Monsieur Delbos, after much research, has determined that the cliffs at Bidart consist of the cretaceous rocks, and that these cease going northward towards Biarritz, and are succeeded by beds of the Lower Eocene. The very lowest of these, however, does not appear on the coast, namely, that which he designates as “Marnes à Terebratules.” The first, which is found to the north, beyond the chalk formation on the coast, is a calcareous rock, containing a species of serpula. Mons. Delbos writes as follows:—
“I now propose definitely the following divisions for the nummulitic deposits of the basin of the Adour.
M. Delbos then gives an explanation of his section of the coast, starting from the point a, and going northward.
“North of the mass of siliceous limestone, of which I have already spoken, and which belongs incontestably to the chalk formation, there is an extensive depression, occupied by sands blown in from the shore, and which interrupts the continuity of the escarpment for the distance of rather more than a quarter of a mile. Beyond this depression the cliff recommences, and from the point where it first appears abundant specimens of fossils characteristic of the nummulitic formation may be collected from a large fragment which lies detached at the foot of the cliff. (Nummulina, Serpula spirulæa, Vulsella falcata, &c.)