STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

Kaiser (1945, P. 1089) discovered about 100 feet of green and purple
slate between the Schodack and the Zion Hill in some places. This he
called the Wallace Ledge formation and suggested a correlation with
division J of Dale's Rensselaer County section (1904a). No Wallace
Ledge strata are recognized south of the Castleton River.
Age: No fossils have been found in the Zion Hill. Most geologists have
regarded this formation as the top of the Lower Cambrian, but Larrabee
(1939, p. 47) found an angular unconformity "exposed in the large
roadcut at Hampton, New York, where at a near contact, the Cambrian
Schodack shales dip 78 deg. east, and the Ordovician Zion Hill quartzite
dips 48 deg. east. The latter contains pebbles of what appears to be
Schodack."
I interpret these relations as only an abrupt bend in the rocks and
recognize no Schodack at the Hampton locality. Above the Zion Hill in
this locality there are at least 10 feet of banded black slate, then 75 feet
of limestone conglomerate, and finally a great mass of undoubted Ordovician
slate. I put the Cambro-Ordovician boundary between the Zion
Hill quartzite and the overlying banded slate. Such procedure is arbitrary,
but in the absence of fossils it is reasonable to restrict the Zion
Hill to a rock lithologically similar to the quartzite at the type locality.
If the Zion Hill quartzite were basal Ordovician, it might be expected to
crop out near the large masses of Normanskill at Poultney and East
Poultney, and it does not. If it is Cambrian lying beneath an unconformity,
its absence in the large synclines is more easily explained. The
Zion Hill quartzite is accordingly considered to be pre-Ordovician and
probably the uppermost formation of the Lower Cambrian series.
The banded black slate and the edgewise limestone conglomerate
lying above the Zion Hill quartzite at Hampton may well be correlatives
of the Schaghticoke-Deepkill sequence of the Hudson Valley. Until
fossils are found we cannot be certain of the age. No justification exists
for extending the name Zion Hill to include these strata; they are lithologically
distinct and deserve a separate name as soon as their age and
extension to west and south can be determined.
Kaiser (1945, p. 1090) suggested that the Bird Mountain grit is a
"thick phase of the Zion Hill quartzite." This was not unlikely as long
as the Berkshire schist surrounding Bird Mountain was considered to be
metamorphosed Mettawee and Schodack. Inasmuch as the bulk of the
Berkshire is here assigned to the Nassau formation, the Bird Mountain
grit cannot be a facies of the Zion Hill quartzite.
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