The Alleghany Plateau consists of nearly horizontal beds of limestone, sandstone and shales, including important seams of coal; inclines slightly toward the north-west, and is intricately dissected by extensively branching streams into a maze of narrow canyons and steep-sided hills.
In this sea were laid down the shales of the Rolling Downs formation.
But the Blythesdale Braystone is a small local formation, unable to supply all the wells that have been sunk; and many of the wells derive their water from the Jurassic shales and mudstones.
Of these the most interesting are Ichthyornis (= Graculavus) and Hesperornis, from the Cretaceous shales of Kansas.
Free sulphur may also result from the decomposition of pyrites, as in pyritic shales and lignites, or from the alteration of galena: thus crystals of sulphur occur, with anglesite, in cavities in galena at Monteponi near Iglesias in Sardinia; whilst the pyrites of Rio Tinto in Spain sometimes yield sulphur on weathering.
In the extreme north-east are found the oldest rocks in the state - lower Devonian (the New Scotland beds of New York) and, not so old, an extension of the Lower Carboniferous which underlies the Warrior coalfields of Alabama, and which consists of cherts, limestones, sandstones and shales, with a depth of 800 to 900 ft.
Another well-known bed, formerly known as the "Bristol" or "Lias" Bone Bed, exists in the form of several thin layers of micaceous sandstone, with the remains of fish and saurians, which occur in the Rhaetic Black Paper Shales that lie above the Keuper marls in the south-west of England.
Five well-contrasted types of scenery in Derbyshire are clearly traceable to as many varieties of rock; the bleak dry uplands of the north and east, with deep-cut ravines and swift clear streams, are due to the great mass of Mountain Limestone; round the limestone boundary are the valleys with soft outlines in the Pendleside Shales; these are succeeded by the rugged moorlands, covered with heather and peat, which are due to the Millstone Grit series; eastward lies the Derbyshire Coalfield with its gently moulded grasscovered hills; southward is the more level tract of red Triassic rocks.
A series of black shales with nodular limestones, the Pendleside series, rests upon the Mountain Limestone on the east, south and north-west; much of the upper course of the Derwent has been cut through these soft beds.
Next in upward sequence is a thick mass of sandstones, grits and shales - the Millstone Grit series.
Schists in the common acceptance of that term are really highly crystalline rocks; fissile slates, shales or sandstones, in which the original sedimentary structures are little modified by recrystallization, are not included in this group by English petrologists, though the French schistes and the German Schiefer are used to designate also rocks of these types.
We may mention also graphiticschists containing dark scaly graphite (often altered forms of carbonaceous shales), and haematite-schists which may represent beds of ironstone.
Towards the Caspian, especially between Petrovsk and the river Sulak, the Cretaceous system is well represented, and upon its rocks rest marls, shales, and sandstones of the Eocene period.
Particulars of the shales which yield oil on destructive distillation are given in the article on paraffin.
Quartzites, Conglomerates and Shales of Nkandhla, Umfolosi river.
The Ecca shales contain some of the best coals of South Africa, but the seams contain much unmarketable coal.
The Ecca series graduates upwards into the highly coloured sandstones and shales of the Beaufort series.
This consists of sandstones and shales with thin seams of coal.
- a lower group (Hospital Hill series) of quartzites, shales and conglomerates.
The lower group (Hospital Hill slates) consists of quartzites and shales, resting on the eroded surface of the older granites and schists, and estimated to be from 10,000 to 12,000 ft.
The other rocks include igneous breccias, shales, coarse conglomerates and grits.
The Pretoria Series, formerly known as the Gatsrand series, consists of repeated alternations of flagstones and quartzites, shales and sheets of diabase.
In the Marico district the shales become highly ferruginous and resemble the Hospital Hill slates of the Witwatersrand series.
The Lower Cretaceous consists chiefly of sandstones and shales and the Middle Cretaceous of very fossiliferous limestone.
In South Wales the Bala Series contains the following beds in descending order: - the Trinucleus seticornis beds (Slade beds, Redhill shales and Sholeshook limestone), the Robeston Wathen beds, and the Dicranograptus shales.
Lower Cretaceous rocks, consisting of thick limestones, shales and marls, occur in Central Tunisia.
Farther north, in the department of Ancachs, the Mesozoic belt is composed chiefly of sandstones and shales, and the limestones which form so prominent a feature above Lirna seem to have disappeared.
It is formed almost entirely of a succession of sandstones and shales of Cretaceous and Tertiary age - the so-called Carpathian Sandstone - and these are thrown into a series of isoclinal folds dipping constantly to the south.
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.
Upper portion of this group consists of shales and sandstones, known as the Yoredale Rocks, which are highly developed in the moorland region between Lancashire and the north side of Yorkshire.
These are also called the Upper Limestone Shale, a similar group being found in places below the limestone, and called the Lower Limestone Shale, or, in the north of England, the Tuedian group. Going northward the beds of limestone diminish in thickness, with a proportional increase in the intercalated sandstones and shales, until in Scotland they are entirely subordinate to a mass of coal-bearing strata, which forms the most productive members of the Scotch coalfields.
The Coal Measures, forming the third great member of the Carboniferous series, consist of alternations of shales and sandstones, with beds of coal and nodular ironstones, which together make up a thickness of many thousands of feet - from 12,000 to 14,000 ft.
These very thick seams are, however, rarely constant in character for any great distance, being found commonly to degenerate into carbonaceous shales, or to split up into thinner beds by the intercalation of shale bands or partings.
Thick in one connected mass in the neighbourhood of Dudley, but splits up into eight seams, which, with the intermediate shales and sandstones, are of a total thickness of 400 ft.
Cannel coals are generally variable in quality, being liable to change into shales or black-band ironstones within very short horizontal limits.
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.
They are underlain by Jurassic rocks, from beneath which sandstones and shales yielding Glossopteris browniana var.
In the vicinity of Lakes Nyasa and Tanganyika, sandstones and shales of Lower Karroo age and yielding seams of coal are considered to owe their position and preservation to being let down by rift faults into hollows of the crystalline rocks.
In Ankole and Koki rocks consisting of granular quartzite, schistose sandstone, red and brown sandstone, and shales with cleaved killas rest on the Archean platform and possibly represent the Lower Witwatersrand beds of the Transvaal.
The Mataura beds are largely of estuarine formation; they contain oil shales and gas springs.
In southern Otago the Oligocene beds are brown coals and lignites with oil shales, which, at Orepuki, contain 47% of oil and gas, with 8% of water.
There are large deposits of glacial and residual clays and clay shales throughout the state.
The Dwyka Conglomerate forms a narrow outcrop in the north-west, and is known from boreholes to extend over large areas beneath the Ecca Shales and to rest directly on rocks of older age.
They are rarely metamorphosed to the point of recrystallization, though locally shales are altered to roofing slates, sandstones are indurated, limestones slightly marblized, and coals, originally bituminous, are changed to anthracite in northern Pennsylvania, and to graphite in Rhode Island.
Former tributaries have given place to others developed with reference to the distribution of more or less easily eroded strata, the present longitudinal valleys being determined by the out-crop of soft shales or soluble limestones, and the parallel ridges upheld by hard sandstones or schists.
Above these, marine Rhaetic beds appear at intervals, notably near Lame, where they are succeeded by Lower Lias shales and limestones.
The higher olefines are found in the tar which is obtained by distilling bituminous shales, in illuminating gas, and among the products formed by distilling paraffin under pressure (T.
Carboniferous and Permian strata are possibly represented by some black and grey micaceous shales with beds of coal in the Jurjura.
At Jebel-kahar and west of Traras, Pomel attributes certain conglomerates, red sandstones and purple and green shales to the Permian.
The highest beds, consisting of quartzites, shales, marls and sandstones with the remains of fucoids, are found in the Jurjura and Shellata.