VARIATIONS OF TEXTURE IN IGNEOUS ROCKS 593 



Analyses of the rocks are as follows (analyst, Dr. H. N. 

 Stokes") : 



In No. I the ratio of NaaO + K3O : CaO = i : i.i. In No. 

 2 the same ratio is i : 1.13. These ratios are calculated from 

 the quotient figures obtained by dividing the percentages of 

 each by the molecular weights. Similarly in No. i the ratio of 

 KgO : CaO is i : 4.95. In No. 2 the same ratio is i : 4.18. 



No. 2 contains less quartz and more hornblende than No. i, 

 hence the decrease in silica and the increase in magnesia ; other- 

 wise the two rocks are the same. 



Correlation of rocks. — As before stated, just west of Mason's 

 Butte lies the northern end of the Smith Valley and Pinenut 

 ranges. On crossing from Waubuska through Churchill Can- 

 yon, andesites were found which were recognized in the field as 

 similar to those in the butte. The bedding of these rocks is 

 nearly horizontal. They are fine-grained hornblende-andesites, 

 often with fine holocrystalline groundmass ; occasionally they 

 vary to fine-grained diorite porphry. In higher portions of the 

 mountains (these relatively coarse-grained lavas are exposed in 

 the lowest cuts) the lavas are dacites and pyroxene andesites. 



Andesites form the main mass of the Pinenut range at its 

 northern end, which is separated from the Washoe district at 



