2.»0 Geology — Si. Helena, 



and the 1 1th stratum counting from the water at Bengore pro- 

 montory: — in the debris from this stratum, both at Portmoon, 

 and near the causeway, on its west side, I find such cavities; but 

 at the causeway itself, or its more contiguous strata, I never found 

 either water or internal cavity: — at St. Helena this singular fact 

 also occurs, but seems still more rare — " In a quarry, the stone 

 when broken is found to have many large internal cavities, 

 which contain a pure and wholesome water, shut up in the body 

 of the rock." 



The most striking feature of resemblance between the basaltic 

 districts of St. Helena and Antrim, i? to be found in the whyn 

 dvkes, so common to each ; — these mighty walls, which seem 

 peculiar to basaltic countries, though thev are often found to 

 extend and diverge into districts formed of dinerent materials, 

 eeem to have excited little notice until very modern times : even 

 Dr. Hamilton, in his celebrated Letters, which gave the first philo- 

 sophical account of our curious coast, very slightly notices those 

 contiguous to Ballycastle ; letting all the others issuing from the 

 precipices on the ea^t and west of the Giant's Causeway, and 

 burving themselves in the rea, entirely escape him, though more 

 magnificent nnd more decidedly marked than those he ni'^n- 

 tions; nor did he examine in those he notices their singular in- 

 ternal construction, the consummate regularity of their masonry, 

 not less wonderful than their external wall-like forms. 



I have ahvav", considered our whyn dykes as more curious 

 than our prismatic and columnar groups, which seem hitherto 

 to have absorbed most of the attention given to our wonderful 

 coast; — regular internal arrangement is not peculiar to basal tes, 

 nor are the vertical prisms and pillars forming our magnificent 

 colonnades more v/onderf'i! than the ecjually regular horizontal 

 prisms of which our vvhvn dykes are constructed. 



For an account of the whyn dykes on our Antrim coast, I 

 must refer to the Transactions of the Royal Irish Academy for 

 the year 1S02. These dykes, when I gave in my Memoir on 

 that subject, I thought sufhciently grand; but how insignificant 

 do thev now appear, when compared with the St. Helena dvkes, 

 or with those more recently discovered on the rocky mountains, 

 the range that divides the vast American continent, the divnrtia 

 aquamm whence the waters are poured from their elevated 

 sources in opposite directions to the Atlantic and Pacific oceans, 

 at a distance of some thousand miles ! 



Of tlie grandeur of tlie latter dykes we have sufficient evidence, 

 but want particulars; the St. Helena dykes are well described 

 by our author ; he calls them " huge vertical strata of broken 

 and fi«;sured rock, which traverse the whole, from the base to the 

 summit." 



I must 



