CLINTON  OR  RED  ORES  OF  NORTHERN  ALABAMA. 
173 
PROBABLE    METHOD    OF    ORIGIN. 
In  the  present  report  no  attempt  will  be  made  to  discuss  the  arguments  that  have  been 
dvanced  on  both  sides  of  this  question,  though  such  a  discussion  will  be  given  in  the  final 
jport  on  the  district.  For  this  paper,  however,  it  will  be  sufficient  to  say  that  in  the 
Titer's  opinion  the  ores  unquestionably  originated  at  the  same  time  as  their  inclosing 
jdiments,  and  that,  except  immediately  at  the  surface,  they  have  been  subjected  to  no 
iter  alterations  or  enrichments.  As  pointed  out  above,  this  theory  of  origin  implies  thai 
le  ore  bodies  are  practically  continuous  in  depth  and  that  they  could  be  followed  down 
:ie  dip,  in  a  syncline  or  basin,  until  the  dips  changed  and  the  workings  reached  the  surface 
n  the  other  side  of  the  fold.  The  practical  importance  of  this  is  obvious,  for  it  implies 
lat  the  ore  bodies  can  be  traced  and  measured  as  exactly  as  if  they  were  coal  seams  or 
mestone  beds.  The  amount  of  Clinton  ore  in  any  area  can  probably  be  determined  by 
geologist  within  5  or  10  per  cent,  and  estimates  of  red-ore  reserves  can  be  made  by  com- 
etent  men  with  a  degree  of  accuracy  impossible  in  dealing  with  the  magnetite,  hematite 
r  brown  ores  of  other  districts. 
"hard"  and  "soft"  ores. 
The  terms  "hard"  and  "soft,"  as  applied  to  the  two  principal  varieties  of  Clinton  ores, 
re  hardly  expressive  of  the  facts,  for  the  distinction  between  the  two  varieties  in  question 
i  based  on  differences  in  their  chemical  composition  rather  than  on  differences  in  hardness. 
The  red  ore  of  Alabama  is,  in  its  typical  or  "hard"  variety,  a  highly  limey  ore.  The 
re  beds  are  usually  underlain  by  comparatively  impervious  shales  and  in  most  places 
ip  at  fairly  high  angles.  These  conditions  favor  the  penetration  of  the  ore,  near  the 
nrface,  at  least,  by  percolating  water.  The  result  is  that  near  the  outcrop  and  for  some  dis- 
Etnce  down  the  slope  the  lime  carbonate  of  the  original  ore  is  largely  or  entirely  leached  out. 
'his  removal  of  one  constituent  of  course  increases  the  relative  percentages  of  the  remain- 
lg  less  soluble  constituents,  while  it  renders  the  ore  more  porous  and  friable.  The  result- 
lg  "soft  ore"  is  therefore  very  low  in  lime  and  correspondingly  high  in  iron  oxide.  A 
Bcondary  effect  of  the  change,  shown  best  when  the  cover  is  heavy  and  the  dip  low,  is  that 
he  overlying  shales  settle  down  slightly  as  the  bulk  of  the  ore  is  reduced,  so  that  on  the 
utcrops  the  ore  bed  often  appears  to  be  less  than  its  true  underground  thickness. 
RED  ORES  OF  NORTHERN  ALABAMA. 
GEOLOGY    OF    THE    DISTRICT. 
The  geologic  section  found  in  this  district  is  as  follows,  from  above  downward: 
Geologic  section  in  northern  Alabama. 
Formation. 
Age. 
Thickness. 
(angor  limestone 
Feet. 
(           500-800 
J 
ort  Payne  chert 
100-250 
hattanooga  shale . . . 
20-30 
i.ockwood  ("Clinton")  shale 
f            400-800 
\ 
hickamauga  ("Trenton")  limestone 
Ordovician 
[        (iOO-1,800 
oiox  limestone 
2,000-4,000 
Along  the  western  side  of  Lookout  Mountain,  in  Little  Wills  Valley,  the  rocks  dip  at  low 
ngles  (10°  to  30°)  toward  the  mountain;  on  the  eastern  side  the  rocks  dip  steeply  toward 
he  mountain  and  are  often  almost  vertical.  The  crest  of  Lookout  Mountain  is  composed 
i  the  Coal  Measures,  and  the  Bangor  limestone  outcrops  on  the  flanks  of  the  mountain  and 
mderlies  Little  Wills  Valley.  The  ridge  northwest  of  this  valley — the  "Red  Mountain" — 
hows  the  Fort  Payne  chert  along  its  southeastern  face,  while  the  Rockwood  beds,  including 
he  ore  seams,  form  its  crest  and  northwestern  flank. 
