134 Washington — Plauenal Monzonose (Syenite). 



The norm of VII calculates out as foil 



ows: 



Norm. Eatios. 



6-90 ) Sal 



76-95 



9*04 "J 



83-85 T ^ — =5*53, Class II, dosalane. 



F 



^=11*15, Order 5, germanare. 



K,Q' + Na,Q' _ 2-67, Rang 2, 

 5 . 61 \ 13-85 CaO' monzonose. 



K„Q' __Q-69, Subrang 3, mon- 

 Na„0' zonose. 



72 j 



100-23 



The average rock therefore falls in monzonose (II.5.2.3), 

 as do both Cross's specimen and mine, and presumably the 

 others also. It will have been seen that Zirkel's analysis places 

 the rock in the same class, order and rang, but in the dopotassic 

 instead of the sodipotassic subrang. As the somewhat more 

 femic character of his specimen cannot be considered to be 

 connected with, or to bring about, such a radical difference in 

 the proportions of the alkalies, their total amount in I and YII 

 being about the same, we are forced to suppose that the dis- 

 crepancy is due to some analytical error, such as, possibly, a 

 dehydration of the sodium platinichloride. 



Mode. — The mode of the plauenal monzonose was deter- 

 mined by numerous measurements in different directions across 

 a typical section of my specimen. The results were : 



Vol. wt. 



per cent. per cent. 



Quartz 11-50 11 -09 



Soda-orthoclase 67*58 63*96 



Oligoclase 2-90 2-79 



Hornblende 14*26 16-61 



Magnetite 1*38 2-61 



Titanite 1-55 1*97 



Apatite 0*83 0*97 



100-00 100-00 



As the chemical compositions of the hornblende and of the 

 soda-orthoclase, which may contain some lime, are unknown, it 

 is impossible to check the measured mode satisfactorily by cal- 

 culation of the mode from the chemical composition, nor 

 conversely to calculate the chemical composition from the 



