PRESTWICH — BRITISH AND FOREIGN TERTIARIES. 213 



and of the Palceocion primcevus. M. D'Archiac himself* refers these 

 beds to the Lower Landenian of Mons and Ciply, but their Htho- 

 logical structure will answer equally well for the lower part of the 

 upper or next division, whilst their general structure and the character 

 of the few fossils here named incline me to place them generally in 

 a rather higher position. Still it is quite possible that some beds of 

 the Thanet Sands may stretch as far south as some parts of the 

 Department of the Aisne — further than the London Clay, but not 

 so far as the next division of the Lower Tertiary Sands, with which, 

 owing to the want of distinctive characters, they might naturally 

 enough be associated. (See PI. VIII., Diagram, str. ff and h.) 



§ 4. The Woolwich Sands f {lower part of)^ and Sables de 



Bracheux. 



In parallellising another portion of the French series, well developed 

 in parts of the departments of the Oise, Aisne, and Marne, a diiference 

 of opinion as to its exact position renders it necessary to go into this 

 part of the inquiry separately and in greater detail. I allude to those 

 occasionally fossiliferous sands, of which the well-known sections and 

 fossils at Bracheux, Abbecourt, and Noailles, near Beauvais, have 

 been taken as the type. The superposition of these beds is not at 

 first sight very apparent |. By M. D'Archiac they were originally 

 considered sychronouswith theGlauconie inferieure and to underlie the 

 Lignites and Argile plastique, and that view is taken by M. Graves 

 and M. Hebert. From the general absence of fossils, however, with 

 the few exceptions named above, and some later observations showing 

 that in some places a bed of sand with Pectunculus, Nucula, Car- 

 dium, &c., overlies the lignites, M. D'Archiac separates the Glauconie 

 inferieure from the marine sands of Beauvais, leaving the former 

 beneath the lignites, but placing the latter above them. The lower 

 marine sands of the neighbourhood of Rheims and Laon have in 

 consequence likewise been referred by M. D'Archiac to a position 

 over the lignites ; by M. Melleville the lignites are considered sub- 

 ordinate to the sands ; and by M. Hebert the lignites are placed 

 above these sands. 



There is further at a few places in Champagne another deposit, 

 local in its nature, but of much interest from the peculiar group of 

 land and freshwater shells which it contains, viz. the calcareous 

 marls, or concretionary travertin, of Rilly. At this spot these marls 

 repose upon a mass of remarkably pure and white quartzose sands. 

 The infraposition of these various beds to the lignites was proved by 

 M. Charles d'Orbigny, but their exact geological relations were not 

 shown. M. D'Archiac considers these sands to be the equivalents 

 of his Glauconie inferieure, and therefore older than the marine sands 

 of Beauvais. M. Hebert refers both the marls and the sands to a 



* Considering the fossiliferous sands of Beauvais to belong to a higher part of 

 the series. 



t Or the Woolwich and Reading series. 



X As, in the massif oi the Tertiaries, these strata crop out usually at the base of 

 steep slopes, they are generally covered by earth and debris, and therefore are 

 rarely exposed in good or continuous sections. 



