Alnoitic Rocks at Isle Cadieux, Que. 31 



manite (melilite) field and the composition of akermanite 

 is quite close to the border. In view of the demonstrated 

 effect of nephelite in pulling the fields over towards the 

 silica corner the occurrence of Ca 2 Si0 4 in such a rock is 

 perhaps not surprising. 



Analcite Dikes. 



The formation of very basic minerals by a process 

 which may be briefly, if somewhat inadequately, described 

 as desilication has been demonstrated for the case of 

 melilite in the artificial mixtures. The equations that 

 have been written to show the formation of the charac- 

 teristic melilite molecules from diopside show also, of 

 necessity, a molecule that is formed by silication of the 

 nephelite molecule; and the actual experimental results 

 show the formation of a liquid which refuses to crystal- 

 lize under dry melt conditions and has, as a glass, the 

 very low refractive index appropriate to a more sili- 

 ceous sodium aluminum silicate. This has been written 

 NaAlSi 2 6 . Now alnoite is a monchiquite, and as such 

 often contains analcite as a base or a glassy base of the 

 composition of analcite, viz., NaAlSi 2 6 .H 2 0. The Isle 

 Cadieux alnoite shows none of this, but Harvie has found 

 it, or alteration products that may be referred to it, in 

 alnoite s of this vicinity. 29 In this analcitic material we 

 may, then, have the other product of the reaction of 

 nephelite-rich liquid on augite to produce melilite. It 

 appears here as a hydrous mineral, for the whole system 

 was evidently quite rich in water, as witness, the abun- 

 dance of biotite. 



In discussing the replacement of the original minerals 

 of the alnoite, it has been stated as probable that this 

 was accomplished by a nephelite-rich liquid that passed 

 through the partly consolidated rock filling the interstices 

 with reaction minerals and carrying on some of the reac- 

 tion products. 30 These latter were presumably largely 

 analcite and it may be to such liquids that the analcite 

 dikes of this vicinity are to be referred. 31 



29 Op. cit., p. 274. 



30 In this connection the arrangement of the small melilites about the older 

 crystals is significant. They have a ' ' stream-like disposition, ' ' as Eogers 

 and Du Toit describe a similar structure in African melilite basalts. Geol. 

 Com., Cape of Good Hope, Ann. Eep., 1903, p. 47. 



31 F. D. Adams, Twelfth International Geologic Congress, Canada, Guide 

 Book No. 3, p. 45. 



