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strike north 40 degrees west and dip 54 degrees northeast; veins have an
average strike of north 15 degrees west and dip 60 degrees northeast) ; there
has been little replacement of the wall-rocks by the veins, and beds can be
matched across the veins to show no appreciable displacement parallel
with the plane of the vein. There seems no reason to doubt that the veins
fill tension cracks developed during the large-scale drag-folding of the lime-
stone; and it is obvious that the schistosity of the recrystallized micaceous
limestone antedated the development of the fractures. It would seem
inconceivable that non-schistose limestone containing up to 20 per cent vein
material could be metamorphosed in such a way that the limestone between
the veins was recrystallized to a muscovite-bearing schistose rock with
sharp boundaries against the veins while the vein material remained free
from muscovite and retained its coarse ‘vein’ texture; and it is equally
hard to visualize a system of stresses that would open the vein fissures at
the same time as the schistosity was developed.

Although the main metamorphism of the Ingenika group is thus seen
to precede the development of the large folds, there was enough recrystal-
lization during folding to prevent cataclasis and to relieve most internal
stresses. Thus crystalloblastic quartz grains, though strained, are clear
and unfractured. The dolomite (?) porphyroblasts in some of the chloritoid
schists on Swannell River, near the axis of a major syncline, appear to have
grown in a sheared rock; during growth they were rotated slightly, and
after growth were further moved, allowing quartz to be deposited in spaces
formed and protected by the displaced porphyroblasts. The development
of these porphyroblasts, and of the nearby zoisite schists, may well be
connected with the formation of the syncline, and thus later than the
regional metamorphism.

The processes by which schistosity could develop parallel with bedding
have been discussed in the description of the Tenakihi group (See pages 51
to 54). The conclusion that most of the metamorphism occurred during a
period of relatively gentle deformation earlier than, and independent from,
that which produced the present major folds—under directed stresses
probably occasioned by large rising or laterally invading intrusive masses,
or by forces from a widespread irregular zone of anatexis and migmatic
action, accompanied by an increase of temperature gradient due probably
to the same intrusive or anatectic sources—applies equally to the Ingenika
group. The greater local irregularity of the planes of schistosity in the
Ingenika group than in the Tenakihi group is probably due to the greater
inhomogeneity of the strata, with lenticular beds of differing competency
and varying degrees of ease of recrystallization producing local differences
in resistance to stress.

ORIGIN

The Ingenika group is characterized throughout by four dominant
sedimentary rock types and their metamorphic derivatives: greywackes
and subgreywackes, altered to slates, phyllites, chloritic schists, and chlorite
quartzites; sandstones—impure, angular, and poorly sorted, to extremely
pure, well rounded and sorted—now represented by the quartzites; con-
glomerates, which are for the most part fine grained and merely a coarser
phase of the subgreywackes and sandstones; and limestones, which in

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