sentences:  However, the most important factor was the "interpenetration of land and sea," which makes for exceptional harbors, such as those at the Chesapeake Bay, the Port of New York and New Jersey, Narragansett Bay in Providence, Rhode Island, Washington Harbor, and Boston Harbor.The coastline to the north is rockier and less sheltered, and to the South is smooth and does not feature as many bays and inlets that function as natural harbors.Also featured are navigable rivers that lead deeper into the heartlands, such as the Hudson, Delaware, Potomac, and Connecticut Rivers, which all support large populations and were necessary to early settlers for development.