W. G. Foye — Nephelite Syenites of Ontario. 435 



of the granite pegmatites and the nephelite syenites would 

 lead one to suppose that the same agents, i. e. magmatic gases, 

 segregated two very dissimilar magmas at the same time from 

 the granite. It is difficult to conceive how granite, a magma 

 high in silica, and nephelite syenite, low in silica, could both 

 be transported through the primary magma chamber simulta- 

 neously, unless one believes in Rosenbusch's theory that the 

 foyaite and granite kerns are immiscible. 



To the writer it appears more reasonable to suppose that 

 soda solutions given off in response to the interaction of the 

 limestone with the granite magma enriched small, confined 

 portions of the granite pegmatite in those elements character- 

 istic of nephelite syenites and so produced the alkaline types. 



Such a local desilication of the granite was often observed 

 in the field. Near Bancroft, Ontario, large masses of augite, 

 a foot or more in length, are found near the contact of the 

 granite with the limestone. Wherever these occur, the granite 

 is altered to red syenite and often contains lenses of nephelite 

 syenite. Daly* has shown that lime in the formation of the 

 pyroxene molecule binds to itself 2*5 its own weight of silica. 

 That the granite should be desilicated under these circum- 

 stances is not to be wondered at! 



At the limestone contact and within the main mass of that 

 rock the granite has produced amphibolite instead of augite 

 from the limestone. The formation of amphibolite binds still 

 more silica than the formation of augite and is, therefore, a 

 more effective means of desilicating the granite. 



It has already been stated that the contact of the amphibo- 

 lite with the limestone is characterized by a scapolitic zone. 

 Scapolite is a mineral high in alumina and often high in soda. 

 It occurs in large masses associated with the corundum syenite 

 of Craigmont, Ontario, and is an essential constituent of most 

 of the nephelite types described from Gooderham and Torv 

 Hill (Part I). 



The formation of scapolite is decidedly a case in which 

 soda-rich solutions transported by pneumatolytic gases are 

 given off, due to the interaction of limestone with granite 

 magma. V. M. Goldschmidtf has shown this in his study of 

 the Christiania region. The constant association of this min- 

 eral with nephelite in many localities cannot be without 

 significance. 



Meionite and nephelite frequently line cavities in the bombs 

 ejected from Monte Somma. Mierisch^; and Lacroix§ have 

 shown that they were deposited as sublimations from a gaseous 



*R. A. Daly, "Igneous Eocks and their Origin", New York, 1915, p. 431. 

 \V. M. Goldschmidt, "Die Kontaktmetamorphose im Kristianiagebiet," 

 Kristiania, 1911, pp. 28 and 320. 



% Bruno Mierisch, Tscherm. Mitth., vol. viii, p. 188, 1888; 



| A. Lacroix, Mus. d'Hist. Nat., Nouv. Arch., (4), vol. ix, pp. 101-2, 1907. 



