odS 



FOEMATION OF COEAL EEEFS. 



[Ch. XLIX 



accumulation 



while the action of the breakers contributes to raise 



windward barrier.' ^ 



the 



in the Pacific, 



Previously to my adverting to the si,c.ns above enumerated 

 of a downward movement in the bed of the ocean, Dr. 

 MaccuUoch Captam Beechej, and many other writers had 

 shown that masses of recent coral had been laid dry at 

 various heights above the sea-level, both in the Red Sea, the 

 islands of the Pacific, and in the East and West Indies. 

 After describing thirty-two coral islands 

 Captain Beechey mentioned that they were alllormerof 

 living coral except one, which although of coral formation, 

 was raised about 70 or 80 feet above the level of the sea 

 and was encompassed by a reef of living coral. It is called 

 Ehzabeth or Henderson's Island, and is 5 miles in length 

 by 1 m breadth. It has a flat surface, and, on all sides 

 except the north, is bounded by perpendicular cliffs above 

 oO leet high, composed entirely of dead coral, more or less 

 porous, honeycombed at the surface, and hardening into a 

 compact calcareous mass, which possesses the fracture of 

 secondary hmestone, and has a species of miUepore inter- 

 Fig. 158, 



Elizabeth or Henderson's Island. 



spersed through it. These cliffs are considerably undermined 

 by the action of the waves, and some of them appear on the 

 eve of precipitating their superincumbent 



sea. 



Those which are less injured in this way present no 

 alternate ridges or indication of the difi'erent levels which 



a 



the sea might have occupied at difi'erent periods ; but ^ 

 smooth surface, as if the island, which has probably been 

 raised hj volcanic agency, had been forced up by one great 

 subterraneous convulsion.! At the distance of a few hun- 

 dred yards from this island, no bottom could be gained with 

 200 fathoms of line. 



It will be seen, from the annexed sketch, communicated to 



* See Principles of Geol, 1st. edit, 1832, vol. ii. p. 293. 

 t Beccliey's Voyage_to_tho Pacific, &c., p. 46. 



t 



