PHOSPHATE    DEPOSITS    IN    NORTHERN    ARKANSAS.  471 
How  far  west  of  the  quarries  the  bed  now  being  worked  will  hold 
out  is  problematical,  though  it  is  reasonable  to  suppose  that  it  will 
maintain  a  workable  thickness  at  least  halfway  through  the  hill. 
Opposite  the  quarry,  on  the  east  side  of  Lafferty  Creek,  an  adit 
shows  that  the  upper  bed  of  phosphate  is  3  feet  4  inches  thick.  Only 
development  work  can  determine  how  far  this  thickness  is  main- 
tained, but  the  fact  that  phosphatic  debris  occurs  extensively  on  the 
undeveloped  southern  part  of  sec.  14,  immediately  to  the  east,  indicates 
that  this  thickness  might  hold  for  a  considerable  distance.  As  stated 
above,  the  rock  is  about  22  inches  thick  in  the  northern  part  of  sec. 
14,  where  it  was  first  worked. 
Methods  of  working. — At  the  old  workings  on  East  Lafferty  Creek 
the  phosphate  rock  was  worked  by  stripping  and  quarrying  and  run- 
ning short  adits  into  the  hill  on  a  level  with  the  phosphate  beds.  At 
the  present  workings  only  the  former  method  has  been  used  thus  far. 
The  beds  so  outcrop  as  to  permit  the  company  to  work  by  this  method 
for  some  time  if  they  choose  to  do  so;  but  eventually  it  will  be  nec- 
essary to  run  adits  into  the  hillside.  Drilling  is  done  by  hand,  and 
the  rock  is  hauled  in  wagons  to  the  opposite  side  of  the  creek,  where 
it  is  loaded  on  the  cars  for  shipment.  Before  shipment  the  "black 
phosphate"  is  dried  by  ricking  up  the  rock  and  leaving  furnaces  at 
the  bottom,  in  which  fires  are  built.  Much  the  greater  part  of  the 
stone  is  not  weathered  and  is  shipped  without  drying. 
ORIGIN    OF    THE    PHOSPHATES. 
The  comparatively  uniform  thickness  of  the  phosphate  beds  and 
their  occurrence,  within  the  locality  considered,  always  at  the  same 
geological  horizon,  at  once  determine  them  as  of  sedimentary  origin. 
If  any  further  evidence  for  such  origin  is  necessary,  that  furnished 
by  the  microscopic  examination  is  conclusive.  This  examination 
determines  the  gray,  pebblelike  material  not  to  be  concretions  (con- 
sequently waterworn  material)  and  the  white  particles  that  consti- 
tute so  large  a  part  of  the  mass  to  be  organic  remains. 
Doctors  Branner  and  Newsom  think  that  the  beds  are  probably 
deep  sea  (though  not  abysmal)  deposits,  and  that  their  phosphatic 
nature  is  probably  due  to  "the  droppings  of  fishes  and  other  marine 
animals  and  to  accumulations  of  organic  matter  that  settled  to  the 
bottom  of  the  quiet  waters  that  covered  this  part  of  the  world  during 
Silurian  and  Devonian  times."0  But  from  the  conglomeratic  char- 
acter of  the  rock  brought  out  by  microscopic  examination  it  appears 
that  the  deposition  of  the  phosphate  beds  took  place  in  shallow  water, 
having  closely  followed  the  shore  line  as  it  advanced  landward.  This 
is  further  shown  by  the  fragmentary  character  of  the  organic  mate- 
aThe  phosphate  rocks  of  Arkansas:  Bull.  Arkansas  Exp.  Station  No.  74,  p.  69. 
