MANGANESE IN GOLD DEPOSITS 21 



give off gases equal to several times their own volume. While 

 further inquiry of this character is desirable, it is probably true 

 that in general but little chlorine is present in such gases. But 

 gases from certain volcanic rocks, such as obsidian, often contain 

 a high proportion of chlorine and chlorides. Albert Brun 1 has 

 shown that some of the Krakatoa lavas yield gases which equal 

 about one-half the volume of the rock, and that more than half 

 of such gases consist of chlorine, hydrochloric acid, and sulphur 

 monochloride. The average chlorine content of igneous rocks 

 is, according to F. W. Clarke, 0.07 per cent. 



Chlorine is present in nearly all natural waters. Its chief 

 source is from finely divided salt or salt water from the sea and 

 from other bodies of salt water. The salt is carried by the wind 

 and precipitated with rain. 2 The amount of chlorine in natural 

 ponded waters varies with remarkable constancy with the distance 

 from the shore. The isochlores parallel the shore line with great 

 regularity, as shown by the map in Jackson's report. The chlorine 

 contributed from this source even near the seashore appears small; 

 but it may be further concentrated in the solutions by evaporation 

 or by reactions with silver, lead, etc., forming chlorides, which 

 in the superficial zone may subsequently be changed to other com- 

 pounds. Penrose, 3 discussing the distribution of the chloride ores, 

 pointed out long ago that they form most abundantly in undrained 

 areas. 



Carbonates and alkaline earths. — The analyses in Table I do 

 not include those from mines in limestones. The carbonate 

 reported gives an average of 77 parts per million. Even in igneous 

 rocks considerable calcium (295 parts per million) and magnesium 

 (242 parts) are carried by the waters. They are derived in part 

 from reactions between the acid sulphates and the silicates of the 

 wall-rock. 



1 " Quelques recherches sur le volcanisme aux volcans de Java. Cinquieme 

 partie. Le Krakatau," Archives des sciences physiques et naturell.es, Geneve, XXVIII, 

 No. 7 (juillet, 1909). 



2 D. D. Jackson, "The Normal Distribution of Chlorine in the Natural Waters 

 of New York and New England," Water Supply and Irrigation Paper No. 144, U.S. 

 Geological Survey (1905). 



^Journal of Geology, II, No. 3, 314 (April-May, 1894). 



