BROWN    IRON    ORES    OF    RUSSELLVILLE    DISTRICT,  ALA.  153 
Geologic  formations  of  northwestern  Alabama. 
System. 
Formation. 
Character. 
Thickness. 
Tertiary.   .               
Lafayette 
Loam  and  gravel 
Clay 
Limestone 
Sandstone 
Limestone 
Feet. 
100  + 
Very  thin. 
200  + 
350-400 
125-175 
Cretaceous  (?) 
( )ar  1  x >nif erous  (Mississippian ) 
series. 
Tuscaloosa  (?) 
[Bangor 
1  Hartselle 
j  Tusciimbia 
[Lauderdale 
Chert 
200  + 
The  rocks  lie  practically  flat  in  some  places  and  in  others  have  been 
thrown  into  broad,  gentle  folds  or  domes,  with  dips  as  great  as  10°. 
Where  any  systematic  structure  has  been  recognized  the  folds  appear 
to  trend  northwest-southeast  and  to  have  the  steeper  dips  on  the 
northeast  limb,  the  prevailing  dips  being  consequently  to  the  south- 
west. The  oldest  rocks  outcrop,  therefore,  at  the  north,  and  toward 
the  south  each  formation  passes  in  turn  below  the  next  younger  in 
the  series. 
The  Lauderdale  chert  shows  only  along  Tennessee  River,  while  the 
Tusciimbia  limestone  floors  the  wide  flood  plain  of  the  stream.  The 
area  of  Hartselle  sandstone  lies  along  Little  Mountain  or  the  divide 
between  the  main  Tennessee  Valley  and  the  Cedar  Creek  drainage, 
and  on  the  summit  of  the  divide  it  is  covered  by  Lafayette  loam. 
South  of  this  divide,  in  the  ore  district,  the  Bangor  limestone,  overlain 
by  Lafayette,  is  exposed  by  the  stream  at  the  headwaters  of  Cedar 
Creek  wherever  they  have  eroded  through  the  Lafayette  materials. 
Only  the  lower  portion  of  the  Bangor  limestone  is  exposed  about  Rus- 
sell ville,  and  here  it  is  thin  bedded,  shaly,  rather  argillaceous,  and  at 
many  places  contains  characteristic  Bangor  fossils.  The  full  thick- 
ness of  the  formation  is  not  represented  near  Russellville.  The  lime- 
stone appears  to  have  undergone  erosion  to  such  an  extent  that  a  very 
uneven  surface  existed  at  the  time  the  Lafayette  sediments  were 
spread  over  it.  The  Tuscaloosa  formation  has  not  been  positively 
recognized  in  the  ore  district,  but  certain  mottled  clays  that  occur 
along  the  Southern  Railway  near  the  Mississippi  State  line  have  been 
referred  to  the  Cretaceous.  The  Lafayette  materials  cover  the  greater 
part  of  the  area  here  considered.  Where  they  overlie  the  Bangor 
limestone  it  is  to  these  two  formations  that  the  greatest  interest  is 
attached,  for  in  such  situations  conditions  seem  to  have  been  favor- 
able to  the  accumulation  of  iron  ore.  The  Lafayette  sediments  prob- 
ably once  mantled  the  whole  area  as  far  east  as  the  Franklin-Lawrence 
county  line,  but  erosion  has  removed  the  material  along  creek  beds  and 
very  steep  hillsides,  so  that  now  the  thickest  and  most  continuous 
deposits  are  found  only  on  the  highest  parts  of  the  surface. 
