858 STUDIES FOR STUDENTS 



em France is composed of friable and superficially decomposed 

 calcareous schists throughout the whole mass of which are found 

 the nitrifying bacteria which are believed to have been instru- 

 mental in promoting its characteristic decompositions. The 

 organism acts even upon the most minute fragments, reducing 

 them continually to smaller and smaller sizes. Each fragment 

 loosened from the parent mass is found coated with a film of 

 organic matter thus produced, and the accumulation begun by 

 these apparently insignificant forces is added to by residues of 

 plants of a higher order which come in as soon as food and foot- 

 hold are provided. 



Mr. J. E. Mills, ^ as already noted, lays considerable stress on 

 the decomposing effects of the carbonic acid gas which the ants 

 are "continually pouring" into the upper layers of decomposed 

 material. What the original source of this carbonic acid may 

 have been is not stated, but the natural assumption is that it 

 arises from the decomposing organic matter in their burrows. 



Certain species of ants, locally known as saubas, or sauvas, 

 live, according to Branner,"" in enormous colonies, burrowing in 

 the earth where they excavate chambers with galleries that 

 radiate and anastomose in every direction, and into which they 

 carry great quantities of leaves. Certain species of termites, the 

 white ants of Brazil, are also active promoters in bringing about 

 changes in the structure of the soil, and incidentally accelerat- 

 ing decomposition. The organic matter carried by these crea- 

 tures into the ground, there to decompose, furnishes organic 

 acids to promote further decay in the material close at hand, 

 and by its downward percolation to attack the still firm rocks 

 at greater depths. Indeed these numerous channels, through 

 affording easy access of air, and surface waters with all their 

 absorbed gases or alkaline salts, may serve indirectly a geological 

 purpose scarcely inferior to that of the joints in massive rocks. 



The mechanical agency which has already been referred to 

 as instrumental in bringing about a certain amount of decom- 



^ Am. Geologist, June 1889, p. 351. 



2 Bull. Geol. Soc. of Am., Vol. VII, 1895. 



