Experiments on Whinjlone and Lava. 17 



cares, and convey no idea of the real charafter of the lava, which can only be feen in the 

 interior parts of the currents. In forming our colledlion we fcrupuloufly avoided this er- 

 ror, and chofe fuch fpecimens only as were the moft compaft and free from the fcorified 

 appearance of the furface. 



When thefe folid lavas are compared with our whinflones, the refemblance between the 

 two clafles is not only ftriking at firft fight, but bears the clofeft examination. They both 

 confift of a ftony bafis, which frequently contains detached cryftals of various fubftances, 

 fuch as white felfpar and black hornblend. The analogy between the two clafles feems to 

 hold through all their varieties ; and 1 am confident that there is not a lava of Mount ^tna 

 to which a counterpart may not be produced rom the whinftones of Scotland. 



This refemblance in external chara£ler is accompanied with an agreement no lefs com- 

 plete in chemical properties. But before I mention the experiments which tend to prove 

 this agreement, it will be neceflary firft to examine the opinion of two very celebrated au- 

 thors concerning lavas. M. Dolomieu and Mr. Kirwan, though they diiFer widely in many 

 refpeds, agree in believing, that lavas have never been afted upon by heat of fuflicicnt in- 

 tenfity to produce complete fufion; and. endeavour, each by an hypothefis peculiar to him- 

 felf, 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 ftates his opinion in the following paflage, (IJles Ponces, p. 7.) : " II eft 

 " eflentiel de conftater, par beaucoup d'exemples et d'obfervations, quelques verites que 

 " j'ai annoncees il y a plufieurs annees, favoir, que le feu des volcans ne denature pas ordi- 

 *' nairement lea pierres qu'il a mifes en etat de fufion ; qu'il ne les altere pas au point de 

 *' ne pouvoir les reconnoitre, de ne pas diftinguer quelle a pu etre la bafe des laves ; que 

 " ce feu agit diffieremment que le feu de nos fourneaux, tel que nous I'employons dans la 

 " chimie et dans les arts ; qu'il produit dans les laves une fluidite qui n'a aucun rapport 

 *• avec la fluidite vitreufe, que nous operons, lorfque nous traitons a grand feu les memes 

 " matieres qui leur fervent de bafe, et lorfque nous voulons rendre aux laves elles memes 

 " leur fluidite. Celui des volcans n'a point d'intenfite; il ne peut pas meme vitrlfier les 

 '• fubftances les plus fufibles, tela que les fchorls, qui fe trouvent comme parties confti- 

 ** tuantes dans I'interieur des laves ; il produit la fluidite par une efpece de difl"olution par 

 " une fimple dilation, qui permet aux parties de gliflt;r les unes fur les autres, et peutetre 

 " encore par le concours d'une autre matiere qui fert de vehicule a la fluidite." 



Mr. Kirwan cenfures this fuppofition as ftrange and inconceivable ; but in my opinion, 

 that which he has brought forward is not lefs fo. In the Elements of AIineraIogy,fecond edition, 

 vol.1, p. 396. he fays: "Now, there are but three forts of fufion with which we are ac- 

 " quainted : that which produces porcelain ; that which produces enamels and femi-vitri- 

 " fications; and that which produces glafs. By infpeftlng lava we (hall find that very 

 " little of it has been in any of thefe ftates ; fince therefore it has flowed, it is plain it has 

 •• derived its liquifadtion not from the fufion of its own materials, but from that of fome 



Vol. IV.— April 1800. D foreign 



