THE ORT of the EAR ?H. 251 



it will be found to have flowed, and to have been in fufion, by 

 the operation of fubterraneous heat. 



THIS evidence, though moft conclufive with regard to the 

 application of fubterraneous heat, as the means employed in 

 bringing into fufion all the different fubftances with which 

 ftrata may be found confolidated, is not directly a proof that 

 ftrata had been confolidated by the fufion of their proper fub- 

 ftance. It was neceffary to fee the general nature of the evi- 

 dence, for the univerfal application of fubterraneous heat, in 

 the fufion of every kind of mineral body. Now, that this has 

 been done, we may give examples of ftrata confolidated with- 

 s out the introduction of foreign matter, merely by the foftening 

 or fufion of their own materials. 



FOR this purpofe, we may confider two different fpecies of 

 ftrata, fuch as are perfectly fimple in their nature, of the moft 

 diftinct fubftances, and whofe origin is perfectly undc rftood, 

 confequently, whofe fubfequent changes may be reafoned upon 

 with certainty and clearnefs. Thefe are the filiceous and cal- 

 careous ftrata ; and thefe are the two prevailing fubftances of 

 the globe, all the reft being, in comparifon of thefe, as no- 

 thing ; for unlefs it be the bituminous or coal ftrata, there is 

 hardly any other which does not neceffarily contain more or lefs 

 of one or other of thefe two fubftances. If, therefore, it can 

 be fliewn, that both of thofe two general ftrata have been con- 

 folidated by the fimple fufion of their fubftance, no defideratum 

 or doubt will remain, with regard to the nature of that ope- 

 ration which has been tranfacted at great depths of the earth, 

 places to which all accefs is denied to mortal eyes. 



WE are now to prove, Jirft, That thofe ftrata have been con- 

 folidated by fimple fufion ; and, idly^ That this operation is 

 univerfal, in relation to the ftrata of the earth, as having pro- 

 duced the various degrees of folidity or hardnefs in thefe bodies. 



I SHALL firft remark, that a fortuitous collection of hard bo- 

 dies, fuch as gravel and fand, can only touch in points, and 



I i 2 cannot, 



