142 THE JOURNAL OF GEOLOGY. 



moraine lying east of Mad river. It is difficult to determine the 

 precise amount of excavation accomplished in this interval, since 

 the portions of the valley lying beneath or within the later 

 moraine are partially filled, while the portions lying outside the 

 moraines afforded avenues for the escape of glacial waters, and 

 were probably much enlarged thereby. It seems safe, however, to 

 state that an amount of excavation took place that would require 

 some thousands of years with a drainage system of the size of the 

 present Mad river system, and with a gradient such as the region 

 now affords. It may be added that in regions further west, if 

 our correlations are correct, there are found evidences of the 

 same deglaciation interval, but their discussion does not fall 

 within the scope of this paper. 



Main morainic system of later drift. The moraine just re- 

 ferred to (in whose re-entrant angle the Mad river basin lies) 

 belongs to the system mapped and described by Professor 

 Chamberlin, in the Third Annual Report of the U. S. Geol. 

 Survey, as the "Terminal Moraine of the Second Glacial Epoch." 

 As shown by Professor Chamberlin this moraine lies near the 

 glacial boundary in eastern Ohio and north-western Pennsylvania, 

 but farther west it falls short many miles of reaching the glacial 

 boundary. It is a complex system, " constituting a belt rather 

 than a single moraine," there being in places not less than four 

 distinct members. Nearly everywhere in the state it presents a 

 sharply indented surface, a feature which, as suggested by Pro- 

 fessor Chamberlin, appears to indicate forceful or vigorous action 

 of the ice -sheet. Its peculiarly sharp contours and their diag- 

 nostic characters make it the most conspicuous and distinctive 

 morainic belt in the state. Other moraines, newer as well as 

 older than this morainic system, assume in places the form of 

 smooth ridges or have but gently undulating surface, and hence 

 are less conspicuous features even where they have as great bulk 

 as the individual members of this system. In western Ohio one 

 of the members of this system (the second one of the group) 

 carries on its surface large numbers of crystalline bowlders of 

 Canadian derivation and the remaining members are liberally 



