iS4 CORALS AND CORAL LS LANDS. 



in the map), called North Rock. It is broken into a hundred 

 and fifty or more islets — in consequence partly of degradation 

 since the elevation, and partly of the unequal height of the 

 reef formation before its elevation. The surface is made up of 

 hills and low basins. The highest point, Sears' Hill (E), is, 

 according to Lieut. Nelson, 260 feet in elevation above the sea, 

 and Gibbs Hill (D), the site of the lighthouse, 245 feet. 

 Wreck Hill (F), near the western point of the principal island, 

 is about 150 feet high, and North Rock is 16 feet high. H is 

 the position of Hamilton, the seat of Government, and G of 

 St. George's, the other principal town. A (Castle Harbour), B 

 (Harrington Sound), and C (Great Sound), are three encircled 

 bays, looking as if once the lagoons of sub-atolls in a Maldive- 

 like compound atoll. The surface about half way between the 

 sounds A and B is low. Most of the land is covered with 

 cedar-trees, where not cultivated or given over to loose sand. 



The rock of the surface is described as a calcareous sand- 

 rock, analogous evidently to the beach sand-rock and drift 

 sand-rock. Toward the shores the solid reef-rock outcrops — a 

 hard, white limestone. Lieut. Nelson speaks of that on St. 

 George's Island as a " very hard, fine-grained or compact 

 limestone, in which scarcely a vestige of organic structure is 

 to be seen." In one place he observed a Mseandrina (Diploria) 

 four feet above high-tide level. 



The soil is calcareous, modified by vegetation, and in part, 

 according to Lieut. Nelson, " a dry, aluminous earth." The 

 same observer mentions the occurrence on the land of oxide of 

 iron and manganese, and of some titanic iron; but Mr. J. 

 Matthew Jones states {Canadian Naturalist^ Feb. 1864) that 

 all stones not of coral and shell origin have undoubtedly been 

 l)rought in the roots of drift-trees ; and the West Indies were 

 probably their source. 



The greater part of the old atoll is still a submerged reef. 

 Its outer border is mostly from one to three fathoms under 

 water at low tide, though in some parts laid bare at the ebb. 

 It has open channels at a (called the Chub cut), b (Blue cut, 

 shallow), c (N. W. Channel), d (N. £. Channel), e (Mills' 



