STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

ing dark-gray dolomite beds. The dolomites effervesce somewhat with
acid, but they have the craggy, scored weathering habit of other Ordovician
dolomites. Indeed, except for their darker color they may be
mistaken for dolomites in the Bascom or Beldens formations. The thin
beds in the Whipple make it commercially useless in many places, but
where it is greatly crumpled it becomes an attractive black-streaked
marble. Brown sandy limestone in h-inch beds is found in the Whipple
above the northern West Rutland quarries and 2 miles north of West
Rutland. Cream-colored calcite bedding veins are common in the more
deformed strata, and a down-dip lineation resembling slickensides
characterizes the Whipple on Boardman Hill and at Clarendon Springs.
The marble is particularly susceptible to weathering; gray lime sand
surrounds many exposures.
Relations and thickness: Lenses of black slate are abundant in the
Whipple marble, and lenses of Whipple are not uncommon in the overlying
black slate, the Hortonville. At the northern end of the map area
the Whipple forms a great tongue extending far upward stratigraphically
into the surrounding slate. The slate beneath the tongue can be seen in
contact with Bascom below and Whipple above, and the intervening
slate appears to be several hundred feet thick. Throughout the Castleton
area the Whipple maintains a similar relation to the black slate. The
conclusion must be that some of the Whipple is contemporaneous with
some of the black slate; in short, the Whipple is in part a facies of the
Hortonville slate.
Of the lenses of blue limestone in the Hortonville above the main
body of the Whipple the large kidney-shaped outcrop 2 miles west of
Florence is the most puzzling. It is called Whipple here, for the marble
from its quarries seems no different from other Whipple marble. This
rock may be either a lens high in the Hortonville or normal Whipple
marble locally uplifted in an anticline.
In the valley between Florence and Boardman Hill no Whipple marble
was observed. Whipple may be present though not exposed along the
Otter Creek, but it is not impossible that in this area the black slate
facies completely replaces the carbonate facies.
The main body of Whipple is generally about 50 feet thick, including
lenses of slate. In the great tongue northwest of Florence, however,
though thickening by crumpling has taken place, the original thickness
of the marble must have been of the order of 250 feet. Black slate lenses
in the Whipple have been mapped as Hortonville slate.
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