The Schuylerville Volcano (Hint: It is neither!)

The rocky promontory known as “Stark’s Knob” rises a short distance north of the village of Schuylerville and when the leaves are off the trees its summit affords a panoramic view of the Hudson River.

Though its human history is but the wink of an eye compared to its geologic past, it played a pivotal role in the American Revolution. From its summit, the rebelling colonists observed British ships moving up and down the river.

Under the command of New Hampshire General John Stark, they moved cannon and other armaments to a flat area between the Knob and the Hudson River to prevent British troops from escaping after the battle of Saratoga.

But the Knob is also widely known as “the Schuylerville volcano,” and though it is not now erupting, the name conjures up visions of fiery fountains of lava and plumes of sulphurous smoke spilling out over the landscape.

But it was never a volcano and it did not originate in its present location. However — it is made of lava that has solidified in the form of bulbous mounds called “pillows,” and an unweathered chunk of its bedrock shows holes called “vesicles,” which are the remains of bubbles of escaping gasses.

Such “pillows” are forming today from fissures in the waters off the Big Island of Hawai’i as lava is ejected from fractures in the ocean floor. Curiously, some of the rocks in Stark’s Knob have been found to contain tiny fossils of shallow-water dwelling snails that lived in the Ordovician period, some 450 million years ago.

Clues to the past

Exposures of bedrock that have not vanished under the thick foliage that covers much of the Knob show the rounded, humpy “pillows” and in them and in their fossils lie the keys to understanding the Knob’s formation.

Some 450 million years ago during the Ordovician Period, the landmass that would someday be North America lay bordering a vast body of water known as the Iapetus Ocean, the name of which derives from Greek mythology.

Iapetus was a member of the race of giants called Titans and was known as the father of Atlas. The Iapetus long ago vanished as the plates of the Earth were beginning to assemble themselves into the supercontinent Pangaea, which millions of years later broke apart giving birth to a new ocean: the Atlantic.

In the mid-Ordovician Period — roughly 450 million years ago — the east coast of the United States corresponded roughly to today’s Hudson Valley and off that coast lay an arc of islands similar to those that make up Japan.

As the landmass that would become Africa closed in on the coast in a sliding, scraping motion known as a “transform fault,” those islands got caught up in the crunch and were plastered onto the coast. This action resulted in massive earthquakes and submarine fissures extruding lava — hence the formation of the lava making up Stark’s Knob.

As a result of the chaos, huge slabs of terrain were pushed westward, and the solidified mass of igneous rock that would be known as Stark’s Knob was pushed into its present position from the region that would become Vermont.

To use an obscure term that might be the $2,000 answer on Jeopardy — the solidified lava mass making up Stark’s Knob is allochthonous (al-LOCH-thon-ous), which the Dictionary of Geologic Terms defines as “Said of rocks or materials formed elsewhere than in their present place.”

New York state contains within its borders geologic phenomena that make the teaching of geology here the envy of those in many other states. New York has:

— The vast eroded sedimentary rock layers that constitute the Allegheny Plateau, containing fossils that are the keys to understanding Paleozoic life;

— Billion-year-old-plus rocks in Southeastern New York, Manhattan, and the Adirondacks, providing evidence of great upheavals in the Earth’s crust;

— Hundreds of square miles of karst terrain, laced with caves, underground streams, and springs;

— Dinosaur fossils in the rocks that border New Jersey; and

— Perhaps — perhaps — beneath the lofty and mysterious Adirondacks lies a “hot spot”: a plume reaching down into Earth’s mantle that might in some far future break the surface and produce a series of real volcanoes like those in Iceland.

And overlooking the Hudson just north of the village of Schuylerville lies a mass of solidified lava called Stark’s Knob, providing evidence of the titanic forces that drive Earth’s plates and quite literally move mountains.