240 BULLETIN : MUSEUM OF COMPAKAT1VE ZOOLOGY. 



with Algre, Corallines, and Serpulse, there is deeper water, with corals and 

 Gorgonians. Many of the ledges within the lagoon consist of the minia- 

 ture serpuline atolls and reefs described in another section of this Report. 



On the inside of the outer serpuline reef ledge, corals and Gorgonians 

 flourish, according to the depth and the position of the ledges intervening 

 between the outer l'eef and the shore. Off Sinky Bay the bottom outside 

 of the outer reef ledges is hard. Off Castle Harbor, as far as the channel 

 leading into St. George Harbor (Plate XXL), we can readily trace the 

 gradual formation of islands and islets originally constituting the con- 

 tinuous barrier to a sound formed by the breaking through of the lower 

 saddles of the ridges dividing it from the sea. The outer row of these 

 islets and islands differs from the inner one in having comparatively 

 wide ledges, projecting round the base of a central pinnacle more or less 

 undercut. As the central pinnacles are cut away, they leave only a nar- 

 row ridge on the broad platform, the ridge itself also disappears, and on 

 the outer line of ledges have grown Algae, Serpulse, and other organisms, 

 which prevent in some cases the further wearing away of the whole 

 ledge, protecting its most exposed parts. The sea breaking upon the 

 upper surface of the ledge soon forms the more or less regular serpuline 

 atolls and "boilers" of the south shore which will be described later on. 

 They are found on all the breakers on the outer side of the reef ledge 

 flats, like Mills Breaker, the North Rock, and others ; serpuline reefs 

 extend off the headland on the west of Church Bay. The Southwest 

 Breaker is the westernmost of the line of serpuline reefs skirting the 

 south shores. It has three " boilers " on it, a long one and two smaller 

 ones, with a small serpuline atoll to the southwest of the main ledge. 



There are on the eastern part of Castle Harbor itself a number of 

 ledges coming to within a foot or two of the low-water mark. They 

 are covered with corals and Gorgonians, Algse and Corallines. The Gor- 

 gonians are not very flourishing, but the Nullipores and Alga? grow in 

 abundance between the massive corals. The patches are separated by a 

 fine sandy bottom. On the outside of Castle Harbor there are many 

 coral patches, boilers, and ledges extending outward of the outer ledge, 

 to a depth of from seven to eight fathoms, with an occasional ledge 

 rising from ten fathoms (Plate XXL). But, as a rule, outside of the 

 outer reef ledges we come upon the " broken ground." 



The line of reefs to the south of the island extends unbroken from 

 St. David Head to off High Point. The ledges are all reolian shore 

 cliffs which have become separated from the island by the action of the 

 sea, then beaten away, abrad?d and eaten into by the surf, and, accord- 



