THE DAWN OF LIFE 125 



tionate to the great supplies of carbonic acid in the atmosphere 

 and in the waters, and if the Eozoic ocean was even better 

 supplied with salts of lime than those Silurian seas whose vast 

 limestones bear testimony to their richness in such material, 

 we can easily imagine that the conditions may have been more 

 favourable to a creature like Eozoon than those of any other 

 period of geological time. 



Growing, as Eozoon did, on the floor of the ocean, and 

 covering wide patches with more or less irregular masses, it 

 must have thrown up from its whole surface its pseudopods 

 to seize whatever floating particles of food the waters carried 

 over it. There is also reason to believe, from the outline of 

 certain specimens, that it often grew upward in conical or club- 

 shaped forms, and that the broader patches were penetrated by 

 large pits or oscula, admitting the sea-water deeply into the 

 substance of the masses. In this way its growth might be 

 rapid and continuous ; but it does not seem to have possessed 

 the power of growing indefinitely by new and living layers 

 covering those that had died, in the manner of some corals. Its 

 life seems to have had a definite termination, and when that 

 was reached, an entirely new colony had to be commenced. 

 In this it had more affinity with the Foraminifera, as we now 

 know them, than with the corals, though practically it had the 

 same power with the coral polyps of accumulating limestone 

 in the sea bottom a power indeed still possessed by its fora- 

 miniferal successors. In the case of coral limestones we 

 know that a large proportion of these consist not of continuous 

 reefs, but of fragments of coral mixed with other calcareous 

 organisms, spread usually by waves and currents in continuous 

 beds over the sea bottom. In like manner we find in the 

 limestones containing Eozoon, layers of fragmental matter 

 which show in places the characteristic structures, and which 

 evidently represent the debris swept from the Eozoic masses 

 and reefs by the action of the waves. It is with this frag- 



