136 WHAT MAY BE LEARNED FROM EOZOON 



ing on any investigation I might have in hand. It was this 

 habit which induced my old friend, Sir William Logan, in 1858 

 and subsequent years to ask my aid in the study of the forms 

 believed or suspected to be organic, which had been discovered 

 in the course of his surveys of the Laurentian rocks. In one 

 respect this was unfortunate. It occupied much time, inter- 

 fered to some extent with other researches, led to unpleasant 

 controversies. But these evils were more than compensated by 

 the insight which the study gave into the fact of the persistence 

 of organic structures in highly crystalline rocks, and to the 

 modes of ascertaining and profiting, by these obscure remains, 

 while it has guided and stimulated enquiry and thought as to 

 the origin and history of life. These benefits entitle the re- 

 searches and discussions on Eozoon to be regarded as marking 

 a salient point in the history of geological discovery, and it is 

 to these principally that I would attract attention in the pre- 

 sent chapter. 



Perhaps nothing excites more scepticism as to the animal 

 nature of Eozoon than the prejudice existing among geologists 

 that no organism can be preserved in rocks so highly crystalline 

 as those of the Laurentian series. I call this a prejudice, be- 

 cause any one who makes the microscopic structure of rocks 

 and fossils a special study, soon learns that fossils and the 

 rocks containing them may undergo the most remarkable and 

 complete mechanical and chemical changes without losing 

 their minute structure, and that limestones, if once fossiliferous, 

 are hardly ever so much altered as to lose all traces of the 

 organisms which they contained, while it is a most common 

 occurrence to find highly crystalline rocks of this kind abound- 

 ing 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 may have been, or corals were 



