Four members of the Onondaga formation previously recognized in central New York are, in ascending order, the Edgecliff, Nedrow, Moorehouse, and Seneca limestones. In Onondaga County, the type area, each of these members is divisible into two or more zones, which are more or less continuous as far east as the Sangerfield quadrangle. Eastward the zones gradually become indistinct, and horizontal facies changes are of greater interest.

East of Cherry Valley the Seneca member grades laterally into the Union Springs black shale, which overlies the Onondaga formation.

The Nedrow member is well defined as far southwest as Kingston. Equivalent beds farther south are referred to the lower Moorehouse member, which rests directly on the Edgecliff. The Moorehouse and Edgecliff members are recognizable, although greatly changed, as far southeast as Port Jervis.

The lower Edgecliff grades into the Schoharie formation in southeastern New York and is probably represented by pre-Onondaga formations in northeastern Pennsylvania. The Buttermilk Falls limestone of eastern Pennsylvania is equated in time with the Moorehouse member of southeastern New York and the Nedrow and Moorehouse members of central and eastern New York.

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