po s t e I s ia 289 



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 

 "Baird's Point." Here there is a slightly 

 sloping sandstone area, pitted everywhere with 

 small pools which are lacking in life forms, 

 but which exhibit the development in all stages. 

 Plate XXI. fig. 2. 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 



