Weed and Pirsson — Bearpaw Mountains, Montana. 295 



they are various mixtures of alkali feldspars, which agrees with 

 the rock analysis. Nothing definite concerning them could be 

 made out by examination in convergent light. 



The quartz is clear and limpid and occupies minute irregu- 

 lar areas between the feldspars ; a few larger grains were seen. 

 It is small in amount and it does not appear very evenly dis- 

 tributed, some areas being much richer in it than others. 



Au occasional small zircon and one or two scattering biotite 

 leaves complete the list of minerals. The rock, with the excep- 

 tion of the slight kaolinization mentioned, is very fresh. An 

 analysis of it, made for us by Dr. H. N. Stokes, in the labor- 

 atory of the IT. S. Geol. Survey, resulted as follows : 



I. 



Si0 3 66-22 



Al 2 O s 16-22 



Fe,0 3 1-98 



FeO -16 



MgO -77 



CaO. 1-32 



Na 2 649 



K 2 ... 5-76 



H 2 above 110° -24 

 H 2 below 110° -08 



MnO trace 



Ti0 2 -22 



P 2 6 -10 



BaO -29 



SrO '06 



SO s -02 



CI -04 



Fl trace 



Li„0 „ trace 



II. 

 65-54 



17.81 

 •74 

 1-15 

 •98 

 1-92 

 5-55 

 5*58 



•54 



trace 

 •11 



trace 

 not det. 

 not det. 



trace 



III. 

 66*13 



17-40 



2-19 



•04 



•81 



5-28 



5-66 



1-22 



•13 



•74 



9 



IV. 

 64-63 

 18-15 



3-05 



•50 

 1-54 

 5-80 

 4-76 



1-08 



1-00 



? 

 9 



99-92 



9954 



100-54 



= C1 



99.96 



I. Quartz-syenite-porphyry, Gray Butte, Bearpaw Mountains, 

 Montana. H. N. Stokes, anal. 



II. Quartz-syenite, Highwood Peak, Highwood Mountains, 

 Montana. L. V. Pirsson and W. L. Mitchell, anal. 



III. Porphyritic quartz-syenite, near Thinghoug, So. Norway, 

 G. Sarnstrom, anal. (Brogger Min. Syenit pegmatit gange, 

 1889, p. 46.) 



IV. Quartz-syenite (dike), Fourche Mountains, Ark. R. N. 

 Brackett, anal. (Igneous Rocks of Ark., J. F. Williams, Rep. 

 State Surv., 1890, vol. ii, p. 96.) 



