352 



GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



described by Merrill are shown in the first four analyses in the table, 

 which is introduced here for comparison with those of absarokite in the 

 Yellowstone Park. 



Analyses of absarokite and similar rocks. 



Constituent. 



l 



2 



3 



4 



5 



6 



7 



Si0 2 



46.90 



.41 



10.17 



.33 



1.22 



5.17 



.10 



20.98 



6.20 



1.16 



2.04 



.44 



49.13 



.42 



9.05 



.39 



3.57 



5.05 



.15 



17.21 



5.68 



' 2.01 



2.24 



.38 



.05 



50.82 



.59 



11.44 



.03 



.25 



8.94 



.19 



14.01 



8.14 



1.79 



3.45 



.20 



.06 



51. 65 



.55 



13.89 



.80 



2.70 



4.80 



.15 



11.56 



4.07 



2.99 



4.15 



.21 



.19 



.19 



1.30 



1.89 



50.03 



.61 



14.08 



Trace. 



2.92 



6.11 



.08 



10.73 



7.46 



1.46 



2.64 



.42 



.04 



52.33 

 .14 



15.09 



54.15 

 Not det. 



18.92 





AL0 3 



Cr 2 03 



Fe Ot 



4.31 

 4.03 



.09 

 6.73 

 7.06 

 3.14 

 3.76 

 1.02 



.07 



| 6.79 



Not <let. 

 1.90 

 3.72 

 5.47 

 8.44 



Not det. 

 CI. 42 



FeO 



MnO 



MgO 



CaO 



K 2 



BaO 



so. 





H ; Oat 100° 



1.04 

 4.38 



.84 

 3.50 



.58 



3.70 



2.68 





Not det. 



Total 



100. 54 



99.67 



100. 49 



101.09 



100. 28 



100. 45 



99.81 



1. Fort Ellis, 2i miles southeast of Bozernan, Montana. Analyzed by T. M. Chatard. 



2. Bear Creek, Madison Valley, Montana, Analyzed by T. M. Chatard. 



3. South Bowlder and Antelope Creek, Montana. Analyzed by L. G. .Eakins. 



4. Cottonwood Creek, Montana. Analyzed by T. M. Chatard. 



5. Cottonwood Creek, Montana. Analyzed by L. G. Eakins. 



6. Cottonwood Creek, Montana. Analyzed by L. G. Eakins. 



7. Cottonwood Creek, Montana. Analyzed by G. P. Merrill. 



The variability of these rocks within certain limits is evident, the 

 greatest range being in magnesia. While not exactly alike chemically, 

 they agree in being low in silica and alumina, high in magnesia, compara- 

 tively high in alkalies, with high potash. The rock from which the fifth 

 analysis was made is a transitional variety between absarokite and the 

 normal basalt of the region. 



The sixth analysis is from an intrusive rock called augite-porphyrite 

 by Merrill. It corresponds to shoshonite in alkalies, but is lower in alumina 

 and higher in magnesia and lime. It is intermediate between shoshonite 

 and absarokite. It is associated with the rocks whose chemical composition 

 is given by analyses 4 and 5, and plainly belongs to this series. 



