IPostelsia 281 



found in a gently-sloping sandstone region 

 called the "Devil's Billiard Table." This is 

 a region where concretions occur in great num- 

 bers, and scattered at irregular intervals. They 

 lie well back from the high tide line. Approach- 

 ing the shoreline, (Plate XXI. fig. i.), the concre- 

 tions disappear, and a series of depressions, 

 looking as though the concretions had been 

 lifted out of them, is left. Some are empty, 

 and others are filled with water. Still nearer 

 the shore, the depressions become much larger, 

 and are more irregular, many being separated 

 only by a narrow ledge of rock. At the 

 shore line they become mere indentations and 

 irregularities in the coast. These larger pools 

 have acquired a characteristic fauna and flora. 



The irregular shore line caused by many 

 pools, and the wearing away of the seaward 

 wall, is very common. It may be seen in 

 Plate XXII. figs. I. and 2. 



The number, size, and irregularity of pools 

 increase with the slope, the sloping shore being 

 more exposed to the waves than the flat shore. 

 Often the erosion is so great that one pool 

 occurs within another. 



