94 



Whoever has read Mr. Desmarest's Memoir, or even my 

 quotations from it, must admit, that, if his theory be well 

 founded, all our basalt strata must have once been cur- 

 rents of liquid lava; and, of course, should resemble those 

 known to have issued from existing volcanos. But, I 

 apprehend, instead of similarity, the most decided differ- 

 ences will be found between them. 



Currents of lava, we are told, are always narrower and 

 deeper, in the vicinity of the crater; broader and shal- 

 lower, as farther removed from it: but our basalt strata 

 are of uniform thickness in their whole extent. 



There is another point of view, in which the difference, 

 between basalt strata, and currents of lava, is still more 

 decided. Sir William Hamilton, Ferber, Spalanzani, and 

 even Mr. Desmarest himself, inform us, that, in all cur- 

 rents of lava, the materials composing them are invaria- 

 bly arranged, in a regular gradation, according to their 

 specific gravities: thus, at the lowest- part of the current, 

 compact; lava, then cellular lava, then scoria, next cin- 

 ders, and lastly, volcanic ashes. But, in our basalt strata, 

 nothing similar is observed: the material is uniform; both 

 density and specific gravity the same, through the Avhole 

 thickness of our deepest strata. 



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

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

 which, from their nature, could not have sustained the 



heat of a volcano. 



Of 



