PRELIMINARY CONSIDERATIONS. 



17 



conception of the conditions in which we find fossil remains, 

 and of the evidence by which we can refer these to different 

 periods in the history of the earth. 



1 if;. 12. — Protichnites septem-notatus. A supposed series of crustacean foot-prints made 

 in sand, now hardened into sandstone. Cambrian. — ^After Logan. 



Carrying this knowledge with us, and at the same time 

 glancing at the. table of successive formations prefixed to 

 this chapter, we shall be prepared, without any additional 

 geological study, to understand the statements to be made in 



c 



