v Joint Work of Cuvier and Brongniart 2 1 5 



formations which they have to consider were deposited in 

 a vast bay or lake, of which the shores consisted of Chalk. 

 They point out that the deposits took place in a definite 

 order and could be easily recognized by their lithological 

 and palseontological characters throughout the district. 

 They classify them first broadly into two great groups, 

 which they afterwards proceed to subdivide into minor 

 sections. The first of these groups, covering the Chalk of 

 the lower grounds, consisted partly of the plateau of lime- 

 stone without shells, and partly of the abundantly shell- 

 bearing Calcaire Grossier. The second group comprised 

 the gypseo-marly series, not found uniformly distributed, 

 but disposed in patches. 



Starting from the Chalk of the north of France, the two 

 observers succinctly indicate the leading characters of that 

 deposit, its feeble stratification chiefly marked by parallel 

 layers of dark flints, the varying distances of these layers 

 from each other, and the distinctive fossils. Putting 

 together the organisms they had themselves collected, and 

 those previously obtained by Defrance, they could speak 

 of fifty species of organic remains known to occur in the 

 Chalk a small number compared with what has since 

 been found. The species had not all been determined, 

 but some of them, such as the belemnites, had been noted 

 as different from those found in the " compact limestone " 

 or Jurassic series. 



From the platform of Chalk, Cuvier and Brongniart 

 worked their way upward through the succession of 

 Tertiary formations. At the base of these, and resting 

 immediately on the Chalk, came the Plastic Clay a 

 deposit that in many respects presented strong contrasts 



