VALLEY REGION DETAILS ; SHADES VALLEY. 175 
of the first anticlinal of the valley, and adjacent to it towards 
the west but separated from it by a fault, is the flint ridge 
of the North Highlands, (Knox Dolomite). As we have al- 
ready said this ridge isin structure a synclinal, with the 
axis close to the southeastern border, and with most of the 
strata on that side of the axis overridden and concealed by 
the Cambrian of the other side of the fault, a case exactly 
analogous to what we have seen along the southeastern 
border of the Cahaba Coal Field. In the fault above spoken 
of the adjacent halves of the anticlinal of Jones’ Valley and 
of the synclinal of the flint ridge, are engulfed more or less 
completely, though we commonly find along the eastern 
face of the flint ridge a narrow belt of vertical or nearly ver- 
tical rocks which belong to the synclinal, and are the only 
remnants of its eastern half. As is the case on the corres- 
ponding side of the Cahaba Field, these vertical measures 
very rapidly flatten down and begin to rise on the other dip, 
so that the center or axis of the anticlinal is very close to 
this eastern edge. 
As the name indicates, this ridge is formed mostly of the 
flint or chert of the Knox Dolomite, but there may be found 
at intervals between Hast Lake and Bessemer, traces of the 
rocks of other overlying formations, Trenton and Clinton, 
showing that these were also involved in the foldings, but 
have in great measure been removed by denudation. 
Upon this flint ridge at several points, and beyond Besse- 
mer in the Salem Hills, we see great masses of a peculiar 
rock, made up of angular fragments of the chert of Knox 
Dolomite cemented together into a firm and compact rock. 
This breccia is at the top of the Knox Dolomite, or perhaps 
it would be better to say, at the base of the next higher 
series, the Trenton, since it is made of fragments of the 
Knox Dolomite, and must therefore be younger. 
This flint ridge is a marked feature of Jones’ Valley, and 
extends without serious break from near Village Creek at 
Birmingham, to Valley Creek near Bessemer. Northeast of 
the former creek it is seen again, and southwest of Valley 
Creek it appears in the Salem Hills. At the two places 
mentioned the ridge is cut by the creeks, down through a 
good part of the chert of the Knox Dolomite into the red 
