22 G. F. Harris — Geology of the Gironde. 



ridges passing with a very slight obliquity over the side of the 

 spine ; this obliquity increases towards the base as well as towards 

 the anterior aspect, where the ridges are also rather coarser than 

 posteriorly. The ridges are plain at the apex, but soon become 

 crenulated, the crenulations being more pronounced on the anterior 

 aspect. 



That this species belongs to the genus Gyracanthus is fully shown, 

 not merely by the nature of the ornament, but by the obliquity of 

 the posterior area, the prominent edge of which is armed with a row 

 of minute denticles. 



Gyracanthus has hitherto not been known to exist below the 

 horizon of the Carboniferous rocks. Its occurrence in the Lower 

 Devonian of Canada is therefore as interesting a fact as the occur- 

 rence of Cephalaspis in the Upper Devonian of the same country. 



YI. — Notes on the Geology of the Gironde, with Especial 

 Reference to the Miocene Beds. 



By George F. Harris, F.G.S. 



DURING the past summer I had the pleasure of studying the 

 Miocene and Upper Oligocene beds at various places in the 

 Bordelais, mostly under the guidance of the amiable Professor of 

 Geology in the Faculte des Sciences in Bordeaux, Monsieur E. 

 Fallot; and the following notes are mainly intended to give an 

 idea of the present appearance of the classical Miocene sections in 

 that district, and to say something concerning their classification 

 and that of the other Tertiary beds of the Gironde, following the 

 most recent researches on the subject. In doing so, the names of 

 the principal localities rich in fossils will be prominently brought 

 forward (supplemented by a table at the end of the article), chiefly 

 with a view to enable us readily to fix the exact horizons of 

 specimens in museums and private collections in this country. 



The Tertiary beds overlie the Upper Cretaceous, and these, the 

 only Secondary beds cropping out in the Department of the 

 Gironde, are found near Villagrains and Landiras. They mostly 

 consist of yellowish compact limestone with flints and the few 

 fossils that have been collected, especially the Echinoderms, indicate 

 that both the Senonien and Danien divisions are present. 



Eocene. 

 The Lower Eocene nowhere rests on the yellow chalk at its 

 outcrop, but in well-borings, beds probably of this age are met with. 

 M. Benoist believes 1 that a limestone with Crenaster and Orbitoides 

 in a well at the Chateau of Vigneau is about the age of the Calcaire 

 de Mons of southern Belgium, which latter it might be mentioned 

 is intermediate in age between our Thanet beds and the uppermost 

 Chalk. Above the Crenaster limestone, a conglomerate surmounted 

 by clays and lignites appears, and these the same authority regards 

 as the equivalents of the lignites of the Soissonais of the Paris 



1 Journ. d'Hist. Nat. de Bordeaux, 1887. 



