96 MEMOIRS OF 



above the chalk, eacli deposit covered by a ma- 

 rine deposit ; irrefragable proofs cf several irrup- 

 tions and alternate retreats of the sea, in the 

 basin of Paris and its environs, since the period 

 of the chalk formation. This discovery was 

 solely due to M. Cuvier, and it was at Fontaine- 

 bleau that the truth suddenly flashed across his 

 mind. " Brongniart," he cried, '* j*ai trouv6 

 le noeud de I'affaire." " Et quel est-il?" asked 

 M. Brongniart. " C'est qu'il y a des terrains 

 marins, et des terrains d'eau douce," replied M. 

 Cuvier.* It is most interesting to see how, 

 after many years of uninterrupted and difficult 

 investigation, of profound study and meditation, 

 M. Cuvier, in his beautiful Preliminary Dis- 

 course, sums up the facts which afford indis- 

 putable evidence of these great phenomena. " I 

 think," said the learned author, with MM. De 

 Luc and Dolomieu, " that if there be any 

 thing positive in geology, it is, that the surface 

 of our globe has been the victim of a great and 

 sudden revolution, the date of which cannot be 

 carried back further than from five to six thou- 

 sand years ; that this revolution has buried, 



* " I have solved the difficulty." — " And what is it ? " — " It 

 is, that there are fresh water earths, and earths of salt water 

 formation." 



