REPORT OF THE CHIEF ASTRONOMER 320 



SESSIONAL PAPER No. 25a 



Quartz 3-90 



Orthoclase 18-35 



Albite 40-35 



Anorthite 12-23 



Diopside 11-02 



Hypersthene 6-78 



Magnetite 4-18 



Ilmenite 1-98 



Apatite -31 



H,0 -56 



99-66 



Homblende-augite Latite. — A fourth type was collected at the 3,100-foot 

 contour on the slope due east of Sayward railway station. It is a dark gray 

 rock with conspicuous, lustrous, black prisms of phenocrystic hornblende in a 

 gray-tinted ground-mass. The acicular hornblendes vary from 1 mm. to 4 

 mm. in length and are arranged in roughly fluidal fashion. They are accom- 

 panied by a subordinate number of idiomorphic augite prisms, also pheno- 

 crystic but first discovered in thin section. The ground-mass is a rather 

 confused, macrocrystalline aggregate of the same bisilicates and feldspar. In 

 this case there can be no question that orthoclase forms a large proportion of 

 the ground-mass feldspar microlites, which for the rest are probably labradorite. 

 Magnetite, pyrite, pyrrhotite, and a little titanite are accessory minerals; calcite, 

 chlorite, epidote, kaolin, and sericite are secondary products. This specimen 

 (No. 557) is comparatively fresh. Its analysis, by Mr. Connor, resulted in the 

 form shown in Table XXL, Col. 1. 



Table XXI. — Analyses of homblende-augite latite. 



1. 2. 2a. 

 Mol. 



Si0 2 52-17 52-17 -870 



TiO, -80 -80 -018 



A1 2 0, 16-59 16-59 -163 



Fe-A 8-32 1-86 -012 



FeO.. notdet. 3-74 -052 



MnO -11 -11 -001 



MgO 3-87 3-87 -097 



CaO 8-25 8-25 -147 



SrO -05 -05 



BaO -15 -15 -001 



Na,0 3-91 3-91 -063 



K 2 4-00 4-00 -043 



H 2 at 110°C -13 -13 



H 2 above 110°C 1-17 1-17 



P 2 B -24 -24 -001 



C0 2 -56 -56 



S 1-37 



FeSj and Fe,S 8 2-31 



101-69 99-91 



Sp. gr 2-852 



On account of the presence of pyrrhotite the ferrous oxide could not be 

 directly determined. The proportion of this oxide was estimated, as shown in 



