570 



A TREATISE ON METAMORPHISM. 



in all probability the amount of pore space gradually decreases in passing 

 from the upper to the lower part of the belt of cementation. All of the 

 foregoing uncertain factors make any estimate of the water of the belt of 

 cementation little better than a guess. On page 128, assuming there is 



F IG . 7.— Ideal horizontal section of the flow of ground water through a homogeneous medium from one well to another. 



present only one-fifth as much as Dana's estimate of 2.67 per cent by 

 weight as the average amount of water in the upper part of the belt of 

 cementation, supposing that from this amount it gradually decreases to 

 zero at the bottom of the belt, and assuming the belt to extend to a depth 

 of 10,000 meters, I have calculated that the amount of water in the belt, if 

 concentrated in a stratum, would make a sheet 69 meters thick. How- 



