460  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   L906,   PART    I. 
From  a  practical  standpoint  the  limestone  immediately  overlyinJ 
the  main  phosphate  bed  at  Montpelier  is  of  considerable  importance, 
being   very   uniform   in   character  wherever  found   and   containing 
abundant   specimens  of  a  coiled  shell,  Omphalotrochus,  which,  so  farl 
as  observed,  seems  to  be  confined  to  this  bed.     This  limestone  or 
"cap  lime,"  as  it   is  called  by  the  miners,  is  a  valuable  landmark  in 
prospecting  for  the  main  bed  of  phosphate.     It  averages  2  feet  in] 
thickness,  is  dark  gray  in  color,  and  very  hard  when  freshly  exposed,! 
but    rapidly    weathers    brown    and    finally    disintegrates   completely. 
Large  blocks  of  ii  which  have  lain  on  the  ground  less  than  two  years 
crumble  to  pieces  when  lightly  struck  with  a  hammer.     Tn  common 
with  most  of  the  other  bands,  it  emits  a  strong  bituminous  odor  when! 
broken.      Analyses  show  that  some  of  these  limestones  contain  several! 
per  cent  of  P205.      Fossils  are  much  more  abundant  in  some  than  ml 
other-.      In  development   work  the  position  in  the  series  of  some  on 
the  bed-  can   readily  be  determined   from  their  fossils,  even  by  one 
with   no  knowledge  of  paleontology.     Such   characteristic  forms  as 
Omjihalotrochus,    Rhynchonella,   Chonetes,    and   Productus    are    abun- 
dant and  well  preserved.     A  remarkable  specimen  showing  three  largJ 
fish  teeth  in  a  portion  of  the  jaw  was  recently  discovered  in  the  cap] 
lime.     The  shales  contain  Lingula  and  lamellibranchs. 
The  main  phosphate  bed  is  the  lowest  one  in  the  series  at  t  his 
locality  and  is  just  over  the  basal  limestone,  which  contains  much 
silica,  in  many  places  segregated  as  irregular  bands  and  masses  on 
chert.  The  phosphate  layers  are  black  to  brownish  in  color  and 
finely  to  coarsely  oolitic  in  struct  me. 
The  beds  rich  in  P20  for  example,  the  main  phosphate  bed — are 
almost  entirely  oolitic,  the  small  black  granules  being  densely  packed 
together  with  but  little  matrix  material  and  effervescing  but  very 
slightly  with  HC1.  The  phosphate  has  a  bituminous  odor  when 
freshly  broken.  As  the  number  of  oolitic  grains,  and  therefore  the 
P,()  content,  decrease-,  the  beds  assume  more  of  the  character  ol 
oolitic  shales  or  limestones. 
Several  thousand  tons  of  phosphate  from  the  main  bed  at  Montpe- 
lier, the  whole  of  the  material  5^  to  6  feel  wide  between  the  inclosing 
limestones  being  mined  and  shipped,  showed  a  remarkably  uniform 
content  of  P205,  the  average  of  a  large  series  of  analyses  on  carload! 
lots  giving  a  total  of  a  little  over  32  per  cent  P.O.-,,  equivalent  to  70! 
per  cent  bone  phosphate.  As  the  result  of  a  careful  experiment,  itj 
was  found  that  a  cubic  foot  of  t  he  phosphate  in  the  main  bed  weighed; 
150  pounds.     This  gives  13.3  cubic  feet  to  the  ton. 
The  stratum  varies  considerably  in  hardness,  the  lower  2  feet  being 
very  hard  and  blocky  and  the  upper  portion  being  softer,  with  a  more; 
shaly  structure. 
