the Environs of Paris. ^ 



La Sologne is known to be a low and marshy region, of 

 little fertility, and of a sandy nature, situated to the south 

 of the Loire, and to the east of la Touraiue ; its southern 

 part belongs clearly to the chalk formation ; the same sands 

 mixed with unrolled flints may there be recognized as in 

 Touraine. There is only this difference, that the surface is 

 less laid open, consequently the tuffa is more rarely exposed, 

 and lastly, this tuffa is not so well characterized, and more 

 approaches the marly chalk. 



But the part of this country on the north of la Saudre, is 

 covered by a sandy deposit, the origin of which is not so 

 easy to determine. This sand is the same as that of which 

 I have spoken above, as covering the freshwater limestone 

 of le G&.tinais, that is to say, it is composed of grains of white 

 quartz commonly rounded or globular, often very large, some- 

 times extremely small; it is accompanied by fragments of 

 transparent quartz, commonly white, rarely greyish, and by 

 yellowish-brown flint, all more or less rounded, and appa- 

 rently only found on the surface. 



An alluvial origin has often been attributed to these sands; 

 but according to this hypothesis, the debris of the various 

 rocks, of which the neighbouring country is composed, ought 

 to be found there, as actually takes place in the true allu- 

 vion of the Loire, where the mica and felspar of the Au- 

 vergne granites may very easily be recognized, even in the 

 finest sand. There does not exist a country so exclusively 

 quartzose, that the destruction of its rocks should give 

 birth to the sands in question ; the supposition of such a 

 country entirely destroyed or hid, is much more contrary to 

 what we know of nature, than the opinion admitting these 

 sands to have been formed such as they are, in the same 



many relations in common with the Calcaire a cerites of Paris. But the 

 falun of Touraine differs from this last formation, in not passing into a 

 stony state, and in only affording, as Reaumur has already observed, the 

 remains of shells more or less broken. 



More or less extended patches of the freshwater formation, are found 

 on the surface of this country, either in the state of shelly limestone, or 

 that of siliceous limestone. 



