RECENTLY DISCOVERED HOT SPRINGS IN ARKANSAS 275 



with these springs, as with the longer-known ones at Hot Springs, 

 is the possible source of the heat. Is this due to (1) chemical 

 reactions within the rocks through which the water flows, or (2) 

 accumulated heat from friction, or (3) the presence of hot igneous 

 rocks beneath the surface, or (4) the breaking down or other 

 action of radium along the underground course of the water ? 



The unusual purity of the water seems conclusive evidence 

 against the first hypothesis. Granted that heat from friction 

 can be so accumulated as to bring the rocks to a high temperature, 

 there is no evidence of recent crustal movement within the region 

 where the springs occur. The location of the springs is doubtless 

 due in large measure to the fault, but this probably was formed at 

 the time of the folding, and if there ever was any localized heat 

 accompanying the crustal movements, it would be expected to 

 have been dispersed long ago. Dr. J. C. Branner, many years 

 ago, stated that the temperature of the waters at Hot Springs 

 is probably due to their coming in contact with masses of hot 

 rocks. 1 In support of this, there are outcropping igneous dykes 

 in and near the city of Hot Springs, and igneous areas of some 

 extent only a few miles distant. While there are no known igneous 

 rocks in the immediate vicinity of Caddo Gap, there are small 

 outcrops in the vicinity of Crystal Springs 18 miles to the north- 

 east, and a small igneous area near the town of Murfreesboro, 22 

 miles to the south. All these igneous outcrops are of Cretaceous 

 or post-Cretaceous age. So it seems not out of the possibilities 

 that the temperature of the water at Caddo Gap is due to its 

 flowing over hot igneous rocks. Whether or not the radium 

 hypothesis has any value probably could be determined by testing 

 the water for unusual radio-activity. This has not been done. 



1 Ann. Rep., Geol. Surv. of Ark. (1891), I, 10. 



