86 Mr.De la Beche on theGeographical Distribution of Organic 



*' constitute a nearly equal thickness, about 500 metres (IG^O 

 English feet) from the lias to the coral rag inclusive. 



"The maximum of absolute height is 350 metres (ll-tS 

 English feet) in England, and 400 metres (1312 English feet) 

 in the Ardennes. 



" 1. The marls of Florenville, Houldizy, &c. are charac- 

 terized by the Gryphaea ineurva, plagiostomae, &c. as the lias. 



" 2. The sandy limestones, the micaceous marls, the ferru- 

 ginous limestones of Florenville, Orval, Carignan, Dreux, &c. 

 perfectly represent that great sandy and ferruginous zone so 

 well described by the English geologists, under the names of 

 sand, marly sandstone, and inferior oolite. The Gryphsea cym- 

 bium and Plicatula spinosa are its most characteristic fossils. 



" 3. The fullers' earth is easily recognised in the blue 

 marls of Lamouilly, Vaux, &c. It is also in their lovirer part 

 that the fullers' earth of the Ardennes is found. 



*' 4. The great oolite appears with all its characteristics in the 

 extensive quarries of Chauvaney, Brouesnes, Luzy, Ballon, &c. 



" 5. The white marls of La Jardinette near Stenay, of Luzy, 

 &c. offer the most perfect analogy with the Bradford clay of the 

 English geologists ; the fossils are the same ; we more parti- 

 cularly mention the following : Turritella, Ostrea acuminata, 

 Terebratula digona, T. coarctata, Cydarites ornatus, &c. 



" 6. Above this well-defined geological horizon there reigns 

 some uncertainty. If the forest marble is not I'ecognisable with 

 certainty in the coarse lumachella which covers the marls, in 

 the compact madrepore limestones, and sandy limestones of 

 Stenay ; and if, moreover, the beds which, from their fossils 

 and mineralogical composition, have appeared to me equiva- 

 lent to the Stonesfield slate, do occupy a somewhat different 

 position, and will not permit us to sustain the analogy ; — it is 

 not the same with cornbrash. Its fossils (Avicula echinata, 

 Terebratula subrotunda), and its mineralogical characters, are 

 found in the coarse limestones of Stenay, Beaumont, &c. 



" 7. The marls of Stonne, Belval, Dun, &c. present us in 

 their composition, their thickness and their fossils (Gryphaea 

 dilatata. Pinna lanceolata, &c.), with the most perfect resem- 

 blance to the Oxford clay. 



" 8. The sandy and ferruginous oolite corresponds with the 

 calcareous and ferruginous sandstone which the English place 

 at the base of the coral rag (calcareous grit). 



" Lastly, the coral rag appears with its distinctive charac- 

 ters near Belval, Dun, &c. We have there found numerous 

 univalves, Melania, Turritella, &c. Ostrea gregaria, Lima rudis, 

 and the numerous echinites, mentioned by the English*." 



* Annales des Sciences Naturelles, torn. xvii. pp. 79, 80. 



General 



