Postelsia 203 
There are some instances of a combination 
of sandstone and conglomerate pools. In one 
case, a mass of conglomerate stands surround- 
ing a depression in sandstone. In another case, 
one side of the pool was sandstone, and the other 
was conglomerate, the sandstone being more 
worn than the conglomerate. In one region of 
conglomerate, is found a number of good sized 
pools, exhibiting the characteristics of sand- 
stone pools. Upon examination it was found 
that these pools all have sandstone bottoms, 
surrounded by masses of conglomerate. 
Pools in shale are found rarely. They are 
very long and narrow, following the lines of 
Strammeation | (Plate: XOCVs ire, 2). ) They are 
shallow in comparison with sandstone pools, 
owing to the greater difficulty of erosion of the 
hard crystalline rock. Very few large pools of this 
class are seen. Only occasionally boulders 
occur in shale pools, and generally in a posi- 
tion indicating that they have rolled in from 
the high banks above, and are not native to 
the pool. The fauna and flora usual to the 
sandstone pools are present, but in smaller 
