i8 HIS TORT of the SOCIETY 



WHINSTONE DIKES ON THE COAST OF ANTRIM, 



Dr Richardson defcribes feme particulars in the conftruc- 

 tion of the whinftone dikes on the coafl: of Antrim, which ap- 

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

 fays, are uniformly formed of large mafTive prifms laid hori- 

 zontally, which are always divifible into fcnaller prifms that are 

 likewife horizontal. To prevent confufion, he calls the firft of 

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

 the others break, ccnfiitncnt prifms. 



The component prifms are fometimes of enormous fize, and 

 in the fame dike are nearly equal; the conftituent prifms are 

 fmall, (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 fliiver 

 under the hammer into very neat conftituent prifms. In the 

 dike at Seaport the fame thing is obferved ; the prifmatic ftruc- 

 ture does not penetrate two inches from its edge ; the whole 

 interior feems an amorphous mafs. 



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

 continuity with the adjacent bafaltic rock which it traverfes, and 

 alfo the continuity of the fine bafalt o-f its edge with the granular 

 ftone which compofes the middle of the dike. 



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

 ftones apparently round, and imbedded in a bafaltic pafte, or 

 indurated mortar. The round ftones are formed of concentric 



fpheres, 



animals : That veins often iffue from the beds of this real bafalt, and pervade 

 the luppoled filiceous fpecies ; fome of them connefting together the fep^rate 

 beds of the real bafalt; others dying away in flender ramifications, as they rife 

 through the interpofed ftratum. In no inftance is this rt^verfed : Tlie veins never 

 proceed from what is called the Siliceous Bafalt. It was farther obferved, that 

 both the frafture and external furface of this flone exhibit a Itratified lhudure,.tn, 

 many inftances, which never happens in the true bafaltes. 



