﻿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 
  

  

  