20 



NEW YORK STATE MUSEUM 



The potash-soda ratio is such that the rock comes close to sub- 

 rang 2, Dellenose. 



Mode calculated from measured sections 



Microperthite 

 Orthoclase 

 Microcline. . . 

 Plagioclase. . . 



Quartz 



Biotite 



Magnetite. . . . 



Zoisite 



Zircon 



Apatite 



Total 

 diameters 



1788 



1155 



l8lO 



IOI4 



2717 



500 



90 



60 



21 



13 



9168 



Relative 

 volumes 



19 

 12 



19 

 II 

 29 



5 



50 

 64 



74 

 06 



63 

 45 

 98 



65 

 22 



14 



100.01 



Sp. gr. 



2.6 

 2.6 

 2.6 



2.63 

 2.65 



3.00 



525 

 3.26 



4-5 

 3-2 



Units 

 by weight 



4648 



3003 

 4706 

 2667 

 7200 

 1500 



473 

 196 



94 

 42 



24529 



Percentage 

 weights 



18.95 

 I2.24 

 19.18 

 IO.87 

 29 -35 



6. 12 



i-93 

 .80 



•38 



•17 



99-99 



According to the old classification this rock is a biotite-granite- 

 porphyry while under the new classification it is a biotite-grano- 

 phyro-toscanose. 



From the above it is seen that the Northville syenite and granite, 

 though in different classes, fall in exactly corresponding orders, 

 rangs, and subrangs and this, together with the fact that the syenite 

 is close to the Persalane border, shows that these two rocks are 

 closely related in the quantitative chemical classification. Thus the 

 field relations, examination of thin sections and chemical composi- 

 tion of these two rocks, which present such a marked difference in 

 appearance, afford practically conclusive proof that they are of the 

 same age and represent differentiation products from the same 

 magma, the granite representing merely somewhat more salic 

 (richer in quartz and feldspar) portions of the cooling magma. 



In the following table the Northville syenite and granite are 

 compared with certain other carefully studied Adirondack rocks : 



