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The majority of the smaller pools, as may 
be seen in most of the photographs, are cir- 
cular, but the larger ones are generally ellip- 
tical, and give evidence of having been formed 
by the union of two or more smaller pools, the 
connecting rock ledges having been eroded. 
Such pools are shown in Plate XXIII. fig. 1. 
The pools vary in size from small depres- 
sions a few inches in diameter, to those 30 feet 
long, 20: feet wide, and 16 to 15 feet im Wdepem 
Usually the largest are the most irregular in 
outline, and contain the greatest diversity of 
plant and animal life. 
The temperatures vary ‘with the jimemor 
day, the seasons, the depth, and the position 
with regard to the tides, those lying highest 
being warmest, since they are not subject to 
a change of water with each incoming and 
outgoing tide. One such pool was 30 feet long, 
and 30 feet wide, and showed traces of several 
connecting ridges. 
Many pools, especially those in the region 
of the ‘‘Devil’s Billiard Table,”’ contain boul- 
ders, which appear to have the same composi- 
