30 GEOLOGICAL SURVEY OF ALABAMA. 



case, the southeastern limb of the fold has been pushed up 

 over the northwestern limb, overriding and hiding from view 

 a greater or less proportion of the strata on that side of the 

 fault. 



One who had examined the structure of the valley in the 

 vicinity of Birmingham, would naturally expect to find that 

 its prolongation northeastward into Murphree's Valley would 

 not present any features essentially different ; yet in Mur- 

 phree's Valley we find the strata with gentle northwesterly 

 dips occupying the whole of the valley except its extreme 

 southeastern edge, where they stand either vertical or have 

 been reversed and dip back towards the northwest, the very 

 opposite in all respects to what has been described above as 

 typical for the Appalachian regions. 



The structure of Murphree's Valley is shown in figures 

 1 and 2, which represent sections across the valley, figure 1 

 near its head, and figure 2 in the central parts.* From the 

 inspection of those figures, it will be understood that to the 

 southeast of the valley lies the synclinal trough of Raccoon 

 or Blount Mountain, with its strata nearly horizontal, but in 

 reality gently sloping towards the northwest from the eastern 

 margin of the mountain down nearly to the vertical wall, 

 which, makes the common boundary at once of these meas- 

 ures and of Murphree's Valley. Straight Mountain, as this 

 vertical wall is called, is a part of the connecting limb be- 

 tween the synclinal of Raccoon Mountain and the anticlinal 

 of Murphree's Valley. I say a part, for the great fault shown 

 in the figures has cut out a greater or less proportion of the 

 strata of this connecting limb. In the sharp bending back 



*In constructing these sections to true scale, it has been found that some 

 of the formations occupy on the surface considerably more space than the 

 thickness of their strata, with the observed dips, would justify, This is par- 

 ticularly the case between the summit of west Red Mountain and the rim 

 of Sand Mountain, where, with the average dip observed at many of the 

 outcropping ledges (fifteen degrees to northwest), a thickness of 1,500 to 

 2,000 feet of subcarboniferous strata would be required, A liberal estimate 

 of the thickness of these formations, derived from many actual measure- 

 ments, would be 1,000 feet. We have thus been forced to the assumption 

 that the dips of some of the beds below the surface is considerably less than 

 that shown at the outcrop. E. A. S. 



