1024 A TREATISE ON METAMORPHISM. 



BELT OF CEMENTATION. 



The belt of cementation is the belt between the bottom of the belt of 

 weathering and the top of the zone of flowage. Since in places the rocks 

 are saturated to the surface of the ground, and since in the strong-est rocks 

 the depth of the zone of flowage under the most favorable conditions may 

 reach 10,000 to 12,000 meters, the possible maximum thickness of the belt 

 of cementation is 10,000 to 12,000 meters. The average thickness of the 

 belt of cementation is probably less than 5,000 meters. Since the tempera- 

 ture increases 1° C. for 30 meters, the water in the lower part of the belt 

 of cementation is above the boiling- point for atmospheric pressure. Indeed, 

 if the belt of cementation extends to a depth of 10,950 meters, the water 

 at this rate of increase would have a temperature of 365°, or the critical 

 temperature of water. But it has been shown (pp. 566-569) that, not- 

 withstanding the high temperature of the water up to the critical point, 

 the pressure is sufficient to hold it in the form of a liquid. Where median 

 ical movements or igneous intrusions have taken place the increase of 

 temperature may be higher than 1° C. for 30 meters. But it the critical 

 temperature be not reached, the increment of temperature must be very 

 much greater than this amount in order that the water shall be changed to 

 the form of a gas. (See pp. 566-569, 659-660.) Igneous intrusions at 

 various times and places have doubtless raised the water above the critical 

 temperature, but such water does not come under the subject now being 

 considered. 



The circulation of aqueous solutions in the belt of cementation is vig- 

 orous and extensive. The evidence for this is abundant. First, it is known 

 that a considerable percentage of all meteoric water reaches the belt of 

 cementation. All of this water except the inappreciable portion which 

 enters into combination, after a longer or shorter journey in this belt, must 

 somewhere again issue from it, unless a part of it makes its way downward 

 into the zone of anamorphism, and there is no evidence to show that it does 

 this. (See pp. 665-667.) The vigor of the circulation in the belt of cemen- 

 tation is further shown by the almost incredible number of springs carrying 

 a vast volume of water, all of which are supplied by water from this belt. 

 The water issuing from the belt of cementation in spring's is probably only 

 a small fraction of that which passes to the overground circulation by 

 seepage through many small widely dispersed openings. (See pp. 413—423, 

 571-589.) 



