538 A TREATISE ON METAMORPHISM. 



where humidity is high, and hence it is in the humid regions that vertical 

 transfers of material through the agency of plants is greatest in quantity. 



It will be remembered that by far the greater portion of the plants 

 either decay or are used by animals, which in turn ultimately decay. At 

 the time of decay the mineral material dissolved by the plants either passes 

 into the run-off and is transported to the sea or else joins the soil, to be there 

 again redistributed. Probably the latter is the larger portion. Therefore 

 much of the soluble material abstracted by life from the belt of weathering 

 is but temporarily held. The only permanent loss to that belt is the portion 

 which gets into the streams and thence into the sea. 



Since the part of the vegetation above ground to a large extent decays 

 at or near the surface, the permanent effect of the vegetation in the trans- 

 portation of the dissolved material is to bring it from a depth of one to 

 several meters below the surface near or to the surface. 



The roots decaying in situ to some extent redistribute the material and 

 transfer it toward the surface, but not to so great a degree as the portion of 

 the plants above the ground with the help of the roots. 



MATERIAL TRANSFERRED TO BELT OF CEMENTATION. 



A large amount of material which is dissolved in the belt of weathering 

 is carried downward by the descending waters and joins the subterranean 

 sheet below the level of ground water. It will be shown below and in 

 the following chapter (pp. 612-617) that the material which joins the belt 

 of saturation is again subdivided, a part being precipitated in the belt 

 of cementation and a part joining the surface waters and thus being 

 transported to the sea. 



MATERIAL PERMANENTLY ABSTRACTED BY RUN-OFF. 



A considerable amount of the soluble material of the belt of weathering 

 joins the run-off. In times of abundant rain water flows over the surface. 

 This water takes up the soluble material with which it comes into contact. 

 The amount dissolved is especially likely to be considerable if abundant 

 rains follow a time of drought, for it will be seen below that in tunes of 

 deficient rain capillarity brings the soluble salts to the surface where 

 they can be readily abstracted by the run-off. From seepage waters and 

 springs the streams receive large quantities of water from the belt of 



