Winter on Staten Island
Majestic Glacial Erratics and Serpentinite

With winter hunkering down around Staten Island, the topography comes increasingly to view. As the vegetation and ground cover die back, things we often don't notice during the greener months become noticeable, like the glacial erratics which dot the Island. Glacial erratics are boulders which are "erratic" because they don't match the other (native) types of stone found where they appear, and which are "glacial" because a glacier pushed them from the place where they formed to their present location. The Wisconsin Glacier, which formed to the north beginning 28,000 years ago, advanced down the eastern seaboard, pushing topsoil and rock ahead of it. Its progress transformed the topography of much of the land it covered; the force of the advancing glacier and debris it left behind, for example, formed Todt Hill on Staten Island, which is the highest spot on the eastern seaboard south of Maine. It also carried giant boulders at its leading edge which were left behind when the glacier began to recede 10,000 years ago. The presence of glacial erratics like those found on Staten Island mark the edge zone of the glacier's advance.

Glacial erratics are present on campus, but some of the most interesting examples are found in local parks. In High Rock Park, several smaller glacial erratics are to be found just off the Lavender (or Loosestrife Swamp) Trail; follow the Trail to the left from its starting point, and a glacial erratic rests just to the left after you cross the little footbridge. Sugarloaf Rock in Hero Park (at the corner of Victory Boulevard and Louis Street) is another glacial erratic. The Conference House, in Tottenville, Staten Island, is the southernmost edge of the glacial advance.

Glacial erratics are only one of the ways in which Staten Island is geologically interesting. The native bedrock of Staten Island -- serpentinite -- occurs naturally in only two other places in the world. A metamorphic rock, serpentinite is an odd greenish color, and if you have ever driven along the Staten Island Expressway toward the Verrazano Narrows Bridge, you have probably noticed the exposed serpentinite cliffs near Exit 13. Originally a part of the floor of the ocean, serpentinite was pushed upwards by continental shifts and collisions. Serpentinite's color comes from the combination of the rare green mineral lizardite and white asbestos.

Keep an eye out for glacial erratics and serpentinite!