286 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



must have been several millimetres. It is likewise difficult to be certain of the 

 exact nature of the original feldspars. Microcline, microperthite, and musco- 

 vite are all more abundant in the phase of greatest crushing, and are probably in 

 the main of metamorphic origin. Some part of their volume may thus represent 

 the product of changes wrought in the somewhat sodiferous orthoclase. The 

 soda-potash intergrowttas of the microperthite have not, as a rule, the regularity 

 of form characteristic of this feldspar when crystallized directly from an alkaline 

 magma. In the present case the albitic material has been segregated in irregular 

 lenticules and stringers which seem to represent fractures in the original ortho- 

 clase. A little of the muscovite may be a primary accessory of the rock, for it 

 then occurs in parallel intergrowths with the undoubtedly primary biotite. 



It may be noted that the" accessories, apatite, magnetite, and titanite, are 

 either entirely absent or exceedingly rare in the zones of specially intense shear- 

 ing and crushing; their removal seems to be one of the results of the meta- 

 morphism. In several thin sections prisms of allanite were noted and, in one 

 slide, a little fluorite; these minerals should, probably, be added to the list of 

 primary accessories. 



All phases are generally very fresh and the secondary products, kaolin, 

 chlorite, and sericite, are unimportant. The observation was made in the field 

 that the rock of the zones of maximum shearing and crushing is very consider- 

 ably tougher under the hammer than the coarser porphyritic granite and augen- 

 gneiss alongside. In the bed of Boundary creek the former rock stands out in 

 long ridges or riffles, between which the softer granite has been eroded by the 

 sluicing waters of the creek. This contrast of strength shows that the batholith 

 lay deeply buried at the time of its shearing so that the crush-zones underwent 

 cementation, which made them actually stronger than the rock more closely 

 resembling the original granite. 



The specific gravities of typical specimens from the batholith vary from 

 2-640 to 2-677, with an average for five specimens of 2-658. 



A large type specimen, collected at a point on the Boundary creek wagon- 

 road, about two miles from the ferry at the eastern end of the road, has been 

 analyzed by Mr. Connor. The large phenocrysts are here generally micro- 

 cline, although a few, twinned on the Carlsbad and albite laws, are acid oligo- 

 clase near A^An^. The essentials of the coarse ground-mass are quartz, 

 microcline, orthoclase (sometimes obscurely microperthitie), oligoclase averag- 

 ing apparently Ab„ An,, muscovite and biotite. The occessories are the same 

 as those noted in the foregoing description of the average rock. A trace of 

 secondary calcite was observed in the thin section. 



The analysis of this specimen (No. 962) resulted as follows (Table XVII., 

 Col. 1) :— 



