ROCK ISLANDS IN OHIO VALLEY. 87 



by Veatcli/ From Rockport the maiu channel, with a width of 2^ to 4 

 miles, takes a southward course to Oweusboro, Avhile a narrower channel, 

 known as Lake Drain or Lake Plain, leads westward and connects with the 

 lower course of Little Pigeon Valley through a channel which is reduced at 

 its narrowest 'place to a width of about two-thirds of a mile. The island 

 inclosed by these two channels and the lower course of Little Pigeon Creek 

 rises barely to the 500-foot contour, while the Lake Drain channel falls 

 slightly below 400 feet. The river at Rockport is about 345 feet at low 

 water, or only 50 feet below this channel, while at the highest floods it passes 

 through the channel. Another much smaller island, known as the Bon 

 Hai'bor Hills, appears on the Kentucky side of the river west of Owensboro, 

 and stands in the midst of the broad valley. It rises slightly above the 

 500-foot contour. The channel back of it falls a little below the 400-foot 

 contour, having very nearly the same altitude as the Lake Drain channel. 

 There is some uncertainty as to the interpretation of this peculiar di'ainage. 

 The Bon Harbor Hills are separated from uplands on either side by such 

 broad channels, their width in each case being nearly 3 miles, that this hilly 

 tract seems likely to have been an isolated one for a long period. But the 

 hills back of Rockport appear to have become separated in comparatively 

 recent times from the uplands to the north. Possibly the separation took 

 place alter the partial filling of the Ohio Valley with loess. It will be 

 observed that the local divides are broken down in that vicinity to an altitude 

 so low that but a slighMfcmount of valley filling would be necessary to make 

 it possible for a stream to be diverted across them. There are several 

 island-like tracts along the borders of the Ohio Valley west of the limits of 

 the Owensboro quadrangle, one of which, near Shawneetown, Illinois, is as 

 conspicuous as either of the tracts shown in this quadrangle, but the majority 

 are low and of small area. The history of their development is not as yet 

 understood. 



This somewhat hasty sketch of the present valley leaves untouched a 

 number of important features which throw light upon the development of 

 this great river, and these will now be considered. The several antecedent 

 drainage systems are taken up m order, beginning with the Upper Ohio 

 and passing westward to the lower course of the river. 



1 Arthur C. Veatch: Jour. GeoL, Vol. VI, 1898, pp. £57-272. 



