182 THE PEINCIPLES INVOLVED IN ROCK-WEATHEBING 



penetrate into every little cleft or crevice produced by atmos- 

 pheric agencies, and throughout long periods of time produce 

 results of no inconsiderable geological significance. The depth 

 below the surface at which such may thrive is presumably but 

 slight, and their period of activity limited to the summer months. 

 They have been found on rocks of widely different character — 

 granites, gneisses, schists, limestones, sandstones, and volcanic 

 rocks — and on high mountain peaks as well as on lower levels. 

 The Pie Pourri, or Rotten Peak of the Bernese Alps, is cited as 

 composed of friable and superficially decomposed calcareous 

 schists, throughout the whole mass of which are found the nitri- 

 fying bacteria, which are believed to have been instrumental in 

 promoting its characteristic decomposition. 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 in- 

 significant forces is added to by residues of plants of a higher 

 order, which come in as soon as food and foothold are provided.^ 

 Mr. J. E. Mills,^ and after him J. C. Branner,^ lay stress on 

 the decomposing effect of vegetable matter carried into the 

 ground by ants in certain parts of Brazil, Mills going so far as 

 to describe the ants as continually pouring carbonic acid into 

 the ground. Be this as it may, the excretions of the ants them- 

 selves are undoubtedly of such a nature as to further the proc- 

 esses of decomposition. Certain species of ants, locally known 

 as saubas, or sauvas, live, according to Prof. Branner, in enor- 

 mous colonies, burrowing in the earth, where they excavate cham- 

 bers 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 pro- 



1 It is, perhaps, as yet, too early to say to wliat extent tlie presence of 

 bacteria may be incidental to decomposition, rather than causative. Branner 

 in a recent summary of this subject (Am. Jour. Sci., "Vol. Ill, 1897, p. 442), 

 says: "In other words nitrifying bacteria not only do not penetrate the 

 rocks themselves to any considerable depths, but they do not even penetrate 

 the soil to a depth of more than three or four feet. In the face of this 

 fact, and the other fact that our granites are often decomposed to depths 

 of more than 100 feet, it seems quite improbable, if not impossible, that 

 bacteria are responsible for this deep decay, or for any considerable part 

 of if 



2 American Geologist, June, 1889, p. 357, 



3 Bull. Am. Geol. See. of America, Vol. VII. 



