436  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull. 225. 
In  this  middle  or  Demopolis  division  of  the  Selrna  formation  the 
fossils  are  rarer  than  in  either  of  the  others,  oysters  and  anomias  being 
the  most  common  forms.  This  variety  of  the  rock  forms  the  bluffs 
along  Alabama  River  from  Elm  Bluff  up  to  Kings  Landing.  It  is 
seen  in  its  most  typical  exposure  at  White  Bluff,  where  it  is  at  least 
'200  feet  in  thickness  and  makes  on  the  right  bank  of  the  river  an 
almost  perpendicular  bluff.  On  Tombigbee  River  it  extends  from 
near  Bartons  Bluff  past  Demopolis  up  to  Areola  and  Hatch s  1  Muff. 
Its  lowermost  beds,  a  compact  limestone  of  great  purity,  form  the 
upper  parts  of  Bartons  and  Hatchs  bluffs.  On  Little  Tombigee  River 
the  same  rock  makes  the  celebrated  bluffs  at  Bluffport  and  at  Jones 
Bluff  (Epes),  beyond  which  for  several  miles  it  is  shown  along  the 
stream. 
Judging  from  the  width  of  its  outcrop,  this  division  of  the  Rotten 
limestone  must  be  about  300  feet  in  thickness.  It  underlies  the  most 
fertile  and  typical  "prairie "  lands  of  the  South.  At  intervals  through- 
out this  region  the  limestone  rock  appears  at  the  surface  in  what  are 
known  as  "bald  prairies,"  so  named  from  the  fact  that  on  these  spots 
there  is  no  tree  growth.  The  disintegration  and  leaching  out  of  the 
limestone  leaves  a  residue  of  yellowish  clay,  which  accumulates  some- 
times to  a  thickness  of  several  feet  in  low  places.  .  This  clay  is  used  at 
the  Demopolis  plant  in  the  manufacture  of  cement,  and  in  most  locali- 
ties where  suitable  limestone  is  found  the  clay  is  present  in  sufficient 
quantity  to  supply  the  needs  of  the  cement  manufacturer. 
At  the  base  of  this  middle  or  Demopolis  division  occurs  a  bed  con- 
sisting of  several  ledges  of  compact,  hard,  pure  limestone,  which 
weathers  into  curious  shapes,  and  has  received  the  names  horse-bone 
rock  and  bored  rock.  This  bed,  as  above  mentioned,  appears  at  the 
top  of  Hatchs  Bluff;  also  at  Areola  Bluff,  and  between  Demopolis  and 
Epes,  at  Jordans  Ferry,  and  other  places.  Where  it  outcrops  across 
the  country  it  makes  a  ridge  easily  followed  and  characterized  by  the 
presence  on  the  surface  of  loose  fragments  of  the  limestone. 
The  lower  part  of  the  formation  (the  Selma  division),  like  the  upper, 
is  composed  of  clayey  limestone,  in  man}r  places  being  rather  a  calcare- 
ous clay.  The  color  is  dark  gray  to  bluish,  and  in  most  exposures 
there  is  a  striping  due  to  bands  of  lighter-colored,  purer  limestone  alter- 
nating with  the  prevailing  quality.  Along  Alabama  River  the  strata 
of  this  division  are  seen  in  the  bluffs  from  Kings  Landing  up  to  Selma 
and  beyond.  On  the  Warrior  River  they  are  seen  in  the  bluffs  at 
Areola,  Hatchs,  Millwood,  and  Erie,  occupying  in  the  last-named  local- 
ity the  upper  part  only  of  the  bluff.  On  the  Tombigbee,  the  bluffs  at 
Gainesville,  at  Roes,  and  Kirkpatricks  are  formed  mainty  of  the  rocks 
of  this  division,  while  above  Roes,  at  Jordans,  occurs  the  line  of 
junction  of  this  with  the  middle  division.  Near  this  line  of  division 
there  is  a  very  characteristic  feature  to  be  observed  at  many  points, 
