354 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



Analyses of igneous rocks from Yogo Peak and Square Butte, Montana. 



Constituent. 



l 



2 



3 



4 



5 



SiO, 



61. 65. 



.56 



15. 07 



2.03 



2.25 



.09 



3.67 



4.61 



.27 



4.35 



4.50 



.33 



Trace. 



.10 



Trace. 



54.42 



.80 



14.28 



3.32 



4.13 



.10 



6.12 



7.72 



.32 



3.44 



4.22 



.59 



Trace. 



.13 



Trace. 



48.98 



1.44 



12.29 



2.88 



5.77 



.08 



9.19 



9.65 



.43 



2.22 



4.96 



.98 



Trace. 



.08 



Trace. 



.22 



.26 



.56 



46. 73 



.78 



10.05 



3.53 



8.20 



.28 



9.68 



13.22 



56. 45 



.29 



20.08 



1.31 



4.39 



.09 



.63 



2.14 







FeO 



MuO 



MgO 



CaO 



BaO 



Na,0 



LSI 

 3.76 

 1.51 



5.61 



7.13 



.13 



to 



p.o, 



Cr:0 3 



SrO 







Li,o 



Trace. 

 CI .18 



I 1. 24 







.43 

 1.77 



H"0 at 110° 



.26 

 .41 



.22 



.38 



H*0 above 110° 



Total 



100. 15 



100. 19 



99. 99 

 0=F1 .08 



100. 97 

 0=C1 .04 



100. 45 

 .10 





99. 91 



100. 93 



100. 35 



1. Syenite, Yogo Peak. Analyzed by W. F. Hillebrand. 



2. Mouzouite, Yogo Peak. Analyzed by \V. F. Hillebrand. 



3. Shonkinite, Yogo Peak. Analyzed by W. F. Hillebrand. 



4. Sbonkinite, Square Butte. Analyzed by L. V. Pirsson. 



5. Sodalite-syenite, Square Butte. Analyzed by W. H. Melville. 



These authors state that the three rocks from Yogo Peak grade into 

 one another, and are facies of one mass, whose variations are the result of 

 differentiation. They are granular crystalline, and .consist essentially of 

 orthoclase and augite in different proportions, with subordinate amounts 

 of plagioclase, biotite, magnetite, and in the syenite, hornblende, and in 

 shonkinite, olivine, besides accessory minerals. In the syenite orthoclase 

 exceeds augite, in monzonite 1 orthoclase equals augite, and in shonkinite 

 augite exceeds orthoclase. Chemically the series from Yogo Peak is 

 characterized by comparatively low alumina, with relatively high potash, 



1 The rook called yogoite in the paper cited has been shown by these authors in a subsequent 

 paper to be the same as Brogger's monzonite, and the name yogoite has been withdrawn. See The 

 Bear Paw Mountains of Montana: Am. Jour. Sci., 4th series, Vol. 1, 1896, pp. 351-362. 



