AGASSIZ: BERMUDAS. 263 



south shore I observed a great number of ledges with nearly flat tops, 

 from which the surmounting ajolian pinnacles had been worn away ; some 

 of them were just awash at low-water mark, otljers reached half-tide mark, 

 and a great number were sunken ledges. On these last, if forming the 

 inner part of the outer line of ledges, ai-e found Gorgonians and corals, 

 giving them to a certain extent the appearance of a coral reef. 



Off White Cliff Bay there is an excellent specimen of an irregular 

 crescent-shaped barrier reef formed upon a ledge barely in contact with 

 the beach at low water. The wall on the inside is formed of short irregu- 

 lar steps, and the inner area of the ledge is thickly overgrown with cal- 

 careous Algse, more or less covered with oeolian sand washed from the 

 friable parts of the ledge. 



The narrow pedestals which are the bases of some of the pinnacles of 

 seolian rock are often the remains of extensive flat ledges on which 

 the different organic growths characteristic of boilers have obtained a 

 foothold. The parts of tlie tops and sides of these ledges which have 

 not as yet been covered by such a growth, or only partially so, plainly 

 show that they ditter in uo way except in size from the smaller mush- 

 i-oom-shaped feolian rock ledges, and are formed by the same agencies. 

 The larger piimacles of pcolian rock like those still standing off" Whale 

 Bay will become, when they fall, large flat ledges upon which the sea 

 wlien breaking digs out irregular pot-holes of all shapes and sizes. 

 The remnant of the l)ase of the pimiacle becomes, when worn away by 

 the sea, either a shelf or a flat corrugated ledge, and the more or less 

 vertical sides below low-water mark are worn away by the wash of the 

 sea into mushroom-shaped ledges. 



At the east end of Elbow Beach several patches of linneycombed shore 

 rock ledges have been left stranded in the midst of the lieach sand sur- 

 rounding them. These ledges, if exposed to the action of the sea, would 

 soon be worn flat, and according to the angle of their stratification would 

 be dug out into atolls or other irregularh^ shaped structures protected 

 by Algfe and Serpulte. The same serpuline growths and similar convo- 

 luted walls occur on the North Rock and tiie adjoiniu"; ledLres on the 

 north. Similar structures, forming more oi- less distinct reefs, also occur 

 ff" tlie north sliore and elsewhere on tiie edge of the reef flats, but they 

 are not as numerous nor so well defined as a rule. They consist, how- 

 ever, always of the same mushi'(.)om-shaped ledges, sometimes still sur- 

 mounted by tlieir piimacles of ceolian rock, and of others abraded to the 

 level of low-water mark, or even well below it. The shore ledges on the 

 south coast are acted upon by short, sharp breakers, formed in froi>» 'me 



o 



