275 
tion upon one that the waters of the springs owe their temperature to 
passing over hot rocks or the vapor from such in some part of their under- 
ground course.® The fact that these are practically’ the only hot springs 
within the Ouachita area, though there are scores of cold springs issuing 
from the same formations and under practically the same geologic rela- 
tions, gives this suggestion great weight; but inasmuch as some of the 
springs are said to be unusually radio-active, there is the alternative sug- 
gestion that atomic decomposition in igneous rocks (which may have lost 
their magmatic heat) is the source of the high temperature of the water. 
Fayetteville, Ark. 
6 Dr. J. C. Branner has already called attention to this as the probable source of the heat. 
See Geol. Surv. of Ark., Report on Mineral Waters, pp. 9 and 10. 
7 Recently a spring, said to have a temperature of 98° to 100° F., has been discovered 
issuing from the Arkansas novaculite in the bed of the Caddo River, at Caddo Gap, Mont- 
~omery County. 
