208 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



position from a normal hornblende to one abnormally high in soda, 

 brought about through contact with a magma, becoming increasingly 

 rich in soda molecules. At times the arfvedsonite mineral is 

 slightly decomposed. 



The pyroxene presents nothing novel. Basal sections are rather 

 frequent and exhibit the well-developed prismatic cleavages. It is 

 of the augite variety. This, together with zircon, apatite, biotite, 

 ilmenite, and magnetite, together with a scattering quartz, complete 

 the list of original minerals. 



In the vicinity of the amphibole, much iron oxide has separated. 

 It is black in shade and irregular in outline. It has been derived 

 from the hornblende, but the residual mass of this mineral appears 

 perfectly fresh. Clouds of yellow ocher were noted, chiefly in the 

 vicinity of the pyroxene, and from the analysis ilmenite also appears 

 to be quite abundant. Fluid inclusions in the quartz are not un- 

 common. 



The analysis of this rock follows : 



Analysis of Quartz Monzonite. (W. C. Phalen, Analyst.) 



SiO. 67.27 



ALO3 13.67 



Fe^Os 1.83 



FeO 2.49 



MgO 1.72 



CaO 1.90 



NhlO 2.79 



K.O S.80 



H2O above 100° 45 



H2O below 100° 08 



Ti02 1.70 



P2O5 16 



MnO .19 



1 00.05 

 Part II 



INTRODUCTION 



During the preparation of this article a new rock classification 

 has appeared, based on the chemical relations which obtain in igneous 

 rocks. ^ It was decided by the writer to incorporate the principles 

 of this classification into the body of this present theme, in so far 

 as they were applicable, but on maturer thought this was deemed 

 inadvisable for the following reason. It was held that to introduce 

 so much of an entirely new nomenclature into an article where an 

 old and familiar group of names must of necessity predominate at 



^ Quantitative Classification of Igneous Rocks, by Cross, Iddings, Pirsson, 

 and Washington. Chicago, 1903. 



