TIME BETWEEN EARLY AND LATE WISCONSIN. 353 



It should perhaps be stated that Mad River and its tributaries do not 

 follow to any great degree preglacial lines, the concealed rock surface, if 

 we ma}^ ji^idge from well data, being nearly as elevated along the valleys as 

 beneath bordering uplands. The evidence appears decisive that the valleys 

 are interglacial and not preglacial. 



The evidence of an interval is less striking on the south and west 

 border of the Miami lobe than that on the east, just noted. On the Great 

 Miami, the valley gravels leading away from the later sheet of drift have 

 filled its channels about to the level of the early Wisconsin terraces. On 

 some of the western tributaries of the Great Miami the gravels of the later 

 invasion lie in trenches cut into the drift of the early Wisconsin, but the 

 trenching is not conspicuous, probably because of the small size of the 

 interglacial streams and their moderate rate of fall. In Whitewater Valley 

 the gravel of the late Wisconsin has been built up about to the level of the 

 early Wisconsin gravel, rendering it difficult to separate the two. On the 

 whole, the interval between the early and late Wisconsin appears much 

 briefer than the Sang-ainon interglacial stag-e, and somewhat briefer than 

 the Peorian. 



The difference in the erosion features of the early Wisconsin sheet and 

 those of the outer moraine of the late Wisconsin appear no more striking 

 than between the Shelbyville and the Valparaiso moraines of the Illinois 

 glacial lobe; indeed, the difference in the outwash seems scarcely so strik- 

 ing. It is, however, such a difference as wovdd naturally be found in passing 

 from the outer part of the early Wisconsin to the outer part of the late 

 Wisconsin in Illinois, and is greater than is found in that State in passing 

 from the northern or later part of the early Wisconsin to the southern or 

 outer part of the late Wisconsin. From this it is inferred that the Hartwell- 

 Cuba moraine is a correlative of either the Bloomington or the Shelbyville 

 moraine of the Illinois lobe, rather than the Marseilles. However, the 

 precise coiTclation of this moraine with a inoraine of the Illinois lobe has 

 not been attempted. 



MON XLI 23 



