of the Environs of Paris, 46 



' Thjfe places mentioned above prove, that this stratum of 

 clay is very extensive, and preserves throughout its whole 

 extent its principal characters of formation and position. 



If we compare the descriptions we have given of the 

 beds of chalk and beds of plastic clay, we shall remark s 

 1st, That not only we do not find in the clay any of the 

 fossils met with in the chalk, but we do not even find any 

 fossil in it. 2d, That there is no insensible passage be* 

 tween the chalk and the clay, since the parts of the bed of 

 clay most adjacent to the chalk do not contain lime more 

 than the other parts. 



It appears to us that w^e may conclude from these obser- 

 vations, in the first place, that the liquid which has depo- 

 sited the bed of plastic clay was very different from that 

 which deposited the chalk, since it does mot contain car- 

 bonated lime in any sensible quantity, and since none of 

 the animals live there which inhabited the waters that de- 

 posited the chalk. Secondly, that there must necessarily 

 have been a distinctly-marked separation, and perhaps even 

 a long period of lime between the deposit of the chalk and 

 that of the clay, since there is no transition between these 

 two kinds of soil. The kind of broken fragments of chalk 

 and clay which we remarked at Meudon * even seems to 

 prove that the chalk was solid when the clay was deposited. 

 This earth is insinuated between the fragments oi" chalk 

 produced on the surface of the chalky soil by the motion of 

 the waters, or by some other cause. 



The two kinds of soil which we have described have been 

 produced, therefore, under completely different and even 

 well-defined circun)stances. They are the results of the 

 most distinct and best characterized formations which can 

 be found in geology, since they differ in their chemical na- 

 ture, in the kind of stratification, and above all in the kind 

 of fossils which we meet with in them. 



Article III. Formation of Sand and of coarse Limestone, 



The coarse limestone does not always immediately cover 

 the clay, being frequently separated by a stratum of sand 

 of various thickness. Wt*. cannot say whether this sand 

 belongs to the formation of the calcareous earth, or to that 

 of the clay. We have not found shells in it, in the few 

 j:!laces where we have observed it, which would give it an 



•* See page ^^ 



argilliceous 



