STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

skill in the Castleton area. Several rock types are recognized, and all are
in lenticular bodies. In a few places one type grades into another. No
stratigraphic succession can be established, for the lithologic varieties
do not occupy a consistent stratigraphic position. The isoclinal folding
of the Normanskill does not facilitate interpretation. Units that are
stratigraphically the highest have been found lying directly on the
Cambrian. In no place can the entire sequence be observed in one
traverse. It is necessary to piece together the succession in the Normanskill
beds by statistical methods.
Dale's succession (1899, p. 185-190), although admittedly approximate,
seems to fit the Normanskill in this area. Ordinarily the lowest
strata are black-streaked, rusty-weathering, gray and black slates with
a fine banding showing in cross-section. Above this unit lies a succession
of black slates, in places cherty and feldspathic. These beds have a
white weathered surface and superficially resemble limestone. The slates
are interbedded with fine-grained, brown-weathering, dark-blue-gray
grit containing glistening quartz eyes and fresh angular feldspar grains.
Green, gray, and black slates with white quartzite beds Y4 to 1 inch thick
are found in close association with grit beds. Ordinarily the highest
strata are bright green and red slates that contain some chert and quartzite
beds. These colored slates are extensively quarried south and west
of the Castleton area.
As stated above in connection with the Zion Hill quartzite, the banded
slate and edgewise limestone conglomerate at Hampton is arbitrarily
mapped as Normanskill. These rocks and possibly the lowest slates of
the "Normanskill" at Poultney and East Poultney may be actually
Schaghticoke-Deepkill equivalents.
Thickness and Age: Dale's figure (1899, opp. p. 178) for the thickness
of the Normanskill, 1250 feet, is accepted here. Nearly half of this
thickness is made up of grit in this area. The red and green slates are
probably only about 100 feet thick. The remainder of the Normanskill
is dark slate, chert, and quartzite with an aggregate thickness of 500
feet or more.
No fossils that are unquestionably graptolites were found during this
study. Dale discovered Normanskill fossils in the cherts and grits south
of the present area. The age of the Normanskill formation has been
a perennial question since the first investigation of the rocks of New
York State. As nearly as can be ascertained from the most recent report
56