The western part is formed by the steep fault line at the edge of the Île de France, the “Côte de l’Île de France”, also called Montois (“the mountainous”). It consists of the limestone steps of the Montagne de Reims north of the Marne and the Côte des Blancs, “slope of the whites (wines)”, south of the Marne on the eastern edge of the Brie, and its less high but no less wooded continuation, the Bassée on both sides of the valleys from Aube and Seine.
