STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

eak thmst. The Taconie sequence is a comparatively thin sheet superficially
crumpled into isoclinal folds. The chief problem in this area is
to account for the anomalous juxtaposition of the Cambro-Ordovician
argillaceous Taconic sequence and the Cambro-Ordovician carbonate
Valley sequence. The principal objective of this investigation was to
ascertain the validity of Keith's concept of the Taconic overthrust,
which is assumed to be a huge strip thrust that carried the Taconic
sequence from the east westward to overlie the Valley sequence. Evidence
for the fault in this area consists of lithologic discordance above and
below the fault trace, large-scale structural discordance between the
two sequences, the contrast between contemporaneous sequences of
two dissimilar facies, the presence of klippen and fensters, and the existence
of the late Pre-Cambrian Nassau formation lying above Ordovician
rocks of the Valley sequence. The Taconic overthrust is believed to be
proved. The rocks of the Taconic sequence may have been laid down in
the vicinity of the modem Connecticut Valley, and if so the minimun
net slip on the Taconic overthrust must be about 50 miles.
The folding, faulting, jointing, cleavage, and metamorphism of the
rocks of both sequences took place probably near the close of the Ordovician
period. The earlier stages of the Taconic orogeny produced a
flow cleavage oriented parallel to the axial planes of the folds. During
the later stages of the orogenv the first cleavage was folded by forces
applied in a direction slightly different from those that produced the
first cleavage. These later forces developed an axial plane shear cleavage.
The northwestern third of the Castleton quadrangle was not investigated
in detail, and data on that part of the quadrangle were obtained
for the geological map from previous publications.
INTRODUCTION
General
The Castleton area (Fig. 1) covers about 130 square miles in westcentral
Vermont and eastern New York. During this investigation all
the rocks of the Castleton quadrangle that lie south of the Castleton
River were mapped. In the northern part of the quadrangle only the
rocks lying east of the Taconic Range were mapped. The remainder of
the Castleton quadrangle has been mapped geologically in recent years
by Kaiser (1945) and Cady (1945) . *
*Referenc are given at end of the paper.
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