TRANSPORTATION OF THE METALS. 1077 



calls attention to the frequently observed fact of the decreasing* amount of 

 water contributed laterally as depth increases. As a specific instance of 

 this, he mentioned the Przibram district, in which the amount of water 

 entering the fissures below a depth of 300 meters is so small as to be 

 insignificant, but this may not have been the fact at the time the lode was 

 forming. (See pp. 1063-1065.) 



While the amount of water laterally entering a fissure decreases 

 from near its top to the bottom, the amount of mineral material per unit 

 volume in all probability increases on the average; for the waters entering 

 at a low level take a longer journey through smaller openings and at higher 

 temperatures and pressures than the waters entering at a high level. There- 

 fore it is clear, if the rocks with which the deeper water comes in contact 

 can furnish metalliferous materials, that such water will be heavily loaded. 

 It follows from this, even if the amount of water which is furnished in a 

 short time to a fissure be small, that such water may furnish from the 

 country rock mineral material in solution much more than sufficient to 

 entirely fill a fissure during its long life. 



We now understand that, on the average, the amount of water entering 

 a fissure decreases from the level of ground water to its bottom, but that the 

 amount of mineral matter brought into the fissure by the water (but not 

 necessarily deposited) increases per unit volume from top to bottom. It is, 

 therefore, impossible to make a general statement as to whether more mineral 

 material is contributed to a trunk channel in its upper portion or in its lower 

 portion. Doubtless this varies in different cases. Other conditions than 

 amount of water or depth may be controlling factors. For instance, if 

 igneous rocks be intruded at high or low levels only, such rocks may 

 furnish conditions which determine the amount of metalliferous material 

 contributed by the waters. 



While the foregoing paragraphs imply that the lateral moA'ing waters 

 are also downward moving, this is meant only as a general rule. The 

 lateral movement may be accompanied by no downward movement. 

 Not only this, but lateral movement may be accompanied by an upward 

 component. Indeed, this is believed to be very frequently the case, espe- 

 cially so far as the main branch streams in the deeper parts of the zone of 

 fracture are concerned. In so far as there is an upward component in these 

 branch streams, the reactions which obtain are the same as those of the 

 trunk channels to be considered below. 



