SA.. 

 TA.. 



AlA. 



FeO., 

 MnO. 

 CaO., 

 MgO. 

 NaaO, 

 K2O., 

 H.,0., 



Sp. gr, 



PETROGRAPHY 









66)^ 



ties of the 



porphyry gave the 



following 



results: 



I. 





II. 



III. 









69.48 





77.30 



66 22 









— 





— 



.22 









14.19 





11.08 



16.22 









3.89 





3.91 



1.98 









1.47 





— 



.16 









.12 







Tr. 



P„0, 





0.10 



■ .90 





.68 



1.32 



BaO 





.29 



.68 





.45 



.77 ■ 



SrO 





.06 



5.32 





3.44 



6.49 



SO3 





.02 



4.34 





3.22 



5.76 



CI 





.04 



.72 





.28 



.30 



Fl andLiOa- 



Tr. 



101.11 



100.36 



99.97 



\, 2.63 



Sp. 



gr.,2.64 





= C1... 



... 



.01 



99.96 



I. Quartz-syenite porphyry, Rigaud (analyzed by 0. E. Le Roy). 

 II. Quartz porphyry, Rigaud (analyzed by 0. E. Le Roy). 

 III. Quartz-syenite porphyry, Bearpaw mountains, Montana (analyzed by 

 H. N. Stokes). 



The ratio of the alkalies in I shows that the soda molecule is the pre- 

 dominant one, and that the feldspar is undoubtedly anorthoclase. The 

 ratio is comparable with that of the alkalies of III, in which rock the 

 feldspar is also anorthoclase. In II the soda and potash are in almost 

 equal amount, and as the feldspar is with few exceptions only present 

 in the groundmass, the result indicates a close identity in composition 

 between the feldspar of the base and the phenocrysts. The rather high 

 percentage of iron is accounted for by the magnetite in the groundmass, 

 while the small amount of the ferro-magnesian constituents is shown by 

 the percentage of lime and magnesia. 



A PL I TIC DIKE 



The dike cutting the syenite is a rather coarse grained aplite, which 

 when fresh is gray in color and weathers to a light reddish brown. Ex- 

 amined microscopicall}^ it is seen to, have a granular structure, and is 

 made up of allotriomorphic grains of unstriated feldspar and quartz, 

 with a few small individuals of plagioclase, apatite, and brown biotite. 

 The feldspar is untwinned with the exception of a few Carlsbad indi- 

 viduals ; it is very turbid and has numerous small flecks of brownish 

 limonite along the cleavage and contact planes. Associated with it are 

 a few striated individuals of oblong form, also much kaolinized. The 

 former is probabl}^ orthoclase, the latter an acid plagioclase. The quartz 



