Weed and Pirsson — Bearpaw Mountains, Montana. 357 



from it ; further, the author proposes to erect a new series co- 

 equal with the granite-syenite and diorite-gabbro series ; the 



middle members of this series are the " monzonites " and in 

 minerals, structure, and chemical composition they are the 

 equivalents of our Yogoites. 



I. II. III. la. 



Si0 2 52-81 54-42 54*20 -8801 



Al 2 O s . 15-66 14-28 1573 -1520 



Fe 2 3 3-06 3-32 3*67 '0191 



FeO__ 4-76 4*13 5-40 0661 



M^O 4-99 6-12 3-40 "1247 



CaO „._.._.. 7-57 7-72 8-50 -1352 



Na 2 0.. 3-60 3-44 3'07 '0580 



K 2 U 4-84 4-22 4'42 -0513 



H 2 O + 110° -93 -38 ) 



H 2 O-110° -16 *22 f DU 



Ti0 2 -71 -80 -40 



Fl trace 



CI -07 



P 2 6 .--_ -75 -59 -50 



SO s trace 



MnO _ trace -10 -70 



BaO -24 -32 ? 



SrO -09 '13 ? 



Li 2 - . trace trace 



100-24 100-19 100*49 



= C1 -02 



100-22 



I. Monzonite, " Yogoite," or basic syenite, Beaver Creek, Bear- 

 paw Mountains. H. N. Stokes anal. 



IT. Monzonite, " Yogoite," or basic syenite, Yogo Peak, Little 

 Belt Mountains, Montana. W. F. Hillebrand anal. 



II I. Monzonite (Brogger, Erupt. Gest. Predazzo, 1895, p. 24). V. 

 Schmelck anal. 



la. Molecular proportions in No. I. 



This is also clearly shown by analysis No. Ill, which is that 

 of a typical monzonite. Rosenbusch,* however, regards these 

 as being representatives of the basic syenites, or that member 

 of the syenite family rich in the dark-colored components as 

 its distinguishing characteristic. He calls it the monzoni 

 type. 



As this type of granular rock corresponds so closely in all 

 essential features and in chemical composition with our yogoite 

 and the name " monzonite " has priority in date, we desire to 



*Mikr. Phys. Mass. Gest., 3d ed., p. 123, 1895. . 



