HISrORT of the SOCIETT. ig 



fjiheres, Hke the coats of an onion ; they exceed a foot i n dia- 

 meter, and, together with the mortar by which they are united, 

 they form a very compact and highly Indurated rock. 



Besides thefe large dikes, Dr Richardson remarks, that 

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

 the bafaltic flrata on that coaft in all directions. The materials 

 of thefe veins are never the fame with the contiguous bafalt, 

 but are generally finer. At Portrufh is a large vein, and near 

 it a fmaller vein, not an inch thick, which, proceeding from be- 

 low, terminates in the folid rock before it reaches ihe furface. 



MISCELLANEOUS OBSERVATIONS. 



Some of the fpecimens in Dr Richardson's catalogue are 

 from a quarry in a mafs of bafalt at Ballylugan, two miles foutk 

 of Portrufla. This bafalt contains fmall cavities in its interior ;, 

 many of them full of frefli water, which gufhes out when the 

 ftone is broken by the hammer, as if it had been in a ftate 

 of compreffion. The ftone is fo hard, and flies fo in pieces^ 

 that Dr Richardson has not been able to colledl any of the 

 water for the purpofe of analyfis. 



The face of the quarry in which this variety of the bafalt is 

 found is ^bout 15 feet high, and is cut into a flratum, the 

 thicknefs of which is not yet afcertained. The rock is entirely 

 columnar, the pillars fomewhat fmaller than thofe of the 

 Giant's -Caufeway, lefs perfedl, not articulated, fometimes 

 bent, and varioufly inclined. The fides and the interior of 

 the pillars are full of cavities. In confequence of the obfervations 

 of Dr Hamilton and Mr Whitehurst refpefting the porous 

 texture of the air or bladder holes of the bafaltes of the Caufe- 

 way and its vicinity, Dr Richardson has examined a great va- 

 riety ; butin no inftance,. except this of Ballylugan, has he found 



canities,. 



