182 H. S. Washington — Solvshergite and Tinguaite. 



scription and the lack of CaO to be a mixture of riebeckite 

 and glaucophane. Here also it much resembles the Quincy 

 granite, though albite is higher and quartz and orthoclase 

 lower. The hornblende is much the same in character and is 

 of about the composition Eb B Gl 9 , the glancophane here also 

 being purely ferrous. 



A comparison with the paisanite of Osann (III and Ilia) is 

 also of interest. On the whole they are closely similar, though 

 in paisanite the iron oxides, especially FeO, are lower and K,0 

 higher. Corresponding to this the mineral composition (calcu- 

 lated by Osann) shows rather more orthoclase, and the horn- 

 blende is almost a pure riebeckite containing only traces of 

 glaucophane. 



All the above calculations are of interest in pointing to the 

 existence of a purely iron-alumina glaucophane. 



Two analyses of grorudites given by Brdgger are cited in 

 IY and Y, their mineral composition as calculated by Brogger 

 being given in YVa and Ya. These show, relatively toward 

 the riebeckite granites and paisanite, much the same state of 

 affairs which we remarked on in the solvsbergites ; in the 

 aegirite-bearing grorudites Fe Q 3 is much higher relatively to 

 FeO. In the grorudites however A1 9 0, is very considerably 

 lower than in the others — facts which have been commented 

 on by Brogger (op. cit. 128) and by Osann (op. cit. 441). The 

 grorudites are much higher also in dark minerals. 



It is to be seen from the above that from the classificatory 

 standpoint, grorudite and solvsbergite do not stand on pre- 

 cisely the same plane, the latter being broader than the former. 

 The solvsbergites include both soda-pyroxene and soda-horn- 

 blende rocks, the latter being distinguished from the former in 

 nomenclature by the use of the name of the hornblende. The 

 grorudites are essentially aegirite rocks, (katoforite and other 

 soda-hornblendes occurring in subordinate amounts), while 

 their hornblende-bearing equivalents are known as paisanite, 

 the effusive form being the comendite of Bertolio.* This is, 

 of course, a small matter, but significant of the present state 

 of confusion in petrographical nomenclature and classification, 

 and of the pressing need of some systematization. 



Tinguaite. 



Analcite- Tinguaite. — The rock which is here discussed forms 

 a small dike cutting the granite of Pickard's Point, south of 

 Singing Beach, at Manchester. It also cuts a wide dike of 

 diabase, or rather labradorite-porphyrite, with large pheno- 



*I follow Brogger (op. cit. 63-65) rather than Rosenbusch (op. cit. 614), who 

 correlates the comendites with the paisanites and the grorudites with the pan- 

 tellerites. 



