Marshall's Beach: Slip n' slide

Large serpentinite blocks on Marshall's Beach

The serpentinite here is part of a mélange, a mish-mash of serpentinite, hard ancient sea floor lava and sedimentary rocks as well as soft mud deposits. The mélange likely formed when a variety of marine rocks slipped down into a deep-sea trench during giant earthquakes many tens of millions of years ago.

At this location, the mélange includes gray shale and sandstone, blue-green serpentinite and the hard, dark metamorphic blocks that form the sea stacks just offshore at the point to the north. At the point to your south the mélange includes bedded red chert (a silica-rich sea floor sedimentary rock) and sandstone blocks.

Large landslides form all along the bluff here in the highly fractured mélange. The Batteries to Bluffs Trail crosses the toes of many of these old landslide deposits.