■6o The American Geologist. •^"'^■' ^^''2- 
an area of sheared granite or dioryte about half a mile in 
width. At the junction of the eneiss with the clastic schists, 
the river is bordered by a high scarped bank affording an 
excellent section. The gneisses in this area contain more 
hornblende than is usually the case and in places pass into a 
dioryte. They are coarse grained in the central part of the 
mass, but towards the boundaries the texture becomes finer and 
the foliation increases in intensity. The gneisses overlie the 
clastic schists resting on them at an angle of about thirty de- 
grees and at the junction the schistosity of the former and 
the bedding planes of the latter are apDroximatelv parallel. 
Narrow dyke-like sheets of sheared granite alternate with the 
elastics for some distance east of the main area. Xear the 
junction of the two formations the silicious beds in the clas- 
tic series have been altered into a hard flinty easily fractured 
rock, and the more argillaceous varieties into glossy mica 
schists. The dips at the contact are comparatively regular, 
but a short distance away the clastic beds have been thrown 
into almost vertical attitudes and in places are violently con- 
torted. The relationship of the gneiss to the altered elastics 
suggests faulting in some respects, but this explanation fails 
to account for the presence of the gneissic dykes, and besides 
no evidence of extensive faulting has so far been found in 
the district. 
A section from Fortymile river south to Sixtymile river, 
east of the international boundary crosses two bands of 
sheared granite alternating with altered elastics. The most 
northerly of these has a width of less than a 'mile and in strike 
and dip conforms to the enclosing elastics, both formations 
striking approximately east and west and dipping steadily to 
the north. The second area has a width where crossed by 
the trail of about six miles but narrows rapidly to the east and 
in a few miles is cut off by andesytes. The rocks in this band 
consist of the ordinary grey biotite gneisses along the northern 
boundary and southward across the strike for two miles, 
beyond which point they pass into or are replaced by light 
colored well foliated sericite schists derived from an acid 
granite or quartz porphyry. The exact contact at the nortli- 
ern boundary between the gneissic granite and the clastic 
schists is concealed by debris, the nearest outcrops of the 
