286 ORIGIN OF BASALT. 



Facts and ob- <i>d not encounter them in a state of fusion ? which is the point 

 servations re- jn question. 



in the county Seventhly, Upon the last difference I shall mention be- 

 of Antrim; ad- Iween basalt and lava, I must dwell a little longer; both be- 

 that^it is'not"^ cause it seems radical and essential; and also, because it lays 

 Tolcanic. open some new and curious facts, relative to basalt, which 



have hitherto escaped notice. 



I allude to that property which all basalt strata, that I ever 

 examined, have, of dividing or separating into regular forms, 

 generally with plain sides. For that this is a principle inhe- 

 rent in (he mass, and coeval with its original formation, is 

 obvious, from the striking difference between the plain brown 

 side of the figure and the irregular, granular fracture, gene- 

 rally blue or grey : the former an arrangement of nature, the 

 uniform effect of a cause, with which we are unacquainted; 

 the latter the irregular effect of a violent stroke or impulse. 



If the theory we are discussing be well founded, all our 

 basalt strata were once currents of lava, flowing from volcanos. 

 For this we have the authority, or, rather, the assertion, of the 

 founder, and the most accredited supporters of the opinion. 

 In substances, therefore, by their accounts, exactly the same, 

 and of the same origin, (for they use basalt and lava as syno- 

 nymous terras,) we have a right to expect similar properties; 

 and lo look for, in lava, an internal arrangement of the mass 

 into regular forms, conformable to what we meet with in all 

 basalts. But nothing similar has been observed in lava, and 

 the description of the Volvic lava is irreconcileable to this 

 property; for we are told it breaks in all directions, casse 

 en tout sens: and Mr. Desmarest himself mentions this, as 

 a mark of distinction between it and the neighbouring ba- 

 salt. 



In distinguishing the varieties of lava, we have a clew to 

 guide us. We know the process by which it was formed ; 

 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 different intensity of heat, and different gradations in 

 cooling. 



On the contrary, we get little information from inspecting 

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

 stituent 



