Geologic units in Erie county, Pennsylvania

Chadakoin Formation (Devonian) at surface, covers 33 % 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.

Venango Formation (Devonian) at surface, covers 27 % of this area

Light-gray siltstone interbedded with some flaggy, gray sandstone and some bluish-gray shale; Panama Conglomerate and Woodcock Sandstone are, respectively, the lower and upper key beds defining the formation; referred to as "Cattaraugus" by some workers; includes some red shales where it interfingers to the east and south with the Catskill Formation; marine fossils present.

Girard Shale (Devonian) at surface, covers 14 % of this area

Argillaceous, ashen-gray, flaky shale and siltstone; included in Conneaut Group and "Chemung" of earlier workers; marine fossils rare.

Northeast Shale (Devonian) at surface, covers 7 % of this area

Medium-gray shale and some thin light-gray siltstone interbeds; included in Canadaway Formation of New York; included in ""Chemung"" of earlier workers; contains sparse fossil marine fauna.

Corry Sandstone through Riceville Formation, undivided (Devonian) at surface, covers 7 % of this area

Same as Berea-through-Riceville (MDbr) interval, but uppermost sandstone unit is recognized as Corry, not Berea.

Berea Sandstone through Venango Formation, undivided (Devonian) at surface, covers 6 % of this area

Greenish-yellow and gray sandstone, siltstone, and shale succession, becoming more shaly and more gray downward; bottom of interval is bottom of Panama Conglomerate; Venango not mapped separately because upper key bed (Woodcock Sandstone) is missing. Includes, in descending order: Berea Sandstone, Bedford Shale, Cussewago Sandstone, Riceville Shale, and Venango Formation equivalent; contains marine fossils.

Berea Sandstone through Riceville Formation, undivided (Devonian) at surface, covers 3 % of this area

Sandstone, siltstone, and shale; mostly light to dark gray, but some sandstone is greenish yellow, and a few reddish shales occur. Includes, in descending order: Berea Sandstone, Bedford Shale, Cussewago Sandstone, and Riceville Shale; marine fossils common.

Cuyahoga Group (Mississippian) at surface, covers 1 % of this area

Medium-gray siltstone and dark-gray shale containing interbedded light-gray, flaggy sandstone. Includes, in descending order: Meadville Shale, Sharpsville Sandstone, and Orangeville Shale; marine fossils common.

Sands of Presque Isle (Quaternary) at surface, covers 0.2 % of this area

Fine-grained, unconsolidated sand deposited by lake currents.

Shenango Formation (Mississippian) at surface, covers < 0.1 % of this area

Light-gray sandstone and some beds of medium-gray shale and siltstone; upper third of formation is more shaly; contains a few marine fossils.

Ohio Shale (Devonian) at surface, covers < 0.1 % of this area

Shale; brownish black to greenish gray, weathers brown; carbonaceous to clayey, laminated to thin bedded, fissile parting; carbonate and/or siderite concretions in lowermost 50 feet; petroliferous odor; 250 to 500+ feet thick. Includes Olentangy Shale south of central Delaware Co.