CHAPTER VII. 



THE BELT OF CEMENTATION. 



BELT OF CEMENTATION DEFINED. 



The belt of cementation, like the belt of weathering, belongs to the 

 zone of katamorphism. The belt has been discussed from the physical- 

 chemical point of view in Chapter IV. From this point of view its 

 definition is very similar to that of the belt of weathering. It is a belt 

 in which the reactions take place with liberation of heat and expansion 

 of volume, or come under the first part of van't Hoff's law. From a 

 geological point of view the condition of affairs is very different in the belt 

 of cementation from that in the belt of weathering, and it is primarily the 

 purpose of this chapter to consider the belt of cementation from this point 

 of view, but, as heretofore, the geological treatment is subject to the 

 general principles which have been developed in the previous chapters. 



Geologically the belt of cementation may be defined to include that 

 part of the zone of katamorphism which is below the belt of weathering. 

 It has as its lower limit the zone of anamorphism, the zone in which 

 permanent openings, whether produced by fracture, original sedimentation, 

 or any other cause, are of subcapillary size. It is bounded above by the 

 belt of weathering, the lower limit of which is the level of ground water. 

 All of the classes of openings described on pages 129-146 are found in 

 this belt. But whatever the nature of the openings, whether cracks and 

 crevices produced by mechanical action, such as those of joints, faults, 

 bedding partings, and fissility, or the openings originally present in the 

 rocks, such as pore spaces of the mechanical sediments and the vacuoles in 

 volcanic rocks, they are usually filled with water. 



The belt under discussion is named the "belt of cementation" because 

 cementation is the most obvious and probably the most important single 

 process of the belt. But it is by no means the only process; it will be seen 



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