86 St. Helena. 



PART I. 



augite ; others are of a brown colour, either lami- 

 nated or in a rubbly condition ; and many parts are 

 highly amygdaloidal with calcareous matter. The 

 successive sheets are either closely united together, or 

 are separated from each other by beds of scoriaceous 

 rock and of laminated tuff, frequently containing well- 

 rounded fragments. The interstices of these beds are 

 filled with gypsum and salt ; the gypsum also sometimes 

 occurring in thin layers. From the large quantity of 

 these two substances, from the presence of rounded 

 pebbles in the tuffs, and from the abundant amygdaloids, 

 I cannot doubt that these basal volcanic strata flowed be- 

 neath the sea. This remark ought perhaps to be extended 

 to a part of the superincumbent basaltic rocks ; but on 

 this point, I was not able to obtain clear evidence. The 

 strata of the basal series, whenever I examined them, 

 were intersected by an extraordinary number of dikes. 



Flagstaff Hill and the Bam. — I will now describe 

 some of the more remarkable sections, and will com- 

 mence with these two hills, which form the principal 

 external feature on the north-eastern side of the island. 

 The square, angular outline, and black colour of the 

 Barn, at once show that it belongs to the basaltic 



No. 8. 



Flagstaff Hill. The Barn. 



2,272 feet high. 2,015 feet high. 



The double lines represent the basaltic strata ; the single, the basal submarine strata ; 

 the dotted, the upper feldspathic strata ; the dikes are shaded transversely. 



series ; whilst the smooth, corneal figure, and the 

 varied bright tints of Flagstaff Hill, render it equally 

 clear, that it is composed of the softened, feldspathic 



