.290 ORIGIN OF BASAIT. 



Facts and ob- t^ie basalt incumbent on the columnar at Bolsena, as given 

 scrvations re- by Ferber. It is obviously similar to tho§e at La Trezza 

 in the°county ^"^ T'ont du Baume ; and Mr. Mills's view of the isolated 

 of Antrim; ad- basaltic rock at Ardlun (Phil. Trans. 1790), accurately rer 

 duced to show , .1 • • .^ • r ■, 1 /-.• -> 



that it is not presents this variety, m many ta9ades, near tlie (jiants 



volcanic. Causeway. 



Sir Joseph Banks's account of the stratum, incumbent on 

 the columnar at Staffa, might serve for our irregular pris- 

 matic, in most places ; and the moment I shewed my friend, 

 Mr. Joy, our neat pillars at Craigahulier, he perceived 

 the striking likeness between the stratum, incumbent on Ihem, 

 and that covering the grand colonnade at Staffa. 



The slight accounts we have of the Scotch whyn dykes, 

 shew, that they are formed, like our own, of horizontal 

 prisms. 



And our globular basalts, with concentric spheres, so cu- 

 riously imbedded as we find them at Port Cooan, near the 

 Giant's Causeway, and lining some whyn dykes at Belfast 

 Lough, are precisely the same with those taken notice of by 

 Mr. St. Fond, at Ardenne, at Cheidevant, at Montbrul ; and 

 also by Mr. ^Strange, in the Venetian state. 



Until the advocates for the volcanic origin of basalt can dis-? 

 cover, in lavas, something corresponding to these curious cir- 

 cumstances attending our basalts, can they persist in pronounce 

 ing them to be identically the same? The one (if I may he. 

 allowed to use the expression) s. faclitiom substance, of known 

 and posterior formation; the other, bearing evident marks of 

 the hand of nature, both in its general arrangement in mighty 

 strata, and also in its nurnerous varieties. For we know that 

 jiature delights in diversifying her operations, and in exe* 

 cuting what seems to iiS the same work, in many different- 

 ways. 



