The prairies are, in brief, a contribution of the glacial period; they consist for the most part of glacial drift, deposited unconformably on an underlying rock surface of moderate or small relief.
Cambrian System.The lower part of the Cambrian system, characterized by the Olenellus fauna, is restricted to the borders of the continent, where it rests on the older rocks unconformably in most places.
Pennsylvanian SystemThe Pennsylvanian or Upper Carboniferous system overlics the Mississippian unconformably over a large part of the United States.
Widespread changes at the end of the period exposed the areas where deposition has been in progress during the period to erosion, and the (Upper) Cretaceous formations rest upon the Comanchean unconformably in most parts of the country.
Under these conditions sediments from the high lands were washed out and distributed widely over the plains, giving rise to a thin but widespread formation of ill-assorted sediment, without marine fossils, and, for the most part, without fossils of any kind, and resting unconformably on Cretaceous, Eocene and Miocene formations.
The Old Man presents a characteristic section, for it exhibits a thick pile of massive, current-bedded red sandstones, resting, near the foot of the pinnacle, upon a thin bed of amygdaloidal porphyrite, which in its turn lies unconformably upon steeply inclined flagstones.
In the eastern border of the Rhenish Schiefergebirge the Permian rests unconformably upon Lower Carboniferous rocks.
It lies unconformably upon the older rocks; and the limestone contains Fusulina, Phillipsia and Productus, indicating that it belongs to the Upper Carboniferous.
They rest unconformably upon the Carboniferous beds, and have themselves been tilted to a steep angle.
The Ordovician and Silurian are absent here, and the Devonian rests unconformably upon the Cambrian; but along the northern margin of the Palaeozoic area, Ordovician and Silurian rocks appear, and beds of similar age are also exposed farther north where the rivers have cut through the overlying Tertiary deposits.
Except along the southern border of the Ardennes, and at one or two points in the middle of the Palaeozoic massif, Triassic and Jurassic beds are unknown in Belgium, and the Palaeozoic rocks are directly and unconformably overlaid by Cretaceous and Tertiary deposits.
This series is overlain unconformably by a younger quartzite of similar character, and itself rests upon the crystalline schists.
Geology.Germany consists of a floor of folded Palaeozoic rocks upon which rest unconformably the comparatively little disturbed beds of the Mesozoic system, while in the North German plain a covering of modern deposits conceals the whole of the older strata from view, excepting some scattered and isolated outcrops of Cretaceous and Tertiary beds.
The Permian, as in England, is not involved in the folds which have affected the older beds, and in general lies unconformably upon them.
In many instances the Tertiary formation, which occurs betweeii Esna and Cairo, unconformably overlies the Cretaceous, the Lower Eocene being absent.
These ancient rocks, which form the foundation of the country, are overlaid unconformably by a series of conglomerates and sandstones, generally unfossiliferous and often red or purple in colour, very similar in character to the Nubian sandstone of Upper Egypt.
Towards the Manchurian frontier they are covered unconformably by some 1600 ft.
On the north side of North Glen Sannox they rest unconformably on the Lower Old Red rocks.
They are often accompanied by volcanic rocks, which are mainly andesitic, and they commonly lie unconformably upon the older beds.
The Pliocene is of marine origin, and rests unconformably upon all the older beds, including the Post-oligocene igneous rocks, thus proving that the final folding and the last volcanic outbursts were approximately of Miocene age.
The older rocks are overlaid unconformably by Cretaceous beds, consisting chiefly of sandstones with seams of coal, the whole series thinning rapidly towards the north and thus indicating the neighbourhood of the old shore-line.
Along the coast lies a belt of granite and schist overlaid unconformably by Cretaceous and Tertiary deposits; inland the mountains are formed chiefly of folded Mesozoic beds, together with volcanic rocks of later date.
They are strongly folded and are overlaid unconformably by Cretaceous and Tertiary deposits.
The next succeeding deposit is a sandstone, often highly inclined, which rests unconformably upon the Nummulitic beds and resembles the Lower Siwaliks of the SubHimalaya (Pliocene) but which as yet has yielded no fossils of any kind.
The whole is overlaid unconformably by the younger Tertiaries of Hundes, which are perfectly horizontal and have been quite unaffected by any of the folds.
The Lower Carboniferous, which belongs to the " Culm " facies so widely spread in central Europe, occupies a wide area in southern Portugal; but the Upper Carboniferous is very restricted in extent, and occurs in small basins like those of the Central Plateau of France, resting unconformably upon the rocks below.
The rocks of the Devonian system rest unconformably upon the Silurian; but some beds of which the age is still uncertain are called Devono-Silurian.
East of Bolsover, the Coal Measures are covered unconformably by the Permian breccias and magnesian limestone.
The principal folding took place at the close of the Carboniferous period, and was contemporaneous with that of the old Hercynian chain of Belgium, &c. The Permian and later beds lie unconformably upon the denuded folds, and in the space between the Montagne Noire and the Cevennes proper the folded belt is buried beneath the horizontal Jurassic strata of the Causses.
These are overlain, perhaps unconformably, by a great thickness of lavas and volcanic breccias (Pniel volcanic series, Beer Vley and Zeekoe Baard amygdaloids), and these in turn by the quartzites, grits and shales of the Black Reef series.
It includes the following well-defined subdivisions: - In the southern areas the Karroo formation follows the Cape System conformably; in the north it rests unconformably on very much older rocks.
A few patches of Upper Carboniferous are found on the borders of the hills near Ilfeld, Ballenstedt, &c., lying unconformably upon the Devonian.
They rest unconformably on the Silurian rocks on the King river and to the west are faulted against the schists by a powerful overthrust fault, traversing the Mount Lyell copper field.
The inner or eastern ridge farther north of Argentina consists of crystalline rocks with infolded Ordovician and Cambrian beds, often overlaid unconformably by a sandstone with plant-remains (chiefly Rhaetic).
The " Potomac Formation " of Virginia and Maryland is doubtless also mainly of Neocomian age, for though it rests unconformably on much older strata, the successive floras found in it are so allied to those of S.
These highest plant-bearing strata rest, according to Lester Ward, somewhat unconformably on the Dakota No.
This rests unconformably on the pre-Cape rocks.
This system rests unconformably on the Witwatersrand series and is unconformably overlain by the Transvaal system.
The Waterberg Series lies unconformably on the Pretoria series.
The Oceanic series is generally overlaid directly, and unconformably, by coral limestones; but at Bissex Hill, at the base of the coral limestones, and resting unconformably upon the Oceanic series, there is a Globigerina marl.
The deposits belong to the Lower Eocene, where it rests unconformably upon the Cretaceous.
At Hoopstad and at Stinkhoutboom the Witwatersrand series is unconformably overlain by 500 ft.
The Black Reef series of quartzites and conglomerates and dolomite form a narrow outcrop resting unconformably upon the last-mentioned system.
There is an older series, ranging from the Devonian to the Cretaceous, which is folded and faulted and forms all the higher hills, and there is a newer series of Tertiary age, which lies nearly horizontal and rests unconformably upon the older beds.
It is of greater altitude (Mt Marcy 5344 ft.) and of much greater relief than the Superior Oldland; its heights decrease gradually to the north, west and south, where it is unconformably overlapped by Palaeozoic strata like those of Minnesota and Wisconsin; it is of more broken structure and form on.