Appleton’s Dictionary of Greater New York And Its Neighborhood (1905):

Long Island

…is a narrow, fish-shaped strip of land extending along the mainland from the mouth of the Hudson River nearly to the eastern boundary of Connecticut, being separated from the mainland on the north by the Long Island Sound and washed on the south by the ocean. Its greatest length from west to east is 115 miles and its average breadth from north to south is 12 miles. The resemblance to a fish extends to the bi-lobed tail; the southern, which is the longer lobe, ends in Montauk Point, the northern in Orient Point. Between them lies Peconic Bay. The total area of the island is 1,682 square miles… Along the north shore there is a narrow range of hills called the “backbone” of the island, but the rest of the surface slopes gradually to the ocean. The south shore is one immense sand-bank, called the Great South Shore, nowhere more than a mile wide and separated from the island proper for nearly its entire length by inlets from the ocean. The largest of these inlets is the Great South Bay, which extends for 60 miles without a break behind the Great South Beach. Rockaway and Coney Island beaches, which have become famous summer resorts, owing to their proximity to New York, are western extensions of the Great South Beach. The island is divided into four counties of Kings, Queens, Nassau and Suffolk.      

Map of Long Island and the southern part of Connecticut (1870)

Atlas of Long Island, New York. From recent and actual surveys and records (1873)