FOSSIL SHELLS. 133 



rising from the interior, near Longwood, obtain 

 a lively and variegated hue from an almost alter- 

 nate deposition of chalk and red- clay strata on 

 their exposed surfaces. Rocks of breccia also 

 obtain ; and the more arid hills on the coast are 

 covered with so much small cinders, clinkers, 

 lavas, &c., as renders the ascent of their acclivi- 

 ties not only difficult and fatiguing, but often 

 somewhat dangerous. On these rocky heights 

 I have frequently found large boulders of basalt, 

 which, on their exterior, present tokens of having 

 been exposed to an intense heat ; while their in- 

 terior contains vast numbers of small cells, each 

 containing a spherical, colourless, and transpa- 

 rent spar, apparently vitreous felspar. 



Amongst the most curious geological pheno- 

 mena this island affords, we may notice the 

 existence of the fossil shells of Helix dextra, on 

 the summit of a hill, and at the height of 1,900 

 feet above the level of the sea ; and the presence 

 of salt-water pools, and salt contained in caves, at 

 an elevation of more than seven hundred feet 

 above the ocean's level. 



The more valuable mineral productions are 

 several kinds of jasper, capable of being applied 

 to ornamental uses ; excellent gypsum, or plaster 

 of Paris ; rock-crystal ; and limestone ; which last 

 abounds in many parts, but chiefly at Sandy Bay. 



