1076 



A TREATISE ON METAMORPHISM. 



surface on the average decreases to the bottom of the zone of fracture. It 

 has been explained that all fissures and other openings gradually die out 

 below as the zone of rock flowage is neared. (See pp. 187-191, 766-768.) 

 Therefore, for a given fissure, the waters enter it mainly from the side or 

 top, not from the bottom. Furthermore, the water does not enter the 

 fissure at a single place, but at numberless points all the way along its 

 course, from the deepest parts to the surface. Somewhere, however, the 

 water which enters a fissure must flow from it. This place may be at the 



Fig. 20. —Ideal vertical section of the flow of water entering at a number of points on a slope and passing to a valley 

 below through a homogeneous medium interrupted by two open vertical channels, one on the slope and one in the 



surface or at a considerable depth below the level of ground water. (See fig. 

 2(3.) The streams entering the fissure at high levels may have a downward 

 movement and contribute water abundantly. Below the level at which 

 water escapes laterally from a channel of given size the water contributed 

 to it decreases on the average with increase of depth, until in the deeper 

 part of the zone of fracture the contributions are very small. Posepny" 



"Posepny, F., Genesis of ore deposits: Trans. Am. Inst. Mill. Eng., vol. 24, 1875, p. 971. 

 Posepny, F., The genesis of ore deposits, Am. Inst. Min. Eng., 2d ed., 1902, pp. 242-243. 



Also 



