chap.it. Central Curved Ridge. 95 



projecting in the form of a cylinder or circular 

 parapet. 



From the points of structure in the central ridge, 

 now enumerated, — namely, from the convergence to- 

 wards it of the beds of the upper series, — from the 

 lavas there becoming highly cellular, — from the flat 

 ledge, extending along its inner and precipitous side, 

 like that within some still active craters, — from the 

 parapet-like wall on its summit, — -and lastly, from its 

 peculiar curvature, unlike that of any common line of 

 elevation, I cannot doubt that this curved ridge 

 forms the last remnant of a great crater. In endeavour- 

 ing, however, to trace its . former outline, one is soon 

 baffled ; its western extremity gradually slopes down, 

 and, branching into other ridges, extends to the sea- 

 coast ; the eastern end is more curved, but it is only 

 a little better defined. Some appearances lead me to 

 suppose that the southern wall of the crater joined the 

 present ridge near Nest Lodge ; in this case the crater 

 must have been nearly three miles long, and about a 

 mile and a half in breadth. Had the denudation of 

 the ridge and the decomposition of its constituent 

 rocks proceeded a few steps farther, and had this rido-e, 

 like several other parts of the island, been broken up 

 by great dikes and masses of injected matter, we should 

 in vain have endeavoured to discover its true nature. 

 Even now we have seen that at Flagstaff Hill the 

 lower extremity and most distant portion of one sheet 

 of the erupted matter has been upheaved to as great a 

 height as the crater down which it flowed, and pro- 

 bably even to a greater height. It is interesting thus 

 to trace the steps by which the structure of a volcanic 

 district becomes obscured, and finally obliterated : so 

 near to this last stage is St. Helena, that I believe no 

 one has hitherto suspected that the central ridge or 



