CHAP. Y. 



Altered Tuff. 



in 



in size from mere spiracles to huge caldrons several 

 miles in circumference ; they are extraordinarily 

 numerous, so that I should think, if enumerated, they 

 would be found to exceed two thousand ; they are 

 formed either of scorias and lava, or of a brown coloured 

 tuff; and these latter craters are in several respects 



Culpepper 7. 



Wenman I. 



No. 11. 



60 Miles 



Narhorough Z,i® 



Albemarle I, 



I Abingdon I. 



^ 



Towerl. 



Indefatigable /. 



* Chatham 1. 



Barnngtonl. 



Charles I. 



GALAPAGOS ABCHIPBLAOO. 



Hoods I. 



remarkable. The whole group was surveyed by the 

 officers of the Beagle. I visited myself four of the 

 principal islands, and received specimens from all the 

 others. Under the head of the different islands I will 

 describe only that which appears to me deserving of 

 attention. 



Chatham Island. Craters composed of a singular 

 Icind of tuff. — Towards the eastern end of this island 



