on the Environs of Paris. 11 



that near Damerie and Reims, I shall make a few remarks 

 pu it. 



The chalk, hid on the east of Paris by posterior forma- 

 tions, begins to shew itself in the Talley of the Marne below 

 Dornians, and rises as the valley is ascended, so that arriving 

 at the plain of Champagne this formation is seen constituting 

 the base of the hills for some yards above the level of the 

 plain. This fact, observable in many other places on the 

 border of the Parisian rocks, proves that a part of the valley 

 of the Marne has been hollowed out of chalk, and appears to 

 shew that the existence of the low plain, bordering the 

 Parisian hills, is not the effect of chance, giving this form tq 

 the surface of the chalk, before the deposition of the forma- 

 tions composing the hills, but that it owes its origin, in a 

 great measure, to the same cause which has worn the exterior 

 border of these hills in such a manner as to form those 

 numerous capes, islands, and gulfs^ which are there ob- 

 servable. 



I have not seen the plastic clay formation in this part, 

 but according to the observations of M. Desmarest, jun. it 

 shews itself under the form of black earth, often sandy, 

 sometimes clayey, and almost always impregnated with car- 

 bonaceous matter. This black earth, of which M. Desmarest 

 proposes to publish an account, bears a great affinity to that 

 worked for the preparation of sulphate of iron, and which is 

 very common in the northern part of the Paris basin, and 

 even in the chalky plain, constituting isolated deposits in 

 the form of islands or small basins. The resemblance of this 

 black pyritous earth to plastic clay, will no doubt throw new 

 light upon the history of that formation, of which it spreads 

 the extent, at the same time that the occurrence of fossils 

 characteristic of the calcaire a ceriies in some beds of this 

 black earth,* shews that the plastic clay bears a great affinity 



* I have observed but two places where this earth contains cerithia. 

 One is at St. Marguerite, near Dieppe, (Seine Inferieure), where it forms 

 a small basin in the chalk formation. A series of clay and sandy beds is 

 there seen, the first of which alternate with a few strata strongly im- 

 pregnated with carbonaceous and pyritous matters, worked for the fabri- 



