40 M. Beudant on Freshwater 



bable that there would be more complete success if the opera- 

 tions were carried on upon a greater scale ; that consequently, 

 in the changes and transitions of this kind, that are sup- 

 posed to have taken place in nature, the moluscae may be 

 presumed to have been better able to resist them, always 

 finding their proper food, and not suffering the constraints 

 of every kind which must affect them in our small apparatus. 



Supporting himself then by these considerations, and ap- 

 plying the results of his experiments to many known geolo- 

 gical facts, M. Beudant believes himself able to draw the 

 following conclusions : 



1st. Since the same water, whether fresh or as salt as 

 our seas, or what is better, brackish, can at the same time 

 support marine and fresh-water moluscas, it may be pre- 

 sumed that similar circumstances have existed in nature, and 

 that it is to these circumstances we owe the presence of 

 marine and fresh-water shells in the same bed, admitting, 

 what every thing seems to prove, that the shells are found 

 in the places where they lived. 



2d. It may even be conjectured that in the interval be- 

 tween the existence of fresh and salt water in the same 

 place, that the water was brackish, and supported at the 

 same time animals peculiar to both ; that consequently, 

 between the beds formed by salt water, containing only 

 marine shells, and those formed in fresh-water, containing 

 solely fresh-water shells, we ought to meet with other beds 

 formed of the passage of one into the other, containing ma- 

 rine and fresh-water shells at the same time.* 



3d. If we could suppose against all appearances, with 

 some naturalists, that the rocks named fresh-water rocks had 

 all been formed under the sea water, the otherwise singular 

 absence in the beds of fresh-water bivalves, of the genera, 

 anodonta, unio, and cyclas, might be explained by the above 

 experiments. 



* M. Beudant refers the sandstone of Beaucliamp and the marls of 

 Vaucluse to an analogous circumstance. 



