EXPERIMENTS on WHINSTONE and LAVA. 57 



no idea of the real character of the lava, which can only be £^.t\\ 

 in the interior parts of the currents. In forming our collection 

 we fcrupuloufly avoided this error, and chofe fuch fpecimens 

 only as were the moil compact and free from the fcorified ap- 

 pearance of the furface. 



When thefe folid lavas are compared with our whinftones, 

 the refemblance between the two claffes is not only ftriking at 

 firfl fight, but bears the clofefl examination. They both con- 

 fift of a ftony bafis, which frequently contains detached cryflals 

 of various fubftances, fuch as white felfpar and black hornblend. 

 The analogy between the two claffes feems to hold through all 

 their varieties ; and I am confident that there is not a lava of 

 Mount iEtna to which a counterpart may not be produced from 

 the whinftones of Scotland. 



This refemblance in external character is accompanied with 

 an agreement no lefs complete in chemical properties. But be- 

 fore I mention the experiments which tend to prove this agree- 

 ment, it will be neceffary firfl to examine the opinion of two 

 very celebrated authors concerning lavas. M. Dolomieu and 

 Mr Kirwan, though they differ widely in many refpects, agree 

 in believing, that lavas have never been acted upon by a heat of 

 fufEcient intenfity to produce complete fufion ; and endeavour, 

 each by an hypothefis peculiar to himfelf, to account for their 

 fluidity. The opinion of thefe gentlemen is of fuch importance 

 in the prefent queftion, and the arguments they have ufed are 

 fo extraordinary, that I muft beg leave to quote their words at 

 full length. 



M. Dolomieu flates his opinion in the following paffage, 

 (IJles Ponces, p. y.J : " II eft efTentiel de conftater, par beau- 

 " coup d'exemples et d'obfervations, quelques verit.es quej'ai 

 annoncees il y a plufieurs annees, favoir, que le feu des vol- 

 cans ne denature pas ordinairement les pierres qu'il a mifes 

 en etat de fufion ; qu'il ne les altere pas au point de ne pou- 

 voir les reconnoitre, de ne pas diftinguer quelle a pu etre la 

 Part I. H " bafe 



