KI2 



NEW YORK STATE MUSEUM 



would give an amount of chlorite considerably in excess of the 

 chloritized hornblende of the mode, which has already been ac- 

 counted for. The feldspar percentage should be correspondingly 

 decreased. Even then the difference between the quartz feldspar 

 ratio in the norm and mode, .65 in one case and .56 in the other, 

 is sufficient to shift the rock into another order, .60 being the 

 dividing ratio. The probable cause is that the ratio present in the 

 slide is not quite normal, the quartz not being equably distributed 

 through the rock. 



Syenite. The great amount of differentiation shown by the rock 

 of the syenite bathylith has already been noted. Analyses of a 

 considerable number of these have been already published, but 

 there were yet lacking those of the more basic and more acid 

 phases, and moreover the red syenites which occur in association 

 with the granitic syenite had not been carefully investigated. 



The specimen of basic syenite (1 2-1-6) selected for investigation, 

 was collected a little over a mile n.n.w. from Raquette falls. It is 

 a rather evenly granular, gneissoid rock, feldspar phenocrysts 

 being few and of small size. The thin section shows augite and 

 hypersthene in the parallel growths which are - so characteristic of 

 this rock, hornblende, magnetite, light colored titanite, apatite, 

 patchy, vermicular garnet, a little quartz, a little pyrite, and feld- 

 spar which is in part microperthite and in part oligoclase-andesin. 

 The mode of the rock, by Rosiwal's method, is as follows: 



Mode of basic syenite (12-1-6) 



Feldspar .... 



Quartz 



Hornblende . 



Augite 



Hypersthene. 

 Magnetite. . . 



Garnet 



Apatite 



Titanite 



Pyrite 



Units measured Sp 

 748 X 2 



38x2 



103 X 3 



123 X 3 



in x 3 



44 x 5 



7x3 



15 X3 



4x3 



1 x 5 



Gr. 



64 = 



65 = 

 3 = 

 3 = 

 35 = 

 25 = 

 85 = 



5 = 



Units 

 by weight 



: 1975 

 : IOI 



340 



406 



372 



23I 



2 7 



48 



14 



5 



% weight 



56.12 



2.87 



9-65 



n-54 



10.57 



6-57 

 0.77 



i-37 

 0.40 

 o. 14 



Total, 



1194 



35i9 



:oo .00 



