THEORY of the EARTH. 231 



THERE are to be found, among the various ftrata of the globe, 

 bodies formed of two different kinds of fubftances, ftliceous bo- 

 dies, and thofe which may be termed fulpbureous. With one 

 or other, or both of thofe two fubftances, every different con- 

 folidated flratum of the globe will be found fo intimately mix- 

 ed, or clofely connected, that it muft- be concluded, by what- 

 ever caufe thofe bodies of filiceous and fulphureous matter had 

 been changed from a fluid to a concreted ftate, the ftrata muft 

 have been fimilarly affected by the fame caufe. 



THESE two fpecies of bodies, therefore, the filiceous and the 

 fulphureous, may now be examined, in relation to the caufes of 

 their concretion, with a view to determine, what has been the 

 general concreting or confolidating power, which has operated 

 univerfally in the globe j and particularly to {hew, it has not 

 been by means of any fluid folution, that ftrata in general have 

 been confolidated, or that thofe particular fubftances have been 

 cryftallized and concreted. 



SILICEOUS matter, phyfically fpeaking, is not foluble in 

 water j that is to fay, in no manner of way have we been 

 enabled to learn, that water has the power of difTolving this 

 matter. 



MANY other fubftances, which are fo little foluble in water, 

 that their folubility could not be otherwife detected of them- 

 fe,lves, are made to appear foluble by means of filiceous matter; 

 fuch is feld-fpar, one of the component parts of rock-granite. 



FELD-SPAR is a compound of filiceous, argillaceous, and cal- 

 careous earth, intimately xmited together. This compound fi- 

 liceous body being, for ages, expofed to the weather, the calca- 

 reous part of it is diflblved, and the filiceous part is left in form 

 of a foft white earth. But whether this difTolution is perform- 

 ed by pure water, or by means alfo of an acid, may perhaps 

 be queftioned. This, however, is certain, that we muft con- 

 fider filiceous fubftances as infoluble in water. 



THE 



