MURPHREE'S VALLEY; STRUCTURE. 29 



But as to the fact that these valleys have been thus produced, 

 there is no controversy. Every one of them presents in its 

 structure the most conclusive evidence of its truth that 

 science can demand. 



The most inattentive observer must have noticed that in 

 these valleys the inclining rocks, the stub ends of their strata, 

 are all dipping at some angle with the horizon, and in some 

 definite direction towards one or both sides of the valley. 

 And that if this dip of strata were extended outward and 

 upward, it would describe or produce a fold overarching the 

 valley; and possessing the form and volume which the fold 

 would have had, if it had not been eroded. Thus the struc- 

 ture and contour of all folds, however much eroded, can be 

 represented and studied, and ideally reproduced. 



These upward folds of strata present in their different 

 forms all degrees of flexure, from the incipient or symmetrical 

 fold, with its strata dipping equally on each side from a com- 

 mon anticlinal axis to a completely doubled, or folded axis, 

 lapped over to one side, with its strata all dipping one way, 

 and hence called "monoclinal." 



It has been shown in the Appendix to Squire's Report on 

 the Cahaba Coal Field, that the valley separating the Cdhaba 

 and the Warrior Coal Fields is, in the vicinity of Birming- 

 ham, a double one, Jones' Valley proper on the east and 

 Opossum Valley on the west. Both these component valleys 

 exhibit the regular Appalachian type of structure, i. e., they 

 are unsymmetrical anticlinal folds with the steeper side 

 towards the northwest. The axis of the anticlinal is conse- 

 quently found always near to the northwest edge of each 

 valley, and over the greater part of the area of each the 

 strata have a gentle dip towards the southeast, while the 

 much steeper northwest dips are confined to the extreme 

 northwestern edge of the valley. Very often the fold has 

 been pushed or lapped over towards the northwest, so that 

 the strata on the northwest side of the anticlinal axis stand 

 vertically, or are pushed beyond the vertical so as to be re- 

 reversed. When faulting occurs, as is very generally the 



