\ 



45 



The ftrata are interrupted here, and refumed again, without diftur- 

 bance, at the other fide, as before ; nor in either cafe does the flighteft 

 reparation appear where thefe Dykes meet the contiguous ftrata, all 

 forming one folid mafs. 



The third Dyke is fituated near the weflern point of the bay, by 

 which we begin to defcend to the Giant's Caufeway ; of this an ifolated 

 fragment alone remains, about one hundred feet long by fifty feet high ; 

 like the reft: it is compofed of rude prifms laid horizontally. 



Our fourth Dyke is at the Giant's Caufeway itfelf ; it divides ver- 

 tically part of the cliff, at the foot of which the caufeway is fituated, 

 and defcends quite down to it. 



The precipice is not perpendicular here, as at the other Dykes, by 

 which means our view of this one is partially interrupted ; there 

 is, however, enough of it laid bare, to afcertain its nature beyond a 

 doubt, and efpecially as it is compofed of horizontal prifms, a property 

 that feems efifential to all Whynn Dykes. 



Where this Dyke divides the upper part of the columnar ftratum 

 tvhich forms the Giant's Caufeway, the bafalt pillars on the weft fide 

 of It have fallen from their original vertical pofition, until they lean 

 forward almofl: horizontally j while on the eaft fide of the wall they 

 Aand fl:eadily vertical. 



The bafalt fepts, which frequently divide the fl:rata in mines, and 

 appear to be of the fame nature with our Whynn Dykes, are gene- 

 rally attended by a finking or fubfiding of the ftrata on one fide of 

 them, without difturbing the parallelifm of thefe ftrata. This too is the 

 cafe with our own Whynn Dykes at Fairhead ; but of the fix Dykes 

 at Bengore promontoi7 this fourth is the only one where any thing 

 like a fubfiding or deprefilon of the flrata can be obferved. 



This Dyke is fo accefiible, that we are enabled to examine its ma- 

 terial and internal conftrudlion, from which we are precluded in the 

 former cafes ; the bafalt of which this is compofed, though contiguous 

 to, or rather mixed with the Caufeway-pillars, is very different from 

 the Caufeway-bafalt, it is fomewhat coarfer, more granular in the frac- 

 ture, and though darker than the grey whynn-ftone of the Fairhead 

 Vol. IX. ( D ) pillars. 



