STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

those in the vicinity of the Castleton quadrangle. If an overthrust is
established here, it is presumably present in other areas peripheral to
the Taconic Range.
Evidence of discordance: The Valley sequence and the Taconic sequence
are separated in the Castleton quadrangle by a sinuous contact extending
from the southern border of the quadrangle in Ira township to the
northern border of the quadrangle in Pittsford township. The Taconic
sequence lies west of the contact, and the Valley sequence lies east of
the contact. The contact runs along the eastern flank of the Taconic
Range, and the Taconic sequence lies everywhere above the Valley
sequence.
The highest unit in the Valley sequence, the Hortonville slate, generally
crops out beneath the Taconic sequence. In Ira, however, two
small exposures of Orwell limestone and probable Whipple marble are
exposed beneath the Taconic sequence. The limestone exposures may
represent the crest of anticlinal uplifts truncated by the surface beneath
the Taconic sequence.
Furthermore, a greatly variable thickness of Hortonville slate intervenes
between the underlying marbles of the Valley sequence and the
overlying phyllites of the Taconic sequence. At the foot of the Taconic
Range in West Rutland little or no Hortonville is exposed; a few miles
southward in Ira a minimum of 1000 feet of Hortonville is present.
Different thicknesses of Hortonville are found at several points along the
contact north of West Rutland. These facts demonstrate lithologic discordance
beneath the contact between the two sequences.
The lowest rocks exposed in the Taconic sequence are of different
lithology at various places along the contact. In Ira the lowest exposed
rock of the Tacoriic sequence is commonly a tough, gray, banded,
impure quartzite. Northward toward West Rutland the base of the
Taconic sequence is usually a green phyllite. Just north of West Rutland
white-weathering strata of the Taconic sequence crop out west of the
meadow. West of Whipple Hollow green, greenish-gray, and purple
phyllites are variously exposed above the Hortonville slate. These facts
demonstrate lithologic discordance above the contact between the two
sequences.
Discordance between the two sequences is shown also by the largescale
structural relations between the two terranes. The broad deep
folds in the Valley sequence are in great contrast to the finely corrugated
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