274 



The Collecting Area. — It follows from the above that the collecting 

 area must be in the near vicinity of the springs, and a study of the 

 topography, stratigraphy and structure thereabout locates it with reason- 

 able certainty. A glance at the section (Fig. 2) from Sugar loaf Mountain 

 southeastward through Hot Springs Mountain will indicate the collecting 

 area. The surface of the overturned, anticlinal valley between Sugar- 

 loaf and North Mountains is higher than the level of emergence of the 

 springs. The rocks outcropping over the area are the Bigfork chert and 

 the Polk Creek shale, the former occupying most of the area. 



The considerable thickness of the Bigfork chert, its much fractured 

 nature and the thin layers of which it is composed, all combine to make 

 it a water-bearing formation of unusual importance. The greater num- 

 ber of the fine springs in the Ouachita area between Hot Springs and the 

 western border of the state come from this horizon. In many places this 

 formation occurs in anticlinal valleys with its highly inclinal beds trun- 

 cated, affording the most favorable condition for the intake of water. A 

 glance at figure 2 will show that these conditions obtain in the area be- 

 tween North Mountain and Sugarloaf Mountain. In addition to the favor- 

 able structure for the reception of water there is the stratigraphic condi- 

 tion for its retention brought about by the overlying Polk Creek shale. As 

 a consequence of the topography, structure and stratigraphy the water is 

 collected in the basin shown in the map (Fig. 1), conducted through the 

 Bigfork chert beneath the North Mountain syncline, and rises in the Hot 

 Springs anticline, at the western end of which it emerges in the hot springs. 

 Including several of very weak flow, there are said to be seventy-two of 

 these springs, and they are confined to a narrow strip about a quarter of a 

 mile long. 



The exact location of the springs is attributable to the southwestern 

 plunge of the Hot Springs anticline, and as has been stated by Mr. Walter 

 Harvey Weed~ J probably to fracturing and possible slight faulting in the 

 process of folding, as shown in figure 3. 



While not relevant to the title of the paper, it might be added' that 

 the considerable number of dikes in the immediate vicinity of the hot 

 springs, the large number (eighty are known) only a few miles to the 

 south on and near the Ouachita River, and the areas of igneous rock at 

 Potash Sulphur Spring, Magnet Cove and other places, force the sugges- 



5 Loc. cit. 



