These valleys are generally levelfloored, but at their borders gradually slope upward, and are filled, often to a depth of several thousand feet, with the detritus of gravel, sand and silt from the neighbouring hills.
Even at that period, however, the silt brought down by the rivers rendered access to the harbour difficult, and the historian Philistus excavated a canal to give free access to the sea.
Its fine-grained, unstratified silt contains the remains of many terrestrial animals, including fifteen mammals.
Others that are exceedingly productive are the black calcareous loam of the prairies, the calcareous silt of the bluff belt along the eastern border of the Delta, and the brown loam of the tableland in the central part of the state.
On the Coastal Plain the soil is generally sandy, but in nearly all parts of this region more or less marl abounds; south of the Neuse river the soil is mostly a loose sand, north of it there is more loam on the uplands, and in the lowlands the soil is usually compact with clay, silt or peat; toward the western border of the region the sand becomes coarser and some gravel is mixed with it.
And threaten, unless checked, to be pressed farther inland and silt up the' whole Haff.
This current catches the silt brought down by the rivers and projects it in long banks, or lidi, parallel with the shore.
All that now lies between that point and the modern Ras et-Tin quarter is built on the silt which gradually widened and obliterated this mole.
If such a city was to be on the Egyptian coast, there was only one possible site, behind the screen of the Pharos island and removed from the silt thrown out by Nile mouths.
The artificial harbour was formed (1807-1832) between the mainland and the picturesque island of Ireland's Eye, and preceded Kingstown as the station for the mail-packets from Great Britain, but was found after its construction to be liable to silt, and is now chiefly used by fishing-boats and yachts.
Of undisturbed silt; in a position indicating intentional burial.
Of the bottom consists of sea clay and the more recent silt of the Ysel; 20 per cent.
Towards the sea the solid land gives place to a vast network of streams and creeks, whose sluggish waters are constantly depositing silt, and forming morasses or quicksands.
The rivers having, by the silt of ages, gradually raised their beds, now run along high levels.
Silt-banks and surf-washed bars render the entrance to these rivers perilous.
Long, and protected by a lighthouse and a fort, would admit vessels of considerable tonnage; but it has been allowed to silt up until it shoals off from 2 4 ft.
Similar effects are produced along the boulder-clay cliffs of the Baltic. Where the force of the waves on the beach produces its full effect the coarser material gets worn down to gravel, sand and silt, the finest particles remaining long suspended in the water to be finally deposited as mud in quiet bays.
Most of the large Texas rivers have deposited great quantities of silt along their lower courses on the Coastal Plain, where the current is often sluggish and the banks are periodically overflowed.
The soils of western Washington are chiefly glacial, those of eastern Washington chiefly volcanic. In the low tidewater district of the Puget Sound Basin an exceptionally productive soil has been made by the mixture of river silt and sea sand.
The silt and sand form banks and bars at the mouth, the water is too shallow in winter and the current is too strong in summer, and, further, the bed of the river is continually shifting.
The Tempisque enters the Pacific at the head of the Gulf of Nicoya, and tends to silt up that already shallow inlet (5-10 fathoms) with its alluvial deposits.
Nearly all the Gulf coast rivers, however, are obstructed by bars owing to the quantity of silt brought down from the sierras and the prevailing winds and currents on the coast.
A curious deposit of an impalpably fine and unstratified silt, known by the German name bess, lies on the older drift sheets near the larger river courses of the upper Mississippi basin.
The valley floor is covered with a flood plain of fine silt, having a southward slope of only half a foot to a mile.
The great river receives an abundant load of silt from its tributaries, and takes up ano lays down silt from its own bed and banks with every change of velocity.
The load of silt borne down stream by the river finally, after many halts on the way, reaches the waters of the Gulf, where the decrease of velocity, aided by the salinity of the sea water, causes the formation of a remarkable delta, leaving less aggraded areas as shallow lakes (Lake Pontchartrain on the east, and Grand Lake on the west of the river).
As might be expected under these conditions, it ranges from fine sand to silt which approaches clay in texture.
The finer material constituting alluvium, often described as "silt," is sand and mud.
Quicker or slower, the water that fills it will wash in sand and mud, and year by year this process will go on till ultimately the whole reservoir is filled up. The embankment is raised, and raised again, but at last it is better to abandon it and make a new tank elsewhere, for it would never pay to dig out the silt by manual labour.
Below it, and their water is at all seasons very free from silt or mud.
But while the wisdom of one age thus succeeded in restricting within bounds the tidal water of the river, it was left to the greater wisdom of a succeeding age to improve upon' this arrangement by admitting these muddy waters to lay a fresh coat of rich silt on the exhausted soils.
Spring-tides are preferred, and so great is the quantity of mud in these rivers that from to to 15 acres have been known to be covered with silt from I to 3 ft.
The immediate effect, which is highly beneficial, is the deposition of silt from the tide.
The silt deposited after warping is exceedingly rich and capable of carrying any species of crop. It may be admitted in so small a quantity as only to act as a manure to arable soil, or in such a large quantity as to form a new soil.
Of silt, and the field which has only one sluice can only be warped every other tide.
The silt, as deposited in each tide, does not mix into a uniform mass, but remains in distinct layers.
The water should be made to run completely off and the ditches should become dry before the influx of the next tide, otherwise the silt will not incrust and the tide not have the same effect.
The silt and mud brought down by these rivers is rich in clay and organic matter, and sometimes when dry contains as much as I% of nitrogen.
The low sandy shore of the Delta, slowly increasing by the annual deposit of silt by the river, is mostly a barren area of sand-hills and salty waste land.
Its limits east and west are determined bi the higher ground of the deserts, to which the silt-laden waters 0 the Nile in flood time cannot reach.
This silt consists largely o alumina (about 48%) and calcium carbonate (18%) with smalle quantities of silica, oxide of iron and carbon.
Considerable deposits of mud, silt and sand are accumulating in many of the estuaries.
The shallowness of the lower stream, where the current is sluggish, is probably due to the great quantities of silt brought down by these floods.
The upper end of the gulf is filling up with the silt brought down from the Cordillera.
One of the most interesting facts in the history of the Gondwana series is the occurrence near the base (in the Talchir group) of large striated boulders in a fine mud or silt, the boulders in one place resting upon rock (of Vindhyan age) which is also striated.
In the broad river basins the inundations deposit annually a fresh top-dressing of silt, thus superseding the necessity of manures.
In Behar it has begun to replace indigo, and some success was achieved in Orissa, Assam and Madras; but jute is a very exhausting crop, and requires to be planted in lands fertilized with silt or else with manure.
Towards the San Juan outlet its depth decreases to 6 or 8 ft., owing to the vast accumulation of the silt washed down into the lake by its principal Costa Rican affluent, the Rio Frio.
Much of this silt is again carried away by the San Juan.
Navigation is greatly impeded by shifting banks of silt, and especially by five rapids which can only be traversed when the river is in full flood.