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.
Clays of all qualities and colours abound.
The best soils are in the west section, where limestone clays or shell marls are common.
They yield valuable coals, clays, marls and ganister.
It is marked by grey clays and sands, lignitic fossiliferous clays, beds of lignite or brown coal, sometimes 8 ft.
The Grand Gulf group, of formations of different ages, consisting of sands, sandstones and clays, and showing a few fossil plants, but no marine fossils, extends southward from the last to within a few miles of the coast, and is 750-800 ft.
The Keuper clays yield material for bricks.
The clays of the Rolling Downs formation overlie a series of sands and drifts, saturated with water under high pressure, which discharges at the surface as a flowing well, when a borehole pierces the impermeable cover.
Clays and mineral waters are, however, widely distributed.
They consist chiefly of sands and clays of aeolian and freshwater origin.
Its upheaval above the great sea which submerged all the north-west of the Indian peninsula long after the Himalaya had massed itself as a formidable mountain chain, belongs to a comparatively recent geologic period, and the same thrust upwards of vast masses of cretaceous limestone has disturbed the overlying recent beds of shale and clays with very similar results to those which have left so marked an impress on the Baluch frontier.
Some of the stiff boulder clays or " till " so prevalent over parts of the north of England appear to have been deposited from ice sheets during the glacial period.
In clays whose particles are exceedingly minute the water travels very slowly but may ultimately reach a height of many feet above the level of the " water-table " below.
Kaolin, fire-clays and brick-clays are common to all the states.
The oak grows most luxuriantly on deep strong clays, calcareous marl or stiff loam, but will flourish in nearly any deep well-drained soil, excepting peat or loose sand; in marshy or moist places the tree may grow well for a time, but the timber is rarely sound; on hard rocky ground and exposed hillsides.
The Cambrian is represented by blue clays, ungulite sandstones and bituminous slates in Esthonia and St Petersburg.
For days together the traveller sees no other vegetation; even this, however, disappears as he approaches the regions recently left dry by the Caspian, where saline clays, bearing a few Salsolaceae, or mere sand, take the place of the black earth.
Overlying the Tuscaloosa are the Eutaw sands, characterized by sandy laminated clays, and yellow, orange, red and blue sands, containing lignite and fossil resin.
The latest Cretaceous is the Ripley formation, which lies west of the northern part of the last-named, and, about Scooba, in a small strip, the most southerly of the Cretaceous - it is composed of coarse sandstones, hard crystalline white limestones, clays, sands, phosphatic greensands, and darkcoloured, micaceous, glauconitic marls; its greatest thickness is about 280 ft.
The Jackson formation south-west of the Lisbon beds, is made up chiefly of grey calcareous clay marls, bluish lignitic clays, green-sand and grey siliceous sands.
Its materials are pebbles, clays and sands of various' colours from white to deep red, tinged with peroxide of iron, which sometimes cements the pebbles and sands into compact rocks.
They yield valuable coals, clays, marls and ganister.
In regions where climatic conditions are favourable, cotton grows more or less successfully on almost all kinds of soil; it can be grown on light sandy soils, loams, heavy clays and sandy " bottom " lands with varying success.
Sandy soils are made thereby too dry and leachy, and it is a questionable proceeding to turn the heavy clays upon the top. Planters are, as a result, divided in opinion as to the wisdom of subsoiling.
Eastwards the mountain system, the Jebel Sangeli, maintains the same general character as far as Bandar Gori (Las Korai), where the precipitous northern cliffs approach within 200 or 300 yards of the gulf, their bare brown rocks and clays presenting the same uninviting appearance as the light brown hills skirting the Red Sea.
Tobacco is most generally cultivated on loose red soils, which are rich in clays and silicates; and sugar-cane preferably on the black and mulatto soils; but in general, contrary to prevalent suppositions, colour is no test of quality and not a very valuable guide in the setting of crops.
It is found in the form of oxide (silica), either anhydrous or hydrated as quartz, flint, sand, chalcedony, tridymite, opal, &c., but occurs chiefly in the form of silicates of aluminium, magnesium, iron, and the alkali and alkaline earth metals, forming the chief constituent of various clays, soils and rocks.
Even in the soils which farmers speak of as stiff clays it is rarely present to the extent of more than I or 2%.
Where the soil grains are quite free from each other the smaller grains tend to fill up the spaces between the larger ones; hence it might be concluded that in clays the amount of pore-space would be less than in coarser sands.
This is the case in " puddled " clays, but in ordinary clay soils the excessively minute particles of which they largely consist tend to form groups of comparatively large composite grains and it is in such natural soils that the pore-space is largest.
In certain sandy soils and in a few stiff clays it may amount to less than 4%, while in others in limestone and chalk districts there may be 50 to 80% present.
The addition of small quantities of lime, especially in a caustic form, to stiff greasy clays makes them much more porous and pliable.
It is this power of creating a more crumbly tilth on stiff clays that makes lime so valuable to the farmer.
Generally speaking light poor lands deficient in organic matter will need the less caustic form or chalk, while quicklime will be most satisfactory on the stiff clays and richer soils.
The oldest rocks of Barbados, known as the Scotland series, are of shallow water origin, consisting of coarse grits, brown sandstones and sandy clays, in places saturated with petroleum and traversed by veins of manjak.
Sandstone, and clays suitable for brick-making, are found in the district of Scotland, so called from a fancied resemblance to the Highlands of North Britain.
==Geology== The flat shore of Lough Neagh in the north is due to the thick deposit of pale-coloured clays with lignites, which are probably of Pliocene age, and indicate a reduction of the area of the lake in still later times.
The soft shales or clays of the hills bounding the valley render these hills especially subject to the action of denudation, and the result, in rounded slopes and easily accessible crests, determines the nature of the easy tracks and passes which intersect them.
Are clays, sometimes mixed with loam; those of the central part are mainly loams; while those of the S.
Those of economic value are kaolin, mined chiefly in the vicinity of Hockessin, New Castle county, the static kaolin product being exceeded in 1903 only by that of Pennsylvania among the states of the United States; granite, used for road-making and rough construction work, found near Wilmington; and brick and tile clays; but the value of their total product in 1902 was less than $500,000.
The actual coal measure strata, consisting mainly of shales and clays, are generally impervious to water, but when strata of a permeable character are sunk through, such as the magnesian limestone of the north of England, the Permian sandstones of the central counties, or the chalk and greensand in the north of France and Westphalia, special methods are required in order to pass the water-bearing beds, and to protect the shaft and workings from the influx of water subsequently.
Whilst pyrites is found abundantly in the older crystalline rocks and slates, marcasite is more abundant in clays, and has often been formed as a concretion around organic remains.
There are also deposits of clay suitable for making bricks, terra-cotta and tiles in nearly every county outside of this valley, and there are some pottery clays in Albany and Onondaga counties.
There are large deposits of glacial and residual clays and clay shales throughout the state.
The valley, which extends from the borders of Sussex to Hythe, is occupied chiefly by the Weald clays, which contain a considerable number of marine and freshwater fossils.
The sands and clays found here are fine and soft, and as there is scant vegetation to protect the hillsides they are easily eroded by the rains.
Good clays for the manufacture of tile and brick are found at numerous places.
Near Luang Prabang, just beyond the border, in French territory, limestones with Productus and Schwagerina, like the Productus limestone of the Indian Salt Range, have been found; also red clays and grauwacke with plants similar to those of the Raniganj beds; and violet clays with Dicynodon, supposed to be the equivalents of the Panche series of India.
Brick, potter's and tile clays are obtained most largely along the west border of the Coastal Plain, and fire-clay from the coal region of West Maryland; in 1907 the value of clay products was $1,886,362.
The oldest, bordering the Lower Carboniferous, is the Tuscaloosa formation of clays and sands arranged as follows: dark clays, thin lignite seams, lignitic clays, sands and chert, and light clays; this formation is 5-15 m.
Tuscaloosa clays are used in the manufacture of pottery.
The calcareous Claiborne or ClaiborneLisbon formation-group lies south of the last, in a wedge-like strip with the apex on the Alabama boundary; it is a series of clays and sands, richly fossiliferous.
There are many sandy districts in the uplands, also sandy clays; in the " second bottoms " of the streams fertile sandy loams; abundant tertiary marls in the north-central region; some gypsum in the cretaceous " islands "; and some fossiliferous marls with decomposed limestones.
The " buckshot clays " of the backlands, which are so stiff that they can scarcely be ploughed until flooded and softened, and are remarkably retentive of moisture, are ideal rice soil; but none of the alluvial lands has an underlying hardpan, and they cannot as a rule be drained sufficiently to make the use of heavy harvesting machinery possible.
Underneath the surface are beds of sand, gravel and clays, the last affording material for the manufacture of brick, tiles and pottery.
In the preparation of alum from clays or from bauxite, the material is gently calcined, then mixed with sulphuric acid and heated gradually to boiling; it is allowed to stand for some time, the clear solution drawn off and mixed with acid potassium sulphate and allowed to crystallize.
Generally speaking, soils containing from 30 to 50% of clay and 50 to 60% of sand with an adequate amount of vegetable residues prove the most useful for ordinary farm and garden crops; such blends are known as " loams," those in which clay predominates being termed clay loalns, and those in which the sand predominates sandy roams. " Stiff clays " contain over 50% of clay; " light sands " have less than to %.
Typical clay-marls are tenacious, soapy clays of yellowish-red or brownish colour and generally contain less than 50% of lime.
It is best adapted for application to clays and fen lands and should not be practised on shallow light sands or gravelly soils, since the humus so necessary for the fertility of such areas is reduced too much and the soil rendered too porous and liable to suffer from drought.
Chocolate or dove-colored grounds with delicate diapers in gold and engobe; brown or black faience with white, yellow and pink designs incised or in relief; pottery curiously and deftly marbled by combinations of various colored clays these and many other kinds are to be found, all, however, presenting one common feature, namely, skilful finger-moulding and a slight roughening of the surface as though it had received the impression of coarse linen or crape before baking.
They consist of fine clays with nodular calcareous concretions rich in fossils.
Ironstone is found in the Wadhurst Clay, a subdivision of the Hastings beds, clays and calcareous ironstone in the Ashdown sand, but the industry has long been discontinued.
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 clays used are exclusively American, much being obtained in Missouri.