JURASSIC OF THE PARIS BASIN. 



541 



bedded, unfossiliferous, lithographic limestones. One peculiar fea- 

 ture, however, is to be noted. About two miles south of St. Elorent, 

 and again at Lapan, at a lower level in the series, the soil appears 

 of a peculiar rich red colour, and at the latter locality the cause has 

 been ascertained. Instead of the ordinary limestones there are some 

 beds, at least 3 feet or 4 feet thick, of a crystalline irregular mass, 

 which are suggestive of the strangely altered rock produced from 

 corals and coral-brash ; and in this mass are cavities filled with 

 large, round, concentrically coated, limonite concretions. It is by 

 the decay of these that the fields are covered with the red soil ; and 

 they m&y be regarded as the last vestiges of coral-growths, the lower 

 of which might well correspond to the Coral Rag of Merry. As we 

 approach Chateauneuf the limestone becomes white and more marly, 

 but still almost, if not quite, unfossiliferous ; and it is only to the 

 south of the town that the canaliculate Ammonites set in, associated 

 with abundant sponges and Amm. bimammatus and Amm. Martelli, 

 on which little need be said, since they are so obviously Oxfordian. 

 It may be noted, however, since the authors quoted place these beds 

 as the base of the Corallian, that the first Ammonite to appear 

 going down is Amm. canaliculatus ; and this is far above the 

 sponge-bed. 



The valley of the Indre has not been examined ; but Douville and 

 Jourdy assure us that here even the white limestones are wanting, 

 and the whole mass between the Astartian and Oxfordian consists 

 of nothing but barren lithographic limestones, spreading over an 

 expanse of 30 kilometres from Levroux to Chateauroux. 



II. The two Charentes. 



This district scarcely forms part of the Paris basin, being rather 

 the northerly extension of the Pyrenean, and will doubtless serve 

 as a term of comparison between the two. Nevertheless, being so 

 close to the termination of the great range, it is more conveniently 

 studied on the present occasion. The main question, however, 

 of which the solution has been sought, is the age of the so-called 

 " Portland" and even "Purbeck" beds — whether there are, in fact, 

 in this area any rocks corresponding to those that are known by 

 those names in England. 



1. Department of the Charente. — The Jurassic rocks of the depart- 

 ment have been described by Coquand (24), who divides the upper 

 portion as follows : — 



Upper Jurassic. 



PvrbecJcian. 

 Portlandian. 



Carious limestone. 



Limestones with Nucula inflexa. 



Oolitic limestone. 



Limestone with Cardium dissimile. 

 Sands. 

 Kimmeridgian. 



Virgulian marls. 

 Pterocerian limestones. 

 Astartian limestones. 



