Postelsia 2 
(@2) 
Ne) 
and unite to form one or more large pools. 
Finally, most of the wall of the pool is destroyed 
and a large indentation in the shore line is 
formed. As the waves and the tides work on 
the indentation, it makes its way farther and 
farther inland, becoming finally a long narrow 
channel known as a tide-rift. Such a channel 
is shown in Plate XXIV. Often the sides are 
perpendicular, with overhanging ledges. Under 
these ledges, many life forms find lodging 
places, especially those kelps which require 
the strong wash of the tides for their develop- 
ment. Such a region is found a little east of 
piamd s omt: “eblere »there 1s 9a. ‘slicitly 
sloping sandstone area, pitted everywhere with 
small pools which are lacking in life forms, 
but which exhibit the development in all stages. 
Plate SO feo. is a picture of this region. At a 
point 30. feet above the sea, begins a series of 
depressions, which do not contain water, except 
a little here and there which is stagnant. The 
series begins at the vegetation zone and slopes 
to the sea. They are probably filled during 
the season when the waves and the tides are 
