THE LAURENTIAN AND HURONIAN PERIODS. 69 



controversy it is wholly unnecessary to enter here ; and it will 

 be sufficient to briefly explain the structure of Eozo'on, as eluci- 

 dated by the elaborate and masterly investigations of Car- 

 penter and Dawson, from the standpoint that it is a genuine 

 organism the balance of evidence up to this moment inclin- 

 ing decisively to this view. 



The structure known as Eozo'dn is found in various localities 

 in the Lower Laurentian limestones of Canada, in the form of 

 isolated masses or spreading layers, which are composed of 

 thin alternating laminae, arranged more or less concentrically 

 (fig. 22). The laminae of these masses are usually of different 



Fig. 22. Fragment of Eozoon, of the natural size, showing alternate laminae 

 of loganlte and dolomite. (After Dawson.) 



colors and composition; one series being white, and composed 

 of carbonate of lime whilst the laminae of the second series 

 alternate with the preceding, are green in color, and are found 

 by chemical analysis to consist of some silicate, generally ser- 

 pentine or the closely-related " loganite. " In some instances, 

 however, all the laminae are calcareous, the concentric arrange- 

 ment still remaining visible in consequence of the fact that 

 the laminae are composed alternately of lighter and darker 

 colored limestone. 



When first discovered, the masses of Eozo'dn were supposed 

 to be of a mineral nature; but their striking general resem- 

 blance to the undoubted fossils which will be subsequently 

 spoken of under the name of Stromatopora was recognized by 

 Sir William Logan, and specimens were submitted for minute 

 examination, first to Principal Dawson, and subsequently to 

 Dr. W. B. Carpenter. After a careful microscopic examina- 

 tion, these two distinguished observers came to the conclusion 

 that Eozoon was truly organic, and in this opinion they were 



