438 KIRK BRYAN 



other lines of springs simply mark the position of more open joints 

 like the joints visible in the outcrops but that all the joints are 

 parallel to and related in origin to a thrust fault which lies to the 

 south of them. Doubtless similar cracks might have been formed 

 by simple folding. However, the very absence of outcrops in the 

 western part of the hospital grounds seems to be an argument in 

 favor of faulting which would shatter and comminute the rocks along 

 the line of the fault and thus make them more susceptible to 

 erosion. Folding without faulting, on the other hand, would give a 

 a double thickness of sandstone which would be almost sure to 

 outcrop, and this same folding would presumably so shatter the 

 sandstone as to make the line of the fold the locus of springs. 



Whatever the ultimate origin of the water, it emerges through 

 the cracks and joints of the Hot Springs sandstone and mainly 

 along the strong jointing parallel to and probably related in origin 

 to the postulated thrust fault. The bearing of these relations 

 on development of the springs is obvious. 



THEORIES OE ORIGIN OF THE HOT WATER 



In 1804 William Dunbar^ and Doctor Hunter visited the 

 springs. They observed that the mountain was "principally 

 siliceous, some part of it being of the hardest flint, others a free- 

 stone extremely compact and solid and of various colors. The 

 base of the hill, and for a considerable extent, is composed of a 

 blackish blue shistus, which divides into perpendicular lamina, 

 like blue slate." They make extensive comments on the tufa 

 deposited by the water. They estimated the flow of all the springs 

 at 165 gallons per minute or 237,600 gallons daily. They suggested 

 chemical reactions as the cause of the heat of the water, having 

 found no evidence of volcanic action in the vicinity. 



In 1806 a writer relates that he saw a volcanic outburst and 

 streams of molten rock near Hot Springs. He is generally dis- 

 believed by later writers.^ 



' Thomas Jefferson, Message of the Presidetit of the U.S. Communicating Dis- 

 coveries Made in Exploring the Missouri, Red River, and Washita by Captains Lewis and 

 Clark, Doctor Sibley, and Mr. Dunbar, etc. A. & G. Way, printers, Washington, 1806. 



^ New York Medical Repository, Vol. Ill, No. i (1806), pp. 47-50. 



