22 P. IF. Sfuaii-Menteath—The Ophite of Biarritz. 



300 yards in a north-easterly direction. The springs to which this 

 tufa owed its oiigin have been tapjDed by the recession of the cliffs,^ 

 so that no calcareous deposit now takes place, or has done since the 

 deposition of the ' Warp-drift.' From the presence of a certain 

 proportion of fresh-water forms, and from the beds of sand and clay 

 which are interstratified with the tufa, there were most probably 

 one or more small streams meandering through the area, with 

 frequently changing course, but there does not appear to be any 

 evidence of lacustrine conditions. 



There can be no doubt that the deposit belongs to the Holocen© 

 Period, but no evidence has been obtained to enable us to fix its age 

 with any greater precision. 



VII. — The Ophite of Biarritz. 



By P. "\y. Stuart-Menteath, Assoc. E. S. Miues. 



Ti'^OUR articles in the Biarritz Association Bulletin, and a series 

 X/ in the last publications of the Soc. Geol. de France, discuss the 

 problem of Pyrenean ophite by conjectures regarding the obscure 

 points of greenstone in the shifting sands of the Biarritz coast. 

 When first seeking new facts at Biarritz, I discovered the red marls 

 and gypsum that accompany the ophite to be recurrent in the 

 undisputed Upper Cretaceous of Croix d'Ahetze, and I followed 

 the Biarritz rocks to Zumaya and Loyola in the attempt to trace 

 their relations. Having subsequently proved that the other red 

 clays mapped as Trias are brick clay of post- Glacial origin, con- 

 temporary with a tooth of Elephas primigeniiis and anterior to flint 

 implements described as Pliocene, and having vainly demonstrated 

 the continuity of the rocks of the Spanish coast by both maps and 

 fossils, I would invite geologists to profit by the light railways and 

 other advantages which to-day enable the fundamental section of 

 Pyrenean geology to be easily studied in its unmistakable continuation. 



Ideal constructions represent the Biarritz rocks as sharply trun- 

 cated by an effondrement of the Atlantic basin. Observation proves 

 that they skirt the coast, form the promontory of Abadia, present 

 three species of Nummulites at Pasages, and, although stripped by 

 the waves beyond Zumaya, recur in patches to far beyond Santander. 

 The confusion resulting from treating as a transverse section the 

 almost longitudinal exposures of Biarritz is an example of not 

 uncommon tectonics. 



The fossiliferous red limestones and marls which extend by 

 Abadia and Fontarabia to Zumaya are rich in Ammonites, worked 

 for cement, recognizable by lithologic character, and regularly 

 afiected by sharp local plications and dislocations along the thirty 

 miles of coast in question. Marine erosion between Bidart and 

 Abadia produces the only important break. Exactly as at Biarritz^ 

 so also at Fontarabia, the fossiliferous Danien summit of the Cre- 

 taceous is overlain by Flysch that represents the Lower Eocene and 



1 "The Geology of the Isle of Wio;ht," by Messrs. II. W. Bristow, Clement Eeid, 

 and Aubrey Strahan: Mem. Geol. Survey, 1889, p. 229. 



