﻿Plate 40 



Perch river above the falls at Limerick, Clayton quadrangle [see pi. 23]. The 

 rock is Leray limestone and the stream course here follows enlarged joint 

 cracks, first one set and then another. The enlargement seems wholly owing 

 to solution and likely was formerly an underground channel. Looking north- 

 west and upstream. E. O. Ulrich, photo, 1908 



