36 THE BIOLOGY OF THE SEA-SHORE 



tide and mean high tide, and is twice daily exposed to air 

 and submergence. (3) The Upper Beach : only reached by 

 extreme high tides. From the geographical standpoint this 

 is a satisfactory division that can be applied to practically 

 all shores, and may form the basis for other subdivisions from 

 the biological standpoint. Johnson {op. cit.) discusses this 

 matter in an interesting manner. " The line w^here land 

 and water meet has been called the shore-line, the strand- 

 line, the coast-line, and the water-line. The terms shore, 

 beach, strand, and coast are also loosely used with varying 

 significance. . . . Four zones extend from low water to 

 the base of the cliff, whether large or small, which usually 

 marks the landward limit of effective wave action. This is 

 the zone over which the water-line^ the line of contact between 

 land and sea, migrates : and it will here be called the 

 ' shore.'' Landward is an indefinite zone, the coast. The 

 boundary between coast and shore is the coast-line. The low- 

 tide shore-line marks the seaward limit of the intermittently 

 exposed line, and we have likewise the high-tide shore-line. 

 The shore is subdivided into two minor zones : \hQ foreshore 

 daily traversed by the oscillating water-line, and the back- 

 shore covered by exceptional storms only." At the seaward 

 coast edge is the wave-cut clijf, varying from an incon- 

 spicuous slope to a high escarpment. In front of this, 

 occupying all the shore zone and part, or all, of the shore 

 face, is the wave-cut benchy a sloping erosion plane inclined 

 seaward ; lastly, we have the more extensive, nearly hori- 

 zontal plane produced by long-continued wave erosion, and 

 commonly called the abrasion platform. At the outer margin 

 of this there accumulates an extensive deposit of material 

 moved across the platform and deposited in the quieter 

 water — that is the continental terrace, which together with the 

 abrasion platform makes the continental shelf. Areas where 

 erosion is active are naturally not able to support a rich 

 fauna, and are particularly unsuited to sessile forms of life. 

 The artificial regulation of rivers and harbours may cause 

 great alteration in local conditions. The type of local rain- 

 fall and rock (or soil) porosity will determine whether a 



