THE ORIGIN OF SOIL. 59 



have some influence upon the rocks. It is as yet too early to 

 determine what this action is, or whether the action of the bac- 

 teria in this matter is of primary importance or wholly secon- 

 dary. But that they do assist in rock disintegration is quite 

 certain. The famous Alpine peak Fanlhorn (rotten horn) was 

 rightly named. The rock of this peak appears actually rotten. 

 It is full of bacteria, which are easily found, and it appears 

 certain that the rottenness of the rock in this mountain is due 

 in considerable measure to bacteria. The significance of these 

 peculiar bacteria, which require neither organic food nor light 

 for their growth, will be considered on a later page. 



Whatever be the agency of bacteria in rock disintegration 

 they certainly play an important part in the subsequent changes 

 which occur within the soil formed from the debris. Chemical 

 transformations are going on constantly in soil and many of 

 them are produced wholly by the action of the soil microor- 

 ganisms. 



Sulphur Bacteria. In regard to some of the mineral prod- 

 ucts of the soil, bacteria have a more intimate relation. Among 

 the mineral foods of plants sulphates play a very important 

 part, and certain iron salts of potassium and silica are perhaps 

 of equal importance. Now it is certain that the formation 

 and destruction of these compounds in our soils is largely de- 

 pendent upon bacterial action. This agency of bacteria in the 

 transformations of sulphur is a most intimate one, since differ- 

 ent bacteria are able both to build up and to pull to pieces sul- 

 phur compounds. Sulphur springs which deposit sulphur, and 

 other waters and soils which develop sulphuric acid are chiefly 

 explained by bacterial action. 



In the first place many bacteria produce a decomposition of 

 proteid material. Proteid always contains a certain amount of 

 sulphur. The amount is not large, but this element is always 

 present. As the proteids are decomposed the sulphur is loos- 

 ened from its combinations with the other elements and set 



