1J'A5A.1,TE6. ^S9 



Whinftone Dikes on the Coajl of Antrim. Rirmaiks on the 



v\ i>- 1 1/- 1 /• -1 , -1 • I -I bafaltes of tht; 



ur. Kidiardloii delcnbes lome particulars in the conltruc- ^.^^^^ ^f^^^^^^jj,,^ 



Uon of the whinftone dikes on tlie coaft of Antrim, which ap- 

 pear fingular, and deferving of attention. Thefe dikes, he 

 tays, are uniformly formed oF larj^e maffive prifms laid hori- 

 !/on(ally, which afe always divifible into fmaller prifms that are 

 likewife horizontal. To prevent confiifion, he calls the (irft of 

 thefe component prifms, and the fecond, or fmaller ones into 

 which the others break, confiituent prifms. 



The component prifms are fometimes of enormous iize, and^ 

 HI (he fame dike are nearly equal ; the conftituent prifms are 

 Imali, (the fides about an inch long), and neatly formed. 



The dike which traverfes the Giant's Caufeway, differs from 

 thofe on other parts of the coafl, by having no component 

 prifms. It refembles a plain wall, of which the parts fhiver 

 under the hammer into very neat confiituent prifms. In the 

 dike at Seaport the fame thing is obierved ; the prilmatic Itruc- 

 Jure doss not penetrate two inches from its edge; the whole 

 interior feemsan amorphous mafs. 



The fpecimens of this latter dike, fent to Dr. Hope, exhibit 

 its continuity with the adjacent bafattic rock which it traverfes, 

 and alfo the continuity of the fine bafalt of its edge with the 

 granular done which compofes the middle of the dike. 



The dike of Port-coan is a very folid mafs, compofed of 

 floncs apparently round, and imbedded in a bafaltic parte, or 

 indurated mortar. The round ftones are formed of concentric 

 fpheres, like the coats of an onion ; they exceed a foot in di- 

 ameter, aod, together with the mortar by which they are united,, 

 they form a very corapafi and highly indurated rock. 



Beiides thefe large dikes. Dr. Ricllardlon remarks, that 

 veins from half an inch to an inch and a half thick, often cut 

 the bafaltic ftrata on that coaft in all diredions. The materials 

 of thefe veins are never the fame with the contiguous bai'alt, 



fioin the beds of tliis real bafalt, and pervaae thefuppofcd iiliceous 

 fpecies j feme of them connefting together the feparate beds of die 

 real bafalt; others dying away in Iknder ramifications; as they rife 

 through the inteiuofcd Ifratum. In no inftance is this reverfed s 

 The veins never pioeeed from what is called the Siliceous Bafalt. 

 It was farther obferved, that both the frafture and external furface 

 of this ftone exhibit a ftratified ftrufturc, in many inttances, which 

 nayer happens in the true bafaltes. 



but 



