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Winooski Dolostone, Monkton Quartzite, and Dunham (Rutland) Dolostone

Winooski Dolostone, Monkton Quartzite, and Dunham (Rutland) Dolostone
State New York
Name Winooski Dolostone, Monkton Quartzite, and Dunham (Rutland) Dolostone
Geologic age Cambrian
Comments part of Beekmantown Group, Potsdam Sandstone, and Vermont Valley Sequence up to 2500 ft. (760 m). Secondary unit description from USGS Geologic Names lexicon (ref. NY046): Named the Rutland dolomite for Rutland, Rutland Co., VT. Consists of generally gray dolomite with beds of dark bluish-gray dolomite in lower and upper parts of the formation. Also contains some scattered blue limestones at various horizons. The base contains interbeds of sandstone. Thickness is about 1000 feet. [Monkton Quartzite] Consists of reddish-brown to brick-red, purple, pink, buff, and white quartzite with a few seams and beds of shale, each a few inches thick. White beds are more numerous at top of unit. Thickness is unknown; 300-ft seam is seen in Colchester Twp. Upper contact marked by dolomite, forming a transition to Winooski marble; Winooski marble type locality given as along Winooski River in Burlington, VT, where it was quarried. Consists mainly of red or pink mottled dolomite. Contains interbeds of coarsely crystalline, light-gray dolomite. All dolomite is dense and has conchoidal fracture. Is very resistant to erosion and forms long ledges over hollows and slopes. Base of formation is interbedded with quartzite for about 50 ft, forming a transition to underlying Monkton quartzite (new). Top of formation is marked by red, buff, and purple quartzite layers exhibiting ripple marks, mudcracks, and annelid trails. Top is well exposed at Winooski Falls in Burlington. Although fossils found in this unit were assigned to the Silurian (by James Hall in 1847) and to the Potsdam (by Billings), Walcott (1883) found Lower Cambrian fossils in the pink dolomite.
Primary rock type dolostone (dolomite)
Secondary rock type quartzite
Other rock types limestone
Lithologic constituents
Sedimentary > Carbonate > Dolostone
Metamorphic > Metasedimentary > Metaclastic > Quartzite
Sedimentary > Carbonate > Limestone
Map references
NYS Museum, NYS Geological Survey, NYS Museum Technology Center, 1999, 1:250,000 Bedrock geology of NYS, data is distributed in ARC/INFOr EXPORT format (with ".e00" extension) in 5 seperate files based on printed map sheets,
Unit references
D. W. Fisher; Y. W. Isachsen, L. V. Rickard, 1970, Geologic Map of New York State, consisting of 5 sheets: Niagara, Finger Lakes, Hudson-Mohawk, Adirondack, and Lower Hudson, New York State Museum and Science Service, Map and Chart Series No. 15, scale 1:250000.
USGS Geologic Names Lexicon (GEOLEX)