764 C. R. VAN H1SE 



cannot be discriminated from the concentration resulting from 

 an actual downward transportation of the material of an earlier 

 concentration. In concluding this part of the subject, // is held 

 that the dow7iward tra?isportation of metals already i?i lodes is the 

 most important of the causes explaiiiing the character of the upper 

 portions of ore deposits ; and that their peculiar characters are cer- 

 taiidy due to the effect of descending waters. 



The concentrations by ascending and descending waters have 

 been considered as if they were mainly successive. In some 

 instances this may be the case ; but it is much more probable 

 that ascending and descending waters are ordinarily at work upon 

 the same fissure at the same time, and that their products are, to 

 a certain extent, simultaneously deposited. For instance, under 

 the conditions represented by this chart (Fig. 6) a first concen- 

 tration by ascending waters is taking place in the lower part of 

 the fissure, and a reconcentration by descending waters is tak- 

 ing place in the upper part of the fissure. Between the two 

 there is a belt in which both ascending and descending waters 

 are at work. The rich upper part of an ore deposit which is worked 

 in an individual case may now be in the place where ascending 

 waters alone were first acting, where later, as a consequence of 

 denudation, both ascending and descending waters were at work, 

 and still later, where descending waters alone are at work. 

 The more accurate statement concerning ore deposits produced 

 by ascending and descending waters, is, therefore, that ascending 

 waters are likely to be the potent factor in an early stage of the 

 process, that both may work together at an intermediate stage, 

 and that descending waters are likely to be the potent factor in 

 the closing stage of the process. 



Also, for the sake of simplicity in the consideration of the 

 concentrations I have disregarded the lateral elements of the 

 moving water. In many cases superimposed upon the verti- 

 cal movements in the fissures or other openings are lateral 

 movements, as a result of which the deposits instead of being in 

 vertical positions are inclined, often much inclined, and indeed 

 may be horizontal or even locally descending. Moreover the 



