1S1L] Imperial Institute. J58JT 



mistake, and shows that not only the species, but even the genus, 

 is different. 



This observer has endeavoured to ascertain the limits of this 

 passage of animals and plants from salt to fresh-water, and the 

 contrary. He finds that no animal nor no plant can resist a degree 

 of saltness amounting to eight degrees. He has distinguished, both 

 among animals and plants, those species which affect the sea-shore 

 merely on account of the sand to be found there, and which can 

 live likewise in other sandy places; those which are attracted to 

 that situation solely by the salt, and which live likewise in interior 

 salt lakes or marshes; and, finally, those which require the sea such 

 as it is, and do not remove to any distance from it. 



These observations show that it is not always easy to distinguish 

 whether a shell belongs to salt or fresh-water ; but they do not in 

 the least diminish our certainty of the fact that immense beds exist 

 containing only shells well known to be fresh-water ones. They 

 even explain why we find these shells scattered in marine beds. 



M. de Serres places the lignites, or bituminous wood, among 

 fossils, which are most frequently mixed with land shells and fresh- 

 water shells, which renders it probable that this wood grew in the 

 same place where it is at present buried ; and it agrees with all the 

 other facts, showing that the surface of the globe was dry, and 

 peopled with animals and vegetables, before the last irruption of 

 the sea. 



Two young and skilful naturalists, MM. Desmarets and Lemon, 

 have found in the fresh-water beds in our neighbourhood shells of 

 those small entomoslraceas which have been named cypris, and 

 likewise grains of the genus of plants known by the name of charcu 

 Before them these grains were considered as shells to which the 

 name of gyro<ronites was given. 



The geological system of the environs of Paris, which constituted 

 the principal object of the observations and discoveries of MM. 

 Brogniart and Cuvier, is now studied with great attention by many 

 skilful naturalists. MM. de Tristan and Bigot de Morogue have 

 described with care the parts of it which border on the Loire ; and 

 M. Omalius de Halloy, Engineer of Mines, while aiding them in 

 their researches, and in those formerly made by our associate 

 Desmarets, has employed himself in tracing out exactly all its 

 limits, and in making a map of the whole. The beds of this 

 system deposited upon chalk represent an irregular and curvilinear 

 trapezium, the south side of which, parallel to the Loire, extends 

 along that river south from Cosne to below Blois. On the east side 

 it passes near the towns of Montargis, Nemours, Montereau, Ville- 

 nose, Sezanne, Epernay, Laon, Crepy, La Fere ; on the north 

 *i<!'-, near those of Chancy, Noyon, Compeigne, Clermont, Beau- 

 mont, Chaumont, and Gisors. Finally, on the west side, it de- 

 scends by Mantes, Hon. lam, Bnernon, Auneau, and along the 

 Loire as tar as Vendome, from which it goes to rejoin the Loire at 

 Blois. All this space is surrounded with chalk, and chalk in which 



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