102 



ibiined; and often, upon inspection, we can discover the 

 original material, the mother stone, by whose fusion it 

 was made. The operation itself, too, enables us to make 

 new distinctions, from the diftereixt intensity of heat, and 

 difl'erent gradations in cooling. 



On the contrary, Ave get little information from in- 

 specting the fracture of basalt. We can tell, that in some, 

 the constituent materials are more -completely blended, 

 than in others: Avhich seems the same thing as to say, 

 there is much difference in grain; a great interval between 

 the coarsest and the finest. But all this is by insensible 

 shades; no such thing as drawing lines, (by which we can 

 mark the varieties of this fossil. Even Avhere other dif- 

 ferences are most essential, between the varieties of ba- 

 salt, ins^pection cannot be relied upon. For instance, the 

 siliceous basalt, full of marine exuviae, passes, by gra- 

 dation, from a grain, as fine as jasper, until it becomes 

 indistino-uishable from tlie Giant's Causeway stone, and 

 even coarser. 



If we look to nature for assistance, in chissing the va-, 

 rieties of basalt, we will be no longer at a loss: we will 

 find, she has impressed an indelible character on each 

 variety of this fossil; a specific figure, into which every 

 stratum is divisible, in its Avhole extent: being formed, as 

 it were, by an agglutination of similar figures;* in the same 



stratum, 



* I do not use the word similar, in a strict mathematical sense ; mean- 

 ing no more than a strong, general likeness, so decided, that the figures of 

 one variety cannot be mistaken for those of another. 



