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Updated: May 25, 2025
Indeed, in every region of the globe between the two Arctic circles there are swamps and marshes, steeping-tanks of hemp and flax, large deltas where salt and fresh waters mix, and yet there is no malaria there, although putrid decomposition is on every side.
These conditions are fairly met in the great swamps of river plains and deltas and of coastal plains, such as the great Dismal Swamp, where thousands of generations of forests with their undergrowths contribute their stems and leaves to form thick beds of peat. A coal seam is a fossil peat bed.
During this earlier scene of repose deltas were slowly formed; beds of marl and sand, several hundred feet thick, deposited; siliceous and calcareous rocks precipitated from the waters of mineral springs; shells and insects imbedded, together with the remains of the crocodile and tortoise, the eggs and bones of water-birds, and the skeletons of quadrupeds, most of them of genera and species characteristic of the Miocene period.
But often the load is so large, or the tides are so weak, that much of the waste which the river brings in settles at its mouth, there building up a deposit called the DELTA, from the Greek letter of that name, whose shape it sometimes resembles. Deltas and alluvial fans have many common characteristics.
It is thus learned that our present continent is made up for. the most part of old continental deltas.
The cycle of erosion now in progress and recorded in the layers of stratified rock being spread beneath the sea in continental deltas has therefore been preceded by many similar cycles. Again and again movements of the crust have brought to an end one cycle sometimes when only well under way, and sometimes when drawing toward its close and have begun another.
Here extended deposits of peat may accumulate in swamps, and the remains of land and fresh- water animals and plants swept down by the stream are imbedded in the silts laid at times of flood. Borings made in the deltas of great rivers such as the Mississippi, the Ganges, and the Nile, show that the subaerial portion often reaches a surprising thickness.
Thus, all the land, for three or four miles back from the Lake-margin, both north and south of Rubicon Point, is composed of confluent glacial deltas, and on these deltas the moraine ridges are the natural levees of these ice-streams. e. Parallel Moraines. The moraines described above are peculiar and almost unique.
Archangel is situated on one of the arms of the Dvina River which deltas into the White Sea.
No marine shells were anywhere detected; but this was to be expected, as the borings, though they sometimes reached as low as the level of the Mediterranean, were never carried down below it a circumstance much to be regretted, since where artesian borings have been made in deltas, as in those of the Po and Ganges, to the depth of several hundred feet below the sea level it has been found, contrary to expectation, that the deposits passed through were fluviatile throughout, implying, probably, that a general subsidence of those deltas and alluvial formations has taken place.
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