STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

northeast of Chippenhook the Whipple appears in close proximity to
the Monkton quartzite. At the trace of the Taconic overthrust 1.5 miles
N. 15° W. of Ira Village probable Whipple gray granular limestone lies
near probable Orwell. About 1 mile west of this locality, near the Taconic
overthrust trace, fossiliferous Orwell lies near Hortonville slate with
no intervening Whipple. From the latitude of Florence to that of Boardman
Hill, Whipple is not exposed, and Hortonville lies near, though not
in contact with, the Boardman formation.
To explain such relations we must assume a post-Orwell but pre-
Whipple warping of the crust, followed by erosion and deposition of
Whipple marble and Hortonville slate on the resulting surface of unconformity.
Angular discordance between rocks below and above the unconformity
has not been observed. Bain (1938, p. 10-11) recognized and
mapped a disconformity between the Blue marble (Whipple) and the
Upper West Rutland marble (Beldens) north of the Barnes and Sherman
quarries in West Rutland. Another clear exposure of the surface of
unconformity may be seen on the north face of the active quarry at
Clarendon Springs along the Clarendon River, where 8 feet of black
phyllite intervenes between white Columbian and blue Whipple marble.
Cady fully stated the significance of the areal discordance beneath
the Hortonville at the northern end of the Taconic Range: "In southwestern
Brandon township, at the northeastern corner of the Taconic
Range, . . . phyllites lie on Beekmantown limestone. Westward across
the north end of the range they lie on successively younger limestone
beds and at the meridian of Hyde Manor phyllite known to be the Canajoharie
equivalent is in the normal position above the Cry ptolithus
tesselatus-bearing limestone" (1945. p. 559). It was this areal pattern
that led Keith (1912, 1913) to infer the Taconic overthrust, which will
be discussed later in greater detail. In the vicinity of Government Hill,
Sudbury, indeed, Taconic type slates were interpreted by Kaiser (1945,
p. 1088) as truncating the limestone beds. If the lower black slates at
Government Hill are referred to the Hortonville (Cady), the limestoneslate
contact becomes an unconformity; if the slates are called Schodack
(Kaiser), the contact becomes the Taconic overthrust. Cady (1945,
p. 560) concludes:
"The author has not observed nor does the literature report such a discordance
between the limestone and the (Taconic) phyllite at any other locality in or bordering
the Taconic Allochthone. Several authors (Agar, 1932, p. 36-38; Prindle and Knopf,
1932, p. 297; Knopf, 1935, p. 206-208; Balk, 1936, p. 765-767) indicated the lack of
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