g8 M. D'Omalius D'Halloy on 



La Touraine occurs to the south of this sandy country, a 

 region that extends to the country of the ancient horizontal 

 limestone, which is met with to the south of Chatellerault, 

 and Chatillon sur Indre,^ and whose surface is formed of 

 coarse chalk. This substance, known in our western de- 

 partments by the name of triffeau is sometimes tender and 

 friable ; at others, hard enough to form good building stones ; 

 its colour is most commonly yellowish white, often having a 

 greenish tint, arising from the presence of chlorite j the flints 

 in it are almost always whitish, often passing into the horn-? 

 stone variety, sometimes into jasper and calcariferous sand- 

 stone. Its fossils are very abundant and extremely various : 

 the orbicular gryphite is particularly distinguishable. The 

 thickness that the beds of tufFa ordinarily possess, the faci- 

 lity with which they are worked, the double advantage de- 

 rived from them for building, and the manuring of ground, 

 have given occasion to the hollowing out of immense quarries, 

 sometimes inhabited by modern troglodytes. These quarries 

 form one of the principal features of this rock, which are 

 again found in the tufi"as of the Meuse Inferieure, as well as 

 in those of the banks of the Loire, 



The tuflFa of Touraine is covered by a thick bed of sand, 

 full of whitish flints, and sometimes mixed with clay, which 

 is only the sandy chalk washed by water ; to these two sys- 

 tems is owing the contrast presented in the agricultural con- 

 dition of this country. When the surface is cut into sufficiently 

 deep to expose the tufi'a bed, it becomes extremely fertile, 

 and merits the epithet of Garden of France that has been 

 given it. But the platforms covered with sand and flint are 

 absplutely arid, and only afford extensive heaths.* 



stone beds scattered over some of these plateaux, joined to the existence 

 of a small deposit of freshwater limestone near Mans, renders it pro- 

 bable that there exist some superficial deposits of freshwater sands ; but 

 I have not been able to verify this fact in a positive manner. 



* The marl, or decayed shells (falun), found on some of these plat- 

 forms, contributing, as is known, to fertilize them, is a distinct deposit 

 much more modern than the tuffa. The shells composing it, of which 

 M. de Tristan, an able naturalist, is preparing a descnption, possess 



