1818.] of the Strata of the Environs of Paris. 279 



most common colour is yellowish white, having often a greenish 

 tint occasioned by the presence of chlorite. The flints are always 

 pale, often passing into hornstone, sometimes into jasper or cal- 

 careous sandstone. Fossils are abundant in it, and in great 

 variety; the orbicular gryphcea is particularly to be distinguished. 

 From the thickness of these beds, the facility with which they 

 are worked, and the double advantage derived from them for the 

 purposes of building and manure, immense quarries have been 

 formed in them, which are sometimes inhabited by a modern 

 race of troglodytes. These quarries are characteristic of these 

 strata, and are found in the department of the Meuse-Inferieure, 

 as well as on the banks of the Loire. 



The tuffeau of Tourraine is covered by a thick bed of sand, full 

 of pale flints, and sometimes mixed with clay, which is no other 

 than the sandy chalk washed by the waters. The contrast of 

 the agricultural characters in different parts of this country 

 arises from these two systems of soil. When the soil is enough 

 cut through to expose the bed of tuffeau, it is very fertile, and 

 deserves the name it has acquired of the garden of France. But 

 the elevated plains covered with sand and flints, present to the 

 eye only barren heaths of great extent.* 



The Sologne is a low marshy region, of a sandy nature, and 

 not very fertile, situated to the south of the Loire on the east 

 side of Tourraine ; its southern part clearly belongs to the chalk 

 formation. We easily recognize the same sands mixed with 

 entire flints. There is only this difference between them, that 

 the soil has not been opened to so great a depth, consequently 

 the tuffeau is less frequently exposed; and, lastly, that the 

 tuffeau is not so well characterized, and more resembles the 

 marly chalk. 



The part of this country which is to the north of the Saudre, 

 is covered with a sandy deposit, of which it is not easy to deter- 

 mine the origin. This sand is the same as that before spoken of 

 as covering the freshwater limestone of the Gatinais, that is, it 

 is formed of grains of white quartz, generally rounded or globular, 

 often very large, sometimes very small. It is sometimes accom- 

 panied with fragments of transparent quartz, commonly white, 

 and rarely greyish, and with brown yellowish flints, all of them 

 more or less rounded, and seemingly found only in the superfi- 

 cial parts. 



These sands have often been thought to be alluvial ; but on 



• The/olun which is found on some of these plains, and assists to render them 

 fertile, is a separate deposit much more modern than the tuffeau. The shells com- 

 posing it, of which M. de Tristan is preparing a description, have many points of 

 agreement with those of the Paris limestone with cerithia. Bat thefalun of Tour- 

 raine differs from this last formation in two particulars: it does not occur of a 

 stony consistence, and as Reaumur remarks, it contains only the remains of shells, 

 more or less broken. We find also in this district detached portions of freshwater 

 beds, varying inextent, sometimes in the state of shell-limestone, sometimes in that 

 •f siliceous limestone. 



