THE LAURENTIAN AND HURONIAN PERIODS. /I 



the chambers are simply filled with crystalline carbonate of 

 lime. When the originally porous fossil has been permeated 



Fig. 24. — Portion of one of the calcareous layers of Eozoon, magnified 100 diameters. 

 n a, The proper wall (" Nummuline layer") of one of the chambers, showing the fine ver- 

 tical tubuli with which it is penetrated, and which are slightly bent along the line a' a', 

 c c. The intermediate skeleton, with numerous branched canals. The oblique lines are 

 the cleavage planes of the carbonate of lime, extending across both the intermediate 

 skeleton and the proper wall. (After Carpenter.) 



by a silicate, it is possible to dissolve away the whole of the 

 calcareous skeleton by means of acids, leaving an accurate and 

 beautiful cast of the chambers and the tubes connected with 

 them in the insoluble silicate. 



The above are the actual appearances presented by Eozoon 

 when examined microscopically, and it remains to see how 

 far they enable us to decide upon its true position in the 

 animal kingdom. Those who wish to study this interesting 

 subject in detail must consult the admirable memoirs by Dr 

 W. B. Carpenter and Principal Dawson : it will be enough 

 here to indicate the results which have been arrived at. The 

 only animals at the present day which possess a continuous 

 calcareous skeleton, perforated by pores and penetrated by 

 canals, are certain organisms belonging to the group of the 

 Fora?m?iifera. We have had occasion before to speak of these 

 animals, and as they are not conspicuous or commonly-known 

 forms of life, it may be well to say a few words as to the 

 structure of the Hving representatives of the group. The 

 Foraminifera are all inhabitants of the sea, and are mostly of 

 small or even microscopic dimensions. Their bodies are com- 



