40 Ascension. 



PAET I. 



CHAPTER III. 



ASCENSION. 



Basaltic lavas — Numerous craters truncated on the same side — ■ 

 Singular structure of volcanic bombs — Aeriform explosions — Ejected 

 gran [tie fragments — TrarJiytic rocks — Singular veins — Jasper, its 

 manner of formation — Concretions in jjumieeons tuff — Calcareous 

 deposits and, frondtscent incrustations on the coast — Remarkable 

 laminated beds, alternating with, and passing into obsidian — 

 Origin of obsidian — Lamination ot volcanic rocks. 



This island is situated in the Atlantic Ocean, in lat. 8° 

 S.j long. 14° TV. It has the form of an irregular triangle 

 (see accompanying Map), each side being about six 

 miles in length. Its highest point is 2,870 feet 1 above 

 the level of the sea. The whole is volcanic, and, from 

 the absence of proofs to the contrary, I believe of sub- 

 aerial orgin. The fundamental rock is everywhere of 

 a pale colour, generally compact, and of a feldspathic 

 nature. ■ In the 8E. portion of the island, where the 

 highest land is situated, well characterised trachyte, 

 and other congenerous rocks of that varying family, 

 occur. Nearly the entire circumference is covered up 

 by black and rugged streams of basaltic lava, with here 

 and there a hill or single point of rock (one of which 

 near the sea-coast, north of the Fort, is only two or 

 three yards across) of the trachyte still remaining 

 exposed. 



Basaltic rods. — The overlying basaltic lava is in 



1 < Geographical Journal,' vol. v. p. 213. 



