Lecture Notes: Geology of Long Island at Garvies Point Museum

Overview

• Long Island's Geology consists of various landforms shaped by pre-glacial, glacial, and post-glacial processes.
• These geological processes have occurred over millions of years, influencing the island's topography and natural features.

Pre-Glacial Period

• Formation of ancient metamorphic bedrock, over 400 million years ago.
• Deposition of sands and clays during the late Cretaceous period, 70 million years ago.
• Bedrock exposures are limited, mostly buried beneath newer glacial deposits.

Glacial Period

• Dominated by the advance of the continental glacier during the Wisconsin stage of the Pleistocene Epoch.
• Formation of two major ridges (terminal moraines): Ronkonkoma and Harbor Hill.
  • These moraines mark stationary ice fronts and have contributed to Long Island's highest points.
• Glacial Features:
  • Erratics: Large boulders carried by glaciers, indicating ice movement from the north.
  • Kettle Lakes: Formed by melting ice blocks, varying in size.

Post-Glacial Period

• Coastline Changes:
  • Erosion and reshaping of glacial sediments by waves and currents.
  • Formation of sandy shoreline features and dune-stabilized barrier beaches.
  • Inlets and lagoons form behind barrier beaches.
• Longshore Currents:
  • Transport sand to form spits, tombolos, and baymouth bars.
  • Examples include Fire Island and Truman Beach.

Shoreline Evolution

• Continual wave and current action smooths irregular coastlines.
• Bays and indentations fill with sediments over time.
• Ongoing process expected to continue altering the north shore.

Stream Drainage

• Limited to small rivers due to the island's size.
• Major Rivers:
  • Peconic River, Carmans, Connetquot, and Nissequogue.
• Drainage divides formed by moraines:
  • Streams north of Harbor Hill flow to Long Island Sound.
  • Streams south flow to the Atlantic.
  • Suffolk County has an additional divide at the Ronkonkoma moraine.

Additional Information

• Visitor Information:
  • Location: 50 Barry Drive, Glen Cove, NY
  • Admission: $5 adults, $3 children 5-12
  • Open: Tuesday-Saturday, 10am-4pm
• Highlights: Gift shop with souvenirs, crafts, and educational items.
• Policies: No dogs or collecting allowed; picnic area available.

Contributing Authors

• Information from Educational Leaflet #16 by Herbert C. Mills, 1974.
• Illustrations by Arlene M. Fingerle.

This summary provides an overview of the geological history and features of Long Island as presented by the Garvies Point Museum and Preserve.