The mud brought down by it, calculated at 7150 lb an hour at Bagdad, is not deposited in marshes to form alluvium, as in the case of the Euphrates, but although in flood time the river becomes at places an inland sea, rendering navigation extremely difficult and uncertain, the bulk of the mud is deposited in banks, shoals and islands in the bed of the river, and is finally carried out into the Persian Gulf.
The coast, constantly encroaching on the sea by reason of the alluvium washed down by the rivers of the Pyrenees and Cvennes, is without important harbours saving that of Cette, itself continually invaded by the sand.
The first of these canals, taken off on the right bank of the river a little below Hit, followed the extreme skirt of the alluvium the whole way to the Persian Gulf near Basra, and thus formed an outer barrier, strengthened at intervals with watch-towers and fortified posts, to protect the cultivated land of the Sawad against the incursions of the desert Arabs.
It is easy to distinguish the great primitive watercourses from the lateral ducts which they fed, the latter being almost without banks and merely traceable by the winding curves of the layers of alluvium in the bed, while the former are hedged in by high banks of mud, heaped up during centuries of dredging.
The most fertile soil is the alluvium of the' Delta, deposited during the overflows of the Mississippi.
Much of the Triassic area is covered superficially by glacial drift and alluvium of the Trent.
Reclaimed marsh-land and fresh alluvium (the so-called " front-lands " on rivers and bayous) are choice soil for Indian corn, sugar-cane, perique tobacco, semi-tropical fruits and cotton.
Albert Nyanza, on the other hand, is threatened in the distant future with destruction from another cause - the filling of its bed by the alluvium poured into it by the Semliki, the Victoria Nile and, in a lesser degree, by other streams. The Semliki receives directly or indirectly the whole of the drainage of Ruwenzori, and also that of the eastern face of the Congo mountains as well as the drainage basin of Albert Edward Nyanza.
The main deposits of alluvium occur below Lambeth and Westminster, and in the valley of the Wandle, which joins the Thames from the south near Putney.
It naturally falls into two divisions, the northern being more or less mountainous, while the southern is flat and marshy; the near approach of the two rivers to one another, at a spot where the undulating plateau of the north sinks suddenly into the Babylonian alluvium, tends to separate them still more completely.
Such river-transported material or alluvium is common in all river valleys.
In the alluvium which covers all, the remains have been discovered of several species of elephant, which, according to Dr Edmund Naumann, are of Indian origin.
The Coastal Plain has for the most part a light sandy soil, but there is a fertile alluvium in the river bottoms and good clay soils on some of the uplands.
These branches enclose a deltaic formation, a low tract of marshy alluvium known as the Lezirias, traversed by several minor channels.
In the larger valleys and along the shores of lakes considerable alluvium is mixed with this clay.
Some of the best soil is in the mountain valleys, for these valleys were once lakes and rich deposits of alluvium were made in them.
Calculating from the present rate of deposit of alluvium at the head of that gulf, Eridu should have been founded as early as the seventh millennium B.C. It is mentioned in historical inscriptions from the earliest times onward, as late as the 6th century B.C. From the evidence of Taylor's excavations, it would seem that the site was abandoned about the close of the Babylonian period.
West of the Missouri river the drift gives place to a fine soil of sand aid clay, with deposits of alluvium in the vicinity of streams. Though lacking in vegetable mould, these soils are generally capable of producing good crops where the water-supply is sufficient.
The best soils are the alluvium in the bottom-lands along some of the larger rivers and that of the Blue Grass Region, which is derived from a limestone rich in organic matter (containing phosphorus) and rapidly decomposing.
The greater part of Bechuanaland is covered with superficial deposits consisting of the sands of the desert regions of the Kalahari and the alluvium and saliferous marls of the Okavango basin.
ALLUVIUM, soil or land deposited by running water.
The finer material constituting alluvium, often described as "silt," is sand and mud.
Many shallow lakes have been completely filled with alluvium and their sites are now occupied by fertile plains; this process may be seen in operation almost anywhere; a good illustration is the delta of the Rhone in Lake Geneva.
Formed partly by alluvium carried down by perennial streams from the mountains of Lebanon and Galilee, and fringed by great sand-dunes which the sea throws up, Phoenicia is covered with a rich and fertile soil.
(7) The section of south Sumatra between the eastern chain of old rocks and the east coast with its numerous river mouths is formed of the alluvium of sea and rivers.
The more modern deposits of Holland consist of alluvium, wind-blown sands and peat.'
The northern half of the province is flat, and even marshy along the coast, and consists of a broad band of alluvium formed by the series of parallel rivers descending from the south.
The earlier geologists had been in the habit of dividing the Quaternary deposits into an older Diluvium and a younger Alluvium; the latter is still employed in England, but the former has dropped out of use, though it is still retained by some continental writers.
The Alluvium was distinguished from Diluvium by the fact that its mammalian fossils were representatives of still living forms, but it is a matter of great difficulty to separate these two divisions in practice.
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 flood waters of the Chambezi and other streams, which deposit large quantities of alluvium, are gradually solidifying the swamp, while the Luapula is believed to be, though very slowly, draining Bangweulu.
In some rivers the water is generally pure; in others it is highly charged with fertilizing alluvium, or, it may be, with barren silt.
The second is hardly less valuable, and consists in the remarkable richness of the alluvium brought down the river year after year during the flood.
The object of the engineer is so to utilize this flood-water that as little as possible of the alluvium may escape into the sea, and as much as possible may be deposited on the fields.
Recent alluvium and a thick deposit of black earth border the upper reaches of the Benue and cover wide areas around Lake Chad.
Although the Nil, water is abundantly charged with alluvium, the annual deposit b1 the river, except under extraordinary circumstances, is smaller thai might be supposed.
Few seas are more prolific in fish than the Persian Gulf and the Gulf of Oman; the great proportion of known species are edible and many have a commercial value for the isinglass or oil Shelly conglomerates and dead coral reefs of the littoral; red sandhills of the coast of Trucial Oman; alluvium of Turkish Iraq; river and lake deposits of Oman and the interior of Persia.
Geologically, as well as physically, India consists of three distinct regions, the Himalayas, the Peninsula, and - between these two - the Indo-Gangetic plain with its covering of alluvium and windblown sands.
Ferguson has shown that the sediment is carried away from this area by the set of the currents; probably then it has remained free from sediment whilst the neighbouring sea bottom has gradually been filled up. If so, the thickness of the alluvium is at least 1800 ft., and may be much more.
At Lucknow a boring was driven through the Gangetic alluvium to a depth of 1 33 6 ft.
It lies on rocky heights above a region of stoneless alluvium on the east, and with the largest and richest plain in Korea on the west.
Korean soil consists largely of light sandy loam, disintegrated lava, and rich, stoneless alluvium, from 3 to 1 0 ft.
Except in the valley of the Aroostook and along the Kennebec, the Penobscot, and some other rivers, the soil is generally unfit for cultivation, there being too little alluvium mixed with it to make it fertile.
Among these is the argument from the numerous borings made in the alluvium of the Nile valley to a depth of 60 ft., where down to the lowest level fragments of burnt brick and pottery were always found, showing that people advanced enough in the arts to bake brick and pottery have inhabited the valley during the long period required for the Nile inundations to deposit 60 ft.
Another argument is that of Professor von Morlot, based on a railway section through a conical accumulation of gravel and alluvium, which the torrent of the Tiniere has gradually built up where it enters the Lake of Geneva near Villeneuve.
Coral, alluvium, sand.
The floor of the Basin Region is formed of alluvium washed from the high plateaus and mountain ranges, a part of which has accumulated in alluvial fans, and part in the greatly expanded lakes which existed here in the glacial period.
This alluvium gives gently sloping or level desert plains, from which isolated mountain ranges rise like islands from the sea.
The plain of Sind and of eastern Gujarat is covered by alluvium and wind-blown sand.