Long Islands’ soil started with glaciations. Two moraines were deposited (the hills that go ‘round the world) by a huge continental glacier some 20,000 years ago. Geologists call these hills terminal end moraines. As a glacier retreats, all the rock material it carries is deposited by melt water that flows south of the ice front. When the glacier is stationary, it acts like an escalator bringing rock material (with particle sizes anywhere from clay to huge boulders) to the ice front. It is dumped there and piles up creating mounds called moraines. The moraines act as dams for melt water creating areas where sediments have time to sort themselves out which create distinct layers of sand and clay . The moraines are deposited rather quickly and because of this, rock matter doesn’t have enough time to be sorted out. Sorting is the process whereby particles of similar size and density “condense” in layers. Outwash plains are the flat, gently sloping areas south of the moraines. There are two major outwash plains on Long Island, the Hempstead and Terryville Outwash Plain. These are delta-like formations that form slowly as melt water carries rock material southward. Glacial drift is term used for the unsorted mixture of rock matter in the moraines. It is unsorted with a large spectrum of particle sizes. This is not so in the outwash plains where particles have a chance to layer and be sorted out by sheets of slowly moving water that eventually formed into streams that have coursed along for centuries creating dentritic drainage patterns all across Long Island.
