p. W. Stuart-Menteath—Salt Deposits of Dax, etc. 271 



well as superficial red clays formed by decomposition in quarry 

 fissures and ancient drains, have been gravely classed as Trias by 

 the creators of the charriage theory in the Pyrenees and theAlps. 

 And it matters nothing that the disposition of the real Trias in the 

 neighbouring mountains is as flatly opposed to their theory as it is 

 possible to imagine. 



The presence of the Muschelkalk at Dax and other points of the 

 sub-Pyrenean plain immediately beneath the base of the Oenomanien 

 is curious as evidence of the absence of the entire series between 

 that horizon and the Keuper marls. But in the whole Western 

 Pyrenees I have found these intermediate rocks to ^ be largely 

 represented at one point and entirely absent at another, in the^ most 

 irregular and closely contrasting fashion. The explanation lies in 

 the extensive transgression of the Cretaceous, which is attested 

 by the lignites that alternate with Gault fossils between Ascain and 

 St. Pe, and at Hernani, Cestona, etc., and which, with abundant 

 Orhitolina concava, rest directly on the Trias south of Eoncesvalles. 

 Extensive and irregular denudation appears alone to fit the facts. 

 Such denudation implies that the Pyrenean area was, in Lower 

 Cretaceous times, as irregular and mountainous as it is to-day. 



The best examples of the Muschelkalk can be seen in the valley 

 of the Bastan above Elizondo, and at Urdax and the basin of 

 St. Jean Pied de Port. It alternates with sheets of ophite that 

 usually overlie it and occupy the place of the Keuper. It is thrown 

 into repeated strips by faults that let down bands of Cenomanieu 

 fossiliferous limestone, forming long canal-like intercalations, as in 

 the Alps of Gosau. Both the faults and the ophitic intrusions are 

 consequently of an age later than the Oenomanien. A desire to 

 class the ophites as Triassic, on grounds of micrographic theory, 

 has long hampered the recognition of the facts. 



The salt of the Dax mine is arranged in lenticles coinciding in 

 both dip and strike with the Muschelkalk and the ophite which 

 adjoins it. I have found the same coincidence with the ophite in 

 the similar salt mass of Bassussary, near Biarritz, and it has been 

 ascertained in the mine of Villefranche. In the last two cases the 

 disposition is directly across the strike of the Cretaceous rocks, and 

 in the earlier workings at Dax, described by M. Genreau, the 

 disposition was similarly independent of the Cretaceous. 



The lesson derivable from the Pyrenean salt-mines is that of the 

 extreme danger of hasty generalization, and of the necessity for 

 studying each particular case as it is studied in the practice of the 

 mining engineer. It affords a striking warning against the facile 

 assumption that old rocks must be superposed by superficial 

 transport from a distance, because apparently insuperable difficulties 

 seem to exclude their intrusion from beneath. The most experienced 

 geologists have, after repeated observation, classed the Dax Muschel- 

 kalk as Cretaceous or Tertiary. When that rock is recognized as 

 Triassic it does not follow that it is superposed on later beds. Its 

 relations are merely such as are constantly recognizable within the 

 dislocated and contorted area of the Pyrenees, and these complex 



