470  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1906,  PART    I. 
inch  in  diameter.     These  particles  are  more  or  less  angular,  some  of 
them    strikingly   so,   making   the  stone  distinctly   conglomeratic   in 
appearance.     The  stone  emits  an  earthy  odor.     In  order  to  determine! 
whether  the  gray  particles  arc  really  fragmentary  material  or  concre- 
tions and  also  to  ascertain  the  nature  of  the  white  fragments,  a  speci-1 
men  was  submitted  to  Dr.  Albert  Johannsen,  of  the  United  States! 
I 
Geological  Survey,  for  microscopic  examination,  who  reports  as  follows: 
The  thin  section  is  made  up  chiefly  of  organic  remains,  perhaps  fragments  of  bone] 
in  a  cement  of  calcite,  with  very  little  of  an  isotropic  deep  purplish  mineral,  having 
an  index  very  much  less  than  Canada  balsam  probably  lluorite.  The  sections  show 
no  concretions;  the  calcite  seems  to  be  a  filling  between  the  fragments  of  bone. 
A  small  portion  of  rock  at  the  outer  edge  lias  been  leached  of  lime 
by  surface  waters  and  when  freshly  quarried  is  dark  colored.  This  is 
called  by  the  quarrymen  "black  phosphate."  It  contains  a  consid- 
erable amount  of  water,  to  which  the  color  is  attributable,  and  is 
richer  in  phosphate  than  the  remainder  of  the  bed. 
The  lower  bed  is  similar  to  the  upper  one,  though  darker  in  color, 
more  compact,  and  qoI  conglomeratic,  so  far  as  observed.  The 
darker  color  is  due  to  the  smaller  amount  of  the  white  material  and 
possibly  to  a  larger  amount  of  iron  or  manganese,  or  both.  It  has  a 
greeni-h  tinge,  which  is  suggestive  of  glaucpnite.  This  bed  becomes 
very  ferruginous  in  its  upper  part  and  is  here,  as  in  the  old  workings 
on  East  Lafferty  Creek,  separated  from  the  bed  above  by  a  thin 
layer  of  manganiferoiis  iron  ore. 
The  following  analyses  of  specimens  of  the  rock  were  made  in  the 
laboratory  of  the  United  States  Geological  Survey.  Number  1  was 
a  specimen  taken  from  the  lower  bed;  Xos.  14-18  were  specimens 
from  the  bed  now    being  worked. 
Analyses  of  phosphaU  rockfrom  Arkansas. 
No. 
Where  taken. 
Phosphoric 
acid  <  r  - 
Equivalenl 
in  calcium 
phosphate. 
(Ca8i  P0<)2). 
14 
4  inches  from  top  of  bed 
•J.V  86 
L'7.  24 
27.40 
32.  60 
29.18 
13.46 
56  45 
15 
Middle  of  bed 
.Vi    \i, 
lfi 
8  inches  from  bottom  of  bed 
59  81 
17 
"•  Black  phosphate " 
71  00 
18 
Com positc  sample 
63  70 
1 
From  lower  bed 
29  38 
Amount  of  tin  phosphate  rock. — The  aggregate  thickness  of  the  two 
beds  at  the  quarries  is  from  H\  to  10  feet,  but,  as  already  stated,  only 
the  upper  bed  is  worked  at  present,  Somewhat  more  than  one-half 
a  mile  west  of  the  quarries,  on  the  opposite  side  of  the  hill  and  above 
the  railroad,  the  phosphate  horizon  is  represented  only  by  a  bed  of 
red  calcareous  shale  6  inches  thick,  overlain  by  brown,  compact  lime- 
stone 20  inches  thick.     Both  of  these  beds  are  slightly  phosphatic. 
