In the center of these concentric rings the inner part of the Paris Basin forms a very shallow bowl-shaped depression. When its limestone, sand, and clay of Cretaceous and Tertiary age were uplifted, the edges were raised more than the center. Hence the youngest deposits lie at the center in the so-called Isle de France. Under the influence of erosion the different geologic layers have been converted into a series of concentric zones, especially on the east. Concentric escarpments, with their steep sides away from Paris represent the outcrops of hard rocks and form a natural defense against invaders from the east. The western rivers, such as the middle Loire and the Seine with its branches, run toward the center of the basin. it will be remembered, and then break their way westward. The eastern rivers, the Meuse and the Moselle, on the contrary, follow the escarpment and continue northward towards the Rhine and Holland. At two points in northwestern France local uplifts have brought older layers to the surface. The most northern of these is the continuation of the Weald in England.
The Paris Basin is the chief agricultural region of France. Here, as in Belgium, the limestone soils have a cover of rich loam, brought as loess by dry winds during the glacial period when the northern icesheet lay not far off. The rolling hills near Paris and to the northward are almost entirely used for wheat, oats, and sugar beets, except for a local development of truck gardens along some of the valleys and around Paris. Wheat is the most abundant crop, for relief, soil, and the moderately dry and rather sunny climate make this region well suited for that crop. Here are the best yields of France, and from here comes the greater part of the large French wheat production. So abundant is the crop that in good years the yield here and in the rest of France suffices for the needs of the whole country, even though France consumes more per capita than any other country. Bread is an essential part of every French meal. Oats replace wheat in the eastern part of the Paris Basin where the rainfall increases as a result of elevation. Sugar beets, in spite of yields much lower than those of the Netherlands and Belgium, suffice to supply France with sugar.
The border zone around the Paris Basin shows a type of agriculture different from that of the center. In the northwest intensive grazing once more prevails and dairy products predominate. This is partly a result of more rain and lower temperature, but soil and relief also play a part. Heavy soils are found in the coastal marshes of Flanders of which France has a small share, and the structural uplift or anticline mentioned above as a continuation of the English Weald causes higher altitude. East of Paris the escarpment region shows an especially pronounced zonal arrangement in accord with the geologic structure. Forests cover the sandstones, sheep graze on the dry limestones, and rye prevails as the main food crop except in the more fertile Moselle Valley where wheat once more predominates. But here another use of the land comes to the foreground, namely, the raising of grapes. The last border region is in the south. Here the Loire River as a zone of intense agriculture, vines, fruits, and vegetables, while the uplands, lacking the fertile loam cover of the north, are mainly under rye and buckwheat. The small section of extensive grazing in the bend of the Loire south of Orleans is the Sologne, a region of moors, void of population except for the shepherds.