Natural Resources

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Glacial melt created Lake Albany, which filled much of the present Hudson River Valley.  Streams such as the Poesten Kill fed the lake with runoff, creating river deltas with glacial silt, like the western ridge of Mount Ida.

In addition to glacial geology, the rocks in this region were periodically stretched and compressed due to plate tectonics, that is, the forces of the earth’s crust.  These pressures created faults where layers of rocky plates collided.  One major fault line reaches from Newfoundland to Alabama.  This “thrust fault” consists of layers of older rock that has been heaved onto more recently formed rock layers.  Known locally as the “Emmons Line,” this fault can be seen in the gorge as a lighter colored layer of rock thrust diagonally through darker layers of shale and sandstone.

Geological events have left their marks all along Congress Street.  From the west the street rises in a low grade from downtown Troy, becoming steeper before it flattens out again at the top of the hill near Pawling Avenue.  During this rise, the street bears right, following both the topography and the general outline of Prospect Park, later curving left as the street and the upper rim of the gorge nearly converge.  Along the southern edge of Upper Congress Street, the gorge rim drops steeply to the water below; to the north the slope continues upward, creating rocky ledges and outcroppings along the roadside. Houses cluster above the busy thoroughfare near the top of Mount Ida.

Sketch of a thrust fault showing how layers of the earth’s crust were disrupted as tectonic plates were pushed together over long periods of time.  Older layers of rock gradually slide on top of younger rock.  (Illustration by T.A.Gobert, 2007)

These rocks protrude from the hillside along the north side of Congress Street opposite the AAA building.  The angled rock layers are a result of the thrust fault that runs roughly north-south through the region.  Note the wild day lilies that have sprouted from the ledge in this early April photograph.  (Photo by T.A.Gobert, 2007)



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