510 Geological Society. 



assumes a concretionary or travertine structure : at Le Quiou it 

 is micaceous, and splits into flags ; and at the village of Pas de 

 Hac some pinnacles of soft, white, calcareous aggregate present 

 in the lower part fine examples of cross -stratification. At St. 

 Juvat the variety of building-stone called La jauge, and com- 

 posed of comminuted organic remains, resembles the deposit near 

 Sainteny, but the occurrence of casts of cones and large Cypra?2e 

 convinced Mr. Lyell that it must be assigned to the Faluns. It 

 is overlaid by a bed of clay of variable thickness, having been 

 very irregularly denudated ; and it is penetrated by cylindrical hol- 

 lows, similar to the sand-pipes in the English chalk. From these 

 localities Mr. Lyell obtained twenty-six species of shells, one Cir- 

 riped, five species of Echinodermata, five of corals, and seven of 

 fishes, besides the remains of Cetacea and Mammalia before men- 

 tioned. The shells are for the most part identical with species found 

 in the Faluns of Touraine ; the whole of the corals, are well- 

 known Touraine fossils ; and the fishes, according to M. Agassiz, 

 have been all found in the molasse of Switzerland, with the excep- 

 tion of one species, Carcharias megalodon. In the solid limestones of 

 the localities above enumerated, many of the shells, which in several 

 places in Touraine are beautifully preserved, occur only as casts. 



Rennes. — The country between Dinan and Rennes consists of an- 

 cient rocks. M. Desnoyers states, in the memoir before alluded to, 

 that tertiary beds of the age of the Paris basin and of the Faluns 

 occur near Rennes, but Mr. Lyell is not aware of any published ac- 

 count of the fossils. In the ancient quarries of St. Gregoire, to 

 which he was conducted by M. Pontallier, he found corals and casts 

 of shells of Touraine species ; also a large Spatangus, a claw of a 

 crab, and teeth of sharks, imbedded in soft and hard limestones 

 similar to those near Dinan. At La Chaussairie, five miles south of 

 Rennes, occurs a perfectly distinct limestone, containing Milliolites 

 and casts of marine shells, resembling those of the Paris basin ; and 

 associated with it are green and blue marls, enclosing freshwater 

 Testacea. The deposit is of small extent, and rests upon transition 

 strata ; but Mr. Lyell suspects that it is in places overlaid by the 

 ruins of the true Faluns, and that from these were derived the re- 

 mains of a Lamantin and a tooth of Carcharias megalodon, found in 

 the debris of a shaft sunk at La Chaussairie. 



Nantes. — The district between Rennes and Nantes consists of 

 transition and granitic rocks, but there are many detached patches of 

 Miocene strata around Nantes. At Les Cleons is a soft coralline 

 limestone, containing pebbles of quartz and spangles of mica, the 

 fundamental rock of the country being mica-schist. Mr. Lyell ob- 

 tained from the limestone six species of corals and five of Testacea, 

 the whole of which, capable of determination, belong to Touraine 

 fossils. In the museum at Nantes he saw specimens which indicate 

 the existence of Falun strata at Le Loroux, Vieilleville and Limousi- 

 niere, places within thirty miles of Nantes ; also other organic re- 

 mains which prove that Eocene strata occur at Cambon. 



Angers. — Mr. Lyell was prevented from examining the pits north 



