518  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1901.         [bull.  260. 
Where  the  blue  rock  below  this  hard  cap  rock  comes  to  the  surface 
it  forms  a  belt  of  the  richest  soil  in  the  prairie  region.  The  soil  is 
very  deep,  black,  and  loose.  More  cotton  and  corn  are  raised  to  the 
acre  here  than  any  other  section  of  the  State.  West  of  this  the  land 
becomes  higher,  and  the  Lafayette  occupies  the  surface  on  the  ridges. 
About  6  miles  north  of  Macon,  on  the  Macon  and  Columbus  road, 
the  limestone  begins  to  show  at  the  surface  in  small  gullies.  The 
rock  is  harder  than  the  blue  rock  along  the  Tombigbee,  hence  its  more 
frequent  occurrence. 
A  sample  collected  from  this  locality  by  the  writer  was  analyzed 
by  W.  S.  McNeil  in  the  laboratory  of  the  United  States  Geological 
Survey. 
Analysis  of  Selma  limestone  from  a  point  north  of  Macon,  Miss. 
Silica  (Si02) _^ 8.  52 
Alumina  (A1,03) 6.60 
Iron  oxide  (FeXU 
! 
S3  88 
Lime  carbonate  (CaCOs) 
Magnesium  carbonate   (MgC03)__  0.00 
Water   1.00 
Farther  south,  along  the  Macon  and  Columbus  road,  the  limestone 
begins  to  show  in  every  gully  and  on  every  hillside.  At  some  places 
on  level  ground  the  soil  is  not  over  12  inches  deep.  In  this  vicinity 
are  the  bald  prairies — large  areas  of  this  white  limestone  without 
a  particle  of  soil  or  a  sprig  of  grass.  A  sample  was  taken  3  miles 
north  of  Macon. 
A  sample  of  Selma  limestone  was  taken  from  north  of  Lime  Creek, 
5  miles  east  of  Shuqualak,  on  Oaknoxubee  River,  where  a  bluff  50  feet 
high  is  composed  of  typical  Selma  chalk.  The  following  analysis  of 
this  sample  was  made  by  W.  S.  McNeil  in  the  laboratory  of  the  United 
States  Geological  Survey : 
Analysis  of  Selma  limestone,  near  Shuqualak,  Miss. 
Silica  (Si02) 8.06 
Alumina   (AL03)    1    _  q. 
Iron  oxide   (Fe203) j 
Lime  carbonate  (0aCO3) 84.61 
Magnesium  carbonate  (MgC03) 0.00 
Water 1.  32 
The  Tombigbee  at  Columbus  has  cut  its  channel  into  the  Eutaw 
sands,  forming  a  bluff  on  the  east  side  90  feet  high.  The  material 
rou i posing  the  bluff  here  is  sand,  greenish  when  wet  and  gray  when 
dry.  It  contains  a  small  amount  of  lim'e  carbonate.  At  the  upper 
part  of  the  bluff  the  sands  become  lighter  in  color,  changing  to  a  light 
golden  yellow.  This  was  the  color  of  sand  when  deposited,  and  is  noti 
due  to  oxidation.  Numerous  little  branching  concretions,  which  ail 
perhaps  some  kind  of  poorlv  preserved  fossils,  occur  in  the  lower  nor- 
