CLINTON    ORES    OF    BIRMINGHAM    DISTRICT,  ALABAMA. 
135 
analyses  show  at  the  left  a  typical  hard  ore  and  at  the  right  a  typical 
soft  ore,  with  intermediate  or  semihard  grades  between  them: 
Analyses  of  Clinton  iron  ores,  showing  gradation  from  hard  to  soft  ore. 
Iron,  metallic  (Fe) 
Silica  (Si02) 
Alumina  (A1203)... 
Lime  (CaO.) 
Manganese  (Mn) . . 
Sulphur  (S) 
Phosphorus  (P) . .. 
1. 
2. 
3. 
37.  00 
45.70 
50.  44 
7.  14 
12.76 
12.  10 
3.81 
4.74 
6.  06 
19.20 
8.  Tit 
4.65 
.  23 
.  19 
.21 
.08 
.08 
.07 
.30 
.  49 
.40 
54.  70 
13.70 
5.  66 
.50 
.  23 
08 
.  10 
These  analyses  represent  ore  samples  from  a  single  slope  on  the 
same  horizon  of  the  Big  seam  in  Red  Mountain,  near  Birmingham,  at 
distances  respectively  of  540,  480,  420,  and  240  feet  from  the  mouth 
of  the  slope.  Beyond  the  point  at  which  No.  1  occurs  there  is  no 
great  change  in  the  character  of  the  ore,  for,  as  mined  at  present,  the 
seam  carries  an  average  of  35  per  cent  metallic  iron  in  this  particular 
mine. 
Although  the  soft  ore  carries  a  higher  percentage  of  iron,  the  hard 
ore  has  the  advantage  of  containing  almost  or,  in  places,  quite  enough 
lime  to  flux  the  silica  that  it  contains.  In  case  a  hard  ore  contains 
more  lime  than  is  needed  to  flux  its  silica  soft  ore  or  brown  ore  (limon- 
ite)  may  be  added  to  the  burden  to  take  up  the  excess  of  lime. 
RELATIONS  AND   CHARACTER   OF  THE   ORE  BEDS. 
The  Rockwood  formation,  in  which  the  ores  occur,  is  extremely 
variable  in  thickness  and  in  the  details  of  its  stratigraphy,  although 
the  presence  of  beds  of  hematite  somewhere  within  the  formation  is 
a  remarkably  persistent  feature,  not  only  throughout  the  length  of 
the  Appalachians,  but  in  rocks  of  equivalent  age  in  Wisconsin  and 
New  Brunswick.  In  Alabama  the  formation  is  thickest  at  the  north 
and  there  contains  beds  of  limestone,  which  give  way  to  sandstone 
with  the  thinning  of  the  formation  toward  the  south:  the  proportion 
of  shale  in  the  Rockwood  is  also  greatest  in  the  northern  part  of  the 
State. 
DESCRIPTION    OF    THE    ORE-BEARING    FORMATION. 
BEDS  ON  RED  MOUNTAIN. 
Within  the  district  here  considered  the  Rockwood  formation  shows 
notable  variations  in  composition  from  northeast  to  southwest,  as  is 
indicated  by  the  following  seven  sections  on  Red  Mountain,  beginning 
northeast  of  Birmingham  and  continuing  at  irregular  intervals  for 
about  38  miles  to  the  southwest.  In  each  section  the  observed  thick- 
ness has  been  corrected  for  the  dips,  which  range  between  20°  and 
50°,  so  thai  the  computed  thickness  closely  represents  the  actual 
thickness  of  the  beds. 
