A major mid-Turonian eustatic lowering is associated with the sequence boundary between the Bass River/Raritan and the Magothy sequences. Middle neritic sediments that dominated the Bass River sequences were replaced by sediments representing upper delta plain, lower delta plain and delta front environments during Magothy time.  In general, in cores Magothy sediments are more terrestrial (upper delta plain) to the south and more marine (lower delta plain) to the north. The Magothy Formation in outcrop consists of sands and silty clays deposited in complex non-marine to marginal marine environments (Owens and Gohn, 1985).  Regionally, this unit thickens to over 300 m toward the Long Island Platform and thins toward Delaware where it all but disappears (Perry et al., 1975; Olsson et al., 1988).

In outcrop the Magothy Formation is divided into six members.

1) The Sayreville Sand contains bioturbated and cross bedded, poorly sorted, sands and organic-rich clays interpreted as an estuarine deposit.


2) The Old Bridge Sand sand is a granuliferous medium to very coarse sand with fining upward packages representing channel sediments deposited in a nearshore fluvial delta.


3) The South Amboy Fire Clay is a yellow, white, and red mottled clay containing sphaerosiderite representing paleosols deposited in an upper delta plain environment.
4) The Amboy Stoneware Clay consists of tan clays with thin sand beds and laminae representing soils deposited in a delta plain setting.  Other facies may include: fining-upward successions of interbedded and interlaminated cross bedded, micaceous, fine sand and clay beds probably representing a migrating levee complex; interlaminated gray and reddish brown clay, organic-rich clay beds, and micaceous sand deposited in lower delta plain overbank swamps; and organic-rich clays with interlaminated sands representing lower delta plain overbank deposits including cut-off channels and oxbow lakes.


5) The Morgan Beds generally consist of cross bedded sand with intermittent mud beds deposited in marsh, tidal channel, and tidal channel/bay environments within a delta front to lower delta plain.

6) The Cliffwood Beds are cross-bedded to burrowed, fine sand and interbedded organic-rich, sand deposited in deltaic, lower delta plain to upper delta front environments.  A lower unit consists of thicker bedded, cleaner, heavily burrowed, medium sands representing a proximal upper shoreface deposit and faintly laminated, organic-rich, slightly silty clay interpreted as a bay/lagoon deposit.