1818.] of the Strata of the Environs of Paris. 281 



limestone where they at present occur. To such causes must 

 we attribute also the presence of the rolled pebbles on or near th« 

 surface of these sands. 



The belt of chalk which surrounds the Paris basin is in a 

 manner interrupted on the east of the Sologne by the point of 

 the freshwater limestone, which extends along the Loire as far as 

 Cosne, where it approaches the lias ; but it occurs again beyond 

 this point in a small region covered with trees, hedges, and mea- 

 dows, known under the name of Puysaie, which extends from the 

 valley of the Loire to that of the Yonne, comprehending the 

 greater part of the country between Cosne, Montargis, and 

 Auxerre. 



The soil of this country is not so level as that of Sologne, and 

 shows more frequently the exposure of the different series of 

 beds of the older chalk, such as the chalk with pale flints, the 

 sand, and, above all, the clay, which is the most abundant, and 

 which forms the character of the region. Among these deposits 

 is one which is very remarkable from its utility in an economical 

 point of view ; this is the ochre of Pourrain. It lies in the midst 

 of irregular beds more or less mixed with sand, clay, marl, or 

 even calcareous matter, among which we see distinctly the series 

 of imperceptible shades, which unite mineralogically those quartz 

 substances which are known by the names of flints, jaspers, and 

 sandstones. 



The beds of clay and sand of Puysaie terminate nearly in a 

 line drawn from Chatillon sur Loingto Joigny ; beyond that there 

 is found only the chalk with pale flints, which to the north of 

 Montargis and Joigny, approximates to the chalk, properly so 

 called, which occurs, distinctly characterized, in the plains of 

 Champagne north of the Yonne. 



The space occupied by the older chalk becomes after this much 

 contracted, and forms, as I have already remarked, only a nar- 

 row band, which skirts the whole length of Champagne from the 

 Yonne to the Oise. This band, which has been already described 

 by M. Desmarest, is remarkable for its regularity throughout so 

 great an extent, and its uniformity of appearance, as a valley of 

 an argillaceous nature, bordered on the one side by elevated 

 plains of chalk, and on the other by those of lias ; for it is to be 

 remarked that the land of Champagne, which forms a low plain, 

 where it appears from under the hills of the Paris beds, rises 

 gradually, attains a height at least equal to that of those hills, 

 and terminates on the eastern side in a sort of escarpment, which 

 exposes the marly clay underneath the chalk. This clay is 

 incumbent on the lias, which soon rises to a greater height than 

 the elevated chalk plains, and thus limits the superficial extent 

 of the clay beds. It appears that the property of the clay of 

 being easily worked upon by water, is, in a great degree, the 

 cause of the land being here worn into a valley. 



Although the clay strata form the principal character of this 



