90 St. Helena. 



PART I. 



injected whilst liquefied into the overlying strata; and 

 if we may suppose that a similar body of rock lies in- 

 jected, beneath the ridge connecting the Barn and Flag- 

 staff, the structure there exhibited would be explained. 

 Turk's Cap and Prosperous Bays. — Prosperous 

 Hill is a great, black, precipitous mountain, situated 

 two miles and a half south of the Barn, and composed, 

 like it, of basaltic strata. These rest, in one part, on 

 the brown-coloured, porphyritic beds of the basal series, 

 and in another part, on a fissured mass of highly scori- 

 aceous and amygdaloidal rock, which seems to have 

 formed a small point of eruption beneath the sea, con- 

 temporaneously with the basal series. Prosperous Hill, 

 like the Barn, is traversed by many dikes, of which the 

 greater number range north and south, and its strata 

 dip, at an angle of about 20°, rather obliquely from the 

 island towards the sea. The space between Prosperous 

 Hill and the Barn, as represented in this woodcut, con- 

 sists of lofty cliffs, composed of the lavas of the upper 



No. 9. 



Hold-fast-Tom. 



Flag-staff Hill. 



Prosperous Hill. The Barn. 



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

 the dotted, the upper feldspathic strata. 



or feldspathic series, which rest, though unconform- 

 ably, on the basal submarine strata, as we have seen 

 that they do at Flagstaff Hill. But differently from 

 what occurs in that hill, these upper strata are nearly 

 horizontal, gently rising towards the interior of the 

 island ; they are also composed of greenish-black, or 

 more commonly, pale brown, compact lavas, instead of 

 softened and highly coloured matter. These brown- 

 coloured, compact lavas, consist almosf entirely of small 



