XXI CHANGES IN THE VEGETATION 519 



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 

 valleys 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. According 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 con- 

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

 occur embedded in the soil. It proves to be a Cochlogena, 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 and hogs had been suffered to 

 range about, all the young trees had been killed. It appears 

 also from the official records that the trees were unexpectedly, 

 some years afterwards, succeeded by a wire grass, which spread 

 over the whole surface.^ General Beatson adds that now this 



' It deserves notice, that all the many specimens of this shell found by me in 

 one spot differ, as a marked variety, from another set of specimens procured from a 

 different spot. 



"^ Beatson's .5"/. Helena, Introductory chapter, p. 4, 



