196 RELICS OF TRIMEVAL LIFE 



or is our view limited altogether to Eozoon Cana- 

 dense? In answering this question, we must bear in 

 mind that the Laurentian itself was of vast duration, 

 and that important changes of life may have taken 

 place even between the deposition of the Eozoon 

 limestones and that of those rocks in which we find 

 the comparatively rich fauna of the Primordial age. 

 This subject was discussed by the writer as early as 

 1865, and I may repeat here what could be said in 

 relation to it at that time : — 



" In connection with these remarkable remains, it 

 appeared desirable to ascertain, if possible, what 

 share these or other organic structures may have 

 had in the accumulation of the limestones of the 

 Laurentian series. Specimens were therefore selected 

 by Sir W. E. Logan, and slices were prepared under 

 his direction. On microscopic examination, a num- 

 ber 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 lime- 

 stones. Others, however, were evidently made up 

 almost entirely of fragments of Eozoon, or of mix- 

 tures of these with other calcareous and carbon- 



