STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

of very small and very large dolomite grains with no recognizable impurities.
The quartz knots that are so characteristic of this formation
further north (Cady, 1945, P. 536) are not common in this area. Nor has
the black chert, reported (Rodgers, 1937, p. 1576; Cady, bc. ciL) near
the top of the formation, been encountered in mapping here. In several
places the base of the white Sutherland Falls marble can he seen lying
on normal gray Clarendon Springs dolomite.
Thickness: This unit is between 130 and 175 feet thick in all sections
measured in the Castleton area. Bain (1938, p. 10) suggested a maximum
of 200 feet for the Lower dolomite (Plate I) in this vicinity. Bain's
Lower dolomite is equivalent to the Clarendon Springs dolomite.
Age: Rodgers (1937, p. 1576) correlated most of the Clarendon Springs
with all but the upper 35 feet of Division A of the Beekmantown of
Brainerd and Seely (1890, P. 2) and with most of the Little Falls dolomite
of the Mohawk Valley. A Trempealeau age is indicated. At Milton,
Vermont, dolomite lithologically similar and probably equivalent (S. L.
Stone, personal communication) to the Clarendon Springs contains a
late Trempealeau fauna (Schuchert, 1937, p. 1046). The dolomitic Gorge
formation at Highgate Falls, Vermont, has a very rich late Trempealeau
assemblage (Raymond, 1924; Shaw, 1949).
LOWER ORDOVICIAN (CANADIAN) SERIES
The formations here assigned to the Lower Ordovician are eastern
correlatives of the Beekmantown of the Adirondack border. In general
the Boardman-Bascom succession corresponds to Divisions B, C, and
D of Brainerd and Seely (1890) and to Cady's (1945) Shelburne, Cutting,
and Bascom formations. The highest Canadian unit in the west limb of
the Middlebury synclinorium, the Bridport dolomite (Fig. 3), is not
recognized here. Correlations among the Champlain Valley, Adirondack
border, and Ozark Mountains sections of Lower Ordovician age may be
revised as a result of work now being done in New York State.
Boar Jman Formation
Name: The name Boardman formation is here proposed as a unit to
include all rocks lying stratigraphically between the Clarendon Springs
domomite and the Bascom formation. The type locality lies on the southwestern
slope of Boardman Hill in Clarendon about 1.25 miles S. 50 ° W.
of the top of the hill. Other sections are exposed at the Florence quarries
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