THE DAWN OF LIFE 



185 



the ocean. If in connection with this we consider 

 the rapidity with which the soft, simple, and almost 

 structureless sarcode of these Protozoa can be built 

 up, and the probability that they were more abun- 

 dantly supplied with food, both for nourishing their 

 soft parts and skeletons, than any similar creatures 

 in later times, we can readily understand the great 

 volume and extent of the Laurentian limestones 

 which they aided in producing. I say aided in 

 producing, because I would not desire to commit 

 myself to the doctrine that the Laurentian limestones 

 are wholly of this origin. There may have been 

 other animal limestone-builders than l^Iozoon, and 

 there may have been limestones formed by plants 

 like the modern Nuilipores or b)- merely mineral 

 deposition. 



Its relations to modern animals of its type have 

 been very clearly defined by Dr. Carpenter. In the 

 structure of its proper wall and its fine parallel per- 

 forations, it resembles the Nummulites and their 

 allies (Figs. 48, 49) ; and the organism may therefore 

 be regarded as an aberrant member of the Nummu- 

 line group, which affords some of the largest and 

 most widely distributed of the fossil Foraminifera. 

 This resemblance may be seen in Fig. 48. To the 



