MONTEZUMA EANGE. 765 



of included grains of picotite. Microscopical apatite crystals and magnetite 

 grains are also seen. 



Skirting the southern flanks of the range are the upturned beds of 

 Miocene strata, description of which will be found under the head of the 

 Kawsoh Mountains. 



At the extreme southwestern end of the range occurs the propylitic body 

 already mentioned, where it serves as a depressed connection between the 

 Montezuma and Truckee Ranges. It is found as a group of low hills, largely 

 concealed by the drifting sands of the desert, and presents a gray-green, 

 dense, tough rock, made up of plagioclase and decomposed hornblende. 



An analj^sis of this propylite gave Mr. R. W. Woodward the following 

 ultimate composition : 



Silica 60.33 



Alumina 21.49 



FeiTOus oxide 1.55 



Manganous oxide trace 



Lime 3.73 



Magnesia 4.01 



Soda - 4.36 



Potassa - . . 1.62 



Water 3.13 



100.22 

 Specific gravity, 2.66, 2.7 



Geologically, the lower half of the Montezuma Range is made up of 

 an intricate series of broad, heavy, massive, rhyolitic eruptions, having a 

 northeast and southwest direction, breaking through which are powerful 

 sheets of basalt, frequently capping the higher ridges. In few ranges are 

 the direct relations between rhyolite and basalt so distinctly seen as here. 

 Lithologically, the rhyolites of the Montezuma Range present an almost 

 endless variety of forms, but, in general, they may be said to be poor in 

 types containing secreted minerals, especially quartz-grains, in this respect 

 differing widely from the rhyolites of the Pah-Ute Range and Augusta 



