chap. ii. St. Paul's Rocks. 2>7 



the Atlantic Ocean, nearly one degree north of the 

 equator, and 540 miles distant from South America, in 

 29° 15' west longitude. Its highest point is scarcely 

 fifty feet above the level of the sea; its outline is 

 irregular, and its entire circumference barely three- 

 quarters of a mile. This little point of rock rises 

 abruptly out of the ocean ; and, except on its western 

 side, soundings were not obtained, even at the short 

 distance of a quarter of a mile from its shore. It is 

 not of volcanic origin ; ami this circumstance, which is 

 the most remarkable point in its history (as will here- 

 after be referred to), properly ought to exclude it from 

 the present volume. It is composed of rocks, unlike 

 any which I have met with, and which I cannot charac- 

 terise by any name, and must therefore describe. 



The simplest, and one of the most abundant kinds, 

 is a very compact, heavy, greenish-black rock, having 

 an angular, irregular fracture, with some points just 

 hard enough to scratch glass, and infusible. This 

 variety passes into others of paler green tints, less hard, 

 but with a more crystalline fracture, and translucent on 

 their edges ; and these are fusible into a green enamel. 

 Several other varieties are chiefly characterised by 

 containing innumerable threads of dark-green serpen- 

 tine, and by having calcareous matter in their inter- 

 stices. These rocks have an obscure, concretionary 

 structure, and are full of variously-coloured angular 

 pseudo fragments. These angular pseudo fragments 

 consist of the first-described dark green rock, of a brown 

 softer kind, of serpentine, and of a yellowish harsh stone, 

 which, perhaps, is related to serpentine rock. There 

 are other vesicular, calcareo-ferrugmous, soft stones. 

 There is no distinct stratification, but parts are imper- 

 fectly laminated ; and the whole abounds with innu- 

 merable veins, and vein-like masses, both small and 



