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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 anticlinorium 
dipping southward under the mesozoic and tertiary rocks, and northward 
beneath the Arkansas Valley. The rocks fer 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 of 
this 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 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 60 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 Flowage—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. Likewise 
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. 
