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4:34 W. G. Foye — Nephelite Syenites of Ontario. 



direction. One of the striking facts concerning this area is the 

 predominance of pegmatitic rather than normal granite, show- 

 ing that the Pre-Cambrian granites which intruded the Gren- 

 ville series were abundantly supplied with pneumatolytic 

 gases. 



It is believed that the presence of these gases made possible 

 the lit-par-lit structure of the Haliburton area.* They were 

 capable of penetrating the limestones along planes of weakness, 

 induced probably by static metamorphism,f long before the 

 liquid magma could be intruded. The reaction of the lime- 

 stones with the gases opened passageways through which liquid 

 magma entered. Gradually, in this way, an immense number 

 of alternating layers of granite magma and limestone were 

 formed. The materials of this gigantic steam pack reacted 

 with each other and produced finally a lit-par-lit structure of 

 granite and amphibolite with a few residual layers of lime- 

 stone. 



The nephelite syenites were developed during the period of 

 intrusion of the granites. Their total mass is far less than one 

 per cent of the total mass of the granites and they are transi- 

 tional to granite pegmatite through the intermediate stage of 

 red syenite. The nephelite syenite laccoliths occur as small 

 isolated bodies in the limestone or as border facies of the gran- 

 ite. 



It has been objected to the syntectic theory of the origin of 

 nephelite syenites that the amount of limestone capable of 

 reacting with the granite magma was entirely insufficient to 

 alter the nature of that magma. The method of emplacement 

 of the granite just described and the large scale production of 

 amphibolites from limestones most effectively removes this 

 objection. If from ten to twenty per cent of the Haliburton 

 area is underlain by amphibolites derived from limestone, then 

 some drastic effects must be looked for in the granite magma 

 which gave rise to the solution producing these amphibolites. 



Returning to the question of the origin of the fluids which 

 reacted with the limestone to produce amphibolites, the writer 

 wishes to state very positively that he believes with Smyth 

 that magmatic gases were the effective means of transporting 

 the fluids from the granite into the adjacent rocks. He believes, 

 however, that the soda solutions were given off by the granite 

 magma because lime was capable of replacing soda at high 

 temperatures. The magmatic gases, therefore, were only a 

 means of transportation and were not active in releasing soda 

 solutions from the magma. 



If it is believed that the nephelite rocks were segregated 

 independently of the action of limestone, the close association 



*Cf. C. N. Fenner, Jour. Geol.. vol. xxii, pp. 594-612, 1914. 



tCf. R. A. Daly, Guide Book, No. 8, Inter. Geol. Cong. Can., Part II, p. 

 128, 1913. 



