GEOLOGICAL HISTORY OF THE YELLOWSTONE PARK. 149 

 a nearly i)uit' scoroditc. agieeiug' closely with the theoretical composi- 



*:ioii : 



Ferric oxide 34. 94 



Arsenic acid 48. 79 



Water 16. 27 



100. 00 



Alteration of the scorodite into linionite takes place i-eadily, which 

 in turn nnderi;«>es disintegration by the wea-rini;- of the water, and is 

 mechanically carried away. So far as I know this is the only occur- 

 rence where scorodite has been recognized as deposited from the 

 waters of thermal si)rings. Although i)ure scorodite is only sparingly 

 preserved at a few localities in the Yellowstone Park, it is easily recog- 

 nized by its characteristic green color, in strong- contrast with the 

 white geyserite and yellow and red oxides of iron. After a little 

 piactice the mineral green of scoro<lite is not easily mistaken for the 

 vegetable green of the algeous growths. The latter is associated every- 

 where with the hot waters, while the former, an exceedingly rare min- 

 eral, is obtained only in small quantities after diligent search. In 

 xVmerica traces of arsenic have been reported from several springs in 

 Virginia, and quite recently sodium arseniate has been detected in the 

 hot s])rings of Ashe County, N. C. Arsenical waters of sufticient 

 strength to be beneficial for remedial purposes and not otherwise 

 deleterious ai'e of rare occurrence. In France the curative properties 

 of aisenical waters have long been recognize<l, and the famons sani- 

 taiiuni of La Ijourbonle in the volcanic district of tlu^ Auvergne has 

 achiexed a wide reputation for the el'licacy of its waters in certain 

 tbrins of nervous diseases. Ilygeia Springs, supplying the bath houses 

 at the hotel in the Lower Oeyser Basin, carries .'.i of a grain of sodium 

 arseniate to the gallon. The Yellowstone Park waters, while they 

 carry somewhat less arsenic than those of La I>ourboide, greatly excel 

 the latter in their enormous overflow. It is stated that the entire 

 discharge from the sjjrings of La Bourboule, amounts to 1,500 gallons 

 per minute. The amount of hot water brought to the surface by the 

 hot springs throughout the ])ark is by no means easily determined, 

 although during the i)rogress of our investigations we hope to make 

 an approximate estimate. Some idea of the amount of hot water 

 bionght to the surface ami carried off by the great drainage channels 

 may b*; tbrmed at the Midway Basin. According to the most accurate 

 measurements which could be made, the discharge from the caldron 

 of the Excelsior Geyser into the Firehole Kiver during the pa-st sea- 

 son amounted to 4, 100 gallons of boiling water ])er minute, and there 

 is no evidence that this amount has \aried within the last two or three 

 years. The sample of the Excelsior Geyser winter collected August 

 25, 1884, yielde<l .19 grains of sodium arseniati^ to the gallon. It is 

 impossible to say as yet what curative i)roi)erties these park waters 



