184^6.] PRESTWICH ON THE ISLE OF WIGHT TERTI ARIES. 249 



to the Isle of Wight, it is to be hoped that a more extensive conj- 

 parison with the numerous French species which have yet to be 

 described, will establish many analogues. In the meantime they do 

 not of themselves afford sufficient evidence, since they are as likely to 

 be new species of the age of the calcaire grossier as of the Fontaine- 

 bleau sandstone. It is not from them that we can fix the age of the 

 deposit ; but the superposition of the deposit, as determined by their 

 known associates, will on the other hand prove their date. They 

 must therefore for the present be excluded from the scale, and our 

 conclusions must be founded solely upon the evidence of the species 

 which are known in other strata whose position is recognised. 



With regard to the vegetable remains of these fluvio-marine strata, 

 they cannot be taken in exact evidence. The Gyrogonites occur, 

 it is true, in large numbers in the upper freshwater beds of Paris ; 

 but they are also common in some of the plastic clay beds of Eper- 

 nay, and they occur likewise in the calcaire grossier. The Carpo- 

 lithes also cannot be looked on as characteristic, nor can the animal 

 remains be any longer considered in this light, since the remains of 

 PalcBotherium, Anoplotherium and Lophiodon, at first supposed to 

 be characteristic of the period of the freshwater gypseous marls of 

 Montmartre, have been found by M. Robert in the upper calcaire 

 grossier at Nanterre, and since then by others in several places in 

 the calcaire grossier. I have also met with remains of the Lophio- 

 don and Crocodile in the sands above the plastic clay of Epernay*, 

 and M. Ch. d'Orbigny has found them in the calcaire pisolitique at 

 Meudon. 



It is therefore, I think, very problematical whether the present 

 grouping of the Isle of Wight tertiary formations, with reference 

 to their foreign equivalents, can be maintained. The evidence is 

 slightly conflicting, but still the weight of it is very considerably in 

 favour of their being on the whole of an older date than that usually 

 assigned to them. The occurrence of a bed of London clay ("B,") 

 supposed to represent the calcaire grossier, succeeded by sands re- 

 ferred to the gres de Beauchamp, and then, as is the case with these 

 formations in the Paris basin, overlaid by a series of freshwater 

 green marls and earthy limestones, countenanced the hypothesis of 

 a like chronological order, by exhibiting a very analogous lithologi- 

 cal sequence. But according to M. d'Archiac, about half the fossils 

 found in the gres de Beauchamp are peculiar to itf; and of the 

 other half, which are common also to the calcaire grossier, only about 

 nine species, or not quite three per cent, of the whole, are met with 

 in the lower tertiary beds. In ascending through the lower fresh- 

 water, the upper marine and the upper freshwater formations of the 

 Paris basin, a further departure from the fauna of the lower tertiary 

 beds is perceptible, and very few species of the calcaire grossier are 

 met with. 



* Bull, de la Soc. Geol. de France, vol. ix., and others. Mr. S. Wood has a fine 

 lower jaw of a Crocodile from Ilordwell, and Mr. Bowerbank a palate of Mylio- 

 bates from Ileadon Hill. 



f Il)id., vol. ix. p. 69. The oidy one here characteristic is tlic Cytcna dcpcvilita. 



