54 HIS TORT of the SOCIETT. 



{lone, of porphyry, and of granite, all of them fubftances more 

 or lefs cryftallized, and none of them containing the remains of 

 organized bodies. Thefe are of poflerior formation to the ftrata 

 which they interfedt, and in general alfo they carry with them 

 the marks of the violence with which they have come into their 

 place, and of the difturbance which they have produced on the 

 rocks already formed. The materials of all thefe veins Dr Hut- 

 ton concludes to have been melted by fubterraneous heat, and, 

 wliile in fufion, injedted among the fifTures and openings of 

 rocks already formed, but thus diflurbed, and moved from their 

 original place. 



This conclufion he extends to all the mafTes of whinflone, 

 porphyry, and granite, which are interpofed among ftrata, or 

 raifed up in pyramids, as they often appear to be, through the 

 midft of them. Thus, in the fufion and injedlion of the un- 

 flratified rocks, we have the third and laft of the great opera- 

 tions which fubterraneous heat has performed on mineral fub- 

 ftances. 



V. From this Dr Hutton proceeds to confider the changes 

 to which mineral bodies are fubjedl when raifed into the atmo- 

 fphere. Here he finds, without any exception, that they are all 

 going to decay ; that from the fliore of the fea to the top of the 

 mountain, from the foftefl clay to the hardefl: quartz, all are 

 wafting and undergoing a feparation of their parts. The bo- 

 dies thus refolved into their elements, whether chemical or me- 

 chanical, are carried down by the rivers to the fea, and are there 

 depofited. Nothing is exempted from this general law : among 

 the higheft mountains and the hardeft rocks, its eflPeds are moft 

 clearly difcerned; and it is on the objedls which appear the moft 

 durable and fixed, that the charaders of revolution are moft 

 deeply imprinted. 



On comparing the fir ft and the laft of the propofitions juft 

 enumerated, it is impoflible not to perceive that they are two 



fteps 



