276 ON THE TRANSMUTATION OF ROCKS, &c., 



Taking this fact in common with the different degrees of 

 fusibility of quartz, mica, and felspar, which are the elements of 

 normal granite, it is quite clear that igneous fusion alone cannot 

 have been concerned. 



The fusion point of Silica may be taken at 2800 C. (or 5072 

 F.). According to Fournet, quartz in a state effusion may cool 

 down from 1300 to 1800 (i. e., from 2171 to 3292 F.) below its 

 fusion point, without consolidation. The other minerals fuse at a 

 much lower temperature than quartz, and yet, if you examine 

 granite, you will perceive that quartz very often occurs enveloped 

 in felspar and mica also ; how is this fact to be understood, if no 

 change has taken place in the granitic mass since its formation ? 

 The granite must originally have been in a very different con- 

 dition from a single mass merely fused by igneous action ; and if 

 we admit this and other considerations which we cannot now 

 stay to speak of, then it follows, that whether or not the granite 

 has undergone in itself any transmutation, it is highly probable 

 that the chemical and mineralogical action and the presence of 

 vapours would certainly influence any mass of sedimentar^aaatter 

 in contact with it, and, therefore be a source of what we have 

 seen called exomorphism, altering, where the vapours and heat 

 and mineral matters have had fair play, the surfaces at least of 

 the external substances. And we shall see how hydrated 

 agencies could exist if we recollect what has been demonstrated, 

 that there must have been originally from 1 to 50 per cent, of 

 water in granite. 



It is well known that the vapour of water under pressure at 

 a high temperature is capable of dissolving silica, and, therefore, 

 granite, under the influences stated, may silicify a rock capable 

 of receiving the change, or of producing even veins of quartz in 

 fissures ; and thus we may explain many of the phenomena with 

 which we are familiar, and which are exhibited where sedimentary 

 rocks are in contact with granite, as in the instances illustrated 

 by specimens, and cited from this colony. 



In the same way argillaceous rocks become silicated into 

 siliceous slates and some kinds of gneiss. And thus we have by 

 the presence of water in plastic or heated granite, a true origin 

 for many of the phenomena we designate Transmuted or Meta- 



