370 Account of the Whynn Dykes in the 



direction, is lost under the rubble that has fallen from 

 above; but whenever the precipice becomes perpendicular, 

 it appears again in its last directron, cutting the strata v^t- 

 tically from the bottom ot the precipice to the top, above 

 200 feet ; the height ot the upper part of the cliff above 

 Uje se?i is here 330 feet. 



These strata are almost all columnar, and the horizontal 

 prisms of the dyke are strongly contrasted with the vertical 

 pillars of the strata. 



The basalt ot this dyke is very nearly of the same grain 

 with that of the dyke at the Causeway, rather coarser, its 

 fracture granular, and full of shining points ; but it differs 

 materially from it in another respect^ the latter having but 

 one principle of construction, to wit, the njinute prisms 

 into which it breaks, and the agglutination of these form- 

 ing it into a mere wall ; while the dyke at Port Spagna 

 has, like some other varieties of our basalt, a double prin- 

 ciple of construction, being first formed into huge massive 

 prisms four and five feet in diameter, and these again being 

 divided into small quadrangular prisms whose sidfcs do not 

 ' exceed an inch. 



This property possessed by some varieties of our basalt, 

 and other curious circumstances attending them, — as for 

 instance, that some of our prismatic basalt in thin strata 

 abound with marine exuvise, shells, and impressions of 

 cornua ammcnis*, while others, columnar and prismatic, 

 but not articulated, and others columnar, prismatic, and 

 articulated, coiitain cavities full of ftvsh water to the 

 amc'unt of a thimble-full : all these facts have hitherto 

 escaped notice. 



Naturalists, who visit our coast, rarely allow themselves 

 time enough to examine any thing, and, while there, are 

 occupied in looking for arguments to support the theory 

 they patronize, not in studying nature for information : 

 they never examine any of our basalts but that of the Giant's 

 Causeway ; this, it is true, has none of the properties I 

 mention, it has but one principle of construction, to wit, 



* The nature of this stone is, I know, not yet fully ascertained. Sir 

 Joseph Banks informe nie, that the specimens 1 sent to him are pronounced 

 by his friends not lo be grnm/!€ or legitimate basalt. An eminent Scotch 

 naturalist, who -visited the spot last summer, I am told, asserts this stone to 

 Lc chi.' • t. petrcfiitx or arkislus. 



On the other bide, Mr. Kirwan, to whom I gave specimens, asserts in a 

 late publication, that it is br.salt: our ingenious Mr. Hig-gins is of the same 

 opinion, and tne celebrated Professor Pictet of Geneva, who did me the 

 Jbcnour of a visit last summer', considers it to be basalt containing a greater 

 portiou of siUx thau usual, 1 believe Mons. Pictet is right. 



the 



