the Environs of Paris. 3S 



departments of the Oise, the Seine-Inferieure, and the Eure. 

 It resembles an island that may be considered as the summit 

 pf a mountain buried under the great chalky deposit. 



The parts of this deposit in the neighbourhood of the Pays 

 de Bray are remarked, in the first place, to acquire the cha- 

 racters of ancient chalk ; between Argueil and St. Sausom 

 (Seine Inferieure) that substance is seen which is filled with 

 a great quantity of blackish green chlorite grains, and ano- 

 ther modification of a coarse texture, passing into the state 

 of sandy marl, and containing nodules of greyish calcari- 

 ferous sandstone instead of true flints. It afterwards ap- 

 pears that the sands and marly clay, forming the peculiar 

 character of the country, rise from beneath this coarse chalk; 

 I only say appears, because the moveable nature of these 

 deposits, and the labours of agriculture, conceal the super- 

 positions, and that, on the other hand, the neighbourhood 

 of the sands and plastic clay of the Parisian calcaire a cerites, 

 would allow the supposition that that formation had ex- 

 tended as far as the Pays de Bray. But the presence of 

 limestone that occurs in the central part, among other places, 

 at Menerval, Cuy-St.-Fiacre, '&c., does not leave a doubt, 

 that the greatest part at least of the clays of this canton be- 

 long to the formation intermediate between the chalk and 

 horizontal limestone. This limestone, commonly yellowish- 

 white, or yellowish grey, is remarkable for its hardness, the 

 abundance of spathose parts it contains, and above all for the 

 great quantity of small oysters that enter into its composition, 

 although there are nevertheless some beds quite compact, 

 and without fossils. One cannot very well judge of the 

 position of its principal mass with regard to that of the clay ; 

 but it is clearly seen that beds of the two systems alternate 

 with each other. 



These sketches suffice for recognizing a small formation, 

 very remarkable for the constancy with which it presents 

 the same mineralogical and geological characters in very dis- 



