ON ITS EXTERIOR. VOLCANOES. 385 



ception of the small basaltic group of Gambler and 

 Pitcairn islands. ( 52G ) Volcanic rock, as in these last, 

 is also found in the same parallel (between 25 and 27 

 S.) 1260 geographical miles more to the eastward in 

 Easter Island (Waihu), and probably also 240 miles 

 further, in the Sala y Gomez rock. On Waihu, where 

 the highest conical summit is only about 1000 feet 

 high, Captain Beechey observed a range of craters, none 

 of which, however, appeared to be burning. 



The islands of the Pacific at their extreme eastern 

 termination on the side of the American continent con- 

 clude with the group of the Galapagos; one of those 

 in which volcanic activity is most developed. Scarcely 

 anywhere in so small a space, barely 120 or 140 geogra- 

 phical miles in diameter, have so many conical mountains 

 and extinct craters (traces of ancient communication be- 

 tween the interior and the atmosphere) remained visible. 

 Darwin estimates the number of craters at almost 

 2000. When he visited these islands in the expedition 

 of the Beagle under Captain Fitz-Roy, two craters were 

 simultaneously in fiery eruption. In all the islands, 

 streams of very fluid lava may be seen separating into 

 branches, and often reaching the sea. Almost all are 

 rich in augite and olivine, and some which are more 

 trachytic are said to contain albite ( 527 ) in large crystals. 

 It would be well in the present state of improved mine- 

 ralogical knowledge to examine whether these porphy- 

 ritic trachytes do not contain oligoclase, as at Teneriffe 

 and in Popocatepetl and Chimborazo ; or labradorite, as 

 in Etna and Stromboli. Pumice is entirely wanting in 

 the Galapagos, as in Vesuvius, as a production of the 

 volcano itself ; neither is hornblende ever mentioned as 



VOL. iv. C c 



