To the north as far as the rocky point of St Gildas, sheltering the mouth of the Loire, the shore, often occupied by salt marshes (marshes of Poitou and Brittany), is low-lying and hollowed by deep bays sheltered by large islands, those of Olron and Re lying opposite the ports of Rochefort and La Rochelle, while Noirmoutier closes the Bay of Bourgneuf.
Buckwheat is cultivated mainly in Brittany.
Of the former the remnants are now seen in Brittany and the Ardennes; of the latter the Cvennes and the Montagne Noire are the last traces visible on the surface.
The oldest rocks, the gneisses and schists of the Archean period, form nearly the whole of the Central Plateau, and are also exposed in the axes of the folds in Brittany.
The earlier deposits of that sea now rise to the surface in Brittany, the Ardennes, the Montagne Noire and the Cvennes, and in all these regions they arc intensely folded.
