i 



OPPONENTS AND OBJECTIONS. 179 



pagn the validity of all fossils determined by micro- 

 scopic structure. In like manner all comparisons of 

 these structures with dendritic and other imitative 

 forms have signally failed, in the opinion of those best 



ualified to judge. 



Another and perhaps simpler way of putting the 

 case is the following : — Only three general modes of 

 accounting for the existence of Eozoon have been 

 proposed. The first is that of Professors King and 

 liowney, who regard the chambers and canals filled 

 ^iih serpentine as arising from the erosion or partial 

 dissolving away of serpentine and its replacement by 

 calcite. The objections to this are conclusive. It 

 does not explain the nummuline wall, which has to be 

 separately accounted for by confounding it, contrary 

 to the observed facts, with the veins of fibrous serpen- 

 tine which actually pass through cracks in the fossil. 

 Such replacement is in the highest degree unlikely on 

 chemical grounds, and there is no evidence of it in the 

 numerous serpentine grains, nodules, and bands in the 

 Laurentian limestones. On the other hand, the op- 

 posite replacement, that of limestone by serpentine, 

 seems to have occurred. The mechanical difficulties 

 in accounting for the delicate canals on this theory are 

 also insurmountable. Finally, it does not account for 

 the specimens preserved in pyroxene and other sili- 

 cates, and in dolomite and calcite. A second mode of 

 accounting for the facts is that the Eozoon forms are 

 merely peculiar concretions. But this fails to account 

 for their great diflference from the other serpentine 



