94 PEOP. J. PEESTWICH OlST THE COEEELATIOiff OE THE 



It would appear, therefore, that out of the 28 Pegwell-Bay 

 species, there are 10 common to the Lower Landenian, 12 pass ap 

 into the Woolwich Beds, and 6 extend to the London Clay, while 

 only 5 are common to the Bracheux Sands. 



The Sables de Beachetjx. 



The exact determination of the horizon to which these sands be- 

 long is of importance, not only with respect to the synchronism of 

 the Lower Eocene groups in the London and Paris Basins, but also 

 for fixing the age of the very interesting Mammalian and Avian 

 faunas discovered by M. Lemoine in the neighbourhood of Rheims, 

 of the curious freshwater deposit of Pilly, and of the rich flora of 

 Sezanne. I only regret that in puttiEg forward my views on this 

 subject I have to differ on many points from some of my friends 

 abroad and at home. These differences are, however, as they know, 

 not of recent date, and have often been discussed hj us, and I 

 should not have ventured upon expressing so wide a divergence of 

 opinion unless I had had a long acquaintance with most of the 

 localities concerned. 



It was fortunate for Tertiary geology that Beauvais possessed an 

 excellent local geologist (M. Graves), whose work on the Depart- 

 ment of the Oise, though without map or sections, is full of most 

 complete and accurate details of every part of the Department, with 

 the names of all the localities at which every fossil is found *. He 

 divided the Lower Tertiaries of the Oise into three groups, which 

 I give, with the names by which they have been subsequently 

 known : — 



Grlauconie Superieure = G-lauconie Grossiere forming the base 



of the Calcaire Grossier. 



G-lauconie Moyenne = Sands of Cuise-la-Motte, and possibly 



other zones. 



Glauconie Inferieure and Lignites = Sands of Bracheux ; Lower zone of 



the Sables Inferieurs. 



M. Graves makes the Lignites subordinate to the Sands, and it is 

 the lower bed of these sands, which is about 30 feet thick, that 

 forms the knoll at Bracheux. The Lignites and mottled clays cap 

 this bed in other places, and they are in turn surmounted by another 

 bed of from 10 to 20 feet of sand, with many of the same shells, 

 such as Ostrea hellovacina, Pectunculus terebratularis, Nucula fragilis, 

 Turritella ecUta, Cytherea ohliqua, Natica glaucinoides, &g. The 

 characteristic fossils of the Lignites are Cyrena cuneiformis, Palu- 

 dina lenta, Cerithium variabile, Melania cuneiformis, Ostrea hello- 

 vacina and 0. sjparnacensis. 



* ' Essai sur la Topographie Geognostique du Departement de I'Oise.' Par 

 L. Graves. Beauvais : 1847. 



