754 C. R. VAN HISE 



present. At some distant time in the past suppose the surface and 

 level of groundwater, instead of being as shown, were at much 

 higher levels, having since been greatly lowered by the processes 

 of denudation. Where would the upper part of the fissure shown, 

 the water of which is descending, be with reference to the circu- 

 lation at that time ? It would be where the lower part of the 

 fissure now is, would it not ? It would be where the waters are 

 ascending, as shown in the lower part of the fissure. ■ Therefore 

 for the part of the fissure where the water is now descending it 

 may be that the first contribution of ore was made by ascending 

 waters, although descending waters are now the only impor- 

 tant factor. But as denudation went on the condition would 

 gradually change. The part of the fissure under consideration 

 would pass through a stage in which the waters would mainly 

 come in laterally. As denudation went still farther the waters 

 might all be descending, and in the extension of the fissure 

 below the waters might come in laterally, and still deeper might 

 be ascending. We must now still further amplify our theory, 

 must we not ? To explain the entire ore deposit we have to 

 consider all parts of the ore deposit throughout its entire his- 

 tory. At present ore deposition by descension, by lateral secre- 

 tion, by ascension, is somewhere occurring in the fissure ; but not 

 only is this the case, but all have worked in turn in the upper 

 part of the deposit. Therefore this further complicates the 

 theory of ore deposition. 



Now I wish to give some facts as to the actual occurrences 

 of ore deposits before I go to the next step in theory. At 

 Butte, Mont., are famous copper deposits. In the copper 

 lodes of this district, in the very upper part of the deposits, 

 above the level of groundwater, there were oxidized ores which 

 carried high values in silver and gold, but very low values in 

 copper. At and a short distance below the level of ground- 

 water there were very high values in copper as sulphides. 

 "There follows below a region of varying height, of valu- 

 able rock, which again slowly deteriorates in depth ; this deteri- 

 oration, however, being so retarded finally as to be scarcely 



