GEOLOGY. 239 



arranged in linear directions, like the summits of mountain ranges. 

 " Could we," says our author, " take a birdseye view over the 6,000 

 miles between New Holland and Mexico, we should see some of the 

 most extensive mountain chains in the world; the Samoan, stretching 

 over its 3,800 miles, the Hawaiian its 2,000, and others no less re- 

 markable, all preserving a systematic regularity which seems even to 

 exceed the systematic regularity of continental chains. The height of 

 summits in these chains, measured from the bottom of the ocean, 

 would exceed the most majestic peaks of the Himalaya range. Even 

 allowing but three miles for the depth of the sea near Hawaii, 

 Mount Loa will stand 30,000 feet above its base." 



The islands of the Pacific are either coral, or basaltic (which in- 

 cludes the volcanic), or continental, i. e. of a mixed character, like 

 continents. The coral islands number about 290 ; the basaltic about 

 350, not counting the many green spots large enough for a village 

 site, or a grove of palms, which occur on the reefs that surround the 

 high islands. The principal coral islands are the large archipelago 

 northeast of the Society Islands, called the Paumotu group, and the 

 Carolines; though there are many single ones scattered over the 

 ocean, and reefs of coral about most of the principal islands. 



Coral reefs are barriers of coral rock, varying from a few hundred 

 feet to miles in width, extending around other islands, sometimes con- 

 tinuously, at others broken, and at irregular distances from shore. 

 Generally there is an outer and an inner reef; these are termed the 

 barrier and the fringing reef. The barrier reefs rise usually but a 

 little above low-tide level; sometimes there is shallow water for two 

 or three miles beyond them, but more frequently the ocean is un- 

 fathomable within a few hundred feet of them. The exposed edge ia 

 a few inches higher than the general surface, and presents a smooth, 

 water-worn appearance, as might be expected from its never-ending 

 conflicts with the long surges of the Pacific. Sometimes the outer 

 reefs accumulate coral fragments and sand, until they widen into 

 islands. The coral of the reef rock is not found in its original position 

 of growth ; it is composed of the debris of coral consolidated by a 

 calcareous cement, and often contains, besides corals, shells and fossils 

 of the seas where it is found, resembling in appearance the limestone 

 of the neighborhood of Cincinnati and the Falls of the Ohio. 



Within the outer reefs, corals are found growing in their greatest 

 perfection. These inner reefs bear great resemblance to the outer in 

 structure, though their forms are much less modified by the action of 

 the waves. " There are many regions, in the Feejees examples are 

 common, where a remote barrier incloses as pure a sea as the ocean 

 beyond, and the greatest agitation is only such as the wind may excite 

 on a narrow lake or channel." Generally, the rock of these inner 

 reefs is composed of coral, which stands as it grew, less fragmentary 

 than the outer, but united by a solid cement. Upon its surface the 

 limits of the constituent masses may be often distinctly traced. The 

 corals grow underneath the surface in solid hemispheres, but when 

 the surface is reached the top dies, and enlargement only goes on at the 

 sides. " Some individual specimens of Porites in the rock of the 



