1836.] GEOLOGY OF THE ISLAND. 479 



classes. It was strange to my ears to hear a man, nearly 

 white and respectably dressed, talking with indifference of 

 the times when he was a slave. With my companion, who 

 carried our dinners and a horn of water, which is quite 

 necessary, as all the water in the lower valley is saline, I 

 every day took long walks. 



Beneath the upper and central green circle, the wild 

 valleys are quite desolate and untenanted. Here, to the 

 geologist, there were scenes of high interest, showing 

 successive changes and complicated disturbances. Accord- 

 ing to my views, St. Helena has existed as an island from 

 a very remote epoch ; some obscure proofs, however, of the 

 elevation of the land are still extant. I believe that the 

 central and highest peaks form parts of the rim of a great 

 crater, the southern half of which has been entirely removed 

 by the waves of the sea : there is, moreover, an external 

 wall of black basaltic rocks, like the coast-mountains of 

 Mauritius, which are older than the central volcanic 

 streams. On the higher parts of the island, considerable 

 numbers of a shell, long thought a marine species, occur 

 embedded in the soil. It proves to be a Cochlo^ena, or 

 land-shell of a very peculiar form ;* with it I found six 

 other kinds ; and in another spot an eighth species. It is 

 remarkable that none of them are now found living. Their 

 extinction has probably been caused by the entire destruction 

 of the woods, and the consequent loss of food and shelter, 

 which occurred during the early part of the last century. 



The history of the changes, which the elevated plains of 



Longwood and Deadwood have undergone, as given in 



General Beatson's account of the island, is extremely 



curious. Both plains, it is said, in former times were 



covered with wood, and were therefore called the Great 



Wood. So late as the year 1716 there were many trees, 



but in 1724 the old trees had mostly fallen ; and as goats 



1 hogs had been suffered to range about, all the young 



('s had been killed. It appears also from the official 



ords, that the trees were unexpectedly, some years 



('rwards, succeeded by a wire grass, which spread over 



tiic whole surface. t General Beatson adds that now this 



I I lin "is covered with fine sward, and is become the finest 



It deserves notice, that all the manv spccimcnB of thi« shell found by nir in 

 spotj difTcr, fi« a marked variety, from another set of sprciinens prcn nrrxJ 

 1 a different spot. 

 Hcaison'a "St. Helena." I ntroductor>' chapter, p 4. 



