THE BAHAMAS AND BERMUDAS 



303 



ingr to the angde at which the strata meet the sea, and 

 may in its turn form one of the Serpulse atolls or knobs. 

 The ledge which is left [Fig. 2] below L W M, composed 



Fig. 3 



Fig. 4 



of seolian strata which have been cemented together by 

 the solving action of the sea, is coated by a hard crust. 

 Algse and Serpulse and all the beasts of a Serpula atoll 

 are already growing upon the ledge. But as soon as the 

 water instead of playing round the ledge begins to break 

 upon it, it will soon eat away the softer part of the in- 

 terior, or where not so well protected and, according to 

 the slope of the strata of the ledge, will form an atoll if 

 horizontal, if a little inclined a crescent-shaped reef, and 

 if it is a thin ledge a barrier reef, as per sketches. 



From horizontal strata the Alga? and Serpulse may 

 cover the bottom slope A C or B C [Figs. 3 and 4], but 

 if the surf is too great the sides E F are broken off, 

 and thus are formed 



isolated broken walls -. ,. £rr\ /s \\ 



of all shapes and out- ^"~~^n N \T - ~'0' 



lines. [Fig. 5.] _ FlG 5 



If the strata are dip- 

 ping and in the same block, we may have, as in all 

 seolian rocks, strata dipping at all angles, which will 

 account for the diversified shapes. 



