542 



J. F. BLAKE ON THE UPPER 



Middle Jurassic. 



Corallian. 



Oolite with Nerinace. 



Coral limestone. 



Solid limestone. 

 Oxfordian. 

 Callovian. 



The whole series, as seen between Rochefoucault and Angouleme, 

 is extremely calcareous, and no physical line can be drawn between 

 the Oxfordian and Corallian ; every portion is more compact than 

 usual, and presents no such marked features as are often seen. The 

 Oxfordian near Rochefoucault certainly contains coralliferous beds, 

 and these give place to a sandy oolite. Prom Coquand's descrip- 

 tion it appears that the uppermost portion of the Oxfordian contains 

 in some places such fossils o&Pecten demissus,P. subfibrosus, and Rhyn- 

 chonella Thurmcmni, and in others Amm. oculatus. A. erenatus, and 

 A.Henrici, and is followed by a brecciiform limestone, indicating that 

 the Corallian here also lies on different portions and is really uncon- 

 formable. The massive limestones of the last-named group occupy 

 a wide expanse of country, but finally give way to rather rubbly 

 limestones, doubtless the "Coral Limestone" of Coquand, which, 

 however, scarcely forms a "Rag"; and these, again, are replaced 

 by compact suboolitic limestones, containing Die-eras at Touvres, and 

 in which Coquand records several Nerinazce and Cardium eorallinum, 

 Terebratula insignis, and Rhynclionella corallina. It is obvious, there- 

 fore, that the succession, though somewhat obscure from the similarity 

 of the rocks to each other, is the same that we have seen in the great 

 range before the lower Coral Rag appeared. The Astartian beds are 

 not here of any great importance, consisting of marly limestones, with 

 Pholadomya rostralis and Ceromya ecccentrica. The fossils quoted 

 by Coquand, except the Astarte supracorcrflina ("minima"), are not 

 specially characteristic ; and it is to be noted that he considers 

 some beds at La Rochelle, which d'Orbigny placed in the Corallian, 

 to be the calcareous representatives of these more marly rocks. 

 Traced upwards, however, they become still more marly, and 

 contain abundance of Eocogyrq virgula. Indeed this part of the 

 series is rather exceptional ; and after seeing so much limestone 

 one's eye is refreshed by the sight of veritable clay, extending 

 through a considerable thickness. These irregular beds may be 

 taken up again in the railway- cuttings north of Angouleme ; but 

 the lower portion, distinguished as Pterocerian, which is to be seen 

 some six miles to the north, at Vars, has not been examined. It 

 appears from Coquand's description to be more than usually distinct 

 in this district by its fossils, which include Nautilus giganteus, 

 Pteroeeras oceani, Chemnitzia Danaa?, Pholadomya Protei, Mytilus 

 medus, and Ostrea solitaria. The Yirgulian marls near Angouleme 

 are fairly fossiliferous, the species noted as associated with Exogyra 

 virgula being Natica omata?, Plectomya rugosa, Area cf. rlivmboi- 

 dalis, Trigonia concentrica, T. monilifera^, Gervillia Tcimmeridiensis, 



