The Narrows was most likely formed after deposition of the Harbor Hill Moraine about 18,000 years prior to the end of the last ice age. Previously Staten Island and Brooklyn were connected and the Hudson River emptied into the ocean through the present course of the Raritan River, by taking a more westerly course through parts of present-day northern New Jersey, along the eastern side of the Watchung Mountains to Bound Brook, New Jersey, and then on into the Atlantic Ocean via Raritan Bay.