24 THE EOCENE BEDS 



Siib-divisiotis of the Sables Moyens. 



j Fine or argillaceous sands, or marly limestone j -, p, ,] 

 Upper ) '^'^'^'^—TrUomdea polygona,PotamidesCordieri^P. \ ^Servaf^and^"' 

 ^^ \ pleurotomoides, P. tricar inatus, Avicula fraeilis i a* ^ r ^ • 



\ A n 1, 1 1 i Morteiontaine. 



\ and Lorouia angulata. ! 



T I Sand with jffrtcaw/a ^cro'atva, of Beauchamp, Le Gudpelle, &c., re- 



l I placed by stone at Lizj', Louvres, Mary, Etrepilly, &c., with 



\ \ Potamides Bouei, P. scalaroides, Merelrix elegans, Portunus 



Middle \ \"'^^carti,b-c. 



Sands of Ezanville, of Moiselles, and " curvilinear " sandstone of 

 Beauchamp with Corbiciila deperdita, Cerit/iium tnutabile and C. 

 tuherciilosum. 



1 I Sand with broken fossils and pebbles, Numtmtlites variolarius, Corals, 



I &c. ; Auver?, Acy-en Multien. 



Lower Sables Moyens (Horizon of Auvers). — The lower por- 

 tion of the Sables Moyens may be divided into three levels. 



The lowermost consists of a bed of debris of the Calcaire 

 Grossier ; it contains shells, usually broken and rolled, of species 

 belonging to the Calcaire Grossier, such as Clavilithes deforfnis 

 and Vefiericardia planicosta. With the rolled and derived fossils 

 are associated much-worn pebbles of Calcaire Grossier, often 

 pierced by lithodomous Mollusca. Several species of Ostrea, as 

 O. dorsata, O. gryphina, are abundant at this level, which 

 was well exposed in the Railway cutting near Mery-sur-Oise 

 (" Tranchee de M. Lamoig?wn "), and its contact with the under- 

 lying Upper Calcaire Grossier clearly shown.* 



Above this horizon the Sables Moyens are often consolidated, 

 forming a thick, pure sandstone without fossils. This bed is very 

 well shown in the section at Auvers (fig. 8), where the stone in the 

 lower part, at least twenty feet in thickness, is quarried for road 

 metal and paving-setts. 



This classical section was figured by A. d'Orbigny in 1852, t and 

 at that time the sandstone was only exposed to the depth of nearly 

 seven feet. Prof. Prestwich described the section^ in 1857, and 

 the sandstone was then as fully exposed as at the time of our visit 

 (1889). The upper part of the Lower Sables Moyens is also well 

 shown at Auvers ; and we here see that the component beds are 

 variable in their characters, sands predominating, often calcareous, 

 sometimes false-bedded, and occasionally consolidated into thin 

 bands of sandstone. A yellow calcareous sand in -the upper part 

 of the section is full of fossils, the most noticeable being 

 NutiwiuUtes variolarius. The Mollusca are also exceedingly 

 numerous ; thefoUowing maybe particularly mentioned in addition 

 to those indicated in the explanation of fig. 8 : — Venericardia 



* G. Dollfus, Bull. Soc. Geol. Fr., 36. s6r., t, vi. (1I78), p. 256. 



+ D'Orbigny, Cours. EUm. de Pal. et Geol., Paris (1852), p. 748, Fig. 577. 



Prestwich, Qieart.Journ. Geol. Soc, vol. xiii. (18; 7), p. no. 



