Born about 3 million years ago, the Seine displays a succession of meanders in its lower part. The concave bank is more eroded and its slope is steeper than the convex bank, which is more alluvial. Towards Les Andelys, white chalk cliffs, fossils of friable algae, still outcrop and border the loop of the river. Flints form darker strata, and some cliffs are adorned with caves.