39 6 



POPULAR SCIENCE MONTHLY 



Fig. 10. Pot-holes, Watkins Gi.en. 



like walls with smooth, straight sides, sometimes leading the stream 

 into sharply rectangular courses where the water departs from one set 

 of joints to the other, which extends at right angles. Both the hori- 

 zontal stratification and the vertical joint planes also affect the outline 

 of the gorge walls, giving rise to some striking and picturesque effects. s 

 Still another feature prominently illustrated in these gorges is the 

 pot-hole, formed where the cascading waters bore into the stream bed 

 and. grinding pebbles about in the swirling waters, form large, deep 

 pools (Fig. 10), adding interesting variety to the scenery of the gorges, 



8 For further description of these phenomena see Tarr, Bull. Amcr. Geog. 

 Soc, Vol. XXXV1L, 1905, pp. 193-212. 



