94 HOT SPRINGS, ARKANSAS. 



upward. The composition of the gases given off by the waters shows 

 that they contain atmospheric air as well as carbon dioxide. That the 

 heat of the waters is due to the heat developed by the folding of the 

 rocks, which is the theoiy given to account for the heat at the Virginia 

 Hot Springs, is not probable, for the folding at Hot Springs is not 

 more intense than elsewhere in the mountain regions of Arkansas, and 

 no evidence of hot spring action has been found at any other locali- 

 ties except where igneous rocks are present. 



It is believed that the heat comes from a great body of still heated 

 igneous rocks intruded in the earth's crust by volcanic agencies and 

 underlying a large part of central Arkansas. The existence of such a 

 mass is shown by the great bodies of granite seen at Potash Sulphur 

 Springs and Magnet Cove, where the rocks have been exposed by the 

 wearing down of the overlying sediments, though the igneous rocks 

 seen were of course long since cooled. At Magnet Cove, moreover, 

 there are tufa deposits which show the former occurrence of hot 

 springs. 



This hypothesis is strengthened by the occurrence of intrusive dikes 

 at various localities about the springs, and their trend and occurrence 

 indicate that the molten material which filled the fissures did not come 

 from the bodies of rock now exposed at Potash Sulphur Springs or at 

 Magnet Cove, but had some deep-seated source, whose location is indi- 

 cated by the dikes as being approximately under the hot springs. Deep- 

 seated waters converted into vapors by contact with this "batholith" 

 of hot rock probably ascend through fissures toward the surface, where 

 they probably meet cold spring waters which are heated by the vapors. 

 As the igneous dikes near by are fissures reaching down to this great 

 mass of igneous magma which have been filled by it to form dikes, it is 

 not unreasonable to suppose that fissures extend down to the now solid 

 but still hot igneous mass. 



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