Environs of Lons k Saunkr. 159 



gryphites, as more modern than that of the true compact 

 limestone of the Jura, which easily breaks into conchoidal 

 splinters. 



The cause of this error was owing to the respective extent 

 and limits of these formations not being known, organic 

 remains were supposed to be extremely rare in the second, 

 and very abundant in the first, and lastly the beds were con- 

 sidered to be more horizontal in the latter than the former ; 

 so that the limestone formation, the beds of which were 

 arched, appeared referable to the transition series, whilst 

 that of the gryphite limestone was regarded, and with 

 reason, as a secondary formation in all the force of the 

 term. 



The most important geological fact that I have proved in 

 this memoir, and of which the hollowing out of the valleys 

 and caverns of this country ought to be a necessary conse- 

 quence, was unknown. I speak of the existence of enor- 

 mous masses of marl beds, beneath the gryphite limestone, 

 and beneath the diflFerent stages of oolitic limestone ; in 

 order to explain these great eifects, recourse must be had to 

 purely gratuitous hypotheses. 



Lastly, these marls, which always appear as if over- 

 lapping, either at the bottom of valleys, at the foot of 

 platforms, or on their summit, not having been distin- 

 guished, as to their formation, from those found in irregular 

 beds among the clays, sands, and gravelly soils • they 

 were considered as deposited after the formation of the 

 valleys. 



It followed that the gypseous masses of the Jura, which 

 are the most ancient of all the mineral masses of that 

 chain, appeared to be of an infinitely more modern for- 

 mation. 



This memoir is very incomplete, and partakes greatly of 

 the haste with which it was written ; but the subject is so 

 vast, that it would require many years of observation and 

 study, in order to understand the immense quantity of 



