252 Geology — St. Helena , 



we suspect the latter, by diligent attention we may perhaps be 

 able to trace the eifect to the cause, and so be able to establish 

 the existence of these posterior operations^ and their manner of 

 acting. 



The striking difference between the present appearance of 

 St. Helena and the basaltic coast of Antrim, seems to consist in 

 the superior magnificence of the vvhyn dykes of the former, and 

 their exhibition of their real form of walls, by their immense ele- 

 vation above the surface in their proper shape — while our dykes, 

 as accurate walls as the other, and also of prodigious height, 

 rarely emerge from the stratified materials they cut through, so 

 as to show their real form of wall to a careless observer 5 yet in 

 some few instances they do exhibit themselves as actual walls, 

 rising above the surface, and pointing in the direction of the 

 greater remains of the wall, unequivocally displayed in the con- 

 tiguous facade, as at Port Cooan and Portnabaw. 



Another material difference occurs between St. Helena and 

 Antrim. — I have sustained that the latter has never been the 

 seat of volcanic fires, nor exhibits any marks of having been 

 acted upon by that powerful element; — while the marks of 

 dreadful combustion are imequivocal over the whole island of 

 St. Helena. Our author tells us : 



*' The structure of St. Helena seems to demonstrate that it 

 is the work of subterraneous fire." 



" The ancient seat of volcanic fires, and subterraneous explo- 

 sion." 



HoNV have these fires operated ? Not by that instrument we 

 call a volcano, whose mode of acting is quite familiar to us, ever 

 since Sir W. Hamilton has been so particular in his account of 

 ou: two great European volcanoes : — the combustion of St. He^ 

 lena has been general ; fire has acted violently upon its whole 

 surface, but its intensity seems gradually to abate as we ascend 

 from the water edge to the highest point of the island; at a low 

 level the matters are so scorched and scorified, as not to admit 

 degradation and decomposition into vegetable mould ; hence 

 the lower parts of the island are black and torrificd, naked and 

 barren, incapable of sustaining plants ; but as we ascend, vege- 

 tables bugin to appear ; and where the elevation is great, the 

 verdure becomes spendid. 



Thus we are told — " the exterior parts of the island, all round 

 where they border on the sea, present the appearance of a burnt 

 and scorified shell, black, rugged, and mouldering, without the 

 least trace of vegetation." 



" Some of the interior ridges of hills, which are much higher, 

 arc covered with verdure." 



*' The central ridge is covered to the summit with the most 



luxuriant 



