smith.]  CEMENT    RESOURCES    OF    ALABAMA.  441 
Eocene  strata,  is  in  general  equivalent  to  the  Vicksburg  limestone  of 
the  Mississippi  geologists. 
In  Alabama  it  exhibits  three  rather  well-defined  phases,  which, 
in  descending  order,  are  (1)  the  Upper  or  Salt  Mountain  division, 
observed  at  one  locality  only  in  Clarke  County;  (2)  the  Middle  or 
St.  Stephens  division;  and  (3)  the  Lower  or  Jackson  division.  Of  these 
it  is  only  the  Middle  division  with  which  we  are  here  concerned, 
since  the  first  is,  so  far  as  known,  restricted  to  one  locality,  and  the 
third  is  seldom  exposed  along  Alabama  rivers  and  railroads. 
The  following  section  of  the  St.  Stephens  Bluff,  Tombigbee  River, 
will  give  an  idea  of  the  strata  of  this  division: 
Section  of  St.-  Stephens  Bluff. 
Feet. 
1.  Red  residual  clay 1  to    5 
2.  Highly  fossiliferous  limestone  holding  mainly  oysters,  and  full  of  holes 
due  to  unequal  weathering 10  to  12 
3.  Orbitoidal  limestone  (chimney  rock),  a  soft,  nearly  uniform  porous  lime- 
stone, making  smooth  perpendicular  face  of  the  bluff  except  where 
bands  of  harder  limestone  of  very  nearly  similar  composition  alternate 
with  the  softer  rock.  Both  varieties  hold  great  numbers  of  the  circu- 
lar shells  of  Orbitoides  mantelli.  These  harder  ledges  are  nearly  pure 
carbonate  of  lime,  take  a  good  polish,  and  are  often  burned  for  lime. .  60 
4.  Immediately  below  3,  for  5  or  6  feet,  the  strata  were  not  visible,  being 
hidden  by  the  rock  falling  from  above,  but  the  space  seems  to  be  occu- 
pied by  a  bluish  clay.  Then  follows  a  soft  rock  somewhat  of  same 
consistency  as  No.  3  above,  but  containing  a  good  deal  of  green  sand. 
The  fossils  are  mostly  oysters  and  Plagiostorna  dumosa.  This  bed  is  in 
places  rather  indurated  superficially,  and  forms  projecting  ledges 10  to  15 
5.  Bluish  clayey  marl  with  much  green  sand,  containing  the  same  fossils  as 
No.  4.     It  washes  or  caves  out  from  under  No.  4,  which  overhangs  it..     4  to    5 
6.  Massive  joint  clay,  yellow  on  exposed  surface,  blue  when  freshly  broken; 
no  fossils   observed.      Extends  below  the  water  level   to   unknown 
depth;  exposed 3  to    4 
The  rock  of  this  formation,  which  seems  to  be  the  best  suited  for 
cement  material,  is  the  soft  "chimney  rock"  or  orbitoidal  limestone 
of  bed  No.  3  above.  This  is  usually  quarried  for  chimneys  and  other 
constructions  by  sawing  it  out  and  dressing  it  down  with  a  plane  into 
blocks  of  suitable  size,  which  are  then  laid  like  brick. 
The  numerous  analyses  given  below  will  show  that  this  rock  is  a 
purer  limestone  than  most  of  the  material  of  the  Selma  chalk  of  the 
Cretaceous  formation  above  considered.  In  cement  making  it  will,  in 
consequence,  require  a  larger  proportion  of  clay  to  be  mixed  with  it, 
and  the  question  of  obtaining  suitable  clay  in  sufficient  quantity  and 
in  close  proximity  becomes  one  of  some  importance.  The  residual 
clay  left  after  decomposition  and  leaching  of  the  limestone  seems  to 
be  fairly  well  adapted  to  the  purpose.  Besides  this  residual  clay  some 
analyses  have  been  made  of  the  clays  of  the  river  and  creek  bottoms  of 
the  country  near  the  limestone  outcrops,  and  of  the  clays  of  the  Grand 
