Below it, and their water is at all seasons very free from silt or mud.
This current catches the silt brought down by the rivers and projects it in long banks, or lidi, parallel with the shore.
Much of this silt is again carried away by the San Juan.
The immediate effect, which is highly beneficial, is the deposition of silt from the tide.
As might be expected under these conditions, it ranges from fine sand to silt which approaches clay in texture.
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.
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.
Considerable deposits of mud, silt and sand are accumulating in many of the estuaries.
Of undisturbed silt; in a position indicating intentional burial.
And threaten, unless checked, to be pressed farther inland and silt up the' whole Haff.
The rivers having, by the silt of ages, gradually raised their beds, now run along high levels.
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 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.
The upper end of the gulf is filling up with the silt brought down from the Cordillera.
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.
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.
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.
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.
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.
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 finer material constituting alluvium, often described as "silt," is sand and mud.
Of silt, and the field which has only one sluice can only be warped every other tide.
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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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.
Three rivers emptying into the bay - the San Juan, Canimar and Yumuri - have deposited much silt, necessitating the use of lighters in loading and unloading large ships.
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.
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 silt, as deposited in each tide, does not mix into a uniform mass, but remains in distinct layers.
In the broad river basins the inundations deposit annually a fresh top-dressing of silt, thus superseding the necessity of manures.
About 1880, while the Gediz Chai was throwing its silt unchecked into the Gulf of Smyrna and gradually filling the navigable channel, there was talk of reviving Fokia as a new port for Smyrna, and connecting it with the Cassaba railway.
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.
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.
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.
Lakes of this class are sometimes formed by the choking of the mouth of feeble tributaries by silt deposited by the Red river where the currents meet.
In the mechanical analysis of the soil, after separation of the stones and fine gravel by means of sieves, the remainder of the finer earth is subjected to various processes of sifting and deposition from water with a view of determining the relative proportions of sand, silt and clay present in it.
05 mm., and the " silt " from 05 to 005 mm., the " clay " being composed of particles less than .005 mm.
In the valleys of rivers which have overflowed their banks and on level bench lands there is considerable silt and vegetable loam mixed with glacial clay; but on the hills and ridges of western Washington the soil is almost wholly a glacial deposit consisting principally of clay but usually containing some sand and gravel.
The river is always charged with a great quantity of silt which during flood season is deposited over the surrounding plain to the great enhancement of its fertility.
As the silt-laden waters debouch from the rocky bed of the upper reaches on to the plains, the current slackens, and the coarser detritus settles on the bottom.
But in the " Drift " maps many other types of deposit are indicated, such, for instance, as the ordinary modern alluvium of rivers, and the older river terraces (River-drift of various ages), including gravels, brickearth and loam; old raised sea beaches and blown-sand (Aeolian-drift); the " Head " of Cornwall and Devon, an angular detritus consisting of stones with clay or loam; clay-with-flints, rainwash (landwash), scree and talus; the " Warp," a marine and estuarine silt and clay of the Humber; and also beds of peat and diatomite.
The points which require constant attention are - the perfect freedom of all carriers, feeders and drains from every kind of obstruction, however minute; the state and amount of water in the river or stream, whether it be sufficient to irrigate the whole area properly or only a part of it; the length of time the water should be allowed to remain on the meadow at different periods of the season; the regulation of the depth of the water, its quantity and its rate of flow, in accordance with the temperature and the condition of the herbage; the proper times for the commencing and ending of pasturing and of shutting up for hay; the mechanical condition of the surface of the ground; the cutting out of any very large and coarse plants, as docks; and the improvement of the physical and chemical conditions of the soil by additions to it of sand, silt, loam, `` chalk, &c.
The first difficulty that presented itself in carrying this out, was that during the months of highest flood the Nile is so charged with alluvial matter that to pond it up then would inevitably lead to a deposit of silt in the reservoir, which would in no great number of years fill it up. It was found, however, that the flood water was comparatively free from deposit by the middle of November, while the river was still so high that, without injuring the irrigation, water might go on being stored up until March.
Covering the higher parts of the south-western Palaeozoic area in most places are rolling hills of boulder clay or stony moraines; while the lower levels are plains gently sloping toward the nearest of the Great Lakes and sheeted with silt deposited in more ancient lakes when the St Lawrence outlet was blocked with ice at the end of the glacial period.
Occasional breaches during floods cause the overloaded stream to spread in a great lake over the surrounding country, where the silt covers the ground in consequence.
Sections of the Missouri flood plain made by the United States geological survey show a great variety of material of varying coarseness, the stream bed being scoured at one place, and filled at another by currents and floods of varying swiftness, so that sometimes the deposits are of coarse gravel, sometimes of fine sand, or of fine silt, and it is probable that any section of such an alluvial plain would show deposits of a similar character.
The Guayas or Guayaquil river is in part an estuary extending northward from the Gulf of Guayaquil, bordered by mangrove swamps and mud banks formed by the silt brought down from the neighbouring mountains.
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.
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).