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844 C. A. FISHER GIAKT SPKIKGS AT GREAT FALLS^ MONTANA 



Field Analysis 



(Parts per million) 



Turbidity 



Color 



Iron 



Calcium 142 



Total hardness 97.30 



Total alkalinity 339.15 



Alkaline carbonates 



Allcaliue earth carbonates 339.15 



Sulphates 250 



Chlorides 9.96 



SOUGCK OF THE SPRINGS 



The source of the Giant springs has alwaj's heen a matter of consider- 

 ahle interest to people living in the vicinity of Great Palls, and repeated 

 attempts have been made to tap this water above the springs by sinking- 

 deep wells along its supposed underground course.^ It has been thought 

 by previous observers that the water of Giant springs is of deep-seated 

 origin, and that its source is far from the vent and in the neighboring- 

 mountains to the south and west. Such a source is improbable for the 

 following reasons : First, if the water came from a great depth it would 

 have a temperature higlier than 50 degrees, and would be expected to be 

 more highly mineralized than is shown hj the analyses. Second, the 

 geologic structure of the general region is unfavorable for such a source. 

 Southwest of Great Falls the rocks dip gently to the west toward the 

 mountains, instead of normally away from the uplift. The formation 

 from which the water issues (the Kootenai) in its westward extension 

 passes beneath a considerable thickness of impervious Colorado shales, 

 and in the vicinity of the Big Belt and Lewis ranges, Avhere a large 

 thrust fault occurs, it is buried by many hundred feet of sediments. 

 Under these conditions it is apparent that these porous beds of the 

 Kootenai and strata beneath them are completely sealed off from a sur- 

 face water supply which might be derived under more favorable struc- 

 tural conditions from melting snow on the mountain slopes. 



Soutli of Great Falls, between Giant springs and Little Belt moun- 

 tains, tlie geologic and structural conditions, although different from 

 those above described, are equally vinfavorable for the occurrence of deep- 

 seated springs an3'where in the vicinity of Great Falls. The general dip 



» E. S. Nettleton : Op. cit. 



