[Illustration: A. _North face of the ridge west of Eagles Rest Peak.
The face is about 700 feet high. Notice the extreme contortion of
the gneiss layers._]
[Illustration: B. _Closeup view of some of the folds near the bottom
of the face in figure A. The light-colored layers are composed
principally of quartz and feldspar. The darker layers are rich in
hornblende._]
Irregular bodies of granite gneiss are interleaved with the layered
gneisses in the northern part of the Teton Range. The _granite gneiss_
is relatively coarse grained, streaky gray or pink, and composed
principally of quartz, feldspar, biotite, and hornblende. It differs
from enclosing layered gneisses in its coarser texture, lack of
layering, and more uniform appearance. The dark minerals (biotite and
hornblende) are concentrated in thin discontinuous wisps that give the
rock its streaky appearance.
The largest body of granite gneiss is exposed in a belt 1 to 2 miles
wide and 10 miles long extending northeastward from near the head of
Moran Canyon, across the upper part of Moose Basin, and into the lower
reaches of Webb Canyon. This gneiss may have been formed from granite
that invaded the ancient sedimentary and volcanic rocks before they were
metamorphosed, or it may have been formed during metamorphism from some
of the sediments and volcanics themselves.
At several places in Snowshoe, Waterfalls, and Colter Canyons the
layered gneisses contain discontinuous masses a few tens or hundreds of
feet in diameter of heavy dark-green or black _serpentine_. This rock is
frequently called “_soapstone_” because the surface feels smooth and
soapy to the touch. Indians carved bowls (fig. 22) from similar material
obtained from the west side of the Tetons and from the Gros Ventre
Mountains to the southeast. Pebbles of serpentine along streams draining
the west side of the Tetons have been cut and polished for jewelry and
sold as “_Teton jade_”; it is much softer and less lustrous than real
jade. The serpentine was formed by metamorphism of dark-colored igneous
rocks lacking quartz and feldspar.