MacKenzie — Analcite of the Crowsnest Volcanics. 573 



The statements there made are strikingly applicable to the 

 analcite rocks of the Crowsnest volcanics. In particular it is 

 not reasonable to suppose the complete transformation of leu- 

 cite to analcite could take place in the presence of the easily 

 altered nephelite, and the latter remain unaffected, and the 

 same argument applies to the segirite and segirite-augite. Both 

 nephelite and aegirite, in fact, according to Brdgger,* may alter 

 to analcite, and if conditions were favorable for the complete 

 transformation of leucite into that mineral, surely the nephe- 

 lite, aegirite, and aegirite-augite would not remain unaffected. 



Washington also, in discussing the primary nature of the 

 analcitef in some basalt flows of Sardinia, presents a similar 

 line of arguments, and in view of these, and the facts and rea- 

 sons stated above, the possibility that the blairmorites of the 

 Crowsnest volcanics were originally leucite rocks seems to be 

 highly improbable. 



(3) Finally, the possibility of primary analcite forming in 

 eruptive lavas remains to be considered. From the character 

 of the analcite-bearing rock (op. cit., p. 20) it is quite apparent 

 that the analcites did not form in lavas " undergoing explo- 

 sion " as suggested in the review. 



Plainly, one- inch analcites could not form in a lava " under- 

 going explosion" unless we assume a virtually instantaneous 

 growth of the crystals. The obviously intratelluric nature of 

 these phenocrysts meets the objection that the pressure in the 

 magma was not sufficient for their formation. 



In order that analcite may form in a magmatic solution, 

 it is necessary, so far as the water is concerned, that when the 

 crystallization temperature of the mineral is reached, the 

 pressure on the magma must be in excess of the partial pres- 

 sure of the (gaseous) water at that temperature. It may be 

 well to point out that the amount of analcite forming in a 

 given case is not proportional to the pressure, but to the 

 amount of water present. That the necessary pressure was 

 realized in the magma chambers feeding the Crowsnest vol- 

 canoes is made evident by the nature of the blairmorite de- 

 scribed. It is not a rock crystallized wholly under surface 

 conditions, and on the face of it, the first generation of anal- 

 cite phenocrysts formed before and not during explosion. This 

 intratelluric nature of these phenocrysts necessitates their 

 formation under pressure — obviously enough for analcite to 

 form. 



While it is not necessary in the case of the blairmorite to 

 assume the actual formation of analcite in lavas undergoing 

 eruption, such a thing is by no means impossible. The above 



* Zeitschrift Kryst. Min., vol. xvi, pp. 223-333, 1890. 

 f Jour. Geology, vol. xxii, pp. 749-750, 1914. 



