473 
SKETCH OF THE GEOLOGY OF BIARRITZ. 
Chiefly drawn from a Thesis^ hy Monsieur Joseiili DeTbos. 
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 serj^ula. Mons. Delbos writes as follows : — 
" I now propose definitely the following divisions for the nuramu- 
litic deposits of the basin of the Adour. 
"3rd Upper Series I ^psrculine free-stones. 
( 2nd. Limestones with Eupatagus ornatus. 
"2nd. Middle Series — Nummulitic limestone vf\i\\ Serpida spirulcea. 
" 1st. Lower Series — Clays with Terchratida'' 
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, Seipula sjnr^dcea, 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.N.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, whei'e 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 spiridcea, &c. 
* Theses presentees k la Faculty des Sciences de Paris pourobtenir le grade de 
Docteur es Sciences Naturelles. Par M. Joseph Delbos, Pr^parateur d'Histoire 
Naturelle k la Faculte des Sciences k Bordeaux. Soutennes le 4 Ddcernbre, 18.54. 
VOL. IV. 3 F 
