1836-38.] ARM AND GRESSLY. 131 



Soleurois," but waited until after the session was over 

 to call at Agassiz's home and present it for publication 

 in the " Memoires de la Societe Helvetique des Sciences 

 Naturelles." After reading the first twenty pages, Agas- 

 siz promptly saw that it was a paper of the first order, 

 containing a quantity not only of new materials, but 

 also of new ideas. In it Gressly proposed the theory 

 of fades or " aspect des terrains," as he called it, an 

 expression which has been constantly used the world 

 over to explain the different association of species of 

 fossil form, according to the deposits in which they are 

 buried, or more exactly according to the character of 

 the sea-bottom on which these animals had lived and 

 associated. 



Not only was the long memoir of Gressly, with a 

 quantity of coloured sections and panoramic geological 

 views, accepted by the committee of publication of the 

 Swiss Society, of which Agassiz was the president, but 

 Gressly was also closely interrogated and, as it were, 

 interviewed by Agassiz. Although Agassiz had already 

 met all the leaders of geology and palaeontology, and 

 a great number of practical collectors of fossils, he 

 had never met such a curiously original observer. 

 Gressly possessed in a rare degree precisely what 

 Agassiz wanted, the ability to observe the stratig- 

 raphy and to classify the different groups of rocks of 

 a formation. Agassiz saw at once all the service he 

 would get from such a rare practical geologist, and 

 he offered to purchase his collection for the young 

 Neuchatel Museum, just organized, and proposed to 



