geology of the hudson highlands
Hudson River Journeys: The Geology of the River
The Dynamic Earth
Geology is the study of the Earth, the materials of which it is made, the structure of those materials, and the processes acting upon them. Geology also deals with the study of the history of all life that's ever lived on or is living on the earth now. Studying how life and our planet have changed over time is an important part of geology.
The Hudson Highlands provides a great place to study geology. Plate tectonics – collisions and shifts of the earth’s plates – shaped our region. Then, during glacial periods, ice sheets at least a mile high covered this land, scraped it, reshaped it, and dragged rocks to new resting places. The Hudson Highlands and the Adirondacks have the oldest exposed rock in New York State. This Precambrian and Early Paleozoic metamorphic and igneous rock is estimated to be 1.3 to 1.1 billion years old! When land masses collided, the land faulted and folded, creating what geologists call the Highlands Province. During this great upheaval, the oldest rock was pushed upward, above the younger levels of rock.
Four stages of mountain-building shaped our landscape — the Grenville orogeny, the Taconic orogeny, the Acadian orogeny, and the Alleghenian orogeny. "The Acadian orogeny helped to shape the northern Appalachian Mountains, but the Alleghanian orogeny gave the final squeeze to the margin of the continent to form today's Appalachian Mountain chain," says the Paleontological Research Institute in Ithaca. "At one time the Appalachians were probably as tall as the modern Himalayas, but today the Appalachians are the rounded, weathered and aged peaks of a more mature mountain range that has seen millions of years of erosion and uplift."
We have no shortage of rocks in the Hudson Highlands! As you hike, bike, or drive in our area, you see lots of stone outcroppings and walls made of stone. Here and there, you see very large rocks sitting by themselves. These are called "glacial erratics." Some glacial erratics in Putnam and Westchester counties are as large as small houses! How did those rocks land where they are? Well, as glaciers progressed, they picked up and carried rocks with them. After the glacier melted, these rocks were left behind.
Learn more about glaciers, plate tectonics, rocks, mining, and other aspects of geology below.
glacial legacies of new york state, by thomas mcguire
Thomas McGuire created Glacial Legacies of New York State, a presentation of digital images illustrating the origins of the glacial record in New York. McGuire (B.A., M.A.T. Geology), is a retired earth science teacher who taught in Briarcliff Manor, New York.
The Hudson Highlands sits in the Appalachian mountain range. The following resources explain the geology of our area. Explore information for students and teachers from the U.S. Geological Survey (USGS), the Paleontological Research Institution in Ithaca, New York, and other organizations.
iron minES & granite quarries in the HUDSON HIGHLANDS
Deposits of a hard crystalline iron ore called magnetite were discovered in the Hudson Highlands in the 1700s. This ore was first mined in the western Hudson Highlands during the Revolutionary War. The great chain used as a barricade on the Hudson River was created by the Sterling Iron Works near Sloatsburg, New York using using ore mined from the Hudson Highlands.
The West Point Foundry, a federally-subsidized foundry, opened in 1818 in Cold Spring. The foundry created cannon, round shot, grape shot, stoves, and a variety of machine components. Its location was perfect, because magnetite was discovered nearby. Mines were dug in Philipstown, Putnam Valley and eastern Putnam County. Teams of oxen hauled iron from the mines to the foundry. Workers cut down lots of trees in the forests of our area to make charcoal for the foundry's furnaces. Local streams provided water-power to engage the bellows of the furnaces. The foundry shipped its products on sloops and steamboats that traveled along and beyond the Hudson River. The former site of the foundry is now a park called the West Point Foundry Preserve.
The Croft mine in Putnam Valley was one of the earliest mines in Putnam County. It was worked until 1881. Its ore was suitable for the Bessemer process, which created steel. The Williams mine in Putnam Valley was last worked in 1864. The Denny mine, owned by Robert Parrott, was located west of Canopus Hollow. It was last worked in 1880. The Pratt mine, Sackett mine, and Sunk mine were in the area of the current Dennytown Road and Sunken Mine Road. They were on land that was near or now part of Fahnestock State Park. The Canada mine was two miles to the northeast and extended into Philipstown. The Todd mine was in south Philipstown. And, the Phillips mine was located near Anthony’s Nose. Iron, copper, and sulfur were mined at the Phillips mine. The Tilly Foster mine, located near Brewster, was the most productive mine in Putnam County.
Granite was quarried in our area for building construction. Quarries were located at Little Stony Point and Mount Taurus in Cold Spring, and at the site of Manitoga, in Garrison, where designer Russel Wright built his home.