In a central position from the human standpoint, but well to the north of the center geographically, lies the Paris Basin consisting of nearly level deposits of recent age surrounded by slightly tilted Mesozoic layers of sandstone, shale, and limestone. Outside of these lies a discontinuous ring of old hard rocks forming a series of four disconnected uplands or highlands. The first of these is the Western Upland including the Upland of Brittany, Normandy, and the Vendée south of the Loire. The next unit is the Central Plateau. The third is the Vosges, forming a small upland east of the Paris Basin; and the fourth is the Ardennes in the northeast, of which only a small section extends into France. These four are separated by broad lowland passages, through which the rock structure and relief of the Paris Basin project outward and connect more or less closely with another concentric although incomplete ring of lowlands. The northwest part of the highland ring seems to be open, but in reality the Pennine Chain and the highlands of Cornwall and Devon in England are part of this system. All the highland blocks in France, like their English counterparts, display clear evidence of an old peneplain which was finally warped and uplifted into the present uplands during the period of Alpine mountain-building. All four also are rather similar in their agricultural response to an upland climate with relatively heavy rain and poor, leached soil.
The lowland ring outside the highlands includes the Aquitaine Basin in the south, the Rhone Valley in the southeast, the Rhine Graben or rift valley in the east, and the lowlands of Belgium. Still farther out the final ring consists of high mountains of the Alpine type. It is incomplete, however, for it includes only the Pyrenees on the south, the French Alps on the southeast, and the Jura on the east. In spite of various irregularities, France consists essentially of the central Paris Basin surrounded by a ring of disconnected uplands or highlands, an outer ring of lowlands, and a partial ring of high mountains.