GRAY    IKON    ORES    OF    TALLADEGA    COUNTY,  ALA.  181 
strike,  not  over  100  yards  distant,  there  is  a  bed  of  quart  zi  tic  gray  ore 
which  seems  to  be  a  direct  prolongation  of  the  bed  of  pyrite.  In  this 
place,  at  least,  it  would  seem  that  the  gray  ore  had  been  derived  from 
pyrite,  perhaps  having  been  limonite  in  an  intermediate  state.  Van 
Hise,  however,  in  his  monograph  on  metamorphism "  notes  that 
oftentimes  the  sulphides  may  be  directly  converted  into  hematite 
through  heat  and  pressure.  It  is  possible,  therefore,  that  the  pyrite 
may  have  altered  directly  into  hematite  without  having  passed  into 
the  form  of  limonite.  Further  evidence  along  the  same  line  is 
afforded  by  the  ore  itself,  which  in  many  places  shows  areas  of  limon- 
ite that  were  apparently  derived  from  an  iron  sulphide, 
From  the  facts  just  stated  it  would  seem  that  the  iron  ores  are  pre- 
sumably derived  from  two  sources.  The  first  of  these  sources  is 
pyrite,  which  may  have  been  formed  through  the  precipitation  of  iron 
solutions  by  the  decomposition  of  organic  matter  in  the  quartzite. 
The  second,  and  probably  by  far  the  most  important  source,  was 
limonite,  which  was  collected  in  certain  horizons  where  relatively 
impervious  strata  succeeded  relatively  porous  beds  and  so  arrested 
the  free  circulation  of  the  descending  ore-bearing  solutions.  These 
limonite  beds  were  subsequently  metamorphosed  by  the  great  folding 
and  fault  movements  that  the  region  suffered  during  the  period  of 
mountain  building.  Where  the  metamorphism  was  moderate  and 
where  there  was  sufficient  oxygen  the  limonite  was  simply  dehy- 
drated into  hematite,  Where,  however,  the  amount  of  oxygen  was 
not  quite  sufficient  to  oxidize  all  the  iron  the  limonite  changed  into 
hematite  with  some  magnetite,  the  relative  amount  of  the  two  min- 
erals depending  upon  the  amount  of  oxygen  present. 
Some  proof  of  this  hypothesis  is  afforded  by  the  distribution  of  the 
different  ores.  At  Columbiana,  where  the  rocks  are  but  slightly 
metamorphosed,  the  ore  is  a  reddish  hematite  with  practically  no 
magnetite.  In  the  range  near  Mesaba  and  Emauhee  the  rocks  are 
more  metamorphosed  and  the  magnetite  increases  perceptibly.  In 
another  range  in  the  very  highly  metamorphosed  belt  near  Chula- 
finnee,  in  Cleburne  County,  an  iron  ore  which. seems  to  occur  under 
nearly  the  same  conditions  as  the  ore  in  Talladega  County  is  almost 
entirely  magnetite, 
ECONOMIC  IMPORTANCE  OF  THE  ORES. 
In  regard  to  the  economic  importance  of  these  ores  there  are  four 
main  points  which  must  be  considered,  namely,  cost  of  mining, 
value  of  ore,  cost  of  smelting,  and  opportunities  for  marketing  prod- 
uct, To  determine  the  cost  of  mining  it  is  necessary  to  consider 
the  charges  for  timber,  powder,  steel,  labor,  handling  of  ore  and 
waste  underground  and  on  the  surface,  and  pumping.     The  cost  for 
"Mon.  U.  S.  Geol.  Survey,  vol.  47,  1904. 
