On the basis of newly discovered graptolite beds in the Cotentin peninsula (France), certain outcrops can be precisely dated as Silurian. The shales of Hautmesnil represent the upper part of the lower Valentian (lower Silurian). Nodular shales of Saint-Sauveur-le-Vicomte have yielded Monograptus ultimus and are assigned to the Ludlovian (upper Silurian). The entire Silurian-Devonian series has an extent which is of greater importance than was previously thought. No evidence of the Gedinnian (Devonian) was observed, however.