H On the Mineralogical Geographj 



Art. V. Formation of Sea- Sand and of Freeslo7ic, 



This soil is not extensive, and sccnis to form a succession 

 to the fomuiiion ot the marles of gypsum. We should 

 even have brought ihem toccther, it" it ha.(\ accompanied 

 them as constantly as ll^e marks accompany the gypsum, 

 and if it liad not been frenuentlv separated by a consider- 

 able argillaceous mass, stripped of evc;y fossil, and very 

 diflercnt in its nature from that which we are now about to 

 describe." 



What we have said, shows that this formaiion generally 

 covers the gypsous formation. Tt consists in beds of sili«r 

 ceous sand, frequently very pure and agglulinalcd into free- 

 stone, which eoniains sea shells of various kinds, and aH 

 of them of the same kind as those of Grignon. We have 

 here recognized the same oysters, the same calyptrcie, ihe 

 same tcUincs^ and the same ceriics. Sometimes the shells 

 themselves exist, and are in a calcareous state, whije in 

 other places nothing remains of them bat the external im- 

 pressions or moulds. 



We found this freestone and sea sand on the top of Mont- 

 martre, at Romainville, at Saint Prix near Montmorency^ 

 Longjumcau, &:c. In these last we also ren)ark fossil 

 balani. 



We cannot help reflecting, when looking at these free- 

 stones, filled with the same shells as those oiGrii'non, on the 

 singular circumstances that must have presided over the 

 formation of the strata we have examined. On beginning 

 with the strata after the chalk, we may represent to our- 

 selves in the first place a sea \\hich has deposited an irnt- 

 niense mass of chalk and mollusci of a particular species. 

 This precipitation of chalk and the shells which accompany 

 it, suddenly ceases. Strata of a totally diflcrent nature suc- 

 ceed it, and nothing else is then deposited but clay and 

 sand without any organized body. Another sea returns : 

 this last contains a prodigious quantity of testaceous moK 

 lusci, all of them different , from those of the chalk. It 

 forms at bottom thick beds, in a great measure composed 

 of the testaceous envelopes of these mollusci ; but this pro- 

 duction ol- shells gradually diminishes, and also suddenly 

 ceases. The soil seems then to have been covered with 

 fresh water; alternate strata of gvpsum and of marie are 

 formed, wiiich surround both the bones of the animals 

 which these waters nourished, and the baiics of those which 

 lived on their shores. 



