456 A TREATISE ON METAMORPHISM. 



Bacteria, water, and oxygen decompose the iron and other sulphides 

 They further oxidize the iron of carbonates. While oxidation is the rule for 

 the belt of weathering, under exceptional conditions bacteria, moisture, and 

 vegetation, or the two latter, may deoxidize instead of oxidize compounds, 

 and this may result in the reduction of ferric salts and in denitrification. 

 These processes of oxidation and deoxidation are fullv considered on 

 pages 461-473." 



ANIMALS. 



The chemical work of animals is accomplished while alive and while 

 dead the same as that of the plants. 



ANIMALS, ALIVE. 



In chemical work probably the most important of the animals while alive 

 are the earthworms. It has already been seen how great is the number of 

 these animals, and how great is the mechanical work which they accom- 

 plish. These animals differ from other animals in that they pass the soil 

 directly through their alimentary canals, so that the active compounds of 

 the body act upon and decompose the inorganic materials. It is impossible 

 to estimate the effect of this repeated passage of the soil through the 

 alimentary canals of the earthworms, but it can not be doubted that it 

 results in dissolving a vast quantity of earth materials and in rendering 

 undissolved parts of the materials more soluble. 



The ants and termites carry a large amount of vegetable material from 

 above the surface of the ground to below the surface, and thus introduce it 

 into the soil, so that when it decomposes the products formed will be most 

 effective in their chemical action. Branner states: "The quantities of vege- 

 table matter carried into their burrows is almost beyond belief. I have 

 seen a full-grown orange tree completely stripped of its foliage within a 

 few hours. In the coffee regions the damage done by them is so serious 

 that the Brazilian Government at one time offered a large premium for a 

 successful formicida or ant exterminator." b 



A second effect of living animals comes from their constant excreta. 

 These consist in large part of active chemical compounds, of which perhaps 



"See Branner, J. C, Bacteria and the decomposition of rocks: Am. Jour. Sci., 4th ser., vol. 3, 

 1897, pp. 438-442. 



h Branner, J. C, Decomposition of rocks in Brazil: Bull. Geol. Soc. America, vol. 7, 1896, p. 297. 



