Zoological Characters in Geology. 245 



Proceeding still further south, the chalk formation is found 

 in places where it has not until now been noticed. I do not 

 hesitate to refer the grey, hard, sandy, and micaceous rocks 

 which form the base of ground in the environs of Bayonne, 

 and especially the coast and rocks of Biaritz, to this forma- 

 tion. It was in 1808 that I conceived this idea on the epoch 

 of formation of this rock. The subsequent examination 

 that I made of its accompanying circumstances, of its re- 

 semblance to some varieties of the craie tufau, and the 

 spatangus that comes from the environs of Bayonne, which 

 I have named, from M. Defrance, spatangus ornatus, and 

 of which I have giveu a figure pi. v. fig. 6. of the Des- 

 cription geologique des environs de Paris, fully confirm me 

 in the opinion that this rock should be referred to the craie 

 tufau. It occurs as a continuous mass, in which distinct 

 stratification cannot be recognized but by means of the 

 difi'erent degrees of solidity of the parts composing it ; in 

 fact alternating zones are observed in it of a greyish, argil- 

 laceous, or sandy limestone, easily decomposed, and a hard 

 limestone, as it were divided into a suite of irregular hot 

 dules, which project on the surface of the escarpments in the 

 same manner as the flints in the white chalk. 



This mass contains numerous remains of fossil shells, 

 which it was impossible for me to determine, but among 

 which I recognized echinites, the spatangus ornatus, and 

 sp. bufo, to occur. I did not observe any ammonite. 



Notwithstanding the specific difiFerences which many of 

 these shells bear to those of the chalk, the mass of resem- 

 blances teaches us that they approach the species that then 

 existed, more than those of any other epoch. 



§ IV. Chalk of Poland. 



I shall, out of the vast extent of chalk in Poland, select 

 three points at a distance from each other, on which I pos- 

 sess certain data. 



The two first are in the environs of Grodno in Lithuimia, 



