46 FRANK DA WSON ADAMS 



necessairement apportes des profondeurs, sous forme d'emana- 

 tions, ayant une composition chimique different de celle qu'a 

 priori on pouvait supposer, etant connue la composition de la 

 Iherzolite." 1 There is, however, here again the same absence 

 of the chemical evidence which would serve to definitely estab- 

 lish this conclusion. 



It is also to be noted that in the Pyrenees, dynamic action 

 has followed the development of the contact zones above 

 described. Lacroix observes that the minerals produced by the 

 contact metamorphism are often much deformed by subsequent 

 movements, but adds: "J'ai pu constater avec precision que 

 les phenomenes de contact jouent un role preponderant dans la 

 production des nombreuses roches metamorphiques que Ton 

 rencontre dans toute l'etendue de la chaine." 2 As, however, it 

 is a matter of extreme difficulty, if not an impossibility, in all 

 cases to determine to which class of metamorphic agencies cer- 

 tain rocks are due, the question as to how far dynamic action 

 may have at least contributed to some of the changes attributed 

 to contact action is one which cannot be considered as entirely 

 settled. 



To sum up therefore it may be said, that while the transfusion 

 of a certain amount of material into the limestones along the 

 immediate contact of the intrusions and also a solution of the 

 limestone to a limited extent in certain cases seems highly 

 probable ; the wholesale transformation of limestone into diorite, 

 or of shale into gneiss and granite, which has been described in 

 the case of these contact zones of the Pyrenees, is as yet very 

 far, indeed, from being proved. 



Frank Dawson Adams. 



Geological Department 

 McGill University. 



'Livret, Guide, p. 5. 



2 Les Phdnomenes de contact de la Lherzolite et de quelques Ophites des Pyrenees. 

 Bull, des Sciences de la Carte Ge"ol. de la France, No. 42, p. 133. 



