262 Hutton according to Play fair. 



formed. The materials of all these veins, Dr Hutton concludes 

 to have been melted by subterraneous heat, and, while in fu- 

 sion, injected among the fissures and openings of rocks already 

 formed, but thus disturbed and moved from their original place. 



This conclusion he extends to all the masses of whinstone, 

 porphyry, and granite, which are interposed among strata, or 

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

 midst of them. Thus, in the fusion and injection of the unstra- 

 tified rocks, we have the third and last of the great operations 

 which subterraneous heat has performed on mineral substances. 



V. From this Dr Hutton proceeds to consider the changes to 

 which mineral bodies are subject when raised into the atmo- 

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

 goinc to decay ; that from the shore of the sea to the top of the 

 mountain, from the softest clay to the hardest quartz, all are 

 wasting and undergoing a separation of their parts. The bodies 

 thus resolved into their elements, whether chemical or mechani- 

 cal, are carried down by the rivers to the sea, and are there 

 deposited. Nothing is exempted from the general law : among 

 the hio-hest mountains and the hardest rocks, its effects are most 

 clearly discerned ; and it is on the objects which appear the most 

 durable and fixed, that the characters of revolution are most 

 deeply imprinted. 



On comparing the first and the last propositions just enume- 

 rated, it is impossible not to perceive that they are two steps of 

 the same progression, and that mineral substances are alternate- 

 ly dissolved and renewed. These vicissitudes may have been 

 often repeated ; and there are not wanting remains among mi- 

 neral bodies that lead us back to continents, from which the pre- 

 sent are third in succession. Here, then, we have a series of 

 great natural revolutions in the condition of the earth's surface, 

 of which, as the author of this theory has remarked, we neither 

 see the beginning nor the end ; and this circumstance accords 

 well with what is known concerning other parts of the economy 

 of the world. In the continuation of the different species of 

 animals and vegetables that inhabit the earth, we discern neither 

 a beginning nor end ; and in the planetary motions where geo- 

 metry has carried the eye so far, both into the future and the 

 past, we discover no mark either of the commencement or ter- 



