STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

LOWER CAMBRIAN SERIES
Lower Cambrian beds make up almost half of the total thickness of
the Valley sequence in this quadrangle. The four formations of this age
extend far beyond the limits of the Castleton area to the north and to
the south. Thrust faults to the west have concealed whatever Lower
Cambrian equivalents that may have been deposited nearer the Adirondacks.
The clastic rocks and dolomites of the Plymouth series in central
Vermont may be easterly representatives of the Lower Cambrian in the
Champlain and Vermont valleys. Uniformity of environment over a
large region is evident throughout this epoch, more particularly in
Cheshire and Dunham times. The difficulty in separating the three
higher units of the Lower Cambrian in this area is exemplified by Keith's
use (1923, p. 128-129) of the term Rutland dolomite to include all
dolomitic beds between the Cheshire and the Danby.
Cheshire Quartzite
Name: The basal Cambrian quartzite was first named from the town
of Cheshire in Massachusetts by Emerson in an unpublished report
on the Hawley sheet. The approved definition of the unit is found in
another paper (Emerson, 1917, p. 32-34). The Cheshire quartzite in
Massachusetts is similar to the Cheshire in the Castleton area.
Distribution: The Cheshire crops out in a V-shaped band in the Cox
Mountain area of Pittsford township. Cheshire underlies the eastern
slopes of Pine Hill and Boardman Hill on the eastern edge of the Castleton
quadrangle.
Description: The Cheshire quartzite is a pure, massive, white quartzite
with occasional shades of blue, green, and brown. Although individual
beds in the higher part of the Cheshire are in places a dozen feet thick,
beds ranging from several inches to a few feet thick are common in the
lower part of the formation. This rock is well jointed and characteristically
breaks up into small and large fragments bounded by joint
planes. Virtually 100 percent of the Cheshire consists of equidimensional,
amoeba-shaped, interlocking grains of quartz. The Cheshire is the hardest
and most chemically resistant rock in the region, although in Massachusetts
the feldspathic Cheshire weathers to pipe clay and glass sand.
As defined here the Cheshire contains only the massive pure quartzite,
and the subjacent dark-gray quartzites and phyllites hitherto included
17