145 



"At one large plant storage basins that originally had a capacity to 

 hold the water accumulated by several days of ordinary stream flow have 

 been so filled that they cannot now hold the How of a single night. 



"At one dam where two years before, when the dam was first closed, 

 there was a depth of 2S feet, an island has recently appeared. At another 

 place, where a high dam had been bnilt on a small stream, the pond has 



been so filled that its storage capacity has all been lost A ix)nd 



four miles long and forty feet deep at the lower end was in four years 

 entirely filled in its upper part and near the dam was three-fourths full." 



The differences between the southern Indiana region and the southern 

 Appalachians are largely such as arise from the greater relative relief of 

 llie latter region. Plenty of examples on a somewhat less pronounced scale 

 can be found in Indiana, of precisely the same process here so vividly out- 

 lined by Glenn. 



There is only one remedy for this condition, and that is to remove 

 the cause. The writer can vouch for the fact that where the forest cover 

 is adequate, slopes in the Knobstone region, almost too steep to climb, are 

 not suffering an appreciable amount of erosion. The steep slopes of water- 

 supply catcliments must be maintained in forest cover if reservoirs are to 

 be kept free of mud. It would be a blessing to the future citizens of Indi- 

 ana if large sections of the more rugged portions of the driftless area of 

 southern Indiana could be protected by the State from further denuda- 

 tion, and if, furthermore, slopes which have already been denuded, and 

 which are too steep for agricultural purposes, could be reforested. The 

 great Knobstone region, with its innumerable deep valleys and ample rain- 

 fall, and impervious strata, must ultimately be called upon to furnish the 

 water supply of great cities. It should be seen to that the one condition 

 which alone can make this region unfavorable for such purposes, namely 

 erosion of its steep slopes, is remo\-»d by early and adequate steps to for- 

 ever maintain these slopes in forest. 



VI. 



Summary. The driftless area of southern Indiana comprises an east- 

 ern portion of impervious sandstones and shales and rugged topography ; 

 a central portion of cavernous limestone and mild relief, and a western 

 portion of shales, sandstones and limestones, and similar in topography to 

 the eastern region. The mean annual temperature and the mean annual 

 rainfall are slightly greater in the southern than in the northern portion 



[10—29034] 



