278 IP s t e I s i a 



that the conglomerate or the shale forms the 

 surface rock, the strata overlying having been 

 eroded. Plate XX. fig. 2. shows the heavily wooded 

 cliff known as "The Point." The horizontal 

 rock forming the floor leading to the sea is 

 graywacke. 



In all classes of rock are depressions of 

 varying shape and depth, sometimes exposed 

 by the tide, and sometimes covered. They 

 possess characteristic fauna and flora, and are 

 called tide-pools. The typical pools lie in the 

 sandstone, because of the extreme softness of 

 the rock, which renders the work of erosion 

 easy. They are also abundant in shale, but 

 are few in number in conglomerate. 



The pools in sandstone occur generally in 

 strata which are nearly horizontal, so that the 

 pool resembles a depression in a floor. Some- 

 times the lower part of the pool has been worn 

 away more than the upper part, leaving the 

 uneroded strata as a projecting rock shelf, 

 which affords a hiding place for sea-urchins, 

 star fish, and other animals. 



The greatest number of small pools was 



