DRAINAGE OF SOUTHERN INDIANA 7a 
for about eighteen miles before turning to the southwest and 
cutting through the Niagara strata. 
It is seen, from what has been said above, that the area covered 
by the Hudson River strata has its main drainage lines parallel 
with its western rim; that for the most part there are southward 
flowing streams in the area immediately east of and practically 
all along this rim, that the tributaries from the west are short, 
while those from the east are long, and that these features of the 
erosion may be due to the gentle westward inclination of the 
strata at the west edge of the area. As the streams approach 
the Ohio their relations to the watershed at the west are lost, 
as is seen by the abrupt eastward turn of the Whitewater in 
northeast Franklin covnty, and of Laughery Creek in southeast 
‘Ripley county. 
THE CENTRAL DRAINAGE AREA. 
The central drainage area has its eastern watershed formed 
by the Niagara and Devonian limestones, while its western water- 
shed is formed by the Knobstone sandstones and overlying 
limestones that form the crests of the hills known as the Knobs. 
The east-west profile of this area and its geological relations 
are shown on that portion of the cross section (Plate I) extend- 
ing from the Niagara strata to the Knobstone sandstones. The 
east side of the basin has a gentle slope to the west, while the 
west side has a steep slope to the east. 
The shape of the central drainage area is shown on Plate I, 
where its streams are shown by solid lines. This area is about 
fifty-five miles across in its widest part at the north and narrows 
down until it is less than a mile wide along the Ohio river at the 
south. 
On Plate VI this trough, the axis of which extends from near 
Edinburg (A, Plate VI) slightly east of south to the Ohio River 
near New Albany (2), is shown. From Edinburg to the Ohio 
the axis is followed approximately by the line of the Jefferson- 
ville, Madison & Indianapolis railroad. The central area, in 
which the control of the structure upon the drainage is more 
clearly marked than in either the eastern or western areas, is 
