Ice-dozer

striationsThe buck stopped here in what is now Brooklyn; indeed, the buck of glacial ice made Brooklyn and the rest of Long Island, depositing the rubble of rock and soil it had scraped forward until it stopped and retreated and left the jumble behind. Two pulses of glacial activity formed Long Island, leaving ridges that extend out through the North and South Forks; these are called terminal moraines. In Brooklyn the later moraine sort of smeared out the earlier one, so we’ve only one: it has a name — Harbor Hill, capped by Green-Wood and part of Prospect — known to few but geologists, and is best marked by neighborhoods with ridge, heights, hill, and slope as part of their name. Runoff of smaller particles from the moraines made the flatlands to the south, the outwash plain. Rising seawaters then sculpted the Island’s outline.

All this to say that you have to go to Central Park and the Bronx to find glacial striations, the grooves ground into exposed rock by the gritty underside of the glaciers. Here’s a patch of schist in the New York Botanical Garden’s forest. The groves run NW-SE, the direction of the ice. 10,000 or so years of erosion have softened them a bit.

4 Responses to “Ice-dozer”


  1. 1 Lisa January 27, 2015 at 8:34 am

    that’s a neat way to impress your friends! I’ll try that! At first I thought you were talking about today’s ice…which is in abundance outside my door!

    • 2 mthew January 27, 2015 at 9:33 am

      This post was scheduled a while ago, and nicely dovetailed with the snow, which here in Brooklyn isn’t all it was hyped to be (frankly, that’s par for the course in Brooklyn).

  2. 3 Paul Lamb January 27, 2015 at 9:59 am

    Yep, my daughter lives in Park SLOPE, where I will be next week (making the acquaintance of my new grandson).

    • 4 mthew January 27, 2015 at 10:07 am

      Congratulations! Born on the Harbor Hill Moraine! Prospect Park at the top is a great illustration of the local modest geology: cross over Quaker Ridge and the Neathermead and suddenly you drop down to the flat lake area, which stretches for a hundred miles to the south… or would have 12,000 years ago before the ice melted and oceans rose.


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