THE LAURENTIAN AND HURONIAN PERIODS. 69 



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 Eozoon 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 laminie 

 ot loganite and dolomite. (After Dawson.) 



colours and composition ; one series being white, and com- 

 posed of carbonate of lime whilst the laminae of the second 

 series alternate with the preceding, are green in colour, and 

 are found by chemical analysis to consist of some silicate, 

 generally serpentine or the closely-related " loganite." In 

 some instances, however, all the laminae are calcareous, the 

 concentric arrangement still remaining visible in consequence 

 of the fact that the laminae are composed alternately of lighter 

 and darker coloured limestone. 



When first discovered, the masses of Eozoon 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 recognised 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 

 afterwards corroborated by other high authorities (Mr W. K. 

 Parker, Profesor Rupert Jones, Mr H. B. Brady, Professor 

 Giimbel, &c.) Stated briefly, the structure of Eozoon, as ex- 

 hibited by the microscope, is as follows : 



