475 million years ago, the Crozon’s Peninsula was a shallow sedimentary basin with sandy spreading exposed to waves as "ripple marks" show.

Numerous tracks and vertical holes were made by marine worms and trilobites (arthropods).
This period of Crozon’s Peninsula history corresponds to the genesis of the Armorican sandstone. Nowadays, the armorican sandstone is exposed in the high following cliffs :
Cap de la Chèvre, Pointe de Dinan, Pointe de Pen-Hir, residual relief of Menez-Hom.

Drawing : Bernadette COLENO.