The Palisades rise above the western edge of the Hudson River. The Palisades mark the eastern margin of the Newark Basin in Northern New Jersey. The George Washington Bridge and Midtown Manhattan are in the distance.

The great supercontinent of Pangaea held together for nearly 100 million years. Starting around Late Triassic time (about 220 million years ago) Pangaea began to break apart. A great rift system developed along the suture zone between the continents of Africa and North America. This expanding rift would eventually become the modern Atlantic Ocean. The complex rift system probably had characteristics similar to both the modern East African Rift Valley and the Great Basin region of western North America, consisting of multiple block-faulted uplifts adjacent to graben-type valleys with a scattering of volcanic centers. Triassic uplifts and grabens formed all along the Atlantic Margin from Alabama to Newfoundland. Whereas multiple graben valleys formed between the continents, only one continued to widen to eventually become the Atlantic Ocean. The other valleys became "aborted rifts," filling completely with lacustrine and alluvial sediments, and with both intrusive and extrusive mafic volcanic rocks (chiefly diabase and basalt).

The Newark Basin (in New Jersey and Pennsylvania) and the Connecticut River Basin are both "aborted rift" basins (rift basins that are no longer actively widening via rift-style tectonism - see map below). Both basins contain characteristic sedimentary sandstones and mudrocks that usually bear a red or brownish appearance from an abundance of iron oxide minerals (hematite and limonite). (Homes built of stone from the Newark Basin are called "brownstones.") Fossils are not abundant, but early Mesozoic dinosaur skeletons and trackways have been found. Freshwater shell material and poorly preserved fish and plant remains are also found in some areas.

Formation of the Newark Basin and Early Atlantic Basin

Both the Newark and Connecticut river basins contain "traprocks." Traprocks are mineral-rich mafic volcanic rocks. Their resistance to erosion (relative to the surrounding sandstone and shale produce elevated regions above the surrounding terrain. They form the core of gently dipping cuestas throughout the Mesozoic basins along the Atlantic Margin. The volcanic rocks formed in three ways: