86 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



course of Mill Creek (reversed), along the west border of Walnut Hills. 

 The triangular tract lying between Mill Creek, Great Miami River, and 

 Ohio River, and comprising several townships of Hamilton County, Ohio, 

 is also surrounded by stream channels as completely as Walnut Hills, and 

 apparently for the same reason, the present course of the Ohio from the 

 mouth of Mill Creek to the mouth of the Great Miami being comparatively 

 new. This matter is discussed more fully later (pp. 116-118). 



A few miles below the mouth of the Great Miami River a rock island 

 appears on the Kentucky side, and rises about 200 feet above the river. 

 It is separated from the east bluff b}^ a channel nearly one-fourth mile in 

 width which stands scarcely 100 feet above the stream. Well data indicate 

 that its rock floor is above river level. The island seems to have been cut 

 off from the east bluff by the Ohio, probably because glacial deposits filled 

 the main channel sufficiently to give the stream opportunity to flow on each 

 side of the land which forms this island. These deposits filled the 

 main channel in that vicinity to a height of 150 to 200 feet above the 

 stream. 



. Immediately above the mouth of the Kentucky River, and back of the 

 city of Carrollton, l^j., there is an island or prominent group of hills stand- 

 ing 200 to 300 feet above the Ohio, and now separated from the uplands 

 to the east by a gap one-half mile wide that has been filled with glacial 

 deposits to a height of 100 to 150 feet. This separation was probably 

 effected by the encroachments of the Ohio and Kentucky rivers. The 

 gap is much narrower than the valley of either the Ohio or the Kentucky, 

 and this seems to indicate that it is not an old line of drainage. 



Just below Madison, Ind., there is a rock island nearl}^ 300 feet in 

 height, separated from the north bluff by a channel only half as wide as 

 the present stream. This channel, though now above the reach of the 

 river, may have been utilized down to comparatively recent times. The' 

 opening of the channel was perhaps begun by a small tributary of the river 

 which now enters just above the island, but a fully satisfactory interpreta- 

 tion has not been made. 



Some of the most conspicuous of the island-like uplands are found 

 where the Ohio leaves the resistant conglomerate Coal Measures and enters 

 the friable Coal Measures. These are well shown on the Owensboro topo- 

 graphic sheet (PI. VI, in pocket), and have been discussed in some detail 



