the Environs of Paris. 31 



country, where they are now observable. It is to causes of 

 this nature that the presence of the rolled pebbles must be 

 attributed, which occur more or less superficially in these 

 sands. 



The chalky belt of the Paris basin is, it may be said, 

 broken to the east of la Sologne by the point formed of fresh- 

 water limestone along the Loire to Cosne, where it ap- 

 proaches the ancient horizontal limestone; but is again found 

 beyond this point where the last systems of the formation 

 constitute a small physical region, covered with trees, hedges, 

 and meadows, known by the common name of Puysaie, which 

 extends from the valley of the Loire to that of the Yonne, 

 embracing the greatest part of the country comprehended 

 between Cosne, Montargis, and Auxerre. 



The surface of this district, less even than that of Sologne, 

 more frequently exposes the different ancient chalk systems, 

 such as the chalk with pale flints, the sand, and above all 

 the clay, which is most abundant, and which gives a cha- 

 racter to the region. In the series of these deposits one oc- 

 curs very remarkable for its economical utility ; it is the 

 Pourrain ochre, which occurs in the midst of irregular beds, 

 and more or less mixed with sand, clay, marl, and even cal- 

 careous matter, in which may very clearly be seen the series 

 of insensible shades that mineralogically unite the quartzose 

 substances designated by the names of flint, jasper, and 

 sandstone. 



The clay and sandy beds of la Puysaie cease nearly in the 

 direction of a line from Chatillon sur Loing to Joigny ; there 

 then only remains the chalk with pale flints, which, on the 

 north of Montargis and Joigny, tends to approach the true 

 chalk, which occurs extremely well characterized in the plains 

 of Champagne to the north of the Yonne. The space occu- 

 pied by the ancient chalk afterwards narrows considerably, 

 and forms, as I have already noticed, but a narrow band ex- 

 tending the length of Champagne from the Yonne to the 

 Oise. This band, already described by M. Desmarest, is 

 remarkable for its continuity for so great a length, and the 

 uniformity with which it presents itself under the form of a 



