no Galapagos Archipelago. paet i. 



CHAPTER V. 



GALAPAGOS ARCHIPELAGO. 



Chatham Island — Craters composed of a peculiar Mud of tuff — Small 

 basaltic craters, with hollows at their oases — Albemarle Island, fluid 

 lavas, their composition — Craters of tuff, inclination of their ex- 

 terior diverging stro.ta, and structure of their interior converging 

 strata — James Island, segment of a small basaltic crater ; fluidity 

 and composition of its lava streams, and of its ejected fragments — 

 Concluding remarks on the craters of tuff, and on the breached con* 

 dition of their southern sides — Mineralogical composition of the 

 rocks of the archipelago — Elevation of the land — Direction of the 

 fissures of eruption. 



This archipelago is situated under the Equator, at a 

 distance of between five and six hundred miles from 

 the west coast of South America. It consists of five 

 principal islands, and of several small ones, which 

 together are equal in area, 1 but not in extent of land, 

 to Sicily, conjointly with the Ionian Islands. They are 

 all volcanic : on two, craters have been seen in erup- 

 tion, and on several of the other islands, streams of 

 lava have a recent appearance. The larger islands are 

 chiefly composed of solid rock, and they rise with a 

 tame outline to a height of between one and four 

 thousand feet. They are sometimes, but not generally, 

 surmounted by one principal orifice. The craters vary 



1 I exclude from this measurement, the small volcanic islands 

 of Culpepper and Wenman, lying seventy miles northward of the 

 group. Craters were visible on all the islands of the group, except 

 on Towers Islaud, which is one of the lowest ; this island is, however, 

 formed of vo"toanic rocks. 



