EXPERIMENTS on WHINStONE and LAVA. 6 9 



ftone rocks externally refemble very porous lavas, but when 

 broken are always found to be quite compact internally, and to 

 contain numerous round nodules of calcareous fpar. Near the 

 furface, the nodules, being warned out by rain, have left the 

 cavities which have given rife to this deception. The fpherical 

 form of the air holes in lavas, and of the nodules of calcareous 

 fpar in whins, feems to have been produced by a caufe common 

 to both, the mutual repulfion of two fluids intermixed, but not 

 difpofed to unite. 



It muft be owned, that this theory of calcareous fpar is as- 

 yet hypothetical ; but it is fupported by ftrong analogy, and 

 promifes to be of fervice, by leading to decifive experiments and 

 obfervations. I cannot help believing, that, by a careful exa- 

 mination of the volcanic countries, facts may yet be difcovered 

 which will throw light on this fubject. In order to promote 

 and direct: fuch refearches, I fhall beg leave to ftate fome obfer- 

 vations which I made in thofe countries in 1785, before I was 

 attached to any fyftem of geology. 



It is generally fuppofed, that fome lavas of iEtna contain cal- 

 careous fpar and zeolite ; but this I conceive to be a miflake. 

 It is true, as I have feen, that many rocks of iEtna contain thefe 

 fubflances in abundance ; but in my opinion thefe rocks are no 

 lavas, but have flowed fubterraneoufly like our whins, and are the 

 fame with them in every refpect. A particular diflrict of iEtna,, 

 comprehending the Cyclopian Ifles, and the country round La 

 Trezza, and the Caflle of Jaci, is decidedly of this defcription ; 

 and veftiges of the fame kind occur in other parts of the moun- 

 tain. In one place fomle coal has been found, and in another we 

 faw marine fhells. In the neighbourhood of Bronte we obfer- 

 ved a high ridge formed of ftrata of fandltone and limeftone, 

 partly overflowed and concealed by recent lavas, but fo placed 

 as to render it evident that its continuation formed no inconfi- 

 derable part of the mountain. Thus, iEtna being compofed, 

 partly of the fubterranean, and partly of the external produc- 

 tions 



