HOT WATER SUPPLY OF THE HOT SPRINGS 445 



the surface. As postulated by Purdue/ the water falls on the Big- 

 fork Chert in the anticlinal valley between West and Sugarloaf 

 mountains, is absorbed in the chert and passes below the syncline of 

 North Mountain and arises in the anticline of Hot Springs Moun- 

 tain. The course of the water is shown in Figure 2. The contact 

 of the Bigfork Chert with overlying beds along the southwestern 

 base of Sugarloaf Mountain (see the geologic map, Fig. i), is about 

 850 feet above sea-level. Other parts of the chert outcrop as low 

 as 650 feet, this being the elevation at the point nearest the hot 

 springs. The hot springs break out at elevations between 600 

 and 694 feet. Parts of the intake area are thus at the same level 

 as the springs and below some of them. Assuming the greatest 

 difference 200 feet, it is doubtful if 200 feet of head or 80 pounds of 

 pressure per square inch is sufficient to force the water through 

 the channel assumed by this hypothesis. Even if this head is 

 sufficient, it is remarkable that the water comes across the strike 

 under the North Mountain syncline, when it could swing north- 

 eastward and around North Mountain into the Hot Springs 

 anticline without notable change in level. This path is possible 

 because the North Mountain syncline plunges southwestward 

 and near the "Gorge" of West Branch brings the Bigfork chert 

 near the surface. From this analysis it appears that the postulated 

 structure is a very special hypothesis of dubious validity. 



Similarly the hypothesis calls for an uncooled mass of igneous 

 rock below the North Mountain syncline to supply heat, for the 

 internal heat of the earth would not raise the temperature the 

 required amount unless the water descended to 5,000 feet and then 

 came to the surface without loss of temperature. Obviously the 

 postulation of such an igneous body is a special hypothesis, par- 

 ticularly when apparently the water could easily avoid the plug by 

 a change in route as shown before. The occurrence of igneous 

 masses in the neighborhood as at Magnet Cove and Potash Sulphur 

 Springs adds probability to this hypothesis, but these intrusions are 

 thought to be of Cretaceous age, a time so remote that it is stretch- 

 ing credulity to believe that rocks of this age are still uncooled at 

 moderate depths. 



' A. H. Purdue, op. cit. 



