Green Flats from USGS Flushing Quad 1966

Green Flats is a reef in

City Island Harbor City Island Harbor is the protected body of water between City Island and Hart Island in the Bronx, New York City, open to Long Island Sound at its northern and southern extremities. It is not a true harbor, but a sound. Other minor islands in ...

, between City Island and Rat Island. It is part of the

Pelham Islands The Pelham Islands are a group of islands in western Long Island Sound that belonged to Thomas Pell in the 17th century. The islands, and most of the surrounding area, were purchased from the Siwanoy Indians by Pell in 1654, creating Pelham Ma ...

. The reef is composed of mostly small round

glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betwe ...

alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. All ...

rocks In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's ...

and a number of

glacial erratic A glacial erratic is glacially deposited rock differing from the type of rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by glacial ice, often over distances of hundre ...

s made of

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...

. It is covered in green

seamoss ''Chondrus crispus''—commonly called Irish moss or carrageen moss (Irish ''carraigín'', "little rock")—is a species of red algae which grows abundantly along the rocky parts of the Atlantic coast of Europe and North America. In its fresh ...

and

kelp Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms. Kelp grows in "underwa ...

. Like all true reefs, it is completely underwater (and a hazard to navigation) at high

tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

and visible at low tide. Seagulls take mussels from the shallows and fly about 30 feet above the reef and drop them and smash the shells on the rocks and then eat the broken up mussels there. Great blue herons may be seen there hunting at low tide.

References

Geography of the Bronx Long Island Sound Islands of the Bronx City Island, Bronx {{Bronx-geo-stub