TEACH YT1C EHYOLITE. 



Analyses of trachytic rlvyolite. 



[Analysts: 1, J. E. 'TC'liitfield; 2, L. G. Eakins/ 



325 



Constituent. 



l. 



2. 



SiO- 



64.65 



Trace. 



17.80 



2.33 



2.10 



Trace. 



69.45 



.19 



14.92 



3.16 



.23 



.07 



.03 



1.19 



.05 





Al 0, 



Fe-.0 ; 



FeO 



MuO 



BaO 



CaO 



1.73 

 .81 

 .17 



4.18 



2.83 



Trace. 



.43 



3.06 



MgO 



Li,0 



Na,0 



3.19 

 5.95 



.06 



1 K->0 . . 



P,0. 



SO, 



H 2 



1.69 





100. 09 



100. 18 



Trachytic tuffs similar in composition occur in two other localities in the 

 Park. One is on the south fork of Beaverdam Creek, where it overlies 

 shoshonite, and the other is at Two Ocean Pass, where it occurs in the 

 bottom of the andesitic breccia near the basaltic lavas (shoshonite). They 

 are all alike in being composed of a glassy groundmass, with phenocrvsts 

 of sanidine and lime-soda feldspar, besides biotite, magnetite, or ilmenite, 

 and many inclusions of other rocks, pyroxene-andesites for the most part 

 (1650, 1722, and 1725). In the rock from Two Ocean Pass there are 

 labradorite crystals and fragments and numerous broken augites, as well as 

 pieces of andesite. In this rock it is possible that the labradorite crystals 

 may have been derived from the andesite dust. The presence of labradorite 

 in association with orthoclase in parts of this rock corresponds to the simi- 

 lar association of these two feldspars in shoshonite and banakite, and indi- 

 cates a genetic relationship, which is also indicated by the close association 

 of these rocks in the held. 



