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of the city of Hot Springs stands on this formation, only the waters of 

 those springs that issue at the lowest levels move through it. 



Structure and Rocks of the Highland Area. — The general structure of 

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

 kansas Valley. The rocks of the Boston Mountains and the area to their 

 north lie for the most part horizontal, but in the south half of the Boston 

 Mountains they dip perceptibly to the south, passing in the Arkansas Val- 

 ley under several thousand feet of younger rocks. 



The general structure of the Ouachita area is that of an antielinorium 

 dipping southward under the mesozoic and tertiary rocks, and northward 

 beneath the Arkansas Valley. The rocks for the most part are intensely 

 folded, to which, with erosion, is due the narrow valleys and parallel 

 ridges of the area. The hot springs are located in the eastern part pf 

 this area. 



The folds in the main have au east-west direction, but at Hot Springs 

 and for some distance to the west their direction is northeast-southwest. 

 The individual folds are as a rule 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, are com- 

 mon in the Ouachita Mountains and the Arkansas Valley. 



Structure 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 are all overturned to the south. As 

 a result the dips are to the north. Some of these are as low as 15 de- 

 grees, and they seldom exceed GO degrees. This means that at the points 

 of greatest overturning the rock layers lie literally upside down, and in 

 folding have described an arc of 165 degrees. 



Possibilities of Ground-Water Floicage. — While the altitude of the 

 Boston Mountains is sufficient to give the ground-water enough head for 

 it to emerge at the height and distance of the hot springs, the intervening 

 structure makes such impossible. The closely compressed folds, overlap- 

 ping, and faulting of the Ouachita area are such as to prevent the unin- 

 terrupted movement of ground-water except for short distances. LikeAvise 

 the stratigraphy, structure and topography to the south of the hot springs 

 eliminate that area as a possible source of the water ; and the same is 

 true of the highlands of central and eastern Kentucky. Tennessee and 

 Alabama and the intervening area. 



