The abundance of fossilized corals
in some regional rock formations confirms that most of Western New York was once
covered by a warm, shallow sea. Great quantities of sand and silt, eroded off
high eastern mountains over millions of years and squeezed under millions of tons
of pressure, developed into sandstone and shale. Abundant corals and shelled animals
were the basis of sedimentary rock, the bedrock that lies beneath the region's
Two million years ago, the snow and ice that had been accumulating
in monstrous quantities in the northern hemisphere became, in some places, two
miles thick; the tremendous pressure of its weight caused the ice to flow, forming
a massive continental ice sheet. During the Ice Age, glaciers invaded all but
a small area of New York state.
Due to long-term temperature changes, the
southern edge of this glacier retreated and advanced several times, scraping,
pushing and dragging huge volumes of rock and soil. Stream valleys deepened; others
filled with glacial debris. Colossal boulders were picked up and deposited many
miles away. Glacial runoff streams deposited piles of smaller, sorted sentiments
like sand and gravel.
Mounds of glacial debris called drumlins have a characteristic
steep north slope and gentle south slope, and are common in the northern Finger
Lakes region. Eskers, kames and kettle holes are other glacial formations that
can be explored and studied at Mendon Ponds Park in southeastern Monroe County.
New York's sparkling lakes, lofty hills, deep gorges, raging waterfalls and broad
fertile valleys owe their beauty to their geologic beginnings.
Genesee River once had two branches that converged in Livingston County and flowed
north to join the east-west flowing Ontarian River, whose valley eventually became
the Lake Ontario basin.
As the Ice Age waned and the glacier retreated,
great piles of rock and soil, called moraines, dammed the southern ends of many
valleys. Vast amounts of water poured off the melting glacier and collected in
these valleys, forming, among others, Western New York's beautiful appendage-like
Twelve thousand years ago, the Genesee
River's northward trek was blocked by the Valley Heads moraine near Portageville,
Allegany County, and forced over the rocky Letchworth Plateau, beginning an erosional
process that would create the two gorges and broad valley now found in Letchworth
State Park. The Rochester gorge and waterfall had similar beginnings.
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