101 



I allude to that property, mIucU all basalt strata, that 

 I ever examined, have, of dividing or separating into re- 

 gular forms, generally with plain sides. For, that this is a 

 principle inherent in the 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, generally blue or grey: the former an 

 arrangement of nature, the uniform efl^ect of a cause, with 

 which we are unacquainted; the latter the irregular ef- 

 fect of a violent stroke or impulse. 



If the theory we are discussing l)e well founded, all 

 our basalt strata were once currents of la.va, flowing fiom 

 volcanos. For this we have the authority, or, rather, the 

 assertion, of the founder, and the most accredited sup- 

 porters of the opinion. In substances, therefore, by their 

 accounts, exactly the same, and of the same origin, (for 

 they use basalt and lava as synonymous terms,) Ave have 

 a right to expect similar properties ; and to look for in lava, 

 an internal arrangement of the mass into regular formSj 

 conformable to what we meet with in all basalts. But 

 nothing similar has been observed in lava, and the de- 

 scription of the Volvic laA a is irreconcileable to this pro- 

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

 tout sens: and Mi'. Desmarcst himself mentions this, as a 

 mark of distinction, between it and the neighbouring 

 basalt. 



In distinguishing the varieties of lava, we have a clew 

 to guide us. We know the process by which it was 



VOL. X. o formed: 



