1^2 MARYYA.H OF POXD-LIFE. 



it brings putrescent particles under the influence of 

 a species of combustion, which, though slow, is as 

 effectual as that which a furnace could accomplish. 

 Microscopic animal life helps the regenerative 

 process, and restores to the zoological system myriads 

 of tons of matter, which death and decay would 

 have handed over to the inorganic world. In a 

 very small pond or tank the quantity of this 

 kind of work is soon appreciable, and if we reflect 

 on the amazing amount of water all over the globe, 

 including seas and oceans, which swarm with 

 infusoria, the total effect produced in a single 

 year must seem considerable, even when com- 

 pared with that portion of the earth's crust that 

 is subject to alteration from all other causes put 

 together. If we add to the labour of the Infusoria 

 those of other creatures Avhose organization can 

 only be discovered by the microscope, and take in 

 the foramenifera polyps, polyzoa, etc., we shall have 

 to record still larger obligations to minute forms of 

 living things. The coral polyp builds reefs that 

 constitute the cliief characteristic of certain regions 

 in the Pacific; foramenifera are forming or helping 

 to form strata of considerable extent, while diatoms 

 are making deposits many feet in thickness, com- 

 posed of myriads of their siliceous shells, or adding 

 their contributions of silex, very large in the ag- 

 gregate, to all sedimentary rocks. Testimony of 



