So-CaUcd Basal Granite. — McCoiiiicll. 6r 
two formations being fifty feet apart. The principal contact 
phenomena observed consisted of a tilting of the beds to near- 
ly vertical attitudes, the partial brecciation of the clastic rocks,, 
and the shattering of the included siliceous beds. The latter 
have been altered into hard brittle rocks seamed with a net- 
work of irregular interlacing fine lines consisting of quartz 
and calcite. At the southern boundary the igneous and clas- 
tic schists alternate for some distance, the latter dipping un- 
der the former at angles of from lo to 30 degrees. The clas- 
tic beds are highly altered but are rendered easy of identifica- 
tion by the presence of included crystalline limestones. 
Evidences of eruptive contact somewhat similar to the 
above and more or less marked were noticed at several points 
in the Yukon valley section, but it will be unnecessary to des- 
cribe them in detail here. 
Jr^urther proof of the invasion of the clastic schists by the 
gneissic granites is afforded by the frecjuent inclusions of 
the former in the latter. In the lower part of the Sixtymile 
valley and in the Yukon valley for some miles above the 
mouth of this stream, the gneisses enclose irregular shaped 
fragments, short bands, and large masses of the clastic schists. 
The inclusions range from a few feet to half a mile or more 
in width, and here consist in great measure of white coarsely 
crystalline limestones, the argillaceous and siliceous beds us- 
ually associated with them having been mostly destroyed. 
The boundaries between the limestones and the enclosing 
gneisses are usually sharply defined,- but in one or two places 
an apparently gradual transition was noticed from pure crys- 
talline limestone to typical gneiss. Inclusions of quartzytes 
and altered argillaceous rocks occur also in the gneisses a few 
miles below the mouth of Selwyn river and of the same rocks 
accompanied by crystalline limestone on Henderson creek 
and in the Yukon valley above Fortymile river. The inclus- 
ions are usually highly altered and when unaccompanied by 
limestone it is often impossiblle to separate them with cer- 
tainty in the field, from some of the fine grained varieties of 
the gneissic granite. 
The dyke like sheets of sheared granite interbanded with 
the clastic schists, referred to previously as bordering some 
of the larger areas, can hardly be explained otherwise than 
