We are inclined to view our Hudson Valley, with the Catskill Mountains on the west and the Taconics on the east, as a landscape that has remained unchanged since the earth was formed. It is difficult to imagine the extraordinary changes that have occurred in the hundreds of millions of years up to this tiny quarter of a second in geological time. Our region experienced earthquakes and flows of lava. The crust has split, folded, settled and then thrust upward. As the continents moved--continental drift--and the magnetic pole wandered, climate changed from tropical to arctic cold.
Over 450 Million
During periods over 450 million years ago, the region sank and was covered with oceans, then rose and was again submerged. Seas left their deposits of the remains of small shells of invertebrate animals. Forests of tree-size ferns spread over regions on the edges of quiet seas.
The continents, once welded together, split and then collided, the Afro-European plates crushing our land plate and forcing the crust upwards and westward into high folds of tilted rock, forming our mountain ranges. The erosion of these mountains deposited the materials in a flow westward, some lifting above sea level to form the Catskill Mountains.
About 200 million years ago, more stresses forced the continents apart and the Atlantic Ocean was formed. The region was semi-tropical, with lush plant life and deep basins containing swamps and lakes. Here the dinosaurs flourished, in a period from 225 to 65 million years ago; 50 million years ago, the dinosaurs were gone and the age of mammals had begun.
About two million years ago, during the Pleistocene Epoch, the climate changed to bone-chilling cold. Several great ice sheets, or glaciers, formed and advanced into New York State, receding during warmer periods. The last glacier, known as the Wisconsin glacier, began expanding about 30,000 years ago and reached its terminus on Long Island approximately 20,000 years ago.
The slow-moving mass of ice overwhelmed the Hudson Valley. Not even the highest peaks of the Catskills rose above the glacier, and the thickness in the center of the valley is estimated to have been from one to two miles thick. The weight of this ice forced the land to lower, or subside, with the greatest subsidence to the north where the ice was thickest. As the glacier flowed slowly southward, it smoothed, ground and gorged the land beneath. It also carried large quantities of material with it. One such substance was made up of clay, silt-clay and boulder clay, called till, deposited under the glacial ice in Columbia County. Like the Lake Albany clay, it is wet, nearly impermeable, and unstable, with slopes prone to slippage.
Geologists are divided in determining exactly when the glacier began to retreat, but it is estimated that it receded from New York State about 11,000 years ago.
This was not a simple melting of all the glacial ice. The southern area was the first to be free of the heavy mantle of ice. Dams of ice were blocked by rock barriers, backing up the melt waters and remaining ice, forming a series of ice-filled lakes. Lake Hudson formed first in the lower Hudson Valley from Staten Island to the margin of the retreating glacier. Glacial Lake Albany, held by a dam of ice and rock near Kingston, eventually extended a length of 120 miles and a width of 8 to 12 miles.
Too Cold for Life
The lake was too cold to contain life of any sort. It was filled with ice that gradually broke apart, floated then melted, dumping its cargo of rock and soil onto the lake floor. Deltas of sand and gravel, left by slow moving streams of melt water draining into the lake, are found in several places in Columbia County. An example is on the Kinderhook Creek--on what is known to geologists as the Niverville Plain.
The materials we call Lake Albany clay, consisting of fine silts and clays, were lighter and were carried by streams of melt water into the deep water areas of the lake. This lake of wasted ice and water had an approximate depth of 300 feet near Albany and between 240 and 260 feet along the Columbia County limits of the lake shore.
Geologists believe that Lake Albany existed for about 4,000 to 6,000 years. Near the end of that time, evaporation and drainage had probably reduced it to a collection of lakes and swamps, perhaps with a few blocks of stagnant ice still floating in their centers.
Mastodon roamed the perimeter of the lakes and the fossilized remains of one were found in Claverack in 1705. Whether this mastodon came to its end by being mired in swamp or was part of a Paleo-Indian feast will never be determined, because the authorities, sure that it was the remains of a giant man, sent the bones to England and oblivion.
When the dam holding back the lake finally failed, the water slowly drained away. There remains a controversy as to how quickly the land rebounded after the weight of ice and water gone, possibly less than 2,000 years ago. It is known that there was a gradual elevation from the south to the north. The material deposited in the lake, and left after the lake disappeared, comes under the geological name of lacustrine or glaciolacustrine (lacustrine--pertaining to lakes).
Lacustrine beach and lacustrine delta are deposits, usually of sand and gravel, that were dropped at the shoreline of the lake. Lacustrine sand is generally a quartz sand on a near shore deposit. Lacustrine silt and clay, the material of concern in this series, is made up of layers of different clays and silts, deposited in beds up to and over 300 feet deep. Strata of sand and gravel between the clays are filled with flowing water.
The colors vary from very dark and mottled gray to a brownish gray and to the very light gray that was called blue clay. A light olive brown clay may have been what was defined as yellow. Variations in color were also caused by the season when it was deposited and by weathering.
Regardless of the color, lacustrine clay and sit deposits can present extreme difficulties.
COPYRIGHT 1988 MARGARET SCHRAM