CHAPTER V. 



THE PRESERVATION OF EOZOOX. 



PERHAPS nothing excites more scepticism as -to this 

 ancient fossil than the prejudice existing among 

 geologists that no organism can be preserved in rocks 

 so highly metamorphic as those of the Laurentian 

 series. I call this a prejudice, because any one who 

 makes the microscopic structure of rocks and fossils 

 a special study, soon learns that fossils undergo the 

 most remarkable and complete chemical changes 

 without losing their minute structure, and that cal- 

 careous rocks if once fossiliferous are hardly ever 

 so much altered as to lose all trace of the organisms 

 which they contained, while it is a most common occur- 

 rence to find highly crystalline rocks 'of this kind 

 abounding in fossils preserved as to their minute 

 structure. 



Let us ? 'however, look at the precise conditions 

 under which this takes place. 



When calcareous fossils of irregular surface and 

 porous or cellular texture, such as Eozoon was or 

 corals were and are, become imbedded in clay, marl, 

 or other soft sediment, they can be washed out and 

 recovered in a condition similar to that of recent 



