THE BAY OF BISCAY. 151 



the Mill of Sopite to these formations. In accord- 

 ance with this view, the Pyrenees must have been 

 upheaved subsequently to the formation of these 

 strata ; and consequently they would be more recent 

 than has generally been supposed.* 



A special circumstance complicates the question 

 and renders its solution still more difficult. Very 

 long after the appearance of the Pyrenees, and after 

 the deposition of the tertiary strata, a new cataclysm 

 occurred which convulsed the whole region, changing 

 the primary inclination of the strata, and occasion- 

 ally modifying their relations to one another. Ser- 

 pentine, a kind of porphyritic rock, penetrated 

 through all the preceding formations, and gave rise 

 at several points to centres of partial upheaval. M. 

 Dufrenoy had drawn attention to this remarkable 

 fact, and he made a sketch of one of these masses of 

 serpentine surrounded by gypsum, which had exerted 

 an upheaving action on the cliffs lying between 

 Biarritz and Bidar.f 



I did not fail to visit this remarkable locality; 

 but twenty years had passed since M. Dufrenoy had 

 made the sketch which accompanies his memoir, and 

 the aspect of the district had been strangely changed 

 since that time. The gypsum had almost entirely 



* Among those geologists who have maintained this opinion, -we 

 must especially mention M. d'Archiac, who amongst other works 

 has published a very important memoir on the fossils of Biarritz 

 (Mcmoires de la Societe geoloyique de France, 1846), and M. Alcide 

 d'Orbigny, a geologist who has most strenuously maintained the 

 principle of the characterisation of strata by fossils. 



f Mcmoires pour servir a une description geologique de la France, 

 by MM. Dufrenoy and Elie de Beaumont, t ii. pi. 7. 



L 4 



