SERIES OF INTRUSIVES. 



263 



The order of crystallization of the minerals throughout the series is due 

 to their relative solubility in the eruptive magma. Among various factors 

 affecting solubility the fusion point of the chemical compounds constituting 

 the different minerals, the temperature of the magmas, and the pressure 

 under which the minerals crystallized, are important. The porphyritic and 

 the ophitic textured rock facies, having cr.ystallized under different condi- 

 tions of pressure and of temperature from those under which the granular 

 rocks were formed, show, as is to be expected, a different order of crystal- 

 lization of minerals. 



CHEMICAL COMPOSITION OF THE SERIES. 



In the following tables there are reproduced the analyses which have 

 been obtained of the various types. They are arranged according to dimin- 

 ishing acidity. Nos. 1 and 4 were analyzed by Dr. H. N. Stokes, Nos. 2 

 and 3 by Mr. George Steiger, both of the United States Geological Survey: 



Table I. — Analyses of Crystal Falls rocks. 



(1) Mica-diorite (quartzitic); (2) Hornblende-gabbro ; (3) Norlte; (4) Peridotite (wehrlite). 



