358 Rev. W. D. Conybeare on a Geological Map of [May, 



is regular horizontal beds, sometimes confusedly heaped toge- 

 ther. They form a kind of submarine forest, extending in a band 

 a league and a half in breadth from the north-west of the Isle of 

 Oleron, 14 leagues to the interior of the mainland along the 

 right bank of the Charente, about a metre below the level of the 

 high tides. They are associated with a coarse grit containing 

 bones of large marine animals. The geological constitution of 

 the neighbourhood is said to be follpwing an ascending order : 

 1. Compact lithographic limestone of an even fracture (La 

 Rochelle St. Jeand'Angely), beds of oolite (point of Chatelaillon 

 and Matha). 3. Lumacheile and beds of polypiers, with 

 impressions of gryphcea angustata. (These three deposits are 

 considered as representing the Jura limestones, and the latter as 

 identical with the coral rag of England). 4. Great bed of lig- 

 nite with marine peat, succin asphalte, and plastic clay. 

 5. Ferruginous and chloritose sand, slate clay, and argillaceous 

 and calcareous beds with trigoniae and cerithia, and fragments 

 of lignite. On the south-west of the Charente, No. 4 and o are 

 wanting, and a very white limestone said to be the lowest chalk 

 rests immediately on the oolites. M. Boue has traced the pro- 

 longation of these lignites from Rochefort by Perigueux to 

 Sal tat in the Perigord. 



Similar instances of the occurrence of lignite in this formation 

 have been observed in England in the Isle of Purbeck, the Isle 

 of Wight, and in the Weald of Sussex. Mr. Mantell has described 

 the vegetable remains of the last-mentioned deposits in the forty- 

 second page of his work on the geology of that district. 



The iron ores of Perigord occur in this formation. M. Boue 

 has also observed iron sand, green sand (with crabs and echi- 

 nites), and chalk marie, on the SW. of the basin of the Garonne 

 between Bayonne, St. Severs, and Dax. These deposits repose 

 on the Jura limestone, which forms a band at the foot of the 

 Pyrenees. Quadersandstein with lignites succeeds — then a 

 few beds of Muschelkalk covering the great saliferous sand- 

 stone. 



(C.) Alps. 



On the northern borders of the Alps, the highest beds of the 

 exterior calcareous chains consist of a dark-coloured limestone 

 often mixed with sand and green particles, and agreeing in its 

 fossils with this part of the English series, with the addition of 

 nummulites, which are rare (although they do occasionally occur) 

 in these beds in England. Similar beds are mentioned, and in 

 a similar position, on the skirts of the Maritime Alps, near Nice, 

 in Mr. Allan's account of that neighbourhood. (Ed. Phil. Trans.) 

 They form the second limestone of the memoir referred to. 



In Cuvier and Brogniart's Description Geologique des Envi- 

 rons de Paris, will be found an account of a formation of the 

 same epoch with the craie chloritee, (the English green sand, and 

 chalk marl,) in the chain of Buet, with a particular enumeration 



