By the Shore

By the Shore explores the dramatic beauty of Long Island’s glacial erratics— rocks transported to this area and deposited some 20,000 years ago by the Late Wisconsin glacier. This glacier, estimated to have been over 1,000 feet thick, gouged out vast amounts of boulders, cobbles, pebbles, and soil from an area approximately 10 miles north of where Long Island now lies. As the glacier retreated it deposited this till in two spines of glacial moraine and a large sandy outwash plain, creating Long Island and Long Island Sound. Reflecting their journeys, erratics take their name from the Latin word “errare”, to wander. This ongoing portfolio concentrates on glacial erratic boulders that are visible on Long Island’s shorelines: in the waters, on the beaches, and amidst the bluffs. As the bluffs erode, boulders and rocks continue to tumble down to the beaches—evidence that the cataclysmic changes brought about by the glacier continue to unfold to this day. The connection between these shoreline erratics and the water reinforces the notion of glaciers as rivers of ice that flow in response to gravity. Reflecting the geology of their origins, these boulders are composed of an array of mostly granite, granite gneiss, and basalt. A coarse grain igneous rock, granite’s large range of colors, predominantly pink, grey or white, derive from its primary components of quartz and feldspar while its characteristic shiny black flecks are due to the inclusion of smaller amounts of mica. Granite gneiss is formed from granite by high pressure and temperatures that reduce the grain, usually leaving behind alternating layers of light and dark bands. Basalt is a fine grain igneous rock, usually grey or black, which is formed by the rapid cooling of lava flow. The array of colors and patterns present in the boulders is often altered by a covering of lichen—complex, symbiotic organisms made up of algae or bacteria and fungi. Lichens in the high and low tide marks are black; whereas, lichens just above high tide marks are often gray, brown or yellow. These organisms grow very slowly and scientists estimate that some of the largest lichens on erratics could be thousands of years old. While the diversity in their composition is a testament to their origins, the varying sizes and shapes of these boulders speak to the journeys they have taken to get here. Rounded erratics were formed by traveling great distances; whereas, more angular ones have traveled less far. Occasionally, a slab-like shape reminiscent of a table or block of wood will appear. Pyramid-shaped erratics are rare on the East Coast and more prevalent on the West Coast. Boulder trains consist of a pattern of many rocks and can indicate the direction along which they were transported. In some cases a gigantic boulder was broken up over the course of its journey and came to rest surrounded by smaller remnants of the same rock. Some boulders have striations: straight ones caused by rock fragments frozen on the bottom of the moving glacier as it scraped across the earth, and curved ones shaped by water under great pressure at the glacier’s base. Boulders which ended their journeys in water or tidal areas are often worn quite smooth. The above description summarizes some of the science behind the glacial erratics’ composition, form, and transport. The glacial erratics themselves serve as a dramatic and enduring testament to the immense geological forces that created Long Island, its beaches, and its sound. Presented in black and white these images seek to abstract and distill our scientific understanding of glacial erratics in order to foster a more reverential appreciation for these forces of Nature.