the Environs of Paris. J 9 



eastward, especially towards the borders of Champagne, this 

 formation occupies a considerable space of a triangular form, 

 dips under the later formations the same as the preceding, 

 and disappears in the neighbourhood of a line drawn from 

 NW. to SE. which shall pass by Houdan, Arpajon, and 

 Nemours. Throughout the greater part of this surface, that 

 is to say, that which is covered by the siliceous limestone, 

 the calcaire a cerites is, as Messrs. Cuvier and Brongniart 

 have observed, altogether wanting; it is only represented ia 

 some places by the plastic clay, separating the siliceous lime- 

 stone from the chalk. The formations of the third series 

 are differently disposed from those of the tvio former, but 

 before I commence any observations, I should state the geo- 

 logical extent to be given to it. 



Messrs. Cuvier and Brongniart, with that luminous pre- 

 cision they have shewn throughout their work, have dis- 

 tinguished and characterised three separate rocks between 

 the two fresh-water formations ; namely, the marine marls 

 above the gypsum, the sand and sandstone without shells^ 

 and the superior sand and sandstone with shells. I conceive, 

 that considering these rocks generally, a great formation may 

 be observed, constituting the second marine epoch of the 

 Paris basin. The sand and sandstone without shells are, in 

 reality, placed between two formations, whose fossil system 

 is nearly the same. The superior is of the same nature as 

 the rock without shells, which can only be distinguished 

 here by this negative character ; the inferior formation is 

 not so different as it would appear to be at first sight, as it is 

 known that the same system may be calcareous or quartzose, 

 according to situation ; this is actually the case in this in- 

 stance, for at Etaples the sand and sandstone without shells 

 rest immediately on a sandy deposit containing many shells, 

 where a great quantity of pectunculi, cythereae, &c. may be 

 distinguished ; that is, the same fossils as in the sand, which 

 elsewhere covers the sandstone without shells. Finally, the 

 absence of organised bodies in this last mass, is but the 

 repetition of a fact, observable in numerous instances, name- 

 ly, that the moluscce diminished and even disappeared often 



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