146 Marvels of Pond-Life. 



restores to tlie organic 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 whose organization can only be discovered 

 by the microscope, and take in the foraminifera, polyps, 

 polyzoa, &c., we shall have to record still larger obli- 

 gations to minute forms of living things. The coral 

 polyp builds reefs that constitute the chief characteristic 

 - of certain regions in the Pacific ; foraminifera are 

 forming or helping to form strata of considerable 

 extent, while diatoms are making deposits many feet in 

 thickness, composed of myriads of their silicious shells, 

 or adding their contributions of silex, very large in 

 the aggregate, to all sedimentary rocks. Testimony of 

 this kind of work is found by the navigator who 

 examines the ice in arctic seas, and it comes up with 

 soundings from the ocean depths. 



On the surface of the earth the amount of change 

 produced is equally remarkable, although it leaves less 

 permanent traces behind. As a rule no decomposition 

 of organized matter takes place, no death of plants or 

 animals, without infusorial life making its appearance, 

 and disposing of no small portion of the spoil. Even 



