374 coSxMos. 



and Asia. There is a feldspathic rock on the small islands 

 of Borabora and Maurua, near Tahiti, designated by late 

 travelers with the name of syenite, and by Ellis in his Poly- 

 nesian researches described as a granitic aggregate of feldspar 

 and quartz, which, on account of the breaking out of porous, 

 scoriaceous basalt in the immediate neighborhood, merits a 

 much more complete mineralogical investigation. Extinct 

 craters and lava streams are not now to be met with on the 

 Society Islands. The question occurs : Are the craters on 

 the mountain tops destroyed; or did the high and ancient 

 structures, now riven and transformed, continue closed at the 

 top like a dome, while the veins of basalt and trachyte poured 

 immediately forth from fissures in the earth, as has probably 

 been the case at many other points of the sea's bottom? Ex- 

 tremes of great viscidity or great fluidity in the matter poured 

 out, as well as the varying width or narrowness of the fis- 

 sures through which the effusion takes place, modify the shapes 

 of the self-forming volcanic mountain strata, and, where fric- 

 tion produces what is called ashes and fragmentary subdivis- 

 ion, give rise to small and for the most part transitory cones 

 of ejection, which are not to be confounded with the great 

 terminal cinder-cones of the permanent structural frames. 



Close by the Society Islands, in an easterly direction, are 

 the Low Islands, or Paumotu. These are merely coral isl- 

 ands, with the remarkable exception of the small basaltic 

 group of Gambier's and Pitcairn's Islands.* Volcanic rock, 

 similar to the latter, is also found in the same parallel (be- 

 tween 25° and 27° south latitude), 1260 geographical miles 

 farther to the east, in the Easter Island (Waihu), and proba- 

 bly also 240 miles farther east, in the rocks Sala y Gomez. 

 On Waihu, where the loftiest conical peaks are scarcely a 

 thousand feet high, Captain Beechey remarked a range of 

 craters, none of which appeared, however, to be burning. 



In the extreme east, toward the New Continent, the range 

 of the South Sea Island terminates with one of the most act- 

 ive of all island groups, the Archipelago of Galapagos, com- 

 posed of five great islands. Scarcely any where else, on a 

 small space of barely 120 or 140 geographical miles in diam- 

 eter, has such a countless number of conical mountains and 

 extinct craters (the traces of former communication between 

 the interior of the earth and the atmosphere) remained visi- 

 ble. Darwin calculates the number of the craters at nearly 

 two thousand. When that talented observer visited the Gala- 



* Dana, p. 137. 



