SKETCH OF THE GEOLOGY OF BIARRITZ. 
477 
of all the formations of the valley of the A dour ; but I do not wish 
to extract details beyond those which relate to Biarritz. 
With regard to the rich beds of well-preserved shells found near 
Dax, and in some other parts of the Landes, the same author places 
them in the upper beds of the j\Iiocene. 
He writes on this point as follows : — 
" The shelly deposits of the Upper Miocene of the basin of the 
Adour are represented at three points — one is in the Commune of 
St. Paul, near Dax. * * * 
"At St. Paul, the yellow sandy beds contain an enormous quantity 
of fossils, and crop out at a great number of points from beneath the 
sands of the landes." * * * 
In the Upper Miocene of this region there appears to be one limited 
deposit, but a well-defined one, of fresh-water origin. 
" Upper group, Sand of the Landes." This he places decidedly as 
the Upper Tertiary, or Pliocene. 
He says, " This formation, which plays so important a part in the 
valley of the Adour, is, except towards the south, most uniform in its 
composition. It covers all the INIarensin with a thick mantle, re- 
appears at the tops of all the hills, and on the central plateau of La 
Chalosse, and traverses the river-bed {Gaul), disappearing finally 
under the form of ' molasse and macigno,' beneath the diluvial 
deposits, from which it is often difficult to distinguish it." 
Mons. Delbos' account of the diluvial drifts is very brief, and he 
makes no mention of the modera deposits, rich in vegetable remains, 
south of Biarritz. Near the ophite rock they form a cliflT from 
thirty to forty feet high at least. They lie perfectly horizontal, and 
are composed of alternate beds of sand and gravel, the stratum of 
vegetable matter appearing at its base, just above the seashore 
sands. 
Further on in his thesis, M. Delbos speaks of the Ophite. He 
says that in general fibrous gypsum is found near it, but that this 
does not appear to be the case at Biarritz. 
Probably when M. Delbos examined this coast the seashore sands 
were rather higher opposite the Ophite rock than they are at present. 
Under the clitf, at about thirty yards from the Ophite rock, I found 
a very good example of the fibrous gypsum. It lay — as he states it 
generally does — " dans des argiles rouges." At the point where I 
saw it, the gypsum, not much more than an inch thick, lay imbedded 
like a wedge in clays of the most beautiful colours, veined grey, red, 
and yellow, and of the texture of stiff paste. 
In conclusion, there seems to be little or no question that the 
Nummulitic rocks belong to the Lower Eocene period ; that is to say, 
to the Lowest Tertiary, and that in general they repose directly on 
the Chalk. 
The researches of geologists seem to have established that the 
Kummulitic rock exists very extensively in Southern Europe. Mont 
Perdu, in the Pyrenees, is composed of it, and also La Montague Noire 
de Corbieres. On the south of the Pyrenees it extends from Yittoria 
