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beds; competent but flexible assemblages of thin beds of limestone and
phyllite, schist, or slate; and thick assemblages of weak, incompetent
argillites and phyllites has resulted in a great diversity of structural forms,
produced in response to what may have been originally simple deforming
stresses. On the whole, however, in all rocks south of Ingenika River, and
in Tucha Range, the small-scale deformation has been quite gentle, involv-
ing deviations of usually less than 30 degrees from the general plane of
bedding in any one area, and the deformed beds show little evidence of
faulting or rupturing. The entire assemblage of Ingenika group rocks on
the north flank of the Mount Lay-Wrede Creek anticlinorium, and in Wrede
and Tucha Ranges, is relatively free from small folds, and is only gently
flexed into wave-like anticlines and synclines, 500 to 5,000 feet from crest to
crest and with closures of from 50 to 600 feet, parallel with the major
anticlinorial structure. In places, intercalated medium-bedded micaceous
limestones, slates, and phyllitic schists have developed regular parallel
folds, and adjacent slates and phyllites have accommodated themselves to
the deformation by shearing. The most extreme examples of deformation
are shown by the limestone beds. Near the axis of the major syncline that
crosses Swannell River near the Swannell mineral claims, impure limestones,
together with interbedded calcareous and carbonaceous slates and phyllites,
have been bent into isoclinal folds in which single beds up to 2 feet thick
have been folded back on themselves for as much as 20 feet, and slightly
more open structures have developed a multitude of drag-folds. The
relatively pure, thin-bedded, grey limestones exposed on the north face of
Forres Mountain show a large number of superimposed folded structures
of different scales; on the major folds, about a mile across, are secondary
folds 100 to 500 feet across; on these, in turn, are drag-folds up to 25 feet
from crest to crest; and these drag-folds carry smaller folds, 1 foot to 3
feet across, which are themselves minutely corrugated. The axial planes
of all of these series of folds are essentially parallel with that of the large
structures; and it would appear that the entire composite structure was
produced simultaneously. It was estimated in the field that the minor folds
alone, seen in the cliffs on the south ridge of Forres Mountain, must have
required a shortening of beds to less than half their length, exclusive of the
shortening occasioned by the development of the large anticlines and
synclines. On other parts of Forres Mountain the folds are large and
mainly simple.

The thick belt of limestones east of Pelly Creek shows numerous
regular isoclinal folds up to 500 feet from limb to limb and more than
1,000 feet from crest to trough. In general, these folds appear to be
regular and smooth, free from small-scale drag-folds, although such struc-
tures, if present, would be hard to recognize in the massively bedded,
uniform limestones. On what appears to be the southern prolongation of
this belt, however, in Ingenika River Valley near Lookout Hill and
Ferguson and Onward mineral claims, the limestones have been deformed
into structures of extreme complexity. Detailed mapping of outcrops,
surface strippings, and underground workings in this area has revealed
that, around what appears to be the nose of a large, northwest-plunging
drag-fold, the limestone has been plastically deformed into infolded,
digitate, and fan-shaped structures.