414 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



with minute prisms or grains of apatite, magnetite, pyroxene, and probably glass. 

 These inclusions have a tendency to concentric arrangement within^ their host. 

 The extremely sharp definition and idiomorphism of the crystals and the all but 

 perfect freshness of the rock are, of themselves, sufficient proof of the primary 

 nature of the mineral. The well-known demonstrations of Lindgren, Pirsson 

 and others, as to the occurrence of analcite as a primary, magmatic product in 

 igneous rocks seem amply sufficient to show the possibility that the mineral with 

 these optical properties may be truly aualcite. The convincing fact as to the 

 truth of this conclusion is furnished by the chemical analysis of one of the 

 specimens. The analysis was made by Professor Dittrich with all his accus- 

 tomed accuracy and thoroughness. The high percentage of combined water 

 indicates that the isotropic mineral is analcite, rather than a member of the 

 sodalite family. Moreover, Mr. Connor found, by test, that chlorine shows no 

 more than a mere trace. 



A rough determination of weight percentages by the Eosiwal method gave 

 the following result : — 



Feldspar phenocrysts (' anorthoclase ') 10-5 



Augite phenocrysts 5-5 



Olivine phenocrysts 2-6 



Analcite 29-2 



Feldspar of ground-mass (' anorthoclase ' and sodiferous ortho- 



clase) 230 



Glass 25-0 



Magnetite 2-0 



Apatite and titanite 2-0 



Biotite -2 



100-0 



A principal error in this estimate may consist in the figures for glass and 

 analcite. These were distinguished in the thin section only where the crystal 

 form of the analcite was clearly seen; where the crystal form was not seen, the 

 colourless, isotropic, or nearly isotropic material was referred to glass. It is 

 probable, therefore, that the percentage for glass is too high and that for anal- 

 cite is too low in the foregoing table. 



Professor Dittrich's analysis of a non-vesicular specimen (ISTo. 1064) resulted 

 as follows : — 



Analysis of ' shackanite/ 



MjI. 



Si0 2 52-24 -871 



Ti0 2 -73 -009 



ALO, 19-28 -189 



Fe 2 3 4-34 -027 



FeO 1-13 -015 



MnO tr 



MgO 1-85 -046 



CaO 4-43 -079 



SrO -42 -004 



BaO -36 -002 



Na,0 6-34 -102 



K,6 2-40 -026 



