5G THE DAWN OF LIFE. 



often known to be, of which there is a noted instance in the 

 Trenton Hmestone of Ottawa. But the circumstance is alluded 

 to for the purpose of comparing these dolomitized portions of 

 the skeleton with the specimens from Burgess, in which the 

 replacement of the septal layers by dolomite appears to be the 

 general condition. In such of these specimens as have been 

 examined the minute structure seems to be wholly, or almost 

 wholly, destroyed; but it is probable that upon a further in- 

 vestigation of the locality some spots will be found to yield 

 specimens in which the calcareous skeleton still exists unre- 

 placed by dolomite ; and I may safely venture to predict that 

 in such specimens the minute structure, in respect both to 

 canals and tubuli, will be found as well preserved as in any of 

 the specimens from Cote St. Pierre. 



" It was the general form on weathered surfaces, and its 

 strong resemblance to Stromatopora, which jfirst attracted my 

 attention to Eozoon ; and the persistence of it in two distinct 

 minerals, pyroxene and loganite, emboldened me, in 1857, to 

 place before the Meeting of the American Association for the 

 Advancement of Science specimens of it as probably a Lauren- 

 tian fossil. After that, the form was found preserved in a third 

 mineral, serpentine ; and in one of the previous specimens it 

 was then observed to pass continuously through two of the min- 

 erals, pyroxene and serpentine. Now we have it imbedded in 

 limestone, just as most fossils are. In every case, with the ex- 

 ception of the Burgess specimens, the general form is composed 

 of carbonate of lime; and we have good grounds for supposing 

 it was originally so in the Burgess specimens also. If, there- 

 fore, with such evidence, and without the minute structure, I 

 was, upon a calculation of chances, disposed, in 1857, to look 

 upon the form as organic, much more must I so regard it when 

 the chances have been so much augmented by the subsequent 

 accumulation of evidence of the same kind, and the addition 

 of the minute structure, as described by Dr. Dawson, whose 

 observations have been confirmed and added to by the highest 

 British authority upon the class of animals to which the form 

 has been referred, leaving in my mind no room whatever for 

 doubt of its organic character. Objections to it as an or- 



