MOUNT RAINIER 



Of how large a part of the lava flows the crater still 

 remaining was the point of origin is a queston to be 

 answered only after more detailed observation has 

 been made. The best section for the study of the suc- 

 cession of flows and ejectamenta is the amphitheater 

 at the head of the Carbon Glacier. The 4,000 feet of 

 rock in this bold wall would afford an excellent oppor- 

 tunity for this were it not that frequent avalanches 

 preclude the possibility of geologic study except at 

 long range. 



MEGASCOPIC CHARACTERS 



The volcanic rocks of Rainier are of varying color and 

 texture. Dense black rocks with abundant phenocrysts 

 of glassy feldspars, rough and coarse lavas of different 

 tints of pink, red, and purple, and compact light-gray 

 rocks are some of the types represented upon the slopes 

 of this volcanic cone. In color, the majority of the 

 rocks may be grouped together as light gray to dark 

 gray. The black and red lavas are less common. In 

 texture, the Rainier lavas are, for the most part, com- 

 pact. Slaggy and scoriaceous phases are common, 

 but probably represent only a small part of the differ- 

 ent flows. Near the Guardian Rocks large masses of 

 ropy lava are found which suggest ejected bombs. 

 Agglomeratic and tuffaceous rocks are of quite com- 

 mon occurrence, although less important than the 

 lavas. Vesicular lavas occur at several localities, 

 and fragments of a light-olive pumice, many as large 

 as a foot in diameter, wholly cover some of the long, 

 gentle slopes southeast of Little Tahoma and in Mo- 

 raine Park. 



Contraction parting or jointing is often observed, 

 being especially characteristic of the basaltic types. 

 The platy parting is the more common, but the col- 

 umnar or prismatic parting is well exhibited at several 

 localities. The black basaltic lava east of Cowlitz 

 Glacier shows the latter structure in a striking manner. 



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