Named for exposures along North Chuctanunda Creek within city of Amsterdam, Montgomery Co., east-central NY. Consists of a sequence of blue-gray, buff-weathering, medium-grained, medium- to thick-bedded dolomites. Lower half is dark blue to gray, variegated, noncherty, coarse dolarenite, locally laminated. Upper half is a brownish-gray to blue-gray, fine- to medium-grained, siliceous dololutite that is markedly cherty with much interstitial silica; chert is mainly stringy or hackly. Thickness is 40 ft at type locality. Unconformably underlies Cranesville dolomite (new); unconformably overlies Fonda member (new) of Tribes Hill formation. Offlaps Tribes Hill formation in a northward direction. [Age is Early Ordovician (early Canadian).]

Source: GNU records (USGS DDS-6; Reston GNULEX).