Cameron's Line

Cameron's Line is an Ordovician suture fault in the northeast United States which formed as part of the continental collision known as the Taconic orogeny around 450 mya. Named after Eugene N. Cameron, who first described it in the 1950s, it ties together the North American continental craton, the prehistoric Taconic Island volcanic arc, and the bottom of the ancient Iapetus Ocean.

Cameron's Line winds southward out of New England into Western Connecticut. It has been identified in western Connecticut near Ridgefield before it heads into the Bronx, along the East River in Manhattan, through New York Bay, Staten Island and into New Jersey.

The basement rocks of the Manhattan Formation located on the western side of Cameron's line are metamorphosed sedimentary rocks and can be thought of as the remnants of the edge of the North American continent from 1 billion years ago. They were formed in roughly this location (autochthonous) and have been tectonically stable over a large period of time. Through New England, generally, the rocks to the west of Cameron's line are the remnants of an enormous mountain range (the Grenville orogeny), sometimes called the 'crystalline Appalachians,' which once stretched from Newfoundland to Mexico, the local remnants of which are exposed and create the Housatonic Highlands, the New Jersey Highlands and the Manhattan prong (much of the Bronx).

In general, to the east of the line has allochthonous rocks formed elsewhere, which have experienced great tectonic movement in a westward direction on top of the underlying bedrock. In other words, beginning around 450 million years ago an ocean similar to the Atlantic began to shrink and as it did the North American continent began to collide with island chains which accreted at the edge of the continent and formed the land of what we now call New England. The major exceptions to this directionality are the most southerly remnants of these ancient collisions, the Serpentinite outcrops that form Hoboken, NJ and Todt Hill in Staten Island, which in fact lie to the west of Cameron's line because it makes a u-turn.

...
Wikipedia