SOLUTION AND DEPOSITION. 613 



QUANTITATIVE RELATIONS BETWEEN SOLUTION AND DEPOSITION. 



It has been fully explained that the belt of weathering at any given 

 time represents the partly disintegrated and decomposed material above 

 the level of ground water. During the long-continued erosion of a region 

 the belt of weathering steadily migrates downward. Thus the forces of 

 weathering continually find new material at the bottom of the belt upon 

 which to work. Therefore, as denudation goes on, there is always a belt 

 of a certain thickness in which weathering processes are taking- place. 

 These include solution as a dominant process. It has further been noted 

 that the material abstracted from the belt of weathering is divided into two 

 parts, one of which goes to the overground circulation and thence to the 

 sea, the other of which passes, through the belt of weathering into the belt 

 of cementation below. Each unit of water which passes downward 

 through the belt of weathering into the belt of cementation carries with it 

 in solution a certain amount of material. As a consequence of continuous 

 downward migration of the belt of weathering-, it is certain that an incre- 

 ment of material is continuously added to the belt of cementation from the 

 belt of weathering. 



If this increment which the sea of underground water continually 

 receives were deposited in the belt of cementation, it would furnish a 

 sufficient supply of material for the cementation of that belt. Much of this 

 material is certainly deposited in the belt of cementation, but in that belt 

 solution is also taking place, and the question therefore arises whether or 

 not more material is deposited than is dissolved in the belt of cementation. 

 This question is not easy to answer, but Ave know certain data which have 

 an important bearing upon it. 



One of the fundamental conclusions worked out in Chapter III, on 

 "The agents of metamorphism," is that the quantity of water which passes 

 through the belt of weathering and enters the sea of underground water is 

 substantially equal to that which emerges from this sea through springs 

 and through seepage and joins the run-off. If we knew the relative 

 amounts of material contained in solution in the waters entering and issuing 

 from the belt of cementation, we could answer the third question — i. e., 

 whether more material is dissolved or deposited in the belt of cementation. 

 But the only possible way to get this information is by numerous analyses. 



