201 



of the valley. Its peculiar sand dune flora intensifies its insular character 

 and makes it as fine a field for the student of plant ecology as for tlie 

 student of geology. 



An island terrace at West Terre Haute originally occupied about one 

 square mile, one-fourth of which has been removed by the railroad coni- 

 panies for ballast. 



I\0(1: Tcrrdd K. In the vichiity of Terre Haute the front of the west 

 bluff is bordered for five or six miles by a rock teirace 10-20 fe<'t high and 

 in some places a (|uarter of a miie wide. This is due to a thin stratum of 

 flinty limestone which has resisted erosion more effectually than the shales 

 which lie above it. 



'I'lic Trirc lltnite Terrace occuities the eastern jiart of the valley from 



Figure fi. .-Mherton Island — West Bluff. 

 Lyford. npiidsite Clinton, to the southern boundary of ^■igo ("ou:ty. :i 

 distance cf abuut L'T miles. Its width is generally 3-4 miles, but near its 

 northern end if is divided by the south end of a piece of highland which 

 we call Atherton Island. (Fig. 6.) The eastern branch, 2i miles wide, 

 extends through a gap in the Wabash bluff r» miles northeastward to 

 Rosedale, where it becomes continuous with the floor of the valley of Big 

 Raccoon Creek. The western branch, between the west side of Atherton 

 Island and the river, tapers to a pnint opposite Clinton. At Terre Haute 

 the surface of the terrace lies ."()(t-r.lO feet A. T. or 40-50 feet above flood 

 plain and is diversified ]>y a series of longitudinal ridges 10-20 feet high 

 which resemble sandbars. These are shown in the series of four transverse 

 14—33213 



