from the Canadian Rocky Mountains. 205 



connection witli socialite. (7) Felspar : doubtfully present, but 

 may be represented by one small grain at the edge of the slice. 

 (8) Sodalite: a little, very local in occurrence. It contains a few- 

 colourless belonites, and is associated with eleeolite in a way strongly 

 suggestive of a partial replacement of that mineral. (9) Sphene : 

 two or three fair-sized grains, including apatite, and in one case 

 pierced by a brown augite, may be either this mineral or (possibly) 

 another variety of augite. Thus the rock, which has a specific 

 gravity of 3-12, is more nearly related to the nepheline-dolerites 

 than to the nepheline-syenites. 



These specimens, especially the former, Mr. Whyraper tells me 

 may be taken to represent the country rock in which the masses 

 rich in sodalite occur. 



He also brought a flake-like specimen of fibrous actinolite and 

 a fragment consisting of bits of a pale dull green chloritic or 

 hornblendic rock, cemented with quartz, obviously from a vein. 



One more specimen, though interesting in itself, has no direct 

 bearing on the present investigation. It is a darkish grey rock of 

 slightly foliated aspect, which on microscopic examination proves to 

 consist of granular, calcite and rather elongated prisms of tremolite 

 (occasionally also in needles). Dusky patches of blackish granules 

 occur in both minerals, but especially in the former, and very minute, 

 rather filmy microliths are included in the latter. I do not remember 

 to have seen a rock quite of this type before, but think it may be 

 a result of contact-metamorphism. 



What, then, is the history of the sodalite in the Ice River Valley 

 rock ? Is it an original constituent or of secondary origin? Some- 

 times it occurs in interstitial patches among the other minerals ; 

 sometimes it fills up cracks in the felspars. The first suggests an 

 original constituent ; the second must have formed after consolidation 

 in fissures due to strain. But even in the former, sodalite may have 

 replaced some other mineral, and in the latter obtained materials 

 from it. Professor Harrington's analysis of the Ice Eiver sodalite 

 (rearranged by Dana in " System of Mineralogy," 1900) shows it to 

 be remarkably pure : — 



SiO. AI3O3 NaoO K.3O CI 



37-56 3r-82 25-55 0-27 7-12 = 102-26 



Typical analyses (see Dana) of this and two related minerals are : 



SiO, AI2O3 NaaO KjO CI Total. 



Sodalite 37-2 31-6 25-6 — 7-3 101-7 



NepMine 44-0 33-2 15-1 7-7 — 100 



Albite 68-7 19-5 11-8 — — 100 



If, for purposes of comparison, we reduce the AI2 O3 (as the most 

 stable constituent) to unity, we have : — 



SiO, AI3O3 Na3 KoO 



SodaUte I-17" 1 "80 — 



Nepheline 1-32 1 "45 -23 



Albite 3-52 1 -60 — 



Thus, in forming sodalite like that of the Ice River . from 



