201 



ot the valli'v. Its peculiar saiul diine tinva inteiisilies its insular eliaraeter 

 and makes it as tine a field for tlie student of plant ecoloj^y as for tlie 

 student of geology. 



An island terrace at West Terre Haute originally occupied about one 

 square mile, onc^-fourth of which has been r.'nidved hy the railroad com- 

 panies for ballast. 



Rod' J'crraces. In the vicinity of Terre Haute the front of the west 

 bluff is l)(>r(lercd for five or six miles by a rock teirace 10-20 feet high and 

 in some places a ipiarter of a mile wide. This is due to a thin stratum of 

 flinty limestone which has resisted erosion more effectually than the shales 

 which lie above it. 



77/c Terre llitiilc Tenarf occujiies tlie eastern part of the valley from 



Figure 6. Atherton Island — West Bluff. 

 Lyfiu'd. (ipiinsite Clinton, to the southern boundary of Vigo ("nn:.ty. a 

 distance rt' about 27 miles. Its width is generally 3-4 miles, but near its 

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

 we call Atherton Island. (Fig. 0.) The eastern branch, 2i miles wide, 

 extends through a gap in the Wabash bluff 5 miles northeastward to 

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

 Raccoon Creek. The western branch, l>etween the west side of Atherton 

 Island and the river, tapeis to a point opposite Clinton. At Terre Haute 

 the surface of the terrace lies nOO-ulO feet A. T. or 40-50 feet above flood 

 plain and is diversified I\v a series of longitudinal ridges 10-20 feet high 

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

 14—33213 



