CLINTON    ORES    OF    BIRMINGHAM    DISTRICT,  ALABAMA.  131 
strong  contrast  with  the  irregular,  roughly  dissected  topography  of 
the  coal  fields. 
The  valley  topography  is  characterized  by  long,  narrow,  canoe- 
shaped  troughs,  in  general  parallel  to  each  other  and  separated  by 
well-defined  ridges.  The  trend  of  the  valleys  is  approximately  N.  30° 
E.  Their  form  is  directly  dependent  on  the  geologic  structure  and 
lithology  of  the  underlying  rocks.  They  are  developed  mainly  on  the 
softest  and  most  soluble  rocks,  along  the  axes  of  anticlines,  the  most 
enduring  strata  on  the  limbs  of  the  folds  forming  the  rims  of  the  val- 
leys. At  distances  of  2  to  5  miles  apart  openings  or  '  'gaps/'  some  of 
which  extend  to  the  valley  level,  are  cut  at  right  angles  through  the 
ridges  and  afford  convenient  passageways  between  the  valleys. 
Birmingham  Valley,  the  largest  and  from  an  industrial  standpoint 
the  most  important  of  these  valleys,  extends  from  the  vicinity  of 
Springville  on  the  northeast  beyond  Vance  on  the  southwest,  and 
from  the  Warrior  coal  field,  or  Sand  Mountain,  on  the  northwest  to 
the  Oahaba  coal  field,  or  Shades  Mountain,  on  the  southeast.  To 
the  southwest  the  inclosing  ridges  pass  below  unconsolidated  Cre- 
taceous and  Tertiary  clays  and  sands;  to  the  northeast  lies  Blount 
Mountain.  Birmingham  Valley  thus  has  a  length  of  nearly  75  miles, 
an  average  width  of  more  than  6  miles,  and  an  area  of  nearly  500 
square  miles.  This  valley  is  divided  into  minor  valleys  by  low  ridges, 
such  as  Red  Mountain  and  West  Red  Mountain,  Flint  Ridge,  and 
Cemetery  Ridge,  all  due  to  folding  and  faulting  of  the  main  anti- 
cline; and  this  complicated  structure  finds  expression  in  Shades  and 
Roups  valleys  at  the  southeast  and  southwest  ends  and  in  Jones  and 
Opossum  valleys  at  the  northeast  and  northwest  ends,  respectively. 
This  system  of  valleys  varies  in  the  altitude  of  its  lowest  levels  from 
about  400  feet  at  the  southwest  to  700  feet  at  the  northeast  end. 
These  altitudes  are  higher  than  the  lowest  levels  cut  by  streams  in 
the  dissected  plateau  country,  and  consequently  streams  do  not  flow 
lengthwise  through  the  valleys,  but  after  flowing  a  short  distance 
break  through  the  bordering  ridges  and  flow  out  into  the  lower 
country  beyond.  Birmingham  Valley,  on  account  of  its  relatively 
high  altitude,  really  forms  a  divide,  since  its  northwestern  portion  is 
drained  by  Warrior  River  and  its  southeastern  portion  by  Cahaba 
River. 
Red  Mountain,  the  main  minor  ridge  within  Birmingham  Valley, 
furnishes  nearly  all  the  red  ore  smelted  in  the  district,  and  the 
Woodstock  area,  in  the  southwestern  portion  of  the  valley,  produces 
the  major  part  of  the  brown  ore.  Coking  coal  is  mined  in  the 
Warrior  coal  field,  only  a  few  miles  distant  from  the  furnaces.  Dolo- 
mite and  limestone,  suitable  for  fluxing,  occur  in  the  valley  rocks 
below  and  above  the  red  ore.  Only  in  the  southern  Appalachian 
iron-ore    districts    is    there    grouped    this    series    of    deposits,   each 
