Geologic units in Allegany county, New York

Machias Formation (Upper Devonian) at surface, covers 48 % of this area

Shale, siltstone; Rushford Sandstone; Caneadea, Canisteo, and Hume Shales; Canaseraga Sandstone; South Wales and Dunkirk Shales.

Conneaut Group, undivided (Upper Devonian) at surface, covers 41 % of this area

In west: Ellicott and Dexterville Formations-shale, siltstone. In east: Germania Formation-shale, sandstone; Whitesville Formation-shale, sandstone; Hinsdale Sandstone; Wellsville Formation-shale, sandstone; Cuba Sandstone.

Oswayo and Venango Formations (Upper Devonian) at surface, covers 10 % of this area

Shale, siltstone, sandstone; replaced eastwardly by Cattaraugus Formation-shale, sandstone, conglomerate.

Wiscoy Formation (Upper Devonian) at surface, covers 1 % of this area

Sandstone, shale; Hanover and Pipe Creek Shales.

Nunda Formation (Upper Devonian) at surface, covers 0.3 % of this area

Sandstone, shale.

Chadakoin Formation (Devonian) at surface, covers < 0.1 % of this area

Light-gray or brownish siltstone and some sandstone, interbedded with medium-gray shale; included in Conneaut Group and "Chemung" of earlier workers; marine fossils common; includes "pink rock" of drillers.

Connoquenessing and Sharon Formations (Lower Pennsylvanian) at surface, covers < 0.1 % of this area

Sandstone, shale; Sharon Formation-shale, sandstone, conglomerate; Olean Conglomerate 50-100 ft. (15-30 m).

Catskill Formation (Devonian) at surface, covers < 0.1 % of this area

Grayish-red sandstone, siltstone, shale, and mudstone; units of gray sandstone occur in upper part; lithologies in upper part arranged in fining-upward cycles. In the Altoona area, the Catskill Formation is mapped as the Duncannon, Sherman Creek, and Irish Valley Members, which are described under "Central and Eastern Pennsylvania" provinces.