112 



V. Relation of forests to water supply in tlie driftless area. 

 Runoff and ground water. 

 Erosion. 



Silting <if ponds. 

 VI. Summary. 



I. 



The problem of imiiiiiipal wnui- supjiiy involves a lari^e number of 

 factors, among wblcli the geological conditions enter with varying im- 

 portance, and have received a varying degree of emphasis at the hands 

 of water-supply engineers. Some, as for example Vermeule^ have been 

 inclined to assign to the geological factors an importance second only 

 to that of tlie fundamental factors of rainfall and run-off. Others, as 

 Rafter^, assign only secondary importance to the geological conditions. 

 This difference of opinion is very probably attributable, in some degree, 

 at least, to the sort of regions that have fallen most under the study of 

 the respective students of these problems. In the glaciated portion of 

 the United States, for example, where the geological conditions are apt 

 to be measurably uniform over large areas, and where, at all events, the 

 coiuitry rock is apt to be so deeply buried as to have little effect on the 

 character and movements of surface waters, it is altogether likely that 

 the geological factors, other than topograi)hy, would have received a rela- 

 tively small amount of attention. In driftless areas, on the other hand. 

 such as the area at present under consideration, (he character of the rock 

 formations may powerfully affect the case; and as a matter of fact, in this 

 region, the geological factors are, next to rainfall, the most important 

 factors to be taken into consideration. 



The driftless area of southern Indiana comprises all of the counties 

 of Floyd, Harrison, Perry, Crawford, Orange, Lawren(e. Sjjencer and 

 Warrick, and portions of the counties of Clark. Washington, .Tackson. 

 Brown, Monroe, Greene, Martin, Dubois. Pike. (Jilison. Vanderburgh and 

 Posey. It is a region of varied, but on the whole of rather strongly 

 accentimted topography. The eastern portion of this area, the region of 



' Vcrmriilr. C. C. Ccolouical Survey of Xcw .Tcrsc.v. Ucport on wator-suiipl.v. 

 Vol. Hi of tho Final I{f))ort of the Slalc ( icolot,'is(. ISDI. 



' Itdftcr, O. II'., Ilydroluszy nf llic Sl,ili> of .\cw Voik. Xew Vorl; Slate Miiseiiin, 



I'.iiii. No. s.-., inor>. 



