Analcite-Trachyte Tuffs and Breccias. 277 



was collected by W. W. Leach. Analyst, Dr. C. W. Dickson, 

 Queen's University. In column IIA, the molecular propor- 

 tions of this analysis are given. 



III. Analcite tinguaite, San Jose, Tamaulipas, Mexico. 

 H. S. Washington, analyst. 1 



For comparison two other analyses of analcite rocks are 

 given in columns I and III. No. Ill is an analcite tinguaite 

 described by G. I. Finlay. 2 It is clear, however, from his des- 

 cription that analcite is only an accessory mineral in the rock ; 

 and, further, he himself states that : " analcite, chiefly, results 

 by weathering." In the phonolites, a closely related rock of 

 the tinguaites, analcite is also known to occur as a primary 

 mineral ; " but it was in basic rocks like basalts and monchi- 

 quites that this zeolite was first recognized as primary. 



A comparison of the analysis in column II with trachytes 

 in general shows that it is fairly typical of this type. The 

 silica is a little below the average, but is too high for leucite 

 rocks like wyomingite and leucitites. 3 The alumina and 

 alkalies also come within the range of the trachytes though 

 the alkalies are a little above the average. The soda is not 

 high enough for the phonolites or tinguaites. The high per 

 cent, of water is of course due to analcite. As is usual in 

 the trachytes the potash predominates over soda, while in 

 the phonolites and tinguaites, on the other hand, we find soda 

 predominating. 



If we adopt the new classification of igneous rocks as 

 proposed by Cross, Iddings, Pirsson and Washington, 4 the 

 rock is classified as follows. The standard mineral composi- 

 tion, or norm, is first calculated and by means of the relative 

 percents of the minerals so found it is placed in its class, 

 order, range and subrange. Dr. Berkey, of Columbia Univer- 

 sity, very kindly assisted the writer in these calculations. 



1. Geology of the San Jose District, Tamaulipas, Mexico. G. I. Finlay. 

 Annals Mew York Academy of Sciences, XIV, 247-31S, 1904. 



2. General Geology of the Cripple Creek district. Cross. TJ. S. G. S., 1895, Part 

 II, p. 16. 



3. Rosenbusch p. 364. 



4. Quantitative classification of igneous rocks. 1903. 



