130 THE DAWN OF LIFE. 



tion. On microscopic examination, a number of these 

 were found to exhibit merely a granular aggregation 

 of crystals, occasionally with particles of graphite and 

 other foreign minerals, or a laminated mixture of 

 calcareous and other matters, in the manner of some 

 more modern sedimentary limestones. Others, how- 

 ever, were evidently made up almost entirely of frag- 

 ments of Eozoon, or of mixtures of these with other 

 calcareous and carbonaceous fragments which afford 

 more or less evidence of organic origin. The contents 

 of these organic limestones may be considered under 

 the following heads : — 



1. Eemains of Eozoon. 



2. Other calcareous bodies, probably organic. 



3. Objects imbedded in the serpentine. 



4. Carbonaceous matters. 



5. Perforations, or worm-burrows. 



" 1. The more perfect specimens of Eozoon do not 

 constitute the mass of any of the larger specimens in 

 the collection of the Survey ; but considerable portions 

 of some of them are made up of material of similar 

 minute structure, destitute of lamination, and irregu- 

 larly arranged. Some of this material gives the im- 

 pression that there may have been organisms similar 

 to Eozoon, but growing in an irregular or acervuline 

 manner without lamination. Of this, however, I 

 cannot be certain; and on the other hand there is 

 distinct evidence of the aggregation of fragments of 

 Eozoon in some of these specimens. In some they 



