354 Weed and Pirsson — Bearpaw Mountains, Montana. 



I. II. 



Si0 2 68-34 66-22 



A1 2 3 15-32 16-22 



Fe 2 3 1-90 1-98 



FeO -84 -16 



MgO _ -54 -77 



CaO -92 1-32 



Na 2 5-45 6-49 



K 2 5-62 5-1Q 



H 2 — 110° -15 -08 



H 2 O + 110° -30 -24 



Ti0 2 -21 -22 



Mn0 2 -07 trace 



BaO _ -08 -29 



SrO _ -04 -06 



Li 2 none trace 



P 2 6 -13 -10 



CI __ -04 -04 



Fl none trace 



SO„ _ -02 



99-95 

 •01 



99-94 



III. 



la. 



65-54 



1-139 



17-81 



•149 



•74 



•012 



1-15 



•012 



•98 



•014 



1-92 



•016 



5-55 



•08& 



5*58 



•060 



•54 





•11 





trace 





not det. 





not det. 





trace 





trace 





:::: 





9992 



99-96 



I. Quartz syenite, Beaver Creek stock, Bearpaw Mountains, 

 H. N. Stokes anal. 



II. Quartz syenite porphyry, Gray Butte stock, Bearpaw Moun- 

 tains, H. N. Stokes anal. 



III. Quartz syenite,. Highwood Peak, Highwood Mountains, L. 

 V. Pirsson and W. L. Mitchell anal. 



la. Molecular proportions of No. I. 



The low lime, iron, and magnesia show that the rock belongs 

 in the alkaline series. A couple of analyses are quoted for 

 comparison from the first part of this paper. In la are given 

 the molecular proportions of the essential oxides. These show 

 some interesting features in their mutual relations and may be 

 computed into the minerals shown in the section, as follows : 



K 3 = 060 = 1 ) 



A1 2 3 = -060 = 1 J Orthoclase 



Si0 2 = -360 = 6 ) 



Na 2 = -089 = 1 ) 



Or. 



= 33-9 



A1 2 3 = -089 =■ 1 J. Albite 



Ab. 



= 47-3 



Si0 2 = -534 = 6 ) 



Qtz. 



= 13-2 



MgO =-014 = 1) 



3&;^ii.=l I**-*. 



Pyr. 



= 31 



CaO = -014 = 1 t Pyroxene 



Magn 



= 2-5 



Si0 2 = -028 = 2 ) 













Si0 3 = '211 = free Quartz 





100.0 



The only deviation here is some 0'14 per cent of lime, which 

 belongs in the minute amount of apatite and titanite present 

 and of which no account has been taken. The rock is thus 



