50 Geological Society. 



two district?. In 1839, however, when he compared, with the as- 

 sistance of Mr. G. Sowerby, a large collection of Touraine shells, 

 and ascertained that the recent species amounted to 26 per cent., a 

 nearly similar result to the one at which he had previously arrived 

 respecting the red and corallme crag, he was induced to adopt M. 

 Desnoyers' vie^A's. As some doubts nevertheless remained in his 

 mind respecting the localities and true geological position of certain 

 shells assigned to the Faluns, and as he was desirous of determining 

 the range southwards of the organic remains of the English crag, as 

 well as northwards of those of the Faluns, and ascertaining whether 

 the fossils of the most northern of the Falun deposits approached 

 nearest in character to the shells and corals of the English crag, Mr. 

 Lyell examined in the summer of 1840, first, certain of the newer 

 tertiary deposits in La Manche, particularly those near Valognes, 

 and between Carentan and Coutances ; then the tertiary strata in the 

 neighbourhood of Dinan and Rennes ; and afterwards those along 

 the course of the Loire from Nantes to Tours and Blois, extending 

 his researches northwards of that river as far as Savigne, and south- 

 wards to Bossee and Pontlevoy. The following notices contain sum- 

 maries of the observations made at each locality. 



Crag. 



Tertiary strata near Valognes. — The first geologist who explored 

 the Cotentin was M. De Gerville. M. Desnoyers, in his memoir on 

 that part of Normandy (published in 1825), shows that the newest 

 secondary rock near Valognes is Baculite limestone*, and that it is 

 overlaid Ijy patches of tertiary strata, of the age of the Paris basin ; but 

 he does not allude to any deposit of more recent date. By the advice 

 of M. De Gerville, Mr. Lyell visited a marl-pit at the farm of Cadet, 

 near Ranville la Place, eight miles south-west of Valognes, and he 

 found it to abound with Suffolk crag shells. He obtained twent)^- 

 nine species of Testacea, fifteen of which Mr. Searles Wood has 

 identified distinctly with crag species, and seven doubtfully, the 

 most abundant shell being Lucina radula. In M. De Gerville's col- 

 lection from this locality, Mr. Lyell saw a specimen of the Falun va- 

 riety of the Valuta Laviberti, or of what he considers to be a distinct 

 species of Voluta. It is stated to have been found under an oyster- 

 bed, and beneath the stratum containing the above shells. 



Carentan. — At St. George de Bohon, five miles south-west of Ca- 

 rentan, is another deposit of Suffolk crag fossils. In travelling south 

 from Carentan this formation is first met with at the hamlet of La 

 Flaget. It consists of an iron-stained calcareous tufa, or an aggre- 

 gate of fragments of organic remains, and is in some places thirty 

 feet thick. The shells are difficult to extract, but Mr. Lyell ob- 

 tained fourteen species ; also three species of corals, and a caudal 

 tubercle of a Raia, all of which have been identified with Suffolk crag 



* Mr. Lyell examined this limestone, and recognised its resemblance to 

 the uppermost chalk at Faxoe in Seeland. See ' Proceedings,' vol. ii. p. 191 

 [Phil. Mag. Third Series, vol. vii. p. 412.], and ' Geol. Trans.,' 2nd Series, 

 vo'. V. p. 248, for an account of the Faxoe deposit. 



