126 DESCEIPTIVE GEOLOGY. 



exception of olivine, exhibiting no well-defined mineral constituents. A 

 specimen from a hill southwest of Buffalo Peak, under the microscope, indi- 

 cated triclinic feldspars, augite, olivine, and specular iron in an exceedingly 

 fine groundmass. 



From this same hill, Mr, R. W. Woodward analyzed the rock, with the 

 following result : 



Silica 49.04 49.01 



Titanic acid 2.46 2.55 



Alumina 18.11 18.32 



Fenic oxide 2.7l 2.63 



Ferrous oxide 7.70 7.74 



Manganous oxide trace trace 



Lime 7.11 7.14 



Magnesia 4.72 4.72 



Soda 4.22 4.21 



Potassa 2.11 2.18 



Water 1.29 1.35 



99.47 99.85 

 Specific gravity, 2.8, 2.7. 



This analysis shows a typical basalt, containing, however, a large 

 amount of titanic acid, which is of some interest, when we remember the 

 occurrence of titanite in the eruptive rocks of Parkview Peak, as well as in 

 the trachytes from Whitehead Peak. 



East of Buffalo Peak occur some interesting dikes of basalt pene- 

 trating the Cretaceous strata like ramparts, and standing above the sedi- 

 mentary beds in almost unbroken walls for long distances. Where observed, 

 they strike north 40° to 50° west. They resemble the rock from Buffalo 

 Peak, except that they appear richer in olivine. West of the Platte, very 

 similar basalts extend to Rabbit Ears, a peak which rises with considerable 

 prominence above the surrounding country in rough jagged points of dark- 

 gray vesicular basalt. It lies directly against the Archaean rock-mass of 

 the Park Range, and forms the most westerly outburst of a most interesting 



