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" fliort, from the very rude and irregular appearance of the fum- 

 " mit of the hill (LofEt Hill), from its rifing fo fuddenly from the lime- 

 •' ftone flrata, and from the Whynn Dyke that runs through it, I am 

 *' (Irongly inclined to believe it of volcanic origin." Now, as lime- 

 ftone and volcanic matters are not very congenial, and as we do 

 not find that a Whynn Dyke has been met with in the neighbour- 

 hood of any volcano, I conceive, with great deference to Mr. Mills, that 

 if he was determined to draw a conclufion from thefe data, it fhould 

 have been a contrary one. But it is time to proceed to fadts. 



The wefternmoft Whynn Dyke I have met with on our coaft, is near 

 what is called the Black Rock, at the end of the Bufli Strand. The 

 perpendicular precipice is there not very high (probably fixty feet), it 

 is compofed of horizontal flrata of table bafalts, feparated from each 

 other by red ochreous layers. 



The Dyke, (which is inacceflible) is feen from the water to cut all 

 thefe ftrata vertically, each of them being interrupted in its courfe by 

 this wall, and refumed on the other fide of it, precifely at the fame 

 level. 



The fecond Dyke is three or four hundred yards farther on, towards 

 the north-eaft ; it is a much finer one, and fo happily marked that it 

 cannot be miflaken. 



A folitary rock, about two hundred yards diftant from the main, and 

 vifible from a great part of the coafl on each fide, is called the Mile Stone, 

 from its fuppofed diftance from the Giant's Caufeway, but in reality it 

 is much nearer to it. The precipice here has confiderably encreafed in 

 height, being near to one hundred feet, accurately perpendicular, and 

 ^ratified as at the other Dyke. 



This fecond Dyke reaches from the fummit to the water, beneath 

 which we can fee it continued northwards, until it reaches the Mile- 

 flone, which is a part of it. 



Though this Dyke be alfo inaccefifible, it is plainly formed of prifms laid 

 horizontally, and extending quite acrofs ; it its thicknefs feems to be 

 about twelve feet. 



The 



