56 The American Geologist.' •^"'^'' ^^*^-- 
few miles below the mouth of Pelly river, and recrosses it 
above the mouth of Fortymile river. Between these two 
points areas of g^ranite g-neiss and other igneous schists are of 
constant occurrence. The s'neisses are also found on the 
lower fiftv miles of the Stewart river a northeastern tributary 
of the Yukon and on the lower part of White river, a streain 
entering the Yukon from the opposite direction a few miles 
above the mouth of the Stewart. The width of the gneissic 
belt on the Stewart and White rivers, the only point at which 
it is even approximately known, measures no miles. 
The area roughly defined above, 380 miles in length and 
no miles in width, is only partially underlaid by gneisses. 
In the region examined by the writer, the g^neisses alternate 
with bands and areas of altered elastics consisting mostly of 
dark and lead gray quartz-mica schists, hard quartzytes and 
crystalline limestones, and they are overlaid by wide areas of 
comparatively recent sedimentary and pyroclastic rocks, as- 
sociated with andesytes, rhyolytes and basalts, all of which 
have been referred provisionally to the Tertiary- 
The gneisses, as might be expected considering their wide 
areal distribution, exhibit great variety in texture, composition 
and general appearance in the field. The ordinary variety is a 
grey medium textured, granular rock, passing on the one hand 
into a fine grained schist, difficult and occasionally impossible 
to distinguish from the recrystallized elastics with which it is 
often associated, and on the other hand into an exceedingly 
coarse grained and unmistakable gneissoid granite. Porphyr- 
itic phases are also not uncommon. A wide band of reddish 
augen eneiss crosses the head of Australia creek, the feldspar 
crystals of which are drawn out into lenses often two inches 
in length. Areas and bands of augen gneiss, often alternating 
with the ordinary granular variety, were also noticed at several 
points in the Yukon valley and on the Stewart. Near Selwyn 
river the gneisses have a striped or banded character due to 
the alternation of light grey and dark varieties in bands of 
irregular width. The dark bands differ from the light color- 
ed ones only in containing a larger proportion of the dark 
ferromagnesian minerals. The banding in all cases appeared 
to be parallel to the schistosity. 
