VALLEY REGION ; DISTRIBUTION OF THE ROOKS. 161 
the Warrior to the Coosa Coal Field, through Birmingham, 
exhibits the main types of geological structure occurring in 
this part of the State, with the exception of those folds 
which show a prevailing dip in the northwest direction, of 
which mention has been made above, and which will be 
more particularly described in the proper place. 
It must, however, be borne in mind that the diagram is 
not intended to give with absolute fidelity the section across 
the valley along a particular narrow line, but is rather in- 
tended to give the extremes occurring within somewhat 
widely separated limits. To illustrate: the red ore of the 
Clinton formation appears in Little Oak Mountain “i” in 
one or two places only, in the Cahaba Valley; and still less 
frequently, or rather in a much more fragmentary way, does 
it appear on the flint ridge “a” west of Birmingham ; to the 
west of the fault beyond Opossum Valley we scarcely ever 
see so full a series as here shown of the beds between the 
fault and the Coal Measures in the vicinity of this cross 
section, though it appears further to the northeast towards 
Murphree’s Valley. Keeping these things in mind, we 
shall find the diagram of service. 
Beginning on the right hand of the diagram we see the 
Measures forming the northwestern border of the Coosa 
Coal Field overlooking with a steep face the valley to the 
northwest, the strata of the field dipping back to the south- 
east. Going thence to the northwest across the valley, we 
pass over the beds of the Sub-Carboniferous, Devonian, 
Trenton, Knox Dolomite, and Cambrian ; all dipping south- 
east, and all forming the half of a fold or anticlinal uplift. 
But next beyond the Cambrian we come to the strata of the 
Cahaba Coal Field, with a vertical dip, and in immediate 
contact with the Cambrian; an association of strata which 
could come only from a break and sliding of the beds on one 
side of the break upon and over those on the other side. 
‘We see here that we have only the one side of a fold, or arch, 
and that a break has occurred along the crest of this fold, and 
the southeastern side has glided up over the northwestern 
side. We also observe that the beds of the Coal Measures 
adjacent to this break stand at a vertical angle, as a result 
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