THEORT of the EARTH. 269 



acted in relation to the hardnefs and folidity, or the natural 

 conftitution of the body ; the other, to its fhape or local fitua- 

 tion. The firft has been already considered ; the laft is now the 

 fubject of enquiry. 



BUT, in examining thofe natural appearances, we find two 

 different kinds of veins j the one necefTarily connected with 

 the confolidating caufe ; the other with that caufe of which we 

 now particularly enquire. For, in thofe great mineral veins, 

 violent fracture and diflocation is the principle ; but there is no 

 other principle upon which flrata, or mafles formed at the bot- 

 tom of the fea, can be placed at a height above its furface. 

 Hence, in thofe two different operations, of forming mineral 

 veins, and erecting ftrata from a lower to a higher place, the 

 principle is the fame ', for neither can be done without violent 

 fracture and diflocation. 



WE now only want to know, how far it is by the fame power, 

 as well as upon the fame principle, that thofe two operations 

 have been made. An expanfive force, acting from below, is 

 the power mofl proper for erecting mafles ; but whether it is a 

 power of the fame nature with that which has been employed 

 in forming mineral veins, will befl appear in knowing the na- 

 ture of their contents. Trrefe, therefore, may be now confi- 

 dered. 



EVERY fpecies of fracture, and every degree of diflocation 

 and contortion, may be perceived in the form of mineral veins ; 

 and there is no other general principle to be obferved in exa- 

 mining their form. But, in examining their contents, fome 

 other principle may appear, fo far as, to the diflocating power 

 or force, there may be fuperadded matter, by which fomething 

 in relation to the nature of the power may be known. If, for 

 example, a tree or a rock fhall be found fimply fplit afunder, 

 although there be no doubt with regard to fome power having 

 been applied in order to produce the effect, yet we are left mere- 

 ly to conjecture at the power. But when wedges of wood or 



iron 



