270 ON THE TRANSMUTATION OF ROCKS, &c., 



has occurred, there has been a contact of the changed with the 

 transmuting agent. 



Naturally it will occur to the mind, that in order to determine 

 accurately how such transmutations have taken place, we require 

 a careful analysis of the rocks for some distance beyond the planes 

 of alteration, with a distinct understanding of the way in which 

 physical forces of determinate character act upon materials of the 

 kinds in question, whether considered under a mere mineral or a 

 metallurgical aspect. 



Some facts are so constant under certain conditions that they 

 may be considered as established. If, for instance, an eruptive 

 rock is in contact with a sedimentary rock, both will be changed. 

 And Fournet calls that of the former exomorpliism, and of the 

 other endomorphism. 



As these are the most commonly observed, and as they apply 

 to the examples from this neighbourhood, it may be as well to 

 dwell particularly on such as are abnormal, or special kinds of 

 transmutation ; and we may confine ourselves chiefly to the 

 endomorphic or transmuted sedimentary rocks. But all in due 

 order. 



Generally, igneous rocks of different characters produce 

 different kinds of transmutation ; and deposits of calcareous, 

 aluminous, or siliceous composition, will, of course, be affected 

 differently by the same kind of transmuting agent. 



Thus it is found that granitic rocks, trappean rocks, and 

 lavas, all produce varying changes when in contact with rocks of 

 the same name. 



I propose not to dwell upon rocks of great antiquity. But I 

 may mention one remarkable fact in Victoria which I noticed, 

 in company with Messrs. Selwyn and Aplin, where the granite of 

 Mount Alexander is in contact with the gold-bearing, quartzi- 

 ferous, Silurian schists of Specimen Grully, near Castlemaine. 



Not only do all the quartz lodes cease as lodes at the contact 

 with the granite, proving the probable fact that the granite is 

 younger than the slates ; but at the junction there are numerous 

 striking variations in the slates themselves, together with the 

 occurrence of small amounts of minerals and metals. 



. Iron is often in this way discovered in abundance, as in the 



