Cakalre grossiere and Paris Gypsum. 169 



on some very scarce lymnea found in gypsum (p. 186), and es- 

 pecially in marls, with fresh-water and marine shells, at St 

 Ouen and St Pan tin. Now, it so happens that these shells are 

 not more, nay, even not so abundant, as in the Mayence lime- 

 stone, which he classifies as we do, that is, amongst the marine 

 rocks. Assuredly, if a saline solution like that which deposit- 

 ed gypsum and strontianite at Paris, possessed the property of 

 killing or removing marine animals, it must also have acted on 

 the fresh-water shells ; but some shells, carried down accidentally 

 by rivers, may have been able to remain preserved in the marly 

 beds formed during the moments when the solution was feebly 

 acidulated, or had precipitated all its salts. A particular acci- 

 dent can be even conceived by which a fluviatile shell may have 

 remained entire enveloped in marly gypsum, and even in pure 

 gypsum. Dead animals floated down may have left their skele- 

 tons in the gypsum. The short period during which the solu- 

 tion was feebly impregnated with saline matter, would naturally 

 prevent the marine animals taking possession again of their old 

 stations ; so that the presence of fresh- water shells in the marls 

 below, above, or in the gypsum, seems to be a mere accident, 

 occasioned by the carrying down of a river, a fact easily under- 

 stood, and explaining why these shells are found not in continu- 

 ous beds, but in short beds or nodules. The existence of beds 

 of marine shells in the same position would be more difficullly 

 explained, at least we would be obliged to suppose a succession 

 of deposits formed during very unequal spaces of time. 



Let us leave this subject, let us not attach too much import- 

 ance to a few fresh-water shells, and admit only those deposits 

 to be of fresh-water formation, which are characterized so well 

 by M. Brongniart at page 166 of his Tableau. 



It may occasion surprise that we have not taken into consi- 

 deration the bones met with in gypsum ; but the truth is, their 

 occurrence in the gypsum is, zoologically considered, of no im- 

 portance for geology, as they have been found not only in the 

 clayey marly beds of the marine limestone (p. 172), but also 

 imbedded in that rock itself : now the first, according to Brong- 

 niart, are accidental (p. 170). If this be admitted, what reason 

 can be given for refusing to include the bones found in gypsum 

 n the same category ? Further, La presence du terrain pako- 



