XX. 



Account of Jbme Specimens of Bafaltes from the northern Coaft 

 of Antrim. JSj/ the Rev. Dr. William Richaudson.* 



1 HE Reverend Dr. William Richardfon, late F. T. C. D. Remarks on the 

 having fent to Dr. Hope a colledion of (pecimens from the ^^^^'^'^^^^J)* 

 northern coaft of Antrim, with a catalogue and obfervations, trim, 

 the fpecimens were exhibited, and the obfervations vs'ere 

 read in the Royal Society, March 1803. 



Siliceous Bafalt, 



Dr. Richardfon dlfcovered the foffil to which he gives this 

 name, in the peninfiila of Portrufli, four or five years ago. 

 Ijt abounds alfo in the Skerry iflands, a reef of rocky iflots 

 extending from the northern point of Portrufli-head for about 

 a nrile eaftward. A fraall part of every one of thofe iflots 

 is formed of this ftone, while the remainder confifts of coarfe 

 bafalt, fimilar in all refpedls to that on the eaft fide of the 

 above-mentioned peninfula. it is met with in one or two 

 other places. 



This fione is arranged in flrata, from ten to twenty Inches 

 thick, ,all fleadily parallel to one another, and every ftratum, 

 as fiar as can be obftrved, preferving an uniform thicknefs 

 through its whole extent. When tbefe ftrata are quarried 

 into, they appear to be conftru6ied of large prifms, generally 

 pentagonal, which when broken divide into fmaller prifms. 

 This internal prifmatic conftrudion frequently gives an irre- 

 gular or (hivery appearance to the fraflure, which however 

 is often conchoidal, and the grain as uniform as in the Giant's 

 Caufeway bafaltes. 



The beds of this foflil are remarkable for containing marine 

 exuviae in great abundance, particularly impreffions of cornua 

 ammonis. The flat (hells and impreffions contained in thefe 

 Hones, are fteadily parallel to each other, and perpendicular 

 to the axis of the prifms. It mufl be obferved, that the prif- 

 matic conftrudion is never interrupted by the ftiells difperfed 

 tjirough it ; the planes which feparate (he prifms palling 

 equally through the (hells and the ftone itfelf. 



♦ Edinburgh Tranf. Vol. V. 



Th« 



