169 



Observations, Having for Their Object the Approximate De- 

 termination OP the Time Required for the Erosion of 

 Clifty and Butler Ravines in Jefferson County, Ind. 



Glenn Culbertson, Hanover, Indiana. 



In the Proceedings of the Indiana Academy for 1897, there is given 

 au account of preliminary woric hxtking forward to tlie determination of 

 llie period required for the erosion of Clifty and Butler ravines or valleys. 

 This preliminarj- work consisted in making accurate measurements of the 

 length of the valleys mentioned, and in drilling holes and in driving steel 

 rods into the rocks both above, and in the amphitheater-like si)ace beneath, 

 the falls, and in making accurate measurements from these rods so that 

 the rate of recession of the falls could be determined. 



Nothing of value has resulted from the measurements from the rods 

 driven in the bed of the streams above the falls. From those driven into 

 the softer rocks beneath the falls, as described in the Proceedings of 1897, 

 results so far as Clifty Valley is concerned are quite satisfactory. The 

 evidence obtained in case of P.utler Valley is as yet of little value. 



A comparison of the measurements made at Clifty Falls fourteen 

 years ago and very recently indicate that the sapping, as the weathering 

 caused by the mists carried by the waterfall winds against the rocks be- 

 neath the falls, followed by frost action, is called, has been quite marked. 

 Since 1897 the sapping has amounted to four and one-fourth inches. The 

 sapping has been of a uniform character throughout the whole period, 

 and certainly indicates veiy closely the present rate of retreat of the 

 falls. 



Four and one-fourth inches in fourteen years is very approximately 

 at the rate of two-sevenths of an inch per year. The period required for 

 Ihe retreat of the falls from the edge of the deep valley of the Ohio, a 

 distance of 11,000 feet, if the present rate of erosion has held throughout 

 its history, should be 402.000 years. 



The rock over which the water now flows at the falls is of the same 

 character essentially as that over which the water flowed during the whole 

 of the past history of the valley. Hence so far as that element is con- 



