146  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1906,  PART    T. 
The  seam  at  Compton  ranges  generally  from  30  to  36  inches  in 
thickness,  with  a  thin  parting  of  shale,  irregular  in  position,  as  shown 
in  the  sections.  Locally  the  entire  seam  is  pinched  down  to  a  very 
few  inches  or  entirely  cut  out  by  downward  bulging  of  the  overlying 
shale,  which  at  such  places  has  a  concretionary  or  concentric  struc- 
ture. Such  structures,  which  result  in  the  local  disappearance  of  the 
ore  bed,  are  erroneously  termed  " faults"  by  the  miners,  but  there  is 
no  dislocation  of  the  beds  and  the  ore  is  usually  picked  up  again  if 
the  workings  are  driven  on  in  the  same  plane. 
The  extreme  southwestern  part  of  Birmingham  Valley  is  partly 
covered  by  Tuscaloosa  clay  and  Lafayette  loam,  but  in  places  buried 
rock  ridges  have  been  revealed  by  stream  erosion.  Extensive  pros- 
pecting by  drill,  test  pits,  and  slopes  has  been  carried  on  within  the 
last  two  years  in  tin4  region  between  Dudley  and  Big  Sandy  Creek] 
and  the  Rockwood  formation  has  been  shown  to  contain  workable 
beds  of  ore.  All  the  evidence  heretofore  obtained  regarding  the 
somewhat  obscure  geologic  relations  of  this  district  indicates  thai 
the  workable  beds  of  ore  are  in  a  strip  of  Rockwood  formation  corre- 
sponding with  McAshan  Mountain,  17  miles  to  the  northeast.  In 
other  words,  the  outcrop  of  the  formation  here  has  been  repeated 
byfoldingand  faulting.  In  the  region  south  of  Dudley  the  beds  are 
completely  overturned,  so  thai  the  dips  are  to  the  southeast.  This 
locality  is  in  the  Brookwood  quadrangle  and  has  been  more  fully 
discussed  in  a  previous  paper.0 
MINING   DEVELOPMENT. 
CHARACTER    AND    EXTENT. 
There  have  been  three  stages  in  the  development  of  the  mines  in 
the  Binningham  district.  The  first  stage  consists  of  trenching  the 
ore  beds  along  the  outcrop  on  the  crest  or  on  the  northwest  slope  of 
\l('(\  Mountain,  and  of  mining  the  ore  from  open  cuts  on  the  southeast 
slope.  The  ore  obtained  in  this  way  is  mostly  soft.  This  method 
of  mining  has  been  possible  only  where  the  overlying  beds  are  not 
more  than  20  Peel  thick  and  can  be  stripped  off  profitably.  Most 
of  the  mines  have  passed  beyond  this  stage,  but  at  the  Helen-Bess 
and  the  Green  Spring  workings  this  x^vy  profitable  type  of  mining 
may  st  ill  be  .seen. 
The  second  stage  of  development  combines  the  open  cut  and  incline 
with  underground  work.  A  very  fortunate  relation  between  the  Big 
and  Irondale  seams  and  tin1  topography  of  Red  Mountain  exists  in 
many  places,  particularly  in  the  northern  half  of  the  district ,  wher- 
ever the  dip  of  the  Rockwood  strata  is  approximately  the  same  as 
the  southeast  slope  of  the  mountain.     This  slope  is  cut  by  narrow 
"  Burchard,  K.  F..  Iron  ores  in  tin'  Brookwood  quadrangle,  Alabama:  Bull.  IT.  s.  Geol.  Survey  No. 
260,  1905,  pp.  321-334. 
