WHAT IS EOZOON 



75 



bonate of lime^ resembling tlie cliamber-wall so closely 

 that it is nearly impossible to make out the difference, 

 and thus is likely to pass altogether unobserved 

 by collectors,, and to baffle even the microscopist. 

 (Pig. 24.) Although therefore the layers which contain 

 well characterized Eozoon are few and far between, 



Fig. 21. Foraminiferal Eock Builders. 



(a.) Nnniimilites Itevigata — Eocene. (b.) The same, showing chambered in- 

 terior, (c.) Milioline limestone, magnified — Eocene, Pa,ris. (d.) Hard 

 Chalk, section magnified — Cretaceous. 



there is reason to believe that in the composition of the 

 limestones of the Laurentian it bore no small part, and 

 as these limestones are some of them several hundreds 

 of feet in thickness, and extend over vast areas, Eozoon 

 may be supposed to have been as efficient a world- 

 builder as the Stromatoporse of the Silurian and 



