COLLECTING AREA OF HOT SPRINGS 281 



This valley is from a mile to a mile and a quarter in width. About 

 two miles northeast of the hot springs where West Branch of Gulpha 

 Creek cuts through North Mountain, there is a limited area with an 

 elevation of 620 feet. The greater part of the surface, however, 

 stands above the 700-foot contour, and the highest hills exceed 800 

 feet. The highest elevation at which any of the springs emerge is 

 640 feet. 



Structure and rocks of the highland areas. — The general structure 

 of the highland area is that of a broad syncline with its trough in the 

 Arkansas Valley. The rocks are sandstone, limestone, and shale. 

 Those of the Boston Mountains and the area to their north lie for 

 the most part horizontal, but in the south half of the Boston Moun- 

 tains they dip perceptibly to the south, and in the Arkansas Valley 

 pass under several thousand feet of younger rocks. 



The general structure of the Ouachita area is that of an anticlino- 

 rium dipping southward under the Mesozoic and Tertiary rocks and 

 northward beneath those of the Arkansas Valley. The rocks are 

 intensely folded, to which, with erosion, is due the narrow valleys 

 and parallel ridges of the area. The folds in the main have an east- 

 west direction, but at Hot Springs and for some distance to the west, 

 their direction is northeast-southwest. The individual folds are not 

 continuous for great distances, but are short and overlap each other 

 laterally. Thrust faults, approximately parallel to the strike, and of 

 many hundred feet displacement, occur in the Ouachita Mountains 

 and the Arkansas Valley. The hot springs are located in the eastern 

 part of the Ouachita area. 



The stratified rocks of the Appalachian province are sandstone, 

 limestone, and shale. Their continuity is broken by faulting, and' 

 the rocks of the Cumberland Plateau dip away from the Cincinnati 

 arch toward the southeast. The rocks west of the Cincinnati arch 

 are practically horizontal, and are truncated along the Embayment 

 border. Against their truncated edges, the later rocks of the Em- 

 bayment area rest unconformably. 



Structure and rocks of the area about the hot springs. — Like the 

 remainder of the Ouachita region, the area about the hot springs is 

 intensely folded. The folds are closely compressed and all are 

 overturned to the south. As a result, the dips are to the north. Some 



