RELATIONS BETWEEN SOLUTION AND DEPOSITION. 617 



belt of cementation, there is precipitation of quartz and reduction of the 

 amount of material held in solution, even if the temperature be high. 

 Indeed, it is not improbable that high temperature is favorable to the 

 dehydration of silicic acid." Because of the uncertainty of the effect of 

 the chemical reactions, one can not say whether more material emerges 

 with the solutions than enters with them. Were it not for the enormous 

 quantity of colloidal silicic acid contributed by the belt of weathering and 

 the dominant importance of quartz as a cement (see pp. 622-623), probably 

 solution due to the causes above assigned would overbalance deposition. 

 But in the present state of knowledge I must leave unanswered the question 

 as to which of the processes, solution or deposition, is preponderant in the 

 belt of cementation. Both are of the utmost consequence. 



Concluding, we now see that the unhvv of the belt of cementation and 

 the belt of weathering from a physical-chemical point of view is perfect. 

 Both are belts of oxidation, carbonation, hydration, and solution and 

 deposition. Both are belts of reactions with liberation of heat and 

 expansion of volume. The contrast between the two belts is largely due to 

 the variable quantitative value of each of these processes in the two belts 

 and the resulting condition in which the rocks are left — disintegrated and 

 softened in the one and cemented and indurated in the other. 



RESULTANT PROCESSES. 



The processes resulting from the chemical changes are cementation and 

 metasomatism. 



CEMENTATION. 



By cementation is meant the binding together of the rock particles by 

 deposition of material as minerals in the interstices of the rocks. In the 

 previous chapter on "The Belt of Weathering," we ascertained the source 

 and character of the materials which joined the sea of ground water and 

 which are therefore available for cementation in the belt of induration. It is 

 clear that there are constantly being added from the belt of weathering to 

 the continuous sheet of water in the belt of cementation the following 

 compounds: Sodium, potassium, calcium, magnesium, iron, aluminum, as 

 carbonate, sulphate, nitrate, phosphate, chloride. With these there are also 



"Mendeleeff, D., Principles of chemistry, trans, by George Kamensky, Longmans, Green & Co., 

 London, 1897, vol. 2, pi 112. 



