Ba De

and.-pyrrhotite, in about equal amounts, constitute nearly 15 per cent
of the rock. A few shreds of actinolite and flekes- of: biotite complete.
the mineral assemblage. |

-- ....."Another. section, from the edge of the dyke, shows the grain
size reduced to a maximum of $ millimetre, and-is of interest in that
augite is present in amount about equal to that of hornblende in the
first slide and hornblende is absent. The augite is in part converted
to pale green chlorite and, to a very minor extent, to biotite.
Plagioclase. of the same composition as that in the first slide is almost
entirely replaced by carbonate, which 21s0 occurs™in a few microscopic
veinlets. Quartz, magnetite, and pyrrhotite are present in the same
amount as in the centre of the dyke and there are a few scattered grains
of epidote, SN

"The rock is a fairly typical quartz gabbro; moderately altered
to chlorite and carbonate. The interior portion shows the development
af hornblende at expense of augite that leads some authorities to apply
the name hornblende gabbro or-gabbrodiorite. In the field such dykes,
and particularly the finer grained phases, are generally termed diabase,
though the characteristic ophitic texture of true diabase is lacking in
this case,"

The Precambrian quartzites are also well exposed 1s miles up
MacDonald Creek, south of tho rocl:-cut at mile 1063, Here vertical beds
of quartzite underlie disturbed Middle Silurian coral reef limestones.
Ihe quartzites are jointed and sheeted, and are cut by & number of quartz
veins showing brown anu yellow stains, In a cirque on a mountain to the
east of the creek, rusty quartzite unconforrably underlies nearly
horizontal Silurian limestone, The quintsite is slaty in partys is very’
dark when fresh, but weathers rusty, i 300-foot section of quartzite is
here exposed,

From the river flats large quarteise mountains may be seen to
the souths

Cambrian. (?)

In the west bank of Muncho Iake, about 3 miles north of its
head, Silurian coral-reef limestone is underlain by about 50 feet of limy
shale that is full of worm burrows. Underlying the shale to the north,
and with comparable strike and dip, are outcrops of grey sandstone in _
beds 8 to 10 feet thick. Other sandstone outcrops to the north indicate
a thickness of more than 2,000 fect of these beds. About 2z miles north
of the highest Gandstone) outcrops, coarse red conglomerate is exposed on |
the shore, and from here northward it forms almost continuous cliffs and -
hills along Muncho Lake and the west side of Trout River valley to mile
197.

Assuming the entire section to be sandstone from the base of
the limestone series to the top of the conglomerate as exposed on the
shore, and assuming no great variation from observed dips, and no serious
faulting, the sandstone would have a thickness of nearly 5,000 feet.

The conglomerate near the top is massive and contains boulders
of pink quartzite up to 10 inches in diameter, Fifty yards north the
conglomerate consists of a fine red shale matrix with pebbles 6 inches and.
less in diameter. The great lineal extent of the conglomerate formation
to the north is suggestive of great thiclmess, as is also suggested by
the massive mountains to the west of Trout River where a peak is mapped
with the elevation of 8,300 feet. Until this region is studied in some