M. Keilhau's Theory of Granite, and other Rocks. 99 



longer occupy ourselves with the old, hitherto exclusively cul- 

 tivated ground, where new resources no longer present them- 

 selves for new necessities. 



We shall therefore endeavour to avail ourselves as much as 

 possible of the facts we have announced. When we consider 

 directly the grounds on which we repose, — in such a manner 

 that we avoid all idea of penetrating the subject to the root or 

 foundation, but, separating every reflection tending to obscn- 

 rity, regard them only as mere phenomena, — we may be led to- 

 some general conceptions, in which errors possibly exist, but 

 which are, nevertheless, to be received, at least provisionally, 

 as correct. Thus in certain cases we may imagine, that the 

 materials which are necessary for the formation of the new bo- 

 dies were not derived from any points without the parts of the 

 solid masses where formations take place. Keferstein, when 

 speaking of steatites, (spekstenen) and other similar metamor- 

 phoses (properly speaking metastomatoses), remarks quite cor- 

 rectly, that the chemical constitution of these minerals has not 

 the slightest connection with the chemical composition of those 

 species by whose transformation they are produced, and shews 

 that we can only assume that the chemical substances have been 

 completely converted into one another. Until chemistry can 

 enable us to trace up more successfully the nature of the pro- 

 cess which goes on in the instances mentioned, we may adopt 

 the same idea and retain the same expression. The first of the 

 general conclusions referred to is therefore the assumption of 

 the possibihty of perfect substantial transformation^ by which 

 it is supposed that the conveyance of matter from without is 

 not necessary for the formation of new bodies. It would there- 

 fore be regarded as not at all impossible that a mass of pure 

 carbonate of lime, without the addition of magnesia, and with- 

 out the expulsion of a corresponding quantity of lime, should 

 become a carbonate of lime and magnesia. At all events, we 

 thus remove the necessity of accounting for the origin of the 

 magnesia discovered by analyses in the altered mass. 



Another view springs from the consideration of certain other 

 phenomena. We may assume that, whether the medium itself 

 in which these formations took place afforded the materials, or 

 whether they came from another place, still they did not origi- 



g2 



