l8S RELICS OF PRIMEVAL LIFE 



hope finally to trace it back to the Primordial, and 

 thus to bring it still nearer to Eozoon in time. 



Though Eozoon was probably not the only animal 

 of the Laurentian seas, yet it was in all likelihood the 

 most conspicuous and important as a collector of 

 calcareous matter, filling the same place afterwards 

 occupied by the reef-building corals. Though pro- 

 bably less efficient than these as a constructor of solid 

 limestones, from its less permanent and continuous 

 growth, it formed wide floors and patches on the sea- 

 bottom, and when these were broken up vast quan- 

 tities of limestone were formed from their debris. It 

 must also be borne in mind that Eozoon was not 

 everywhere infiltrated with serpentine or other sili- 

 cious minerals ; quantities of its substance were 

 merel}' filled with carbonate of lime, resembling the 

 chamber-wall so closely that it is nearly impossible 

 to make out the difference, and thus is likely to 

 pass altogether unobserved by collectors, and to 

 baffle even the microscopist. Although therefore 

 the layers which contain well-characterized Eozoon 

 are few and far between, there is reason to believe 

 that in the composition of the limestones of the 

 Laurentian it bore no small part ; and as these lime- 

 stones are some of them several hundreds of feet in 



