MODE IX. GYPSUM. 489 



feet thick, is disposed in contiguous layers, re- 

 posing on marl. 



" The third part, called basse-carrilre, pre- 

 sents a gypsous mass of about fourteen feet, 

 divided into six heds, separated from one another 

 by layers of marl. This last part is in the plain, 

 and is incumbent on limestone. 



" I shall riot undertake to account for the 

 formation of the gypsous hill of Montmartre, as 

 well as those which are contiguous, and form a 

 chain of eight or ten leagues, in a northern di- 

 rection. Among the naturalists who have writ- 

 ten on the quarries of Montmartre, M. Pralon, 

 and the Chevalier de Lamanon, have, among 

 others, given excellent lithological descriptions 

 of this place. The latter affirms, that in this 

 part of the Isle of France there was a lake of 

 gypsous water, which gave birth to these quar- 

 ries. 



" The gypsous hills of Montmartre, Belle- 

 ville, Pantin, and all those of this part of the Isle 

 of France, are incumbent on quarries of lime- 

 stone; the gypsous mass only extending to the 

 level of the soil. The shelly and argillaceous 

 rock which is found on the summit of the hill of 

 Montmartre contains white shells, brittle, of the 

 class of chamites, and screw-shells : these shells 

 e analogous to those which are found in the 



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