27 



The fixth Whynn Dyke is at Port Spagna, the third femicircular bay 

 eaft from the Caufeway ; this is the only one of our Whynn Dykes that 

 has ever yet been noticed. Mr. Mills, (Phil. Tranf. 1790,) faw from 

 the top of the cliff a kind of a Whynn Dyke, which ran into thefea 

 towards the N. N. E ; but he did not go down to examine it, and it 

 is from below only that any obfervations can be made upon it. 



This Dyke runs into the fea, like a quay about twenty feet broad, 

 formed of huge black ftones ; its direftion near the water is S. S. V/. 

 and its two fides accurately parallel ; having proceeded thus about fixty 

 yards from the water, the eaftern fide deflefts a little, forming an obtufc 

 angle, while the weftern fide proceeds farther in its former direftion ; 

 the breadth of the Dyke thus encreafes for a little, but the weftern fide 

 is foon refuraed parallel to, and at its former diftance from the other 



( D 2 ) fide 



Tiie upper furface of this tremendous wall is eafily approached from the top of the hill, 

 and covered with high verdure ; I have frequently dined upon it, as fortunately the fur- 

 face is hollow in the middle, by which the dread of a perpendicular precipice, above 

 two hundred feet high, (and on three fides not more than eight or ten feet diftant) is 

 confiderably abated ; the height of the point of the wall from the fea immediately 

 under it is three hundred and twenty feet. 



1 dwell upon this Dyke both becaufe it is fo eafy of accefs from above, (for even 

 carriages can drive to the edge of the cliff ) and alfo becaufe it is fo happily marked as 

 not to be miftaken ; it forms the middle point between the Giant's Caufeway and the fo- 

 litary pillar called the Chimney, or in other words the common horn of the two cref- 

 cents or femicircular bays next to the Caufeway on the eafl: fide. 



I will add an account of another Dyke lately difcovered by my friend Capt. R. O'Neil ; 

 it is fituated three or four hundred yards N. W. from the beautiful villa called Seaport 

 on Port Ballinftay, a mile and a half weft from the Giant's Caufeway. 



The face of the precipice here feems about fifty feet high, eompofed of horizontal ftrata 

 ofcoarfe bafaJt or trapp, abounding with zeohte, and, of a reddifli tinge, friable, and de- 

 compoCng ; all thefe ftrata, from the fummit to the fea, are cut through obliquely at an 

 angle of about forty five degrees, by a Dy, of found blue bafalt, very fine at its edges, but 

 coarfer in the middle, and nearly five feet thick ; the fine bafalt of this Dyke and the coarfe 

 trapp of the ftrata, notwithftanding the difference of their grain, unite folidly on both fides 

 of the Dyke ; this important faifl is more eafily afcertained here, than in any other Dyke 

 I know, it is fo acceflible; I muft obferve, that this Dyke is not accurately reflilineal. 



