STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

(Ruedemann, 1947), the best opinion today is that the Norrnanskill is
post-Chazy in age, that it probably ranges from the Black River into
the Trenton epoch.
The Pre-Ordovician Unconformity
The Schaghticoke ?-Deepkill ?-Normanskill strata in the Castleton
area lie in a few places on Mettawee, in many places on Schodack, in
one place on Zion Hill, and in one area on the Nassau formation. "At
a point IY4 miles north-northwest of Chamberlin Mills, Mr. Prindle
finds Hudson graptolites in black shales within 15 feet of the Olive grit
[Bomoseen] of the Lower Cambrian" (Dale, 1899, p. 189). Throughout
the slate belt "the Calciferous [Schaghticoke-Deepkill] is not certainly
everywhere present and the Ferruginous quartzite [Zion Hill] is intermittent,
so that in many places but a few feet intervene between the
Hudson graptolites (Normanskill fauna) and the Olenellus fossils. In
other words, the Middle Cambrian (Paradoxides fauna) and the Upper
Cambrian (Potsdam sandstone) are wanting and the section passes at
once from Lower Cambrian to Ordovician, and that not at one exceptional
locality or along one line or plane of fracture, but at many exposures
along intricate boundaries separating masses of complex folds.
Another equally striking fact is that the Lower Cambrian and he
Ordovician, wherever their contact is fairly well exposed, occur in apparent
conformity ......(p. 291).
Erosion of some of the Cambrian before the deposition of the Lower
Ordovician strata will explain these facts. There need not have been
significant diastrophism before this erosion. No proof exists that Middle
and Upper Cambrian beds were not deposited before this erosion; but
no rocks of such ages have been discovered in the Taconic sequence,
with the exception of limestone boulders in the Metis shale and other
formations in Quebec (Rasetti, 1946, p. 703, 1945a, p. 62-63, 1945b).
Red and green Normanskill slate ; Normanskill grit, and Berkshire
schist "all come together," according to Dale, on Rupert Mountain in
Rupert, Vermont. Dale believed this to be additional evidence of an
Ordovician age of the Berkshire. If most of the Berkshire schist is of
Nassau age, as it is considered here, the finding of Normanskill near
Nassau signifies that pre-Ordovician erosion cut down into the Nassau
in some places. Judging from Dale's comments, the boundary between
the Ordovician rocks and the Nassau formation is easier to map than the
boundary between the Cambrian and the Nassau. This must be because
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