Art. I ] Clark, Dramage Modificatiojis. 1 1 



study of the map (Plate II.) already referred to in connection 

 with the tn iJifijations in \.\\t latter stream. 



In view of the preceding descriptions the changes sketched 

 in tije Rocky Fork region will be self-explanatory. Notice that 

 as usual in all this part of the state the mouths of westward 

 flowing streams have been blocked up by the glacial debris until 

 their waters were forced over low cols into adjoining systems, 

 with the final result that new streams were located having their 

 axes at right angles to those of the old streams, but utilizing 

 parts of the old valleys, along with some of their tributaries. 

 It will be seen that Rocky Fork occupies parts of the main 

 valleys and tributaries of two westward flowing pre glacial 

 streams as well as that of an insignificant tributary to the Old 

 Newark River. It now takes practically all the drainage that 

 formerly came to the North Fork of the Licking from the East 

 by way of the two streams, one of whose axes ii follows in a 

 reversed direction, and the other of which, after following for a 

 {q.\m miles, it crosses. There are two points in the development of 

 the Rocky Fork to which special attention might be called. It 

 will be noticed that where the present stream leaves the largest 

 of the old valleys partially occupied by it two cols have been 

 crossed, one a minor col between two unimportant tributaries 

 of the old stream, and tiie other located in the great divide 

 extending through this section in a North and S )ut i direction. 

 The most probable sequence of events was the toeing o; the 

 water across the first col by the easternmost dam in tiie old 

 valley, followed by the blocking of the valley's mouth by a >lill 

 higher one that raised the floods above the second col. 



A phenomenon that proved quite deceptive is to be found 

 where Rocky Fork comes into this old valley by way of one of 

 its northern tributaries. Some half mile above the junction of this 

 tributary valley with the old main valley, there is a rock cut with 

 precipitous sides forty to fifty feet high. The hills open out 

 above and^below into what are evidently pre-i^lacial valle\s, and 

 it would seem clear that this marks the position of an eroded 

 col. At one point along the gorge considerable masses of the 

 rock have been split apart (by the freezing of water in the 



