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



most of the "sections" in the district, is very difficult to find, unless 

 under guidance. Leaving the village and following the course of 

 the stream, which flows through the hamlet, we presently discover the 

 Lagus section in the river banks, and in order to do any work it is 

 necessary to wade in the deep water, and dig into the uneven ledges 

 made by previous observers. The working is about 12 feet in 

 vertical height, being entirely composed of a blue sandy clay. This 

 is another of the classical sections of the district, having furnished 

 many of the " type species " of the Bordeaux Miocenes. The floor 

 of the broadest ledge, containing many deep pools of water, is 

 literally covered over by Turritella terebralis in the finest state of 

 preservation, and, altogether, about 200 species of fossils have been 

 found here. Amongst those I brought away may be mentioned 

 Terebra Basteroti, Dorsanum veneris, Fusus burdigcdensis, Tndicla 

 rusticula, Xenophora (= Pliorus) Deshayesi, and Proto cathedralis. 

 A Pteropod, Vaginella depressa, is also very common. 



On the opposite side of the village the classical section in zone 

 No. 8 is found. This cutting, known as Pont-Porquey, is by the 

 side of the river, and composed of about ten feet (vertically) of light 

 yellow sand. How much longer this section will be open I cannot 

 say, the digging and searching for fossils along the best zone having 

 caused the upper beds to be undermined, part overhanging so 

 much as to be very dangerous to workers beneath. "When this falls, 

 almost the whole section will be obliterated. The best-preserved 

 fossils of the Gironde Miocenes come from this opening, the species 

 are mostly very small, but many still retain their original colour- 

 markings, and, like several of the Vienna mollusca of approximately 

 the same period, the best-preserved tints are orange-red and ver- 

 milion. The Potamides especially are most clearly colour-marked. 

 Some common species are Terebra (Acus) fuscata, Terebra plicaria, 

 Cyllenina baccata, Potamides pictns, Donax transversa, Lacina 

 columbella, and Oliva (Olivancillaria) Basteroti. 



Other localities on the same horizon (No. 8) are Gieux and La 

 Coquilliere, both near Saucats. Fresh-water beds are occasionally 

 found in this falun. 



At two or three other places in the Gironde, passage-beds between 

 the Langhien and Helvetien occur. 



Helvetien, No. 9. — In the commune of Martignas along the Jalle, 

 a greyish yellow mollasse, remarkable for Echinoderms (such as 

 Echinolampas hemisphcericus) crops out. This bed has been well 

 described by M. Benoist, 1 but the best-known Helvetien bed in the 

 Gironde is the falun of Salles on the banks of the Leyre, containing 

 Murex turonensis, Voluta Lamberti, Cardita Jouanneti, Corbula striata, 

 Pectunculus pilosus, etc. Other parts of this assise are seen at Sime 

 and Cazenave. M. Fallot says that the falun of Salles contains 

 many species found in the Tortonien of Baden (Austria). 



It is very doubtful whether any Pliocene beds occur in the 

 Gironde. Some geologists have thought that the "Sable des Landes" 

 is, in part, of this age ; but this view is not now generally held. 

 1 "Actes Soc. Lin. de Bordeaux," t. sxxii. pp. 97, et seq. 



