IOO 



WORK OF RUNNING WATER 



Fig. 96. Figure showing crenate river bank, the re-entrants being determined 

 by joints. Dells of the Wisconsin River, near Kilbourn, Wis. (Atwood.) 



joints allow the ingress of water, roots, etc., which help to weather 

 and disrupt rocks. Their effect on erosion may be seen along many 

 streams which flow in rock gorges. In such situations, the outlines of 

 the banks are in some cases angular, and in some crenate (Fig. 96), 

 the re-entrants being located at the joints. By working into and 

 widening joints, running water in some places isolates masses of 

 rock as islands (Fig. 97). 



Fig. Q7. An island formed by river erosion in jointed rock; Lower Dells of the 

 Wisconsin. (Atwood.) 



