STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

poraneity. Vaughan and Wilson (1934) found what looked like Oldhamia
in the Rensselaer, but Ruedemann (1942b) denied that the specimens
were Oldhamia. Prindle and Knopf (1932, p. 248) tentatively assigned
the Rensselaer to the Lower Cambrian.
Bomoseen Grit
Name: Dale's Olive grit (1899, p. 179) later became the Bomoseen
grit (Cushing and Ruedemann, 1914, p. 69), named from its excellent
exposures west of Lake Bomoseen, Vermont.
Distribution: The Bomoseen grit crops out along the western border
of the Castleton quadrangle in irregular shaped patterns from Hampton,
New York at the south to Point of Pines on the western shore of Lake
Bomoseen. Kaiser (1945) has mapped Bomoseen grit in a large outcrop
1 mile west of West Castleton. This outcrop, which is the type locality
of the Bomoseen grit, extends westward into the Whitehall quadrangle.
Two smaller outcrops, one south of Half Moon Pond and the other east
of Keeler Pond, lie in the northwestern part of the quadrangle.
Description: The Bomoseen grit is a light-brick-red-weathering, finegrained,
olive-green grit containing "spangles of hematite and graphite."
The rock is very hard and uncleaved or poorly cleaved. Thin impure
quartzite beds and lenses are common in the grit, and thick white
quartzites occasionally found just below the Mettawee are included in
the top of the Bomoseen. Green and occasionally faintly red quartzose
slates near the top of the Bomoseen are hard to distinguish from the
Mettawee slates.
Tiny quartz eyes showing dark against the matrix are characteristic
of this rock. Dale reported a "considerable number of plagioclase grains,
rarely one of microcline, in a cement of sericite with some calcite and
small areas of secondary quartz." A mineral that resembles chlorite is
found in the Bomoseen.
Thickness: Nowhere is the bottom of the Bomoseen exposed. Presumably
the Nassau formation lies beneath the Bomoseen that outcrops in
Fennel Hollow, although the actual contact was not seen. Toward the
east the Bomoseen may become thinner or may be missing. A minimum
of about 200 feet of Bomoseen is generally exposed in the Castleton area.
Larrabee (1939-1940) indicated at least 500 feet of Bomoseen near
Poultney. In the slate belt Dale (1899) found 50-200 feet and in Rensselaer
County (1904a) 18-50 feet.
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