60 



the point planes and on the more sohxble parts of the limestones has pro- 

 duced a great variety of sink-holes, caves and "lost rivers." The sink- 

 holes are basin shaped depressions many feet deep, and often hundreds of 

 feet in diameter, witii an opening at the bottom which leads into some un- 

 derground channel ; in some cases the openings have become filled and the 

 water is held in the basin. In many places a stream runs into these lioles, 

 then by underground passages for a great distance, and again comes to the 

 surface in the form of springs. Valleys, sometimes two to four miles in 

 length, are drained through imderground channels. This gives rise to a 

 confusing system of hills and valleys, though a well-defined drainage may 

 be worked out which in itself is usually made up of sink-holes. There are 

 many pure water springs in this region and also many springs of mineral 

 watei's. The best knoN^n of these are the French Lick and West Baden 

 Springs, Trinity and Indian Springs. Lost River, a main branch of the 

 East Fork, through Orange and Martin counties, has many "lost" tribu- 

 taries in Orange County. The luunerous caves and the mineral springs 

 are described in the State Geologist's Reports for the years 1896 and 

 1901-02. 



The greater or less degree of uniformity in the volume of the river in 

 the course of a year is one of its chief physical features and depends very 

 much on the manner in which the water supply is obtained. The streams 

 of this area depend for their increase wholly upon the rains, which, oc- 

 curring frequently and at no fixed periods, and discharging only compara- 

 tively small amounts of water at a time, except in periods of the heavy 

 rainfall of several days' duration, preserve a modei'ate degree of uni- 

 formity in the volume of the streams. This uniformity is aided by the 

 fact that under normal conditions only about one-third of the rainfall finds 

 its way directly over the surface to the streams, the remaining two-thirds 

 sinking into the ground and finding its way to springs, reservoirs, or gradu- 

 ally oozing thi'ough at a lower level until the soil becomes drained of its 

 surplus moisture, a process which continues for weeks and helps to keep 

 up the volume of the stream. But, on the other hand, man has done a great 

 deal to destroy the uniformity of the volume. By the removal of the 

 forests, the cultivation of the soil, and the use of ditches for drainage, a 

 greater part of the water is at once thrown into the stream and greater 

 fluctuations occur. Owing to the streams being hemmed in by lofty, ab- 

 rupt cliffs, which resist the free passage of the swollen streams, and the 

 velocity being checked by winding courses, greater floods occur from the 

 same amount of rainfall than formerly. 



