Around 400 million years ago, a small continent long and narrow collided with proto North America. This created folding and faulting, as compression occurred. Then around 350 million years ago, the African plate collided with North America creating the folding and faulting in the Appalachians. But when the African plate pulled away from North America, an aborted rift valley was created. This half , starts east of Boonton and goes through the middle of Parsippany, south to Morristown, to the south end of Great Swamp. From Parsippany and the Boonton area the half graben goes east to the western side of Paterson, where there was another fault by the lava flows. East of the Ramapo Fault is where there is this aborted rift valley.