moraines 

 occur, which were probably formed in comparatively rapid suc- 

 cession. They each consist usually of a broad ridge one or two 

 miles or more in width, and twenty-five to fifty feet in height. 

 They are each sufficiently bulky to have determined to a large 

 extent the courses of the main drainage lines of northern Ohio 

 (see map) and yet they seldom present a sharply indented or 

 conspicuously broken surface. The overwash aprons and terraces 

 connected with them indicate less rapid discharge of waters than 

 from the earlier moraines, and that too in certain parts of the 

 belts where conditions were very favorable for rapid escape of 

 waters as in the north part of the Scioto basin. It is thought 

 from this feature as well as from the aspect of the morainic 

 ridges themselves, that the ice -sheet had less vigor than when 

 forming earlier moraines. That there was a decrease in altitude 

 seems also highly probable. As noted above, surface bowlders 



