350 M. Brongniart on the different Floras which 



greensands near Graudpre, department of Ardennes, where 

 M. Buvignier has found two very remarkable fossil plants, a 

 stem of an arborescent fern and a cone already observed in 

 England in the same formation. 



But in other places and in beds of certainly different epochs, 

 this period has presented solely marine plants ; such in particular 

 are the fucoid sands or macigno, characterized by Chondrites Tar- 

 gionii, cequalis, intricatus, &c., now designated by the name of 

 fucoid sands, gres a fucoides or flysch, the geological epoch of 

 which has long been problematical, but which all appear to agree 

 in considering as a distinct formation, superior to the chalk and 

 inferior to the most ancient beds of the tertiary formations. 



These fucoid sands form a very distinct epoch, which appears 

 up to the present time characterized solely by marine vegetables, 

 and which, at least in the botanical point of view, would form 

 the line of demarcation between the cretaceous and the tertiary 

 formations ; for it is remarkable that the Euci which occur in it 

 in such great number, have few relations to those of the chalk 

 properly so called, and none at all with those of the most ancient 

 beds of the tertiary formations, such as those of Monte Bolca. 



The study and comparison of these fossils coming from such 

 varied sources, enables us to divide the cretaceous period into 

 three epochs, the middle one being the true cretaceous epoch ; 

 the others, characterized almost entirely by marine plants, are 

 doubtful enough as to their true geological position ; one, more 

 ancient than the chalk, comprises only the subcretaceous lignites 

 of the environs of La Rochelle and of the department of Dor- 

 dogne ; the other, above the chalk, corresponds to the fucoid 

 sands. 



1. Subcretaceous Epoch. 



Cystoseirites Partschii, Sternb. — 



Transylvania. 



filiformis, Sternb. — Ibid. 



Laminarites ? tuberculatus, Sternb. 



— Isle of Aix. 

 Rhodomelites strictus, Sternb. — lb. 



Naiades. 

 Zosterites Orbigniana, Brong. — Isle 

 of Aix. 



Zosterites BeUovisiana, Brong. — Isle 

 of Aix. 



elongata, Brong. — Ibid. 



lineata, Brong. — Ibid. 



Conifers. 



BrachyphyllumOrbignianum,Bron5'. 



— Isle of Aix. 

 BerardianunijjBrora^'. — Pialpin- 



son. 



This little flora is almost entirely based upon the fossil plants 

 collected in the marine lignites of the Isle of Aix, near La Ro- 

 chelle, long since described by M. Fleurian of Bellevue. 



The difference of the plants seems to forbid the union of this 

 flora with that of the lower chalk or greensand, but it will be 

 requisite to study it more completely under the double relation 



