CHAPTER II 



Physiography of the Sea-shore 



The coast-line of all countries exhibits a succession in varying 

 degrees and extent of cliff, headland, reef, bay, estuary, 

 lagoon, delta, inlet, and fiord ; of sand and shingle or of 

 mud flat. These physical features, which are of fundamental 

 importance to animal and plant life, are the outcome of 

 complex geological and geographical factors, and result 

 from the action of the ocean upon varying strata and deposits, 

 generally already moulded and modified by denudation — 

 marine, fluviatile, or glacial action — and now in process of 

 still further modification by the salt waters acting under the 

 rhythmical power of the tides, and by the more spasmodic 

 forces of the wind. 



We are going to deal with the life of a narrow zone, 

 which, although primarily under the influence of the sea, 

 is daily exposed to land influences ; hence the chief peculiari- 

 ties of the zone are periodicity and variability, and we have 

 here, more than anywhere on earth, fluctuating conditions. 

 The relative area of the sea-shore exposed during tidal 

 absence depends on two chief factors, namely, the degree 

 of slope and the vertical tidal range, and some idea of its 

 extent may be gained from the statement that the total 

 frontage of coastal foreshore in the United Elingdom is 9700 

 miles, and that the total area between high and low water 

 marks is about 620,000 acres (Carey and Oliver, 191 8). 



Before dealing further with the characters of the tidal 

 area it becomes needful to consider a few of the vital charac- 

 teristics of the sea, and the manner in which they modify 

 and affect this zone and the life inhabiting it. 



