STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

in the Cheshire (Keith, 1923-24, p. 126-128, 1932, P. 395-396; Cady,
1945, P. 526) are assigned to Type 3 of the Mendon series. The top of
the Mendon is placed arbitrarily above the highest black phyllite or
argillaceous quartzite. A 10-foot bed of conglomerate composed of 2-
to 4-inch cobbles of blue quartzite separates the Cheshire from the black
phyllite of the Mendon series at the northeastern end of Pine Hill. This
conglomerate is probably local.
It is logical to separate the Mendon and the Cheshire above the
phvllite; for the clean Cheshire is a strikingly clear map unit, and clean
Cheshire alone is present above the alleged unconformity at the Falls of
Lana. Limited reconnaissance suggests that clean Cheshire quartzite is
everywhere a homogeneous unit overlying a diverse group of sedimentary
rocks. The nature of the basal contact is discussed in connection with
the Mendon series.
Regional relations: The Cheshire is widespread in a north-south
direction, extending from Massachusetts far into west-central Vermont.
The brown Gilman quartzite (Clark, 1931, p. 225-226, 1934, P. 9-10,
1936, p. 144-146) of the Oak Hill series appears in place of the Cheshire
in northern Vermont and southern Quebec. In west-central Vermont
the Gilman type of quartzite underlies clean Cheshire, apparently becoming
thinner southward, until in the Castleton area no Gilman is
recognized.
Thickness and age: The Cheshire is about 400 feet thick on Cox
Mountain and probably thicker on Pine Hill. Olenellus, Hyolithes, and
Nothozoe were found (Walcott, 1888, P. 285; Seely, 1910, p. 307) in the
Cheshire at Bennington and at Lake Dunmore northeast of Brandon.
The formation is Lower Cambrian.
Dunham Dolomite
Name: From Oak Hill in southern Quebec Clark (1934, p. 9) named
the Dunham dolomite. Although a thrust fault separates the type Dunham
from the lowest Cambrian dolomite in the Champlain Valley, both
units occur in "comparable stratigraphic successions," and Cady (1945,
p. 529) extended the name Dunham to include the beds lying between
the Cheshire and Monkton quartzites. The Dunham dolomite was part
of the "Red Sandrock" series in the last century and has since been
known under several other aliases.
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