sella I

58

biotite are conspicuous in some beds. In places the rock appears consider-
ably recrystallized, and it is difficult to determine whether the large quartz
grains represent original detrital fragments or later metamorphic porphyro-
blasts. The general origin as a coarse-grained sediment, however, is
apparent in most instances. This type of rock, designated in this report
‘quartzite conglomerate’ or ‘quartzitic grit’, depending on its average
pebble or granule size, comprises nearly half of the lowermost 4,000 feet
of the Ingenika group on the northern flank of Tenakihi Range. Most of
it is well bedded, with adjacent beds differing in texture and mineral
proportion to yield all variations toward sericite-chlorite quartzite. Inter-
bedded with the conglomerate, grit, and quartzite are beds up to 40 feet
thick of soft, black or dark grey, lustrous phyllite, for the most part
conspicuously crenulated, with parallel or subparallel corrugations less than
zo inch apart. In a few places, thin beds of black, flaky, velvet-lustred,
graphitic schist are interbedded with the phyllites.

The quartzitic conglomerate-phyllite assemblage is overlain by about
200 feet of interbedded, impure, dark grey to black, slaty limestone, brown
calcareous slate, and calcareous chlorite-sericite schist; and this in turn is
overlain by nearly 4,000 feet of slightly schistose quartzite, slaty argillace-
ous rock, sheared conglomerate, and schistose sericitic limestone, all of
which are intimately interbedded, with a sequence of beds of one rock type
rarely more than 15 feet thick. As in the lower beds of this series of
exposures, the quartzites typically contain rounded grains or ‘eyes’ of
quartz, which may represent either relatively coarse original sedimentary
grains or porphyroblasts formed during recrystallization. The conglom-
erate occurs in uniform, coherent beds up to 12 feet thick, composed of
colourless or light grey, rounded quartz pebbles up to 1 inch in diameter,
and subrounded, light grey, in part rusty, feldspar grains up to 4 inch in
diameter, in a sheared, limonite-stained, sericitic matrix. The beds of
conglomerate are in places separated by partings of dark brown argillaceous
material, which, between the conglomerate beds, has been metamorphosed
into a fairly strong slate, but which, where present as a contorted filling
in cracks and funnel-shaped openings within the conglomerate beds, has
been preserved as relatively incoherent argillite. The limestone in this
finely interbedded section is confined to thin, impure, slaty, schistose, or
sandy bands, which represent all gradations to calcareous slaty phyllites.
Near the bottom of this section the sheared, slaty, calcareous material
produces a conspicuous encrustation of soluble salts, mainly potassium
nitrate and calcium sulphate.

The finely interbedded sequence of quartzite, slaty argillite, conglom-
erate, and impure limestone is overlain by about 2,000 feet of well-bedded
limestone, which is sheared and slaty, more or less micaceous in the lower
beds, but predominantly blue-grey to creamy buff, crystalline, and relatively
pure in the highest exposed beds.

Rocks in Mesilinka River Valley

Ingenika group rocks outcrop on both sides of Mesilinka River, near
the eastern edge of the map-area, in canyons in the mouths of creeks trib-
utary to the river. Each of the canyons examined is cut in a succession of
quartzitic conglomerate, schistose augen quartzite and grit, and quartz-
chlorite-sericite schist, slate, and phyllite. Similiar rocks outcrop on the