REPORT OF THE CHIEF ASTRONOMER 347 



SESSIONAL PAPER No. 25a 



Of the hundreds of square miles which may represent the total area of the 

 Trail batholith, only thirty-five are included in the ten-mile helt along the 

 International line; the following description of the Trail granite is founded 

 on studies made in this portion of the mass. 



Petrography. — The dominant phase is a medium-grained to somewhat 

 coarse-grained rock of pure gray colour. It is rich in the femic constituents, 

 dark green hornblende, and hiotite, as well as in plagioclase, which, with the 

 likewise macroscopically visible quartz and orthoclase, completes the list of 

 essentials found in a typical tonalite or granodiorite. The rock, has, in general, 

 the unmistakable habit of a granodiorite. It generally shows evidences of 

 strain and, in places, is distinctly gneissic through pressure. 



Under the microscope, the accessory minerals are seen to be the usual 

 magnetite, apatite, and titanite, with rare zircons. The orthoclase is often 

 replaced by microcline; the plagioclase is often zoned and averages basic 

 andesine, near Ab, An 3 . The characters of the minerals and the rock-structure 

 are those common in granodiorite and do not need special description. Epidote 

 is a common metamorphic product in the crushed phase of the batholith. 



A typical fresh specimen (No. 509), collected in a railway cutting two 

 miles west of Trail, was analyzed by Mr. Connor with the following result : — 



Analysis of granodiorite, Trail batholith. 



Mol. 



Si0 2 62-08 1-035 



Ti0 2 -73 -009 



Al 2 O s 16-61 -163 



Fe 2 3 1-63 -009 



FeO 3-72 -051 



MnO -11 -001 



MgO 2-44 -061 



CaO 5-20 -093 



SrO -03 



BaO -09 -001 



Na,0 3-18 -052 



K„0 3-29 -035 



H„0 at 110°C -16 



H 2 above 110°C 1-00 .... 



P 2 5 -30 -002 



100-47 



Sp.gr.. 2-754 



Calculated norm: — 



Quartz 15-48 



Orthoclase 19-4-6 



Albite -. 27-25 



Anorthite 21-13 



Diopside 11-52 



Magnetite 2-08 



Ilmenite 1-36 



Apatite -62 



Water ,. 1-16 



100-06 



