THE DAWN OF LIFE 165 



of treating ancient fossils which regards the most 

 obscure or defaced specimens as typical, and those 

 better preserved as mere accidents, of mineral 

 structure. In Tertiary Nummulitcs injected with 

 glauconite it is rare to find the tubuli perfectly 

 filled, except in tufts here and there ; yet no one 

 doubts that these patches represent a continuous 

 structure. 



I have remarked on previous occasions that the 

 calcite constituting the laminae of Eozoon often 

 has a minutely granular appearance, different from 

 that of the surrounding limestone. Under a high 

 power it resolves itself into extremely minute dots 

 or flocculi, somewhat uniformly diffused. Whether 

 these dots are particles of carbon, iron, apatite, or 

 silicious matter, or the remains of a porous struc- 

 ture, I do not know ; but similar appearances 

 occur in the calcareous fossils contained in altered 

 limestones of later date. Wherever they occur in 

 crystalline limestones, supposed to be organic, the 

 microscopist should examine them with care. I 

 have sometimes by this appearance detected frag- 

 ments of Eozoon which afterward revealed their 

 canals. 



(2) The second question requires us to consider 



