2l8 



WILLIAM H. EMMONS 



to 2"^™ long and include a considerable amount of magnetite and 

 minute particles of olivine and biotite. Olivine occurs as rounded 

 or irregular bodies, in part included in pyroxene. It is partly altered 

 to serpentine which either replaces the olivine completely, or occurs 

 along its cracks. The fibers of the serpentine are parallel and not 

 perpendicular to the boundaries and cracks of olivine. Biotite 

 surrounds magnetite and is partially altered to chlorite. Small 

 irregular grains of magnetite are present, wholly or partially included 

 in the ferromagnesian minerals. The feldspar is almost free from 

 magnetite. Apatite prisms are included in all the other minerals. 

 A small amount of calcite is present. 



The order of crystallization is as follows: (i) Olivine, apatite, 

 and some magnetite ; (2) some labradorite, pyroxene, more magnetite, 

 and biotite; (3) more labradorite; (4) orthoclase and quartz. An 

 analysis of F, from a specimen taken near the base of the cliff 

 southwest of Mud Lake (see Fig. 3) is as follows : 



ANALYSIS OF VARIETY F. GEO. STEIGER, ANALYST 



SiO^ 47 ■ 87 H2O + 1 . 25 



Al.Oj 16 



Fe.03.. '. 3 



FeO 7 



MgO 7 



CaO 10 



Na^O 2. 



K,0 



H,0- 



The norm of F calculated from the analysis is given in column I 

 of the following table ; the mode in column II. 



I. Norm II. Mode 



Quartz o Quartz o 



Orthoclase 5.56 Orthoclase 4.9 



Albite 20.44 



Anorthite 30 . 86 



Hypersthene 12 . 00 



Diopside 14 • 34 



Olivine 6.72 



Magnetite 5 . 34 



Ilmenite i . 98 



Apatite i . 01 



Water 1.53 



Total 99.78 



Albite 19.2 



Anorthite 26.7 



Pyroxene 3° • 9 



Olivine and Serpentine 6.8 



Biotite 4.5 



Magnetite and Ilmenite 5.8 



Apatite 1.2 



Total 100. o 



