CONTEMPORARIES OF EOZOON 



201 



associated with these beds Matthew has found 

 what seem to be spicules of sponges, some simple 

 and others hexactinelled like those of Protospongia 

 of the Cambrian. 



Though the abundance and wide distribution of 

 Eozoon, and the important part it seems to have 

 acted in the accumulation of limestone, indicate that 

 it was one of the most prevalent forms of animal 

 existence in the seas of the Laurentian period, the 

 non-existence of other organic beings is not implied. 

 On the contrary, independently of the indications 

 afforded by the limestones themselves, it is evident 

 that in order to the existence and growth of these 

 large Rhizopods, the waters must have swarmed with 

 more minute animal or vegetable organisms on which 

 they could subsist. On the other hand, though this 

 is a less certain inference, the dense calcareous skele- 

 ton of Eozoon may indicate that it also was liable to 

 the attacks of animal enemies. It is also possible 

 that the growth of Eozoon or the deposition of the 

 serpentine and pyroxene in which its remains have 

 been preserved, or both, may have been connected 

 with certain oceanic depths and conditions, and that 

 we have as yet revealed to us the life of only certain 

 stations in the Laurentian seas. Whatever conjee- 



