440 KIRK BRYAN 



are exposed at Magnet Cove, Potash Sulphur Springs, and as 

 dikes in the vicinity of the Hot Springs. 



In 1 910, Purdue^ published an elaborate paper on the origin of 

 the hot water. He follows Weed in believing that the water has a 

 meteoric origin and that in its passage through the ground derives 

 heat from uncooled masses of igneous rock. He goes a step farther 

 and outlines the structural conditions for the collection and trans- 

 mission of the water. He believes that the water falls as rain in 

 the anticlinal valley between North and Sugarloaf Mountains, 

 where it is absorbed by the Bigfork Chert. "The considerable 

 thickness of this chert, its much fractured nature, and the thin 

 layers of which it is composed all combine to make it a water 

 bearing formation of unusual importance." 



The water having been collected in this formation is confined 

 by the impermeable overlying Polk Creek and Missouri Mountain 

 shales. Thus confined the water is conducted beneath the syncline 

 of North Mountain, where it most probably comes in contact with 

 some uncooled mass of igneous rock. Purdue suggests, but 

 rejects the hypothesis that the water is expelled by the cooling 

 of such an igneous mass. 



Lindgren,^ in 1919, accepts Purdue's views and considers that 

 the springs have "clearly derived their saline constituents from the 

 surrounding sedimentary rocks." 



Another hypothesis should be advanced. On this hypothesis 

 the water is of deep-seated origin derived from a covered mass of 

 igneous rock intruded into the sediments, but not showing at the 

 surface, which discharges water expelled from its molten interior 

 by the gradual crystallization of its mass, or the water is derived 

 from a deeper less definite but similar mass and rises to the upper 

 crust through a deep, probably fault, fissure. Such water is com- 

 monly called juvenile, i.e., new water coming to the surface for 

 the first time. 



^ A. H. Purdue, The Collecting Area of the Waters of the Hot Springs, Hot 

 Springs, Arkansas," Jour, of Geol, Vol. XVIII, No. 3 (1910), pp. 278-85, 3 figs. Also 

 Indiana Acad. Sci. Proc. 1909, pp. 269-75, 3 figs. 1910. 



^Waldemar Lindgren, Mineral Deposits, p. 90. New York, 1919. 



