B2 M. D'Omalius D'HalloV on 



clayey valley, bounded on one side by chalk platforms, and 

 on the other by those of ancient horizontal limestone ; for it 

 is to be observed that the rock of Champagne, which formed 

 but a low plain when it appeared from under the Parisian 

 hills, gradually rises, attains a height that appears at least 

 equal to that of those hills, and terminates at the eastern 

 edge of the region, by a kind of escarpment which exposes 

 the marly clay beneath the clalk ; this same clay rests upon 

 ancient horizontal limestone, which soon rising to a level 

 above that of the chalky platforms, prevents the extension of 

 the clay. It also appears, that the property this system 

 possesses of being easily worn by water, has considerably 

 contributed to the valley that it now presents, the more so 

 as in the places where this kind of valley is traversed more 

 or less transversely by a river course, it forms large swellings 

 out, the argillaceous soil of which is mixed with a great num- 

 ber of small rolled pebbles, of a calcareous nature. There 

 occurs among others one of these swellings out at the place 

 where the Marne and its branches traverses it, known by the 

 name of Perthois, and which is remarkable for its great 

 fertility. 



Although the argillaceous rock principally characterizes 

 this border of Champagne, the other systems of the ancient 

 chalk are not altogether wanting ; even the tuifa with chlo- 

 rite occurs, especially at Autry, in the department of the 

 Ardennes; but scarcely any flint is there seen, and it is a 

 very remarkable fact that the ancient chalk of Champagne 

 differs from that of the other parts of the basin, by the same 

 character that is peculiar to the true chalk of the same dis- 

 trict. 



The limits of the chalk formation are too far removed 

 from the Paris basin, on the north of Champagne, to be con- 

 sidered iQ this memoir ; but there is very near this basin, and 

 even at a short distance from Paris, a very small district, 

 where not only the ancient chalk is seen to appear, but also 

 the formation or at least the last member of the limestone 

 formations older than the chalk. This canton, commonly 

 called the Pays de Bray, is situated at the confiaes of the 



