HIS<rORr of the SOCIETT. i 



MINERALOGY. 







1803. 



The Reverend Dr William Richardson, late F. T. C. D., 



March 1 



having fent to Dr Hope a collection of fpecimens from the north- Remarks on the 



ern coaft of Antrim, with a catalogue, and obfervations, the fpe- coaVof A«. e 

 cimens were exhibited, and the obfervations were read in the 

 Royal Society, March 1803. 



SILICEOUS BASALT. . 



Dr Richardson difcovered the foflil to which he gives this 

 name in the peninfula of Portrulh, four or five years ago. It 

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

 ing from the northern point of Portrufh-head for about a 

 mile eaflward. A fmall part of every one of thofe iflots is form- 

 ed of this ftone, while the remainder confifts of coarfe bafalt, 

 fimilar in all refpecls to that on the eafl fide of the above-men- 

 tioned peninfula. It is met with in one or two other places. 



This llone is arranged in ftrata, from ten to twenty inches 

 thick, all fleadily parallel to one another, and every flratum, as 

 far as can be obferved, preferving an uniform thicknefs through 

 its whole extent. When thefe ftrata are quarried into, they ap- 

 pear to be conftrucled of large prifms, generally pentagonal, 

 which when broken divide into fmaller prifms. This internal 

 prifmatic connTuction frequently gives an irregular or fhivery 

 appearance to the fracture, 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 impreilions of corttua 

 ammonis. The flat fhells and impreilions contained in thefe 

 Clones are fleadily parallel to each other, and perpendicular to 

 the axis of the prifms. It muft be obferved, that the prifmai ic 

 conflruclion is never interrupted by the fhells difperfed through 



Vol. V.— P. III. G it; 



