SKETCH OF THE GEOLOGY OF BIARRITZ. 



477 



of all the formations of the valley of the Adour ; 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 Miocene. 



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 Marensin 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 modern deposits, rich in vegetable remains, 

 south of Biarritz. Near the ophite rock they form a cliff 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 cliff, 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 

 Nummulitic 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 



