CHAPTER IT. 



ST. HELENA. 



Lavas of the feldspathic, basaltic, and submarine series — Section Flag- 

 staff Hill and of the Barn — Hikes — Tw/h's Cap and Prosperous 

 Bays — Basaltic ring — Central crateriform ridge, with an internal 

 ledge and a parapet — Cones of phonolite — Superficial beds of cal- 

 careous sandstone — Extinct land-shells — Beds of detritus — Eleva- 

 tion of the land — Denudation — Craters of elevation. 



The whole island is of volcanic origin ; its circumference, 

 according to Beatson, 1 is about twenty-eight miles. 

 The central and largest part consists of rocks of a feld- 

 spathic nature, generally decomposed to an extraordi- 

 nary degree ; and when in this state, presenting a singu- 

 lar assemblage of alternating, red, purple, brown, yellow, 

 and white, soft, argillaceous beds. From the shortness 

 of our visit, I did not examine these beds with care ; 

 some of them, especially those of the white, yellow, 

 and brown shades, originally existed as streams of lava, 

 but the greater number were probably ejected in the 

 form of scorise and ashes : other beds of a purple tint, 

 porphyritic with crystal-shaped patches of a white, soft 

 substance, which are now unctuous, and yield, like 

 wax, a polished streak to the nail, seem once to have 

 existed as solid claystone-porphyries : the red argil- 

 laceous beds generally have a brecciated structure, and 

 no doubt have been formed by the decomposition of 



1 Governor Beatson's ' Account of St. Helena.' 

 5 



