FENNER, THE WATCHVNG BASALT 149 



circulating waters some migration and recrystallization may have fol- 

 lowed, but the survival of such readily oxidizable compounds argues 

 strongly against any oxidizing property in the waters. They have been 

 observed with the naked eye associated with many members of the series 

 under conditions which imply contemporaneous deposition. When surface 

 waters have reached them, the ordinary oxidation products appear, but 

 when seen in their original condition, they are fresh and bright. 



One is apt to consider chalcopyrite as a mineral deposited from highly 

 heated solutions, and its formaition among the later minerals of the 

 Watchung series might be considered an argument that a high degree of 

 superheating still prevailed. This, however, is opposed to evidence from 

 other directions and does not appear necessarily true. W. Lindgren** 

 places pyrite and chalcopyrite among minerals persistent from igneous 

 conditions up to near surface, and also believes that they were formed at 

 times in the lower ground-water zone (zone of sulphide enrichment). 

 Direct evidence on the formation of chalcopyrite at moderate temperatures 

 is supplied by the observations of Daubree*^ upon copper minerals found 

 upon Roman coins at the hot springs of Bourbonne-les-Bains. The 

 temperature of the water in this case was only 58-68 °C. It carried in 

 solution chlorides and sulphates of alkaline bases and of lime and mag- 

 nesia, together with bromides, carbonates and silicates, and traces of 

 various other compounds. A number of copper minerals of recent deposi- 

 tion were recognized: cuprite, chalcocite, tetrahedrite, covellite, tennan- 

 tite and chalcopyrite. The last was recognizable both by its characteristic 

 yellow color and by its octahedral crystalline form. Mammelonated forms 

 were also deposited. 



The minerals so far studied appear to have been formed in the first 

 stage of recrystallization. Some of the new species were limited to a very 

 short period of deposition, while with others the range was more extended. 

 It is interesting to observe that all of the minerals resulting from the 

 primary consolidation of the magma were attacked and recrystallized 

 during this first stage of alteration. The chemical rearrangements, how- 

 ever, were not so complete as is implied in the disappearance of all the 

 mineral species. Of the two molecules which made up the plagioclase 

 feldspar of the basalt, anorthite was broken up, but albite remained stable 

 and recrystallized as such. Several of the molecules which formed the 

 mixed crystals of diopside probably merely suffered a change of phase in 

 their recrystallization into amphiboles. A portion of the magnetite was 



" Econ. Geol., vol. 2, pp. 122, 125, 1907. 



*" "Geologic Exp6rlmentale," Taris, pp. 72-86, 1879. 



