Petrographica I Relations of Laurentian Limestones. 31 



scapolites that are disseminated in the limestones in the 

 bunches of silicates are doubtless due to solutions stimu- 

 lated by the intrusive rocks." It may be added that 

 metasomatic action is especially favored as an accompani- 

 ment to deep seated intrusions such as this Central 

 Ontario occurrence undoubtedly was, — where the vapours 

 and solutions cannot readily escape. 



From these considerations, from their petrographical 

 character, and from their relations in the field, it seems 

 certain that the pyroxene gneisses are in reality altered 

 limestones, that they are the product of metasomatic 

 metamorphism of these limestones by the granite 

 intrusions. 



Regarding the amphibolites, the evidence is less con- 

 clusive. Dr. Adams has found bands of amphibolite 

 which it is certain have been produced exclusively by the 

 alteration of diabase dykes ; and it is also certain that 

 there are bands of amphibolite in the limestone away 

 from the intrusions. These facts concerning the amphi- 

 bolites, added to their probable lower content of lime 

 and their sharper demarkation from the limestones, as 

 compared with the pyroxene gneisses, admit of a lingering 

 belief that none of the amphibolites were produced by 

 metasomatic action, but that they all existed in something 

 like their present condition in the limestone before the 

 intrusion took place. 



But their increased number within the area of meta- 

 morphic action, added to their frequent marked similarity 

 in many respects to the pyroxene gneisses, render the 

 support of such a belief, in the writer's opinion, very 

 feeble ; it seems highly probable that many of these 

 amphibolites have originated in the same way as the 

 pyroxene gneisses — that they are simply more highly 

 altered portions of the original limestone. One thing 

 which may account for the formation of amphibolites in 

 one case and pyroxenites in the other is that where the 



