Analcite-Trachyte Tuffs and Breccias. 275 



because it was no doubt from a magna of this composition that 

 the soda-pyroxenes of the crystal-tuffs were derived. The data 

 accompanying the specimen do not state whether it occurs as 

 a flow or as rock fragments in the breccia. 



Andesite. One thin section of a crystal-tuff contains large 

 quantities of the plagioclase felspar andesine. From this it 

 may be inferred that parts of the magna from which these 

 clastic rocks were derived, had the composition of andesite. 

 This type is quite insignificant, the series as a whole being 

 characteristically trachytic. 



Analcite-trachyte. The presence of analcite in crystal-tuffs 

 whose other dominant mineral is orthoclase, has resulted in a 

 tuff having the chemical and mineralogical composition of an 

 analcite-trachyte. In proposing a new name for this type it is 

 to be understood, however, that no igneous flows have been 

 found, so that the name Blairmorite, as suggested at the 

 beginning of this paper, must at present be applied to the crys- 

 tal tuff having the chemical and mineralogical composition of 

 analcite-trachyte, in other words, a blairmorite-tuff. But a 

 volcanic rock of such composition will no doubt be found in 

 place in some part of the world ; the analcite will occur in well 

 developed phenocrysts (icositetrahedrons), as is shown by the 

 crystal forms found in the tuffs described in this paper. Such 

 a statement does not seem unreasonable since in the series of 

 tuffs and breccias here studied, one small rock-fragment of this 

 type was found. It consists of phenocrysts of orthoclase and 

 analcite less than 1 mm. in diameter set in a ground mass of 

 felspar laths (a few of which have the twinning lamellae of 

 the plagioclases) and a feM smaller analcites. Some titanite 

 is also present. The fragment was certainly derived from a 

 magma having the composition of an analcite-trachyte, and it 

 is possible that further field work in this district may reveal 

 the presence of such a volcanic flow. 



Chemical Composition of Blairmorite. 



In order to study the chemical composition of blair- 

 morite-tuff, a typical specimen was selected for analysis. The 

 writer is greatly indebted to Dr. Dickson of Queen's Univer- 

 sity, Kingston, Canada, for his kindness in preparing this 



