oftk^ .Environs of Paris. 57 



tion small round hollow bodies {cavctes) which M. dc La* 

 niarck has called gyrogor/itas. We are not acquainted with 

 any analogous existing species : but their position inform;* 

 us, that the organized body of which they formed part lived 

 in fresh water. 



The second character of this foriDation is the facilitjf 

 which the limestone composing it has of being dissolved in 

 water, however hard it n)ay seem at the moment of it» 

 being taken out of the quarry. Hence it is used as marie, 

 fertilizing the soil at Trappe near Versailles, and othei" 

 places. 



We refer to this formation, but rather with hesitation, 

 the sands of the eminences which contain wood and parti 

 £)f vegetables changed into silcx. We were led to make 

 this junction, by observing the siliceous wood and vegetables, 

 which we find towards the top of the hillocks of Longju- 

 nieau. The same sand which contains these veoetables, also 

 contains silex filled with coarse lymncae and pjanorbes. 



The fresh-water soli, although always superHcial, is not 

 found in every situation, but rather towards the summits of 

 the eminences, and on the great platforms as well as in the 

 bottoms of (he valleys; if it exists in the latter situations, 

 it has been covered by the soil which constitutes the ninth 

 and last formation. Besides, it is extremely common 

 throughout the whole of the environs of Paris, and proba- 

 bly at distances much further off than we have visited. It 

 seems to us astonishing, that so few naturalists have paid 

 ;^ttention to the subject ; we know no other person than 

 M. Coupe who has mentioned it. 



The presence of tliis soil pre-supposes, in the fresh vv'ater 

 vvhich then existed, properties which we no longer find in 

 Jhose now in existence, 'fhe waters in our marshes and 

 Jakes deposit nothing but friable slime. We have not re- 

 marked in any of them the proj)erty possessed by the fresh 

 waters of the old world to form thick depots of yellowish 

 ^nd hard limestone, oi" white marles and silex, frequently 

 very homogeneous, enveloping all the ruins of the orga- 

 nized bodies which lived in these waters, and even bringing 

 (hem to the siliceous and calcareous nature of their eu- 

 >'elopes. 



Article IX. Formation of Alluvium {Atlerissemeni), 



Not knowing how to designate this formation, we have 

 given it the name o{' alluvmm, which indicates a mixture of 

 ^laltpr deposited by fresh water. In I'act^ the slime of al- 



luviatioa 



