Watchung Outliers

The Watchung Outliers include six areas of isolated low hills and rock outcrops of volcanic and sedimentary origin in the U.S. states of New York, New Jersey, and Pennsylvania. These geologic outliers are primarily diminutive and detached remnants of the Triassic/Jurassic age Watchung Mountain basalt flows with intervening layers of sedimentary rock. All six of the outliers are found along the western edge of the Newark Basin, occupying small synclines adjacent to the Ramapo fault system. The outliers, from north to south, are known as: Ladentown, Union Hill, New Germantown/Oldwick (including Round Top), Prospect Hill, Sand Brook, and Jacksonwald.

The Ladentown Outlier is the most northern of the Watchung Outliers, located along the border of the Town of Haverstraw and Ramapo, New York, approximately seven miles north of the maximum extent of the Watchung Mountains at Campgaw Mountain. The outlier is completely composed of volcanic trap rock, the Ladentown basalt, which covers a considerable area, running at or beneath the surface for a length of about two miles with a width of about a mile. Originally, because of its close proximity to the Palisades, the Ladentown basalt was thought to be an extension of the intrusive sill. It is now known from magnetic and gravity measurements that the Ladentown basalt is linked to the Palisades by a significant subsurface volcanic dike, but it is definitely an extrusive feature, displaying Orange Mountain Basalt characteristic of First Watchung Mountain. This makes the Ladentown basalt unique among the Watchung basalts in that it appears to be rooted to an intrusive feature. In this respect, the Ladentown basalt can be thought of as the remains of a fissure volcano, owing to the extrusion’s slab-like character and ramping profile. New research indicates that the vicinity of Ladentown may have served as the primary vent from which the magma of the Palisades Sill erupted to the surface to form the Watchung flood basalts.

...
Wikipedia