GEOGRAPHICAL DISTRIBUTION. 259 



equator; and the seas of the Galapagos also grow no coral. 

 The northward deflection of the coral boundary line accounts, 

 as has been shown, for their absence. In the Bay of Panama, 

 and elsewhere on the coast, north and south, corals occur in 

 patches, but there are no reefs. There are corals also at La 

 Paz, near the extremity of the peninsula of California (p. 86). 



In Captain Colnett's voyage, allusion is made to a beach of 

 coral sand on one of the Revillagigedo Islands, in latitude 18°; 

 besides this statement we have met with no allusion to corals 

 on any of the islands off the Mexican coast. 



Between the South American coast and the Paumotus are 

 two rocky islands, Easter or Waihu, and Sala-y-Gomez, both of 

 which are stated to be without reefs. 



Captain Beechey mentions, however, that at forty-one 

 fathoms, near Sala-y-Gomez, he found a bottom of sand and 

 coral. 



The Paumotus commence in longitude 130° W., and em- 

 brace eighty coral islands, all of which, excepting about eight 

 of small size, contain lagoons. Besides these, there are, near 

 the southern limits of the archipelago, the Gambier Islands and 

 Pitcairn, of volcanic or basaltic constitution. The former in 

 23^ S., have extensive reefs. About the latter, in 25° S., there 

 are some growing corals, but no proper reefs. 



The Marquesas, in latitude 10" S., have but Httle coral 

 about them ; and this is the more remarkable, since they are 

 in close proximity to the Paumotus. But their shores are 

 mostly very abrupt, with deep waters close to the rocks. An 

 island which, before subsidence has commenced, has some 

 extent of shallow waters around, might have very bold shores 

 after it had half sunk beneath the waves. This would be the 

 case with the island of Tahiti ; for its mountain declivities are, 

 in general, singularly precipitous, except at the base. The 

 Marquesas may, therefore, have once had barrier reefs, which 

 were sunk from too rapid subsidence ; and afterward, on the 

 cessation of the subsidence, others failed to form again on 

 account of the deep waters. 



The Society Islands have extensive coral reefs with distant 



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