284 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



somewhat by resorption carried on by this acid matrix in the late mag- 

 matic period. The hornblende seems also to be truly poikilitic, through the 

 inclusion of minute droplets or microlites of quartz and feldspar. The feldspar 

 is either a sodiferous orthoelase or its chemical equivalent, a poorly developed 

 microperthite. Not a certain trace of soda-lime feldspar could be seen. The 

 surprisingly abundant quartz occurs as glassy-clear, granular aggregates. The 

 garnet is, in thin section, of a very pale pink colour and is probably a common 

 iron-lime variety. 



The garnet is idiomorphic against the hornblende. The order of crystal- 

 lization seems to be: zircon, apatite, and magnetite; followed by garnet; then, 

 in order, hornblende, orthoclase-microperthite, and quartz. 



Calculation shows that the rock must carry about 68 per cent of silica, 

 not more than 8 or 9 per cent of alumina, and not more than about 5 per cent 

 of alkalies. The specific gravity of a typical hand-specimen is 2-894. 



The presence of essential quartz and orthoelase would place this rock 

 among the granites, but it is clearly an aberrant type in that family. It 

 may be questioned that it is advisable to risk overweighting the granite family 

 by including this rock within it, but no other place is offered to it in the prevail- 

 ing Mode classification. Its abnormal composition may be due to some assim- 

 ilation of the quartzite. There are many points of similarity between this 

 rock and certain phases of the Purcell sills across the river and it is quite 

 possible that the abnormal granite is the result of th# solution of the quartzite 

 in an original hornblende gabbro magma. The quartzite is here very poor in 

 feldspathic and micaceous constituents; hence, possibly, the absence of biotite, 

 which is so universal a constituent in the acidified phases of the Purcell sills. 



This abnormal hornblende granite is tentatively correlated with the 

 Purcell sills. Though little more crushed than those sills, it may .also be 

 possible to credit a correlation with the sheared basic intrusives found in the 

 Priest River terrane; for the deformation of the latter must have taken place 

 at a depth several miles greater than that at which the intrusives cutting the 

 much younger Kitchener formation began to feel the post-Paleozoic orogenic 

 stresses. The higher temperatures and pressures of the more deeply buried 

 massive rocks at the time of deformation would seem to be amply sufficient 

 to explain such differential metamorphic effect. 



PiYkert Granite Batholith. 



This granite, as shown on the map, covers some fifteen square miles 

 of the Boundary belt north of the line; it extends in a broad band southward for 

 an unknown distance into Washington and Idaho and the whole body is, doubt- 

 less, of batholithic size. It has intrusive relations to the Priest River terrane, 

 as shown by numerous apophyses, and by the development of a metamorphic 

 aureole about the granite. On the eastern side of the batholith the Kootenay 

 river alluvium conceals the bed-rock relations, but the granite is probably there 



