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The migmatites possess the same simple mineralogical composition as
the gneisses, quartzites, and schists. Typical specimens consist of quartz,
potash feldspar (commonly microcline), sodic plagioclase, and biotite, in
about the same proportions as in granite or granodiorite, alternating in all
proportions with bands much richer in biotite or quartz or both. In some
thin sections it is apparent that the quartz-rich bands, which commonly
make up about half the rock, have been the most mobile, and have flowed
into subparallel fractures in the feldspathic material; in other cases the
outcrop relations seem to indicate that the highly feldspathic bands were
actively intrusive, either filling fractures or replacing the original rock;
but in most places there is no evidence of rock disturbance or bodily move-
ment of material, and the recrystallization and change of composition
seem most easily explained by a quiet pervasion of fluids along the foliation
(bedding?) planes.

Accessory minerals are quite minor in the migmatites, as in the gneisses
generally, and include sillimanite, apatite, tourmaline, zircon, and mag-
netite. Some thin sections were observed to contain euhedral grains of
scapolite.

Lit-par-lit Gneiss

In places the quartz-mica-feldspar gneisses contain bands or sill-like
bodies, commonly between 1 inch and 1 foot thick, of relatively massive,
igneous-appearing material of granitic composition. These rocks differ
only in degree from the rocks here referred to as migmatites, but the gneisses
are commonly finer grained and less well crystallized, the borders of the
granitic bands are sharper, and in places the granitic bands cut abruptly
across the foliation as seams of quartz and feldspar, suggesting that they
have been bodily injected along fractures and planes of weakness. Lit-par-
lit gneisses of this type are less abundant than the migmatites in the highly
metamorphosed rocks northeast of Blackpine Lake, but are more wide-
spread. They are well developed in places near the pass at the head of
Ravenal Creek and in the Butler Range east of Tomias Lake.

Silicated Marble and Skarn

Interbedded with the feldspathic quartzites and quartz-mica-feldspar
schists are highly metamorphosed calcareous rocks, which range in com-
position from slightly altered marbles to lime-silicate rocks and amphibolites
containing no carbonate material. The rocks to which there has been the
least addition of material consist mainly of white, coarsely crystalline
calcite, with scattered tan to resin-brown andradite garnet porphyroblasts,
and irregular, usually interstitial, grains of clinozoisite. With increasing
silicate content the calcite is replaced by plagioclase feldspar and amphibole.
A typical rock found on the south slope of the mountain due north of the
mouth of Tutizika River is conspicuously banded, with irregular layers
up to 4 inch thick alternately rich in brown garnet, green actinolitic
amphibole, white tremolite in radiating clusters of needle-like crystals,
and grey-green calcite-plagioclase-clinozoisite rock. The development of
silicate minerals in these rocks is very irregular; in places the bands end
abruptly against patches composed largely of recrystallized calcite, yet
nearby almost the whole of the same bed is an aggregate of silicate minerals.
In many places, what appear to be the original bedding planes are marked

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