Postelstia 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 shore line, (Plate X XI. fig. 1.), the concre- 
tions disappear, and a series of depressions, 
looking as though the concretions had been 
hited sout 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 
onlys 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 
walleis very common. ‘lt may be Seem Im 
Plate OO: figs. 1 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. 
