92 THE DAWN OF LIFE. 



pared with tlie silicious bodies mentioned in a former paper as 

 occurring in the loganifce filling the chambers of specimens of 

 Eozoon from Burgess." 



These specimens will be more fully referred to under 

 Chapter VI. 



(D.) Additional Structural Facts. 



I may mention here a peculiar and interesting structure 

 which has been detected in one of my specimens while these 

 sheets were passing through the press. It is an abnormal 

 thickening of the calcareous wall, extending across several 

 layers, and perforated with large parallel cylindrical canals, 

 filled with dolomite, and running in the direction of the 

 laminae ; the intervening calcite being traversed by a very fine 

 and delicate canal system. It makes a nearer approach to 

 some of the Stromatoporee mentioned in Chapter YI. than any 

 other Laurentian structure hitherto observed, and may be 

 either an abnormal growth of Eozoon, consequent on some 

 injury, or a parasitic mass of some Stromatoporoid organism 

 overgrown by the laminae of the fossil. The structure of the 

 dolomite in this specimen indicates that it first lined the 

 canals, and afterward filled them ; an appearance which I have 

 also observed recently in the larger canals filled with serpen- 

 tine (Plate YIII., fig. 5). The cut below is an attempt, only 

 partially successful, to show the Amoeba-like appearance, 

 when magnified, of the casts of the chambers of Eozoon, as 

 seen on the decalcified surface of a specimen broken parallel 

 to the laminaB. 



Fig. 21a. 



