24 P. W. Stuart-Mentcath^The Ophite of Biarritz. 



metamorphosed but often freshly marly Flysch, compose a mountain 

 mass nine miles in length anil 2,000 to 3,000 feet in height, whose 

 central portion is solid, and is mapped as solid ophite by the 

 Spanish Survey on a transverse diameter of over three miles. The 

 several intrusions strike in the four directions which in 1886 

 I summarized from a detailed survey of the mineral lodes of the 

 neighbouring Pyrenees. As these lodes are very certainly of 

 Tertiary age, the ophitic intrusions indicate a similar origin. Here 

 only crush and contact breccias are noticeable, and the intrusions 

 are of every variety from typical ophite to typical melaphyre and 

 highly vesicular spilites. The uniquely valuable investigations of 

 Dr. Ogilvie Gordon are especially applicable to this case, which 

 affords ample evidence touching the intrusive character of the 

 Biarritz ophite and its independence of any special formation in 

 spite of constant association with the peculiar /acj'es of the Flysch. 



East of Biarritz a mass of ophite four miles in diameter, between 

 Anglet and Villefranque, resembles that of Loyola in cutting across 

 the Upper Cretaceous beds, and in the freshly irrnptive character 

 which enables both to be largely emploj'^ed for metalling roads. At 

 the Villefranque salt-work the same Nummulitic species are in 

 contact with the gypsum, salt, and ophite as are in similar contact 

 on the Biarritz coast. At both points the rocks of the Lower Eocene 

 are metamorphosed and dislocated as at other Pyrenean localities. 

 The oldest rocks of the neighbourhood are those containing the 

 abundant Greensand fauna which I discovered and described in 

 1887 in Bull. Soc. Geol. The subsequent maps and papers of 

 Captain Gorceix (1894), being filled with new and decisive facts, 

 are never quoted by those who best know them. The salt deposits 

 of Villefranque are analogous to those of Cardona, Suria, Pinos, etc., 

 whose obviously Eocene age has been doubted only in consequence 

 of speculations regarding Biarritz. 



The ophite of Loyola is connected with the similar mass adjoining 

 Biarritz, not only by the coast rocks, but also by two bands of Upper 

 Cretaceous which, constantly accompanied by numerous ophite 

 intrusions, cut across all the rocks of the western Pyrenees. One 

 runs between Tolosa and Cambo, the other between Tolosa and 

 St. Jean Pied de Port. In indifferent contact with rocks of every 

 age, these bands independently connect the Flysch of Loyola with 

 that of Biarritz, and show the intimate relation of the ophites which 

 I have mapped along their unsuspected course. They habitually 

 skirt the Trias; but the Muschelkalk of that formation, which 

 I have compared by fossils and lithologic character to that of 

 Goslar, is constantly broken into three or four strips separated by 

 ophite outcrops, whereas the Upper Cretaceous exhibits con- 

 temporary volcanic conglomerates containing fossiliferous fragments 

 of every age. These conglomerates abound in the Cambo district, 

 and are thence traceable to Biarritz, as habitual constituents of the 

 Upper Cretaceous Flysch. In both the ophitic outcrops of 

 Mouligna and Caseville the ophite is only visible as isolated blocks 

 and fragments in the metamorphosed horizon between the Danien 



