430 Proceedings of the Royal Physical Society. 



as we could see, no olivine. About the north-east corner 

 of the island, among the basalt boulders which cover the 

 beach, there are a great number of masses of olivine crystals, 

 some of them measuring three inches in diameter. A curious 

 pale brown, cherty-looking mineral frequently occurs in the 

 form of veins among the phonolite. The phonolite probably 

 indicates the plugs of the orifices from which the most 

 ancient eruptions took place, as the columns, into which it 

 is everywhere cleft, usually lie inclined at a low angle, or 

 completely horizontal. It is really not at all of a slaty 

 nature, as some of the previous accounts indicated, but 

 distinctly columnar. The basalt occurs principally in sheets 

 with the main joints vertical. In some places, especially 

 towards the north-east, it shows the " cannon ball " method 

 of weathering very well, and in some others, as the East 

 Hills and the place known as Pedras Pretas, or Black Stones, 

 in the south-west, the jointing is quite irregular, and the 

 rock separates into large, angular, scarcely weathered frag- 

 ments, which make a perfect desert of black stones, with 

 cavities between them which go down to an astonishing 

 depth. The small patches of tuff are, I imagine, only the 

 remains of a much larger quantity which must have once 

 enveloped the phonolitic hills to their summits, and through 

 which the basalt subsequently burst. On Eat Island, as 

 also on Tobacco Point, there is a considerable deposit of 

 guano in the form of a brown powder ; it is now being worked, 

 but, not containing any ammonia, is said not to be of a high 

 class. 



The flora of the island is decidedly poor when compared 

 with that of Pernambuco. The seaward slopes to the east 

 and south-east, being continually swept by the trade winds, 

 produce only stunted bushes and herbage. The central region 

 has been mostly under cultivation, and so is now overgrown 

 with weeds. To the west, and, to a certain extent, along 

 the north coast, we have dense bush covered with trailers. 

 Here one principally meets with endemic plants. Trees of 

 any considerable size are few : it seems that the Governor 

 ordered all the larger ones to be cut down, as the convicts made 

 jiuDgadas of them, and so either escaped or were drowned in 



