284 



A. H. PURDUE 



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 number 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 inclined beds truncated, affording the most favorable condition 

 for the intake of water. A glance at Fig. 2 will show that these con- 

 ditions obtain in the area between North Mountain and Sugarloaf 

 Mountain. In addition to the favorable structure for the reception 

 of water, there is the stratigraphic condition 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. i), conducted through the Bigfork chert 



/Mile 



J 



Fig. 3. — Northeast-southwest (longitudinal) section of Hot Springs Mountain, 

 showing the hypothetical water conduits at the plunging end of the anticline. Sym- 

 bols, same as in Fig. 2. 



beneath the North Mountain syncline, and forced up into the Hot 

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

 springs. Including several of 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 south- 

 western plunge of the Hot Springs anticline, and as has been stated 

 by Mr. Walter Harvey Weed' probably to fracturing and possibly 

 slight faulting in the process of folding, as shown in Fig. 3. 



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

 the considerable number of dikes in the vicinity of the hot springs, 

 the large number (eighty are known) only four miles to the southeast, 



I Loc. cit. 



