CLINTON    ORES    OF    BIRMINGHAM    DISTRICT.  ALABAMA.  133 
STRUCTURE    AND    DISTRIBUTION    OF    FORMATIONS. 
A  very  much  generalized  section  beginning  at  the  Cahaba  coal  field 
on  the  southeast  and  passing  northwestward  across  the  valley  at  Bir- 
mingham would  expose  the  rocks  in  the  order  of  the  above  table, 
reading  from  the  top  down,  with  varying  dips  on  the  southeastern 
flank  of  a  nonsymmetrical  anticline  having  the  Conasauga  shale  and 
limestone  on  the  axis  of  the  fold.  A  minor  syncline  follows,  faulted 
down  to  the  southeast,  with  the  Knox  formation  held  in  the  basin. 
The  Conasauga  again  appears  to  the  northwest  of  the  Knox  syncline, 
and  bordering  the  Conasauga,  on  the  northwest  side  of  the  valley,  is 
an  extensive  overthrust  fault  which  brings  the  Lookout  sandstone 
and  coal  measures  in  contact  with  Cambrian  and  Ordovician  rocks. 
For  a  short  distance  northwest  of  the  fault  the  rocks  show  steep 
reversed  or  southeasterly  dips,  so  that  the  only  northwesterly  dips  dis- 
played in  the  section  are  in  connection  with  the  small  syncline  of  Knox 
cheri  and  dolomite  within  the  valley. 
Here  and  there  along  the  overthrust  fault  the  throw  has  not  been 
great  enough  to  engulf  the  Silurian  rocks  completexy,  and  at  such 
places  the  Rockwood  formation,  dipping  steeply,  is  exposed  in  a  nar- 
row outcrop.  The  presence  of  this  formation  in  places  on  the  north- 
west side  of  the  valley  has  given  to  the  ridge  the  name  West  Red 
Mountain.  In  the  section  outlined  above,  the  Rockwood  sandstone 
forms  the  crest  of  Red  Mountain,  with  the  Fort  Payne  chert  overlying 
it  and  the  Chickamauga  limestone  underlying  it,  making,  respectively, 
the  southeast  and  northwest  slopes  of  the  mountain.  All  the  forma- 
tions may  be  considered  to  extend  longitudinally  throughout  the 
valley,  in  practically  the  relationships  already  indicated.  The  minor 
folding  and  faulting  has  duplicated  the  strata  of  West  Red  Mountain 
in  the  southern  part  of  the  valley,  forming  McAshan  Mountain  and  a 
low  ridge  partly  buried  by  post-Paleozoic  sediments,  south  of  Dudley. 
At  the  northeast  end  of  the  valley  the  extent  of  outcrop  of  the  Rock- 
wood and  associated  strata  is  increased  by  the  synclinal  Blount  Moun- 
tain with  the  outlying  Cedar  Mountains,  and  by  the  synclinal  struc- 
ture north  of  Truss ville. 
Red  ore  occurs  in  practically  all  the  outcrop  areas  of  the  Rockwood 
formation,  but  only  in  Red  Mountain  has  it  been  found  of  sufficient 
thickness  and  purity  to  be  worked  on  an  important  scale.  The  work- 
ability of  the  ore  depends  largely  on  the  attitude  of  the  inclosing 
strata.  The  beds  of  Red  Mountain  dip  southeastward  at  moderate 
angles,  which  are  in  the  main  fairly  constant  for  a  mile  or  more  along 
the  strike  and  for  a  quarter  to  half  a  mile  down  the  dip.  Locally 
there  are  abrupt  " rolls"  or  changes  in  the  dip  due  to  minor  folds 
parallel  to  the  main  axis,  and  in  some  places  the  ore  has  been  so  faulted 
that  efforts  to  find  it  or  to  exploit  it  further  have  been  suspended. 
