Beginning with the Aptian and Albian the sea again gradually spread over the country and attained its maximum in the early part of the Senonian epoch, when once more the ancient massifs of the Central Plateau, Brittany and the Ardennes, alone rose above the waves.
The northern slope of this great plateau is drained by the AraguayaTocantins, Xingu, Tapajos and Guapore-Mamore-Madeira, which flow northward, and, except the first, empty into the Amazon; the southern slope drains southward through a multitude of streams flowing into the Parana and Paraguay.
The first industry was that of mining, gold having been discovered in the river valleys on the southern slopes of the plateau, and diamonds on the head-waters of the Paraguay, about Diamantino and in two or three other districts.
The plateau portion of West Virginia is largely covered by hardwood forests, but along the Ohio river and its principal tributaries the valuable timber has been removed and considerable areas have been wholly cleared for farming and pasture lands.
Snows are frequent during the winter, and sometimes deep in the higher plateau and mountain districts.
On the north their most noteworthy offshoots are, in the centre, the plateau of Lannemezan from which rivers radiate fanwise to join the Adour and Garonne; and in the east the Corbire.
Within the northern circle of the 8 lie the Mesozoic and Tertiary beds of the Paris basin, dipping inwards; within the southern circle lie the ancient rocks of the Central Plateau, from which the later beds dip outwards.
Towards the close of the Palaeozoic era France had become a part of a great continent; in the north the Coal Measures of the Boulonnais and the Nord were laid down in direct connection with those of Belgium and England, while in the Central Plateau the Coal Measures were deposited in isolated and scattered basins.
(a) Normandy, Perche, Cotentin and maritime Flanders, where horses are bred in great numbers; (b) the strip of coast between the Gironde and the mouth of the Loire; (c) the Morvan including the Nivernais and the Charolais, from which the famous Charolais breed of oxen takes its name; (d) the central region of the central plateau including the districts of Cantal and Aubrac, the home of the famous beef-breeds of Salers and Aubrac.1 The famous pre-sal sheep are also reared in the Vende and Cotentin.
The more important of the suburbs lie towards the east, where the promontory joins the main plateau, of which it forms the north-western extremity.
The state is divided into two distinct physiographic provinces; the Alleghany Plateau on the west, comprising perhaps two-thirds of the area of the state, and forming a part of the great Appalachian Plateau Province which extends from New York to Alabama; and the Newer Appalachians or Great Valley Region on the east, being a part of the large province of the same name which extends from Canada to Central Alabama.
When the attempt was made to mark this boundary the commissioners were unable to agree on a line across the Puna de Atacama in the north, where parallel ranges enclosing a high arid plateau without any clearly defined drainage to the Atlantic or Pacific, gave an opportunity for conflicting claims. In the south the broken character of the Cordillera, pierced in places by large rivers flowing into the Pacific and having their upper drainage basins on the eastern side of the line of highest crests, gave rise to unforeseen and very difficult questions.
In the area of the Newer Appalachian Mountains, the eastern Panhandle region has a forest similar to that of the plateau district; but between these two areas of hardwood there is a long belt where spruce and white pine cover the mountain ridges.
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.