Sinuous, morainal

Gerelateerde afbeelding

The ice sheets of the present era, in their successive spreadings overland, have borne immense freight-rock they pluck up, shear off, rip from the country as they move. They grind much of it into gravel, sand, silt, and clay. When the ice melts, it gives up its cargo, dumping it by the trillions of tons. The most recent advance has been called the Wisconsinan ice sheet, because its effects are well displayed in Wisconsin. Its effects, for all that, are not unimpressive in New York. The glacier dumped Long Island where it is (nearly a hundred per cent of Long Island), and flexplek huren leeuwarden Nantucket, and Cape Cod, and all but the west end of Martha’ s Vineyard. Wherever the ice stopped and began to melt back, it signed its retreat with terminal moraines-huge accumulations of undifferentiated rock, sand, gravel, and clay. The ice stopped at Perth Amboy, Metuchen, North Plainfield, Madison, Morristown-leaving a sinuous, morainal, lobate line that not only connects these New Jersey towns but keeps on going to the Rocky Mountains. West of Morristown, old crystalline rock from the earth’s basement-long ago compressed, distorted, and partially melted, driven upward and westward in the Appalachian upheavals-stands now in successive ridges, which are called the New Jersey Highlands. They trend northeast-southwest. With a notable exception, they have discouraged east-west construction of roads. When the last ice sheet set down its terminal mora\ne, it built causeways from one ridge to another, on which Interstate 80 rides west. Over the continent, the ice had spread southward about as evenly as spilled milk, and there is great irregularity in its line of maximum advance. South of Buffalo, it failed to reach Pennsylvania, but it plunged deep into Ohio, Indiana, Illinois. The ice sheets set up and started Niagara Falls. They moved the Ohio River. They dug the Great Lakes. The ice melted back in stages. Pausing here and there in flexplek huren rotterdam temporary equilibrium, it sometimes readvanced before continuing its retreat to the north. Wherever these pauses occurred, as in northeastem Indiana, boulders and cobbles and sand and gravel piled up in prodigal quantity-a cadence of recessional moraines, hills of rock debris. The material, heterogeneous and unsorted, has its own style of fabric, in which geologists can see the moves and hesitations of the ice, not to mention its weight and velocity. Scottish farmers, long before they had any idea what had laid such material upon Scotland, called it till, by which they meant to convey a sense of “ungenial subsoil,” of coarse obdurate land.