Unknown ; possibly Prozoic or Azoic Periods. 



Thus three grand recognizable groups of 'Life Periods' in 

 the natural history of the globe arise, in the latest of which Man 

 the minister and interpreter of nature* occupies the last 

 place. Earlier -than all these are monuments which entirely 

 elude our grasp rocks which contain no traces of life, and may 

 perhaps, as many geologists suppose f, have really been formed 

 before the appearance of organic life even in the sea. Let us 

 briefly trace the history of these life-periods. 



* " Homo, naturae minister et interpres." LINN. 

 t Murchison calls them Azoic. 



