Arsenical Waters in the Yellowstone Parle. 173 



SiO„ - 49-83 



A1 2 3 .-.. 4-74 



Fe 2 3 18-00 



As o B __- .17-37 



H 2 -10-62 



Total 100-56 



The scorodite, as it is found deposited from these thermal 

 waters, is evidently a very unstable mineral and unless under 

 favorable conditions for its preservation slowly undergoes oxid- 

 ation, leaving an ochreous material carrying varying amounts 

 of arsenic acid. Alteration into limonite readily occurs and 

 the latter on exposure slowly disintegrates and is mechanically 

 carried away by the action of the running water. Although 

 pure scorodite is only sparingly preserved at a few localities in 

 geyser basins, its identity with the well determined species 

 from Joseph's Coat Springs is clearty made out, as it is easily 

 recognized by the characteristic green color in strong contrast 

 with the white geyserite and the yellow and red oxides of iron. 



It may be well to add here that the vegetable green derived 

 from the algeous growths found in nearly all the thermal 

 waters of the Park is not to be mistaken for the mineral green 

 of scorodite. The former is abundant in all hot spring areas, 

 while the latter, a comparatively rare mineral, is obtained only 

 in small quantities after careful search. 



During the progress of the work of the Geological Survey in 

 the Yellowstone Park, I have had collected a large number of 

 samples of the thermal waters from the most interesting geysers 

 and hot springs. These have since been subjected to search- 

 ing analyses by Dr. P. A. Gooch and Mr. J. Edward Whitfield 

 in the chemical laboratory of the Survey and their results 

 which are of great interest will be "published at an early date. 



Unfortunately no sample of the water from Joseph's Coat 

 Spring was obtained, but a careful analysis was made of the 

 water from the Constant Geyser. This water was collected 

 September 13, 1885 ; temperature 198° Fahr., the boiling point 

 at this altitude ; reaction slightly acid; specific gravity 1-0011. 



For the purpose of comparison there is added here the analy- 

 sis of the water from Old Faithful geyser in the Upper Geyser 

 Basin. Date of collection, September 1, 1884 ; reaction, alka- 

 line ; specific gravity, 1*00096. 



The analyses yielded as follows : 



