FACIES OF THE SHORE ZONE 649 



pebbles, sand and mud. unless the water at the foot of the cliff is 

 sufficiently deep to render the force of the waves ineffective. Thus 

 boulders will seldom accumulate in such numbers as to make a 

 boulder beach at the foot of a cliff, since the destruction of the cliff 

 proceeds with sufficient slowness to allow the reduction of most of 

 the fragments to pebbles or smaller particles. If, however, the sea 

 eats into a morainal or other bouldery deposit, as is the case of many 

 portions of the New England and Long Island coast of the North 

 Atlantic, a heavy boulder beach arranged in the form of a pave- 

 ment by the close approximation of the boulders through wave and 

 shore-ice work will result. In like manner, when the sea en- 

 croaches upon an old subaerial talus heap, a boulder beach may be 

 formed, the waves being able to round off and arrange the boulders, 

 but not to destroy them. The boulders themselves become a natu- 

 ral barrier, against which the waves beat themselves to pieces with- 

 out accomplishing much erosional work. Where the tides are ex- 

 ceptionally high, as in the Bay of Fundy, the boulders broken from 

 the cliffs by the frost and insolation will be rolled and worn at high 

 tide, but the power of the waves is too small, and the time during 

 which the boulders are subject to their influence too short, to pro- 

 duce any other results. Here the accumulation of boulders is really 

 to be compared with a subaerial talus, which is periodically, but for 

 a short time only, exposed to wave activity. On the whole, boulder 

 beaches other than those due to erosion of drift deposits are of com- 

 paratively rare occurrence, and the same thing may be said of an- 

 cient marine boulder beds. It is doubtful if many such existed, 

 most of the boulder beds of former geologic epochs being probably 

 of continental origin. That boulders of even moderate size may 

 for a long time remain entirely unmoved by the waves is shown on 

 the east coast of Scotland, where the boulders and ledges are cov- 

 ered by living Acnijea or by extensive growth of sea weeds. Even 

 delicate sea anemones are found attached to these boulders, often in 

 such a position that a slight movement of the boulders would grind 

 them to pieces. In other cases the boulders and pebbles are en- 

 crusted by a growth of Lithothamnion or Alelobesia. It sometimes 

 happens that in certain zones, or areas, the waves are able to move 

 the boulders, with the result that there they are entirely bare of 

 either vegetation or animal covering. 



3. Gravel fades. 



By far the greater part of the present shore lines of the world is 

 sandy or gravelly, the former predominating. Gravelly beaches or 



