Other precious stones, including the sapphire, emerald, oriental emerald, ruby, opal, amethyst, garnet, chrysolite, topaz, cairngorm, onyx, zircon, etc., have been found in the gold and tin bearing drifts and river gravels in numerous localities throughout the states.
All these are wanting in the Pacific area, though there are indications in its gold-bearing gravels that it once possessed them.
The earlier wells in Pennsylvania consisted of three sections, the first formed of surface clays and gravels, the second of stratified rocks containing water, and the third of stratified rocks, including the oil-sands, usually free from water.
They have also been found in Pleistocene gravels in several parts of England, as Maidenhead, Bromley, Freshfield near Bath, Barnwood near Gloucester, and in the brick-earth of the Thames valley at Crayford, Kent; while their remains also occur in Arctic America.
The somewhat imperfect skull of an extinct species of musk-ox from the gravels of the Klondike has enabled Mr W.
The coarser particles of the sediments are deposited near the shore as gravels, sand and muds, but the very fine particles remain in suspension in the colloidal form, and some of this may be acted upon by marine bacteria or (it is surmised) even utilized by diatoms as a source of silica.
The gold-bearing gravels of East Siberia, especially those of the Lena and the Amur, are relatively more prolific than those of West Siberia.
It is also found in the form of rolled lumps and grains, "stream tin," in alluvial gravels; the latter are secondary deposits, the products of the disintegration of the first-named primary deposits.
Permeability is practically identical with the speed at which percolation takes place; through clay it is slow, but increases in rapidity through marls, loams, limestones, chalks, coarse gravels and fine sands, reaching a maximum in soil saturated with moisture.
Dressing auriferous sands,gravels,&c.; 2.
Disintegrating auriferous gravels by powerful jets of water, and the sluice system described above; in the second case the vein stuff is prepared by crushing and the amalgamation is carried out in mills.
Littoral Deposits (between high andSands, gravels, muds, &c. low-water marks) Kriimmel prefers to simplify this by grouping the deposits in a single category arranged according to their position into: (a) Littoral (including Murray and Renard's littoral and shallow water deposits [II.
De Pourtales pointed out in 1870; they consist of remains of deep-sea corals, serpulae, echinoderms and mollusca united Sands, gravels, muds, &c.
Even the Calaveras man is no exception, since his skull and his polished conical pestle, the latter made of stone more recent than the auriferous gravels, show him to have been of Digger Indian type.
In North America the sites have been examined by the Peabody Museum, the Bureau of American Ethnology, and others, with the result that only the Trenton gravels have any standing.
The latter was a gigantic animal, especially during the Pleistocene period; the skulls and limbbones discovered in the brick-earths and gravels of the Thames valley and many other parts of England having belonged to animals that probably stood six feet at the shoulder.
The most active operations are carried on in Florida, where the phosphate was first worked in 1887 in the form of pebbles in the gravels of Peace River.
In Westland the Miocene includes the Moutere gravels, which rest on the summit of Mount Greenland, 4900 ft.
Valley gravels .border the Thames, and Pleistocene mammalia have been found in fissures in the Hythe beds at Ightham, where ancient stone implements are common.
Denudation in earliest Eocene times has produced flint gravels above the chalk, and an ancient stream deposit of chalk pebbles occurs at Ballycastle.
Glacial gravels are well seen near Antrim town, and as drumlins between Ballymena and Ballycastle.
Recently elevated marine clays, of post-glacial date, fringe the south-eastern coast, while gravels with marine shells, side by side with flint implements chipped by early man, have been lifted some 20 ft.
The central section of the plains thus presents a marked contrast to the northern section; for while the northern section owes its smoothness to the removal of local gravels and sands from a formerly uneven surface by the action of degrading rivers and their inflowing tributaries, the southern section owes its smoothness to the deposition of imported gravels and sands upon a previously I uneven surface by the action of aggrading rivers and their outgoing distributaries.
At the highest western point, nearest the mountains whence its gravels were supplied; and thence it slopes south-eastward at a decreasing rate, first about 12 ft., then about 7 ft.
Gold occurs in quartz veins traversing various formations (some as young as Jurassic), and also in gravels, which were for the most part deposited previous to the uplift of the Sierra block.
Some of the gravels then occurred as piedmont deposits along the western border of the old mountains; these gravels are now more or less dissected by new-cut valleys.
Other auriferous gravels are buried under the upland lava flows, and are now reached by tunnels driven in beneath the rim of the table mountains.
The reputed discovery of traces of early man in the lava-covered gravels has not been authenticated.
The Lafayette formation has been the occasion of much difference of opinion, but is by many held to be a non-marine formation, made up of gravels, sands and clays, accumulated on land, chiefly through the agency of rain and rivers.
On the coastal plain there is the Columbia series of gravels, sands and barns, made up of several members.
Old alluvial deposits are left high above the existing level of many rivers, in the form of "terraces" of gravel and loam, the streams to which these owe their existence having modified their courses and cut deeper channels; such are the alluvial gravels and brick-earths upon which much of "greater London" is built.
Limonite often forms a cementing medium in ferruginous sands and gravels, forming "pan"; and in like manner it is the agglutinating agent in many conglomerates, like the South African "banket," where it is auriferous.
Numerous isolated palaeolithic objects of the Mousterian type have been found in the neighbourhood of Rome in the quaternary gravels of the Tiber and Anio; but no certain traces of the neolithic period have come to light, as the many Pre" flint implements found sporadically round Rome pro- historic bably belong to the period which succeeded neolithic (called by Italian archaeologists the eneolithic period) inasmuch as both stone and metal (not, however, bronze, but copper) were in use.
The majority of minerals are found commonly in masses which can with difficulty be recognized as aggregates of crystalline grains, and occur comparatively seldom as distinct crystals; but the diamond is almost always found in single crystals, which show no signs of previous attachment to any matrix; the stones were, until the discovery of the South African mines, almost entirely derived from sands or gravels, but owing to the hardness of the mineral it is rarely, if ever, water-worn, and the crystals are often very perfect.
The diamond is here found in ancient sandstones and conglomerates, and in the river gravels and sands derived from them.
The diamond is found under three conditions: (1) in the gravels of the present rivers, embedded in a ferruginous claycemented conglomerate known as cascalho; (2) in terraces (gupiarras) in a similar conglomerate occupying higher levels in the present valleys; (3) in plateau deposits in a coarse surface conglomerate known as gurgulho, the diamond and other heavy minerals being embedded in the red clay which cements the larger blocks.
Since the heavy minerals of the cascalho in the river beds are more worn than those of the terraces, it is highly probable that they have been derived by the cutting down of the older river gravels represented by the terraces; and since in both deposits the heavy minerals are more abundant near the heads of the valleys in the plateau, it is also highly probable that both have really been derived from the plateau deposit.
The diamond here occurs in river gravels and sands associated with the same minerals as in Minas Geraes; since 1844 the richest mines have been worked in the Serra de Cincora, where the mountains are intersected by the river Paraguassu and its tributaries; it is said that there were as many as 20,000 miners working here in 1845, and it was estimated that 54,000 carats were produced in Bahia in 1858.
These " dry diggings " were therefore at first supposed to be alluvial in origin like the river gravels; but it was soon discovered that, below the red surface soil and the underlying calcareous deposit, diamonds were also found in a layer of yellowish clay about 50 ft.
African locality must be mentioned.; considerable finds were reported in 1905 and 1906 from gravels at Somabula near Gwelo in Rhodesia where the diamond is associated with chrysoberyl, corundum (both sapphire and ruby), topaz, garnet, ilmenite, staurolite, rutile, with pebbles of quartz, granite, vIII.
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.
It is probable that certain rudely chipped flints, so-called eoliths, in the alluvial gravels (formed generally at the mouth of wadis opening on to the Nile) at Thebes and elsewhere, are the work of primitive man; but it has been shown that such are produced also by natural forces in the rush of torrents.
Above the Boulder Clay are found sands and gravels, along with perched boulders which, by their source and position, indicate the direction and thickness of the ice that carried them.
The hydraulic stream came into use as early as 1852 (or 1853) when prospecting of the higher ground made it certain that the " deep " or " high " gravels - i.e.
Depends greatly on the soil and position in which the trees are grown: the dry slopes of granitic or gneissic mountains, or the deep well-drained sandy gravels of the lower country seem to answer equally well; but on clay or wet peat the tree rarely a c Scotch Fir (Pinus sylvestris).
Its most interesting feature is the occurrence near its summit, north of Cape Mondego, of sands and gravels containing plant remains.
Bones and implements have been found in the Quaternary gravels at Trenton, which have been held by some authorities to prove the presence of Palaeolithic man; but the earliest inhabitants of New Jersey of whom there is any certain record were the Lenni-Lennape or Delaware Indians, a branch of the Algonquian family.
The London Basin occupies a triangular depression in the Chalk which is filled up with clays and gravels of Tertiary and later age.
The last well-marked lowering of the land took place in the Pleistocene period, when it was accompanied by glacial conditions, through which the greater part of northern England and the Midlands was covered by ice; a state of things which led directly and indirectly to the deposition of those extensive boulder clays, sands and gravels which obscure so much of the older surface of the country in all but the southern counties.
Stone, The Glacial Gravels of Maine and their Associated Deposits (Washington, 1899); T.
There seem to have been two periods of eruption, and as some of the lavas have flowed over Quaternary gravels, the latest outbursts must have been of very recent date.
The state of culture reached by Quaternary man is evidenced by the stone implements in the drift-gravels, and other relics of human art in the cave deposits.
There have been recently no discoveries to rival in novelty those which followed the exploration of the bonecaves and drift-gravels, and which effected an instant revolution in all accepted theories of man's antiquity, substituting for a chronology of centuries a vague computation of hundreds of thousands of years.
Many interesting mammalian fossils, rhinoceros, mammoth, &c., with palaeolithic implements, have been found in the valley gravels of the river Ouse and its tributaries.
Speaking generally, the Ozark region is characterized by reddish clays, mixed with gravels and stones, and cultivable in inverse proportion to the amount of these elements; northern Missouri by a generally black clay loam over a clay subsoil, with practically no admixture of stones; the southern prairies, above referred to, share the characteristics of those north of the Missouri.
High-level gravels occur from 600 to 2000 ft.
The Biggleswade well was sunk by processes better known in connexion with the sinking of mine shafts and foundations of bridges across the deep sands or gravels of bays, estuaries and great rivers.
Flint gravels are widely employed for dressing walks and roads, and for rough-cast work in architecture.
After the Irish chalk had been worn into rolling downs, on which flint-gravels gathered, the great epoch of volcanic activity opened, which was destined to change the character of the whole north-west European area.
The more deep-seated type of these rocks is seen in the olivine-gabbro mass of Carlingford Mountain; but most of the igneous region became covered with sheets of basaltic lava, which filled up the hollows of the downs, baked the gravels into a layer of red flints, and built up, pile upon pile, the great plateaus of the north.
Volcanic activity may have extended into Miocene times; but the only fossiliferous relics of Cainozoic periods later than the Eocene are the pale clays and silicified lignites on the south shore of Lough Neagh, and the shelly gravels of pre-glacial age in county Wexford.