St On the Mhieralogical Geographic 



It proves 'that these marles are of fresh-water formaiiorify 

 like the gypsums which they cover. 



Above these white marles a e also seen very nunncroua 

 and frequently thick argillaceous or calcareous marles, in 

 which no fossil has been as yet discovered. 



We aFterwarcb met with a small bed six decimetres (24 

 inches) thick, oi a scaly yellowish marie, which contains 

 towards its lower part scraps of earthy sul phased strontian, 

 and a little above a thin bed of sn>all elongated tellines, which 

 are lying flat, packed closely into each other. This bed, 

 which seems to be unimportant, is nevertheless remarkable 

 in the first place from its great extent : we have observed it 

 over a space more than ten leagues (27i miles) long and more 

 than four ( 1 1 miles) broad, al way9 in the same place and of the 

 same thickness. It is^so thin, that we ought to know pre- 

 cisely where it lies, in order to find it out. Secondly, because 

 it serves as a limit to the fresh -water formations, and indi- 

 cates the sudden commencement of a new marine formation. 

 In fact, all the shells wliich we meet with above this bed 

 of tellines are also marine. 



We find at first, and immediately afterwards, a strong 

 and constant stratum of greenish argillaceous earth, which 

 from its thickness, colour, and continuity, may be recog- 

 nized at a great distance. It serves as a guide to the tellines, 

 since it is beneath it that we find them. It contains no 

 other fossil, but merely argillo- calcareous geodites and 

 scraps of sulphated strontian. This earth is employed in 

 the manufacture of coarse pottery. 



The four or five beds of marie which succeed the green 

 earths are not thick, nor do they seem to contain fossils ; 

 but these beds are immediately covered by a stratum of yeU 

 )ow argillaceous marie, which is strewed with fragments, 

 of sea shells which belong to the genera ceritcs, trochi, 

 mactrcs, venus, cardium, &c. We also meet wiih frag- 

 ments of the bones of a thornback. 



Almost all the beds of marie which succeed the latter 

 present fossil sea shells, but they are bivalves only ; and 

 the last strata (those which arc inmiediately below argilla- 

 ceous sand) contain two very distinct oyster beds. The 

 first and lowerniost is composed of very thick large oyster- 

 f hells: some of them exceed a decimetre (4 inches) in length. 

 Afterwards comes a stratum of whit is*!) marie, without shells, 

 then a second very strong oyster bed, but subdivided int<i 

 several beds. These oyster shells arc brown, much smallcf 

 and thinner than the above. These last beds of oysters axC' 

 Very frequent, and we have not perhaps seen them twice 



