512 



OGILVIE 



weathered, in which it resembles the second type (monzonose). 

 It differs from both in that the ground-mass is lighter colored, 

 and the general tone of the rock is greenish gray rather than 

 black. 



Microscopic Character. — The lighter color is found to be due 

 to the presence of a larger proportion of orthoclase, albite and 

 quartz, with less mica, and the green tone to the presence of 

 green hornblende. 



Hornblende is the prevailing femic mineral and is of two 

 varieties, a deep reddish, basaltic variety and a colorless or green- 

 ish one. The latter is frequently twinned. Biotite is present, 

 frequently intergrown with the colorless hornblende, in which 

 relationship the biotite appears to be the older. Titanite and 

 apatite are abundant. The titanite is remarkable for having 

 double refraction and slight pleochroism from colorless to red- 

 dish. It has deep irregular cracks and polysynthetic twinning. 

 It encloses apatite, and is frequently surrounded by rims of 

 magnetite with the colorless hornblende. Pyroxene is entirely 

 lacking. The analysis of umptekose is given in Column III of 

 Table VIII. 



Table VIII. 





Analyses and Molecular Proportions of Mon 



zonites. 





I. 



II. 



III. 



Si0 2 



5S-i7% 



.919 



59-64% 



■994 



58-74% 



•979 



A1 2 3 



18.01 



.176 



14.76 



•145 



14.61 



•143 



Fe 2 3 



.08 



.001 



• 41 



.003 



.48 



.003 



FeO 



5-4i 



■°75 



3-57 



.0^0 



3-7° 



■051 



MgO 



5-29 



.132 



5-53 



.138 



5-47 



■137 



CaO 



5-64 



.119 



3-i7 



•°57 



3-34 



.060 



Na 2 



2.12 



• 034 



3-27 



■o59 



5-7° 



.092 



K 2 



5-48 



•059 



6.69 



.071 



3-79 



.040 



H 2 + 



.29 





• 14 





•27 





H 2 0- 



.01 





■°3 





•17 





Ti0 2 



2-33 



.029 



2.1 1 



.026 



1.87 



.024 



CO, 



none 





none 





none 





P 2 5 



•25 





.60 





1. 00 





Total 



100.86 



99.92 



99.14 





