282 ORIGIN OF BASALT. 



Facts and ob- lowest part of the current, compact lava, thei) cellular lava, 



servations re- (^qj^ scoria, next cinders, and lastly, volcanic ashes. But, in 



spectmg basalt , , ,...,., , , 



in the county ^"^ basalt strata, nothmg similar is observed : the material is 



of Antrim ; ad- uniform ; both density and specific gravity the same, through 



that it is not ^^^ whole thickness of our deepest strata. 



volcanic. Fifthly. That basalt never was in fusion, appears plainly 



from the substances found it, and never in lava; and which, 

 from their nature, could not have sustained the heat of a 

 volcano. 



Of these, zeolite, chalcedony, and calcareous spar, seem to 

 abound in the basalt of all countries, but never have been no- 

 ticed in unquestioned lava. The first fuses, and the third cal- 

 cines, in a very moderate lieat; and, though chalcedony be 

 more refractory, yet exposed to a strong heat, it loses its 

 beauty, and the delicacy it exhibits in its natural state. These 

 substances are most copiously dispersed, also, through our 

 basalts; but as this topic has already been often urged, I will 

 pass on to substances peculiar to my own country, 



A variety of basalt, found in abundance at Portrush and the 

 Skerrie Islands, is full of pectinites, of belemnites, and, above' 

 all, of cornuaammonis: these are dispersed through the whole 

 mass, equally abundant in the interior and on the surface. 

 This basalt vitrifies, and the marine substances it contains cal- 

 cine in the fire of a common salt-pan ; of course, never could 

 have sustained a volcanic heat. 



Another fact occurs, which seems decisive against the vol- 

 canic origin of basalt. Some varieties of this fossil, contiguous 

 to Portrush and the Giant's Causeway, upon being broken by 

 a sledge, discover, in their interior, cavities, some filled with 

 fresh water, others bearing evident marks of having once con- 

 tained it. Of these basalts, some were of a difl^erent variety 

 from that of the Giant's Causeway, but of similar grain and 

 liardness; others were precisely of the same variety, columnar, 

 prismatic, articulated, and exactly the same in grain. At the 

 Causeway itself, I never found any ; but in some basalts very 

 near it, on the west side, I have met with it : these had fiiUen 

 from an upper stratum. 



A most respectable correspondent, to whom I communicated 

 this fact, as new in natural history, fells me, he suspects the 

 water passed in by percolation. Determined to pay all atten- 

 tion 



