STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

West Rutland anticline and adjacent syncline: Wing (Dana, 1877) early
recognized the anticlinal structure of the marbles at West Rutland. In
plan the 6-mile-long fold is cigar-shaped, and its core is covered principally
by swampy meadow. The rocks are strongly overturned toward
the west. Judging from surface exposures, the axial plane of the antidine
is regularly inclined at an angle of 40 degrees east. Underground
data show an average dip on the eastern limb of 23Y2 degrees (Bain,
1931, p. 516). Flowage is extreme in the West Rutland marbles and will
be discussed below.
Between this fold and the Otter Creek valley to the east is a major
synclinal ridge underlain by Trenton phyllite. Although bedding in the
phyllite is obscure, it is safe to assume that the syncline is overturned
toward the west, for axial plane cleavage dips 30 or 40 degrees east. The
syncline loses its identity in homogeneous masses of phyllite to the north
near Proctor and to the south in the latitude of Clarendon Springs.
Folds in Taconic sequence: Where formations can be recognized, as for
example in the slate belt, the rocks in the Taconic sequence are crumpled
into long narrow folds that trend roughly north. The folds are seldom
over a mile wide, and all are overturned toward the west. Inasmuch as
the cleavage and minor structural features of the "Berkshire schist"
terrane are very similar to those of the slate belt, it is evident that the
folding of the entire Taconic thrust sheet is uniform. The repeated
disappearance and reappearance of comparatively thin units in the slate
belt suggests shallow folding. Indeed, looked at from a broad perspective,
the rocks of the Taconic sequence are a sheet superficially crumpled but
essentially flat-lying. With better evidence Kaiser (1945, p. 1093)
reached a similar conclusion at the northern end of the Taconic Range.
Little justification exists in this latitude for calling the structure of the
Taconic thrust sheet a synclinorium.
Faults
Pine Hill thrust: Along the eastern boundary of the Castleton quadrangle
runs the trace of a reverse fault by which Lower Cambrian rocks
have been brought westward so as to overlie strata as young as Middle
Ordovician. The trace of the fault passes eastward into the Rutland
quadrangle about 2 miles south of Pittsford Mills and southward into
the Pawlet quadrangle south of Chippenhook. Measured along its trace
the fault extends about 14 miles within the Castleton area. The thrust
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