48 



THE DEPTHS OF THE SEA. 



[CHAP. i. 



of their bodies of matter in solution, developing 

 but little heat, and incurring a very small amount 

 of waste by any manifestation of vital activity. 

 According to this view it seems probable that at 

 all periods of the earth's history some form of 

 the Protozoa rhizopods, sponges, or both predomi- 

 nated greatly over all other forms of animal life 

 in the depths of the warmer regions of the sea. 

 The rhizopods, like the corals of a shallower zone, 

 form huge accumulations of carbonate of lime, and it 

 is probably to their agency that we must refer most 

 of those great bands of limestone which have resisted 

 time and change, and come in here and there with 

 their rich imbedded lettering to mark like milestones 

 the progress of the passing ages. 



TINDHOT.M. 



