AMOUNT OF WATER IN BELT OF CEMENTATION. 571 



ever, it may be that this estimate is too small, and that the amount of 

 water of the belt of cementation may be two or three times this amount. 



CIRCULATION OF WATER IN BELT OF CEMENTATION. 



VIGOR OF CIRCULATION. 



The vigor of the circulation in the belt of cementation is best shown by 

 the amount of work which has been accomplished in cementation of rocks 



Fig. 8.— Ideal vertical section of the flow of ground water through a homogeneous medium from one well to another. 



by ground waters. It is shown in another place that great sandstone for- 

 mations, which must originally have had a pore space of from 32 to 40 per 

 cent, have been completely cemented by the deposition of silica. (See pp. 

 865-868.) It is further shown that the amount of silica thus deposited is 



