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New York - Geology It is no unfounded boast to say that North American geology had its beginning in New York State. Largely pioneered by Amos Eaton, Stephen Van Rensselaer, his patron, and Ebenezer Emmons, his student at Rensselaer Polytechnic Institute, the geology of the State became an impetus for scientific debate that still flourishes. Several of the formations of the State— Potsdam, Trenton, Normanskill, Helderberg—became reference rocks for those of similar age investigated later. Since the North American continent rose out of primordial seas, the land area has undergone a rhythmic cycle of rise and fall, of elevation above and submergence beneath prehistoric waters, as land formations were eroded away in one place and deposited as sediments in another. The oldest rocks, nowhere surpassed in antiquity, occupy much of the northern lobe of New York State. A highly altered granite is probably the oldest formation, but the Grenville series of altered and considerably contorted gneiss, quartzite, and limestone, formed from sediments at the bottom of the first sea to flood the Adirondack region, is of about the same age. After their consolidation into rock, the Grenville strata were penetrated by several generations of igneous rocks that rose molten from the interior of the earth. The high peak area of the Adirondacks is made up of what appears to be the oldest intrusion, a soda-lime feldspar rock called anorthosite. Surrounding the anorthosite and responsible for a group of mixed rocks by virtue of their having dissolved some of the Grenville series, are, in probable order of genesis: syenite, granite, gabbro, and basalt. The Highlands of the Hudson comprise a pre-Cambrian area of granite and granite-injected crystalline rocks, apparently faulted as a block upward through the younger sedimentary strata. Although some recent investigators do not concur, it is generally accepted that the crystalline rocks of Manhattan and Westchester, the Fordham gneiss, Inwood limestone, and Manhattan schist are similar in age to the Grenville of the Adirondacks. Tough and relatively resistant to erosion, they form a substantial rock foundation for the skyscrapers of New York City. Following the creation of the pre- Cambrian rocks, a long period elapsed during which the land stood well above sea level. Erosion, tearing down the Adirondack highland, deposited sediments far to the east in an unrecorded sea. As the land wore down and the sea gradually encroached on the Adirondack region, the Cambrian sediments were laid down. The lowermost Cambrian strata are now found east of the Hudson, a position they took during the close of the Ordovician period, when they were thrust westward. Beginning as sandstones, locally altered to quartzite, they are succeeded by limestones and shales. The limestones of the Massachusetts-Connecticut boundary and the Wappinger limestone of Dutchess and Orange Counties have a somewhat anomalous position, but their lower portion is of Lower Cambrian age. A mountain-building movement in the Middle Cambrian re-elevated the land, so that only one formation, the Stissing dolomite of Dutchess County, represents that era within the State. While the east remained elevated, the west was depressed, and Upper Cambrian sediments collected in a sea that surrounded the Adirondack region. The lowermost formation, the Potsdam sandstone, almost completely encircles the mountains; coarse sediments in its lower part indicate shallow-water conditions. As the sea deepened, with fluctuations indicated by the Theresa beds of alternating sandstone and dolomite, deposition of sand gave way to lime and formed the Hoyt and Little Falls formations, both built on foundations of lime-secreting algae known as Cryptozoon. Popularly called 'fossil cabbages,' the Cryptozoon were recently found by scientists of the Saratoga Reservation, near which they appear in classic exposure, to contain a high degree of radioactive potassium, which may contribute to the therapeutic value of the Saratoga mineral waters. In the Upper Cambrian, fossils become profuse; beds contain relatively high forms of life represented by the lobsterlike trilobites and bivalve brachiopods. The creatures of earlier eons, from which these evolved, were probably too soft-bodied to be preserved, or mineral alteration in the preCambrian wiped out the harder-shelled forms. The first rocks of the following period, the Ordovician, occupy the area east and slightly west of the Hudson. A series of shale and sandstone with minor inclusions of limestone, they extend in age to the Middle Ordovician and appear to have been deposited in a sedimentary basin distinct from that of the rocks of similar age to the west. The Deepkill and Normanskill black shales are characterized by large numbers of many species of graptolites, extinct ancestors of modern bryozoa, which float on the surface of the sea. Other Ordovician strata, predominantly limestones, in the Champlain Valley, contain a large fossil fauna of cephalopods, progenitors of the modern squid and pearly nautilus. In the eastern part of the Mohawk Valley the Middle Ordovician rocks are mainly shales and sandstones; westward they become increasingly limy, until in the western Mohawk Valley and in the Black River Valley they are true limestones. The Trenton limestones are exceedingly fossiliferous; bryozoa, brachiopods, and trilobites are the outstanding forms. Upper Ordovician rocks outcrop in the vicinity of Utica and through the Black River Valley northwest to the vicinity of Watertown. The great thickness of shale in the lower part is succeeded by shaly sandstones and, finally, by pure sandstones. Graptolites and brachiopods are the principal fossils. The Ordovician period closed in the east with a mountain-building movement of great magnitude. The Lower Cambrian and Lower Ordovician strata of the east were crumpled and broken and thrust 100 miles or more westward to their position along the present Hudson Valley. West of the Hudson the folding rapidly died; and the central and western parts of the State were undisturbed. The present Taconic Mountains are but eroded stumps of the original Taconics, which must have been of Alpine proportions. While the Taconics rose in the east, sedimentation continued in the sea which still covered central, western, and extreme southeastern New York. Thus the only formation of the Lower Silurian in the east is the Shawangunk conglomerate, which makes up the mountain range of the same name in Ulster and Orange Counties. Westward from the vicinity of Utica, Silurian strata are the principal surface rocks; and Lower Silurian beds cover most of the Lake Ontario Plain. Where the Silurian sea became deeper in the west, the basal Medina sandstone was succeeded by limestones. The Niagara limestone of the Middle Silurian forms the crest of Niagara Falls. The Middle Silurian Clinton formation contains red iron ore, now mined only for paint pigment. The lower part of the Upper Silurian is dominated by the Salina formation, which contains beds of salt and gypsum of great commercial importance. These rocks indicate a period of transient, shallow seas and a warm climate. The remainder of the Upper Silurian is composed mainly of limestones, the various 'waterlimes' furnishing raw material for cement. The Rondout, Cobleskill, and Manlius limestones were deposited in the seas which once again flooded eastern New York in the Upper Silurian. No shallow-water formations preceded these limestones in the east because they were coral reefs, the Manlius limestone being built on a foundation of coraline algae called Stromatopora. The pteropod, Tentaculites, brachiopods, clams, and snails augment the fauna of corals and the algae. Brief emergence of the land separated the Silurian from the Devonian. The deposition of limestones continued until shallower seas prevailed and the Oriskany, Esopus, and Schoharie grits were deposited. While the west remained submerged and true marine sediments accumulated, the east commenced an emergence that was the forerunner of the great Appalachian Mountain uplift. Thus, in the east, the Middle Devonian rocks became typical continental deposits, probably formed in a great delta off some westward-flowing river, and characterized by their oxidized red color and fossil remains of land plants, notably Eospermatopteris, the earliest seed fern tree. The Upper Devonian, all across the State, is like the Middle Devonian of the east—a series of red and green beds containing beach marine fossils and the remains of fresh-water fish and plants. Continental and seashore sedimentation continued from the Devonian into the Carboniferous with hardly a break. The Appalachians rose gradually in the east, throwing the Cambrian and Ordovician shales and Silurian and Devonian limestones into folds and still more complex structures. Sediments became more typically continental as the seas drained off the flanks of the rising mountains. Fossils found in these rocks are of predominantly nonmarine types; and land plant remains are common. Probably the Carboniferous rocks once extended far north into New York but were eroded away, leaving only the small patches in Allegany and Cattaraugus Counties near the Pennsylvania line. The absence of rocks of Permian age in the State indicates that the Appalachian Mountains had attained their maximum elevation and the seas had retreated to the west. Erosion attacked the range and began its relentless work of reducing the land to sea level once more. During that, period, amphibians splashed in sylvan marshes and enormous insects hummed through giant ferns in what is now New York State. In Triassic time, after the Permian period, the seas retreated farther east than the Atlantic now is. The sediments that were being stripped from the newly created Appalachians were spread out in fresh-water lakes of the coastal plain. These muds and sands, periodically exposed to oxidation by the atmosphere, formed the red beds now exposed in Rockland County. The basin into which the Triassic muds were dumped suffered a depression that dropped the strata, through a system of breaks, down into the older rocks. From time to time the unstable crust of the earth let basalt lava through to spread out on the surface of the red beds. A mass of this basalt forms the Palisades and Hook Mountain. The dominant creatures of the Triassic were reptiles, including dinosaurs. Their remains have not been found in New York, but that they roamed the region is indicated by the discovery of their footprints in similar Triassic red beds of the Connecticut River Valley. During the succeeding or Jurassic period, the State stood well above sea level, and the sea was probably many miles east of the present New York harbor. In the next period, the Cretaceous, the ocean lapped farther up on the continent, and Long Island and Staten Island, as well as the entire coastal plain to the south, received deposits. By this time mammals had evolved from reptiles, but fossil remains of them are very rare within the State. There are only small outcrops of Tertiary coastal plain sediments on Long Island, but they are known to underlie much of that island. The Tertiary was a period of erosion during which the State was evolving the basic features of the topography it now has. The Adirondacks stood higher than now; and streams carried mud to a sea which was inhabited by forms of life little different from those of today. In the Pleistocene period, an ice sheet swept over the State. Two miles thick in places, it moved southward, scraping soil from the land surface, rounding off hilltops, and scouring out valleys. For 500,000 years or more the ice advanced or retreated as annual temperatures varied. Only the hardy plants and animals remained near the ice front; all others perished or fled south. Finally the ice sheet melted back to the north, while parts of it were left to rot. Large amounts of gravel, sand, and clay, frozen into the ice, were deposited as the ice melted. Such deposits form the Long Island terminal moraine, the Syracuse drumlins, and the Mendon kames, as well as the stony soil over much of the State. Banks of glacial debris provide clay for brick manufacture in the Hudson Valley and sand and gravel for concrete throughout the State. Although man is supposed to have made his appearance during the glacial period, there is no trace of early man in New York. Many skeletons of mastodons and mammoths, kin of the modern elephant, have been found entombed in the muds of once-existing glacial lakes. The great load of ice depressed the State area several hundred feet. Despite a partial return to the old elevation, the bedrock channel of the Hudson River is still well below sea level. During this lowering of the surface, the sea came up the St.Lawrence River and flooded Lake Champlain, around which shells of Pleistocene marine clams have been found. Since the termination of the Ice Age, about 10,000 years ago, erosion has been the dominant geologic process active in the State.