MOUNT RAINIER 



below on Gibraltar, hypersthene andesite occurs with 

 considerable variation of color and texture. On the 

 spurs west of Nisqually Glacier the andesites contain 

 both pyroxenes, the augite being somewhat the more 

 important. 



The distribution of the volcanic rocks, as deter- 

 mined in the study of reconnaissance collections, in- 

 dicates that the cone has been built up by eruptions of 

 lava and of fragmental material. The successive lava 

 streams were doubtless of considerable thickness, but 

 were limited in lateral extent. The beds of fragmental 

 material are of the nature of flow breccias and of coarse 

 agglomerates on the higher slopes, while tuffs occur at 

 a greater distance from the center of eruption. This 

 composite cone appears to be remarkably free from 

 radial dikes, which may indicate that the volcanic 

 energy was expended chiefly at the crater. The 

 variation in rock types on different sides of the volcanic 

 cone may be evidence of changes in position of the 

 center of eruption. The destruction of an earlier 

 crater and the eccentric position of a later would give 

 rise to such a radial distribution of lavas as has been 

 described above. 



GRANITE 

 OCCURRENCE 



The presence of an acid holocrystalline rock on the 

 slopes of Mount Rainier was first reported by Lieu- 

 tenant Kautz in 1857, from whose accounts Dr. George 

 Gibbs was led to announce the occurrence of granite 

 as a dike in recent lavas. 1 Emmons in 1870 observed 

 a cliff of "beautiful white syenitic granite" rising 

 above the foot of Nisqually Glacier and correctly 

 interpreted the geologic relations. In 1895, on a 

 reconnaissance trip, the writer identified granite among 

 the bowlders composing the lateral moraines of Carbon 



1 Emmons, Bull. Am. Geog. Soc., 1877, No. 4, p. 45. 

 250 



