v Rouelle, Lamanon 209 



were grouped in exactly the same kind of arrangement 

 and distribution as on the floor of the present sea a fact 

 which, in his eyes, disproved the notion that these marine 

 organisms had been brought together by some violent 

 deluge ; but, on the other hand, showed that the present 

 land had once been the bottom of the sea, and had been 

 laid dry by some revolution that took place without pro- 

 ducing any disturbance of the strata. Rouelle recognized 

 a constant order in the arrangement of the shells. Thus, 

 immediately around Paris, he found certain strata to be 

 full of screw shells (Turritella, Cerithium, etc.), and to 

 extend to Chaumont, on the one side, and to Courtagnon 

 near Rheims, on the other. He pointed to a second 

 deposit, or "mass" as he called it, full of belemnites, 

 ammonites, gryphites, etc. (Jurassic), forming a long and 

 broad band outside the eastern border of the Chalk, and 

 stretching north and south beyond that formation up to 

 the old rocks of the Morvan. Desmarest's account of his 

 teacher's opinion was published in the third year of the 

 Republic. 1 It is thus evident that Rouelle had formed 

 remarkably correct views of the general stratigraphy of 

 the Paris basin probably long before 1794. 



Desmarest himself published many valuable observa- 

 tions regarding the rocks of the Paris basin in separate 

 articles in his great Qdographie Physique. Lamanon had 

 written on the gypsum deposits of the region, which he 

 regarded as marking the sites of former lakes, and from 

 which he described and figured the remains of mammals, 

 birds and fishes. Noting the alternations of gypsum and 



1 G&grapJiie Physique (Encydoptdie Methodiqiw), tome i. (1794), pp. 

 409-431. 



