Beekmantown Group

Mohawk Valley: Little Falls Dolostone-chert; Hoyt Formation-limestone, dolostone, oolite. Washington county: Whitehall Formation-dolostone, limestone; Ticonderoga Dolostone-chert.
State New York
Name Beekmantown Group
Geologic age Cambrian
Lithologic constituents
Sedimentary > Carbonate > Dolostone
Sedimentary > Carbonate > LimestoneHoyt Formation-limestone, oolite. Whitehall Formation-limestone
Sedimentary > Chemical > ChertLittle Falls Dolostone-chert; Ticonderoga Dolostone-chert
Comments part of Beekmantown and Stockbridge Groups, Potsdam Sandstone, and Vermont Valley Sequence up to 3500 ft. (1100 m). Secondary unit descriptions from USGS Lexicon website (Ref. NY046) and references NY037, NY038, NY039, NY040 and NY041. The Beekmantown Group in east-central NY includes the (ascending) Potsdam Sandstone, Ticonderoga Formation, Whitehall Formation, Great Meadows Formation, Fort Ann Formation, and Fort Cassin Formation. The Cambrian-Ordovician boundary is within the Whitehall Formation, and therefore, the Beekmantown Group is of Late Cambrian to Early Ordovician age (Croixian to Canadian). Unit overlies the Lake George Group and underlies the Black River Group (Fisher, 1984). Paleozoic cover sequence adjacent to Adirondack massif in western part of Glens Falls quad consists of (ascending): Late Cambrian Potsdam Sandstone, Late Cambrian Ticonderoga Formation, Late Cambrian and Early Ordovician Beekmantown Group (with Whitehall Formation at base), early Middle Ordovician Chazy Group, Middle Ordovician Black River and Trenton Groups, and Mohawk Valley shales (Canajoharie Shale and Snake Hill Formation). Potsdam and Ticonderoga are partly correlative with Danby Formation of Middlebury synclinorium in VT. Beekmantown and part of Chazy correlate directly with limestones and dolomites above Danby. Paleozoic cover sequence is interpreted as a platform sequence. [Text states Beekmantown "as used by Fisher (1984)", but this appears to be an error because Fisher (1984) included Potsdam and Ticonderoga in his Beekmantown. Fisher (1977) abandoned Canajoharie but USGS still recognizes it.] (Thompson, 1990). Little Falls - Unit is well known for its exceptionally clear, doubly terminated quartz crystals, known as "diamonds" and for the irregular masses of algal stromatolites, which occur at several levels, particularly in informal unit B. Brachiopods have been reported at several localities, but except for the stromatolites, the unit, for the most part, is unfossiliferous. Lithology is quite varied. Though dolostone is predominant, sandstone and mixed sandstone and dolostone beds are common. The mineralogy of the Little Falls is extremely varied. Unit includes quartz, calcite, dolomite, pyrite, marcasite, galena, sphalerite, limonite, chalcopyrite, hematite, glauconite, and anthraxolite. Inferred age of the quartz crystals is Carboniferous, while deposition of the limestone occurred during the Late Cambrian (Muskatt and Tollerton, 1992). Hoyt - Named the Hoyt limestone member of the Little Falls dolomite for Hoyt's quarry, Saratoga Co., eastern NY. Unit is basal phase of the Little Falls. Consists of blackish, subcrystalline, pure or only slightly magnesian limestone alternating with beds of blue and light gray dolomite; quartz sand grains in some of the beds, increasing in amount below; contains many beds of black oolite, most abundant near the base. Fossils include Cryptozoan, trilobites, gastropods, and LINGULEPIS ACUMINATA at many horizons. Thickness is 80 to 120 feet. Gradationally overlies the Potsdam sandstone and underlies the remainder of the Little Falls dolomite. Unit occurs locally. The Hoyt is of Late Cambrian age (Ulrich and Cushing, 1910). The base of the Whitehall formation is raised to coincide with contact of Little Falls dolomite and Hoyt limestone, and Hoyt is revised as lower member of Whitehall formation. The Hoyt limestone member is about 40 feet thick and underlies the Skene dolomite member (Wheeler, 1942).

Fisher, D.W., Isachsen, Y.W., and Rickard, L.V., 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 1:250,000.

Fisher, D.W., 1984, Bedrock geology of the Glens Falls-Whitehall region, New York: New York State Museum Map and Chart Series, 35, 60 p., 1 sheet, scale 1:48,000.

Thompson, J.B., Jr., 1990, An introduction to the geology and Paleozoic history of the Glens Falls 1 degrees x 2 degrees quadrangle, New York, Vermont, and New Hampshire, IN Slack, J.F., ed., Summary results of the Glens Falls CUSMAP project, New York, Vermont, and New Hampshire: U.S. Geological Survey Bulletin, 1887-A, p. A1-A13.

Muskatt, H.S. and Tollerton, V.P., Jr., 1992, The Little Falls Dolostone (Late Cambrian); stratigraphy and mineralogy, IN April, R.H., ed., Field trip guidebook: New York State Geological Association Guidebook, no. 64, 64th Annual Meeting, Hamilton, NY, September 18-20, 1992, p. 200-215.

Ulrich, E.O. and Cushing, H.P., 1910, Age and relations of the Little Falls dolomite (calciferous) of the Mohawk Valley: New York State Museum Bulletin, no. 140, p. 97-140.

Wheeler, R.H., 1942, Cambrian-Ordovician boundary in the Adirondack-border region: American Journal of Science, v. 240, no. 7, p. 518-524.

USGS Geologic Names lexicon found at:

NGMDB product
Counties Fulton - Hamilton - Herkimer - Montgomery - Saratoga - Schenectady