473 



SKETCH OF THE GEOLOGY OF BIARRITZ. 



Chiefly drawn from a Thesis* by Monsieur Joseph Delbos. 



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 a 

 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 nummu- 

 litic deposits of the basin of the Adour. 



"3rd U er Series i ^ S ^' Op ercu ^ ne free-stones. 



■ * ( 2nd. Limestones with Eupatagus ornatus. 



"2nd. Middle Series — Nummulitic limestone with Serpula spirulcea. 

 " 1st. Lower Series — Clays with Tercbratida" 



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 spirulcea, Vulsella 

 falcata, &c.) 



" Starting from this fallen fragment, the cliff is formed of a yellow 

 limestone, somewhat sandy in its texture, in which here and there 

 softer bands occur. These beds dip E.1ST.E. Further on, these yellow 

 beds alternate with blue ones of the same texture ; presently, their 

 inclination suddenly changes, and they dip south at an angle of 25°, 

 and this continues to the end of this part of the cliff, where the blue 

 argillaceous beds gain the predominance. The calcareous rock has 

 been worked in several quarries which have been opened in this cliff, 

 and it affords a sufficiently good stone for rough building-purposes. 

 It is rich in fossils; among the species which it contains, I may 

 mention Guettardia Thiolati, Serpula spirulcea, &c. 



* Theses presentees a la Faculte des Sciences de Paris pour obtenir le grade de 

 Docteur es Sciences Naturelles. Par M. Joseph Delbos, Preparateur d'Histoire" 

 Naturelle a la Faculte des Sciences a Bordeaux. Soutennes le 4 De'cembre, 1854. 

 VOL. IV. 3 F 



