516  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.  [bull.  260. 
The  rock  breaks  down  easily  when  exposed  to  the  weather  and 
hence  is  not  now  used  for  extensive  building  purposes.  It  is,  how- 
ever, the  only  road  material  found  in  this  section  of  the  country.  It 
has  been  used  on  the  road  across  Bogue  Chitto  Swamp,  but  is 
unsatisfactory. 
Men  familiar  with  the  country  say  that  this  hard  limestone  is  only 
about  4  feet  thick  and  occurs  near  the  surface.  Below  this  hard 
stratum  comes  the  soft,  whiter,  4i  rotten  limestone,"  which  is,  on  an 
average,  20  feet  thick.  Below  this  comes  the  "  blue  rock,"  which 
holds  water.  In  digging  cisterns  the  farmers  always  dig  down  to  the 
"  blue  rock/'  which  requires  no  curbing. 
There  are  two  kinds  of  soils  in  the  prairie  section — the  "  post- 
oak  "  land  and  the  prairie  proper.  The  former  is  the  highest  land 
between  the  stream  divides,  which  has  suffered  but  little  erosion.  It 
is  very  level,  sloping  gently  to  the  streams.  This  post-oak  land  is 
covered  with  a  thin  coating  of  Lafayette  clayey  sand,  never  over  10 
feet  thick,  which  has  never  been  all  carried  away  by  erosion.  The 
uncleared  land  produces  post-oak  and  some  black-oak  timber.  The 
soil  is  not  so  rich  as  the  prairie  soils  and  has  been  largely  abandoned 
for  cultivation. 
The  prairie  land  is  that  from  which  the  Lafayette  has  been 
removed,  and  the  black,  rich  loam,  formed  from  the  decomposition 
of  the  Selma  chalk,  comes  to  the  surface.  The  limestone  rarely  out- 
crops except  along  the  streams.  This  black  prairie  soil,  when  the 
country  was  first  settled,  was  too  strong  for  cotton.  It  produced  a 
large  stalk,  but  very  little  cotton.  Until  recent  years  all  the  cotton 
was  planted  on  the  poorer  "  post-oak  "  lands,  and  the  prairie  lands 
were  put  in  corn.  But  after  years  of  continuous  crops  of  corn  the 
prairie  land  became  the  best  cotton  land,  and  now  the  finest  cotton 
grows  on  the  prairie  lands. 
The  following  well  sections  are  of  interest  in  this  connection : 
Well  sections  near  Columbus  and  Aberdeen,  Miss. 
(a)  Well  at  ravine  on  land  of  J.  Q.  Poindexter :  Feet. 
Selma  chalk 250 
Sand,  water  bearing,  and  principal  source  of  water__  475 
Red    clay 50 
Depth   of  well 725 
Water  soft ;  rises  to  within  2(5  feet  of  surface. 
(b)  Well  2  miles  due  east  of  ravine  on  Sebe  Gavin's  land: 
Depth  of  well  431 
Water  flows  16  feet  above  surface. 
(c)  Well  on  Doctor  Patty's  land,  near  Bigbee  Valley  post-office: 
Depth  of  well 431 
Water  flows  20  feet  above  surface. 
Water  found  in  sand,  and  soft. 
