452  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1906,  PART    I. 
At  the  top  of  the  limestones  the  beds  become  sandy  and  the  quart  zite 
series  generally  begins  with  an  alternation  of  sandy  limestones  and 
sandstone  beds,  and  continues  through  several  hundred  feet  of  sand- 
stone weathering  red  and  yellow.  These  are  succeeded  by  yellow, 
white,  and  gray  sandstones  and  quartzites,  the  upper  half  of  the 
series  being  quartzite,  readily  recognizable  as  such. 
This  quartzite  in  most  places  grades  into  a  dark,  rather  coarse 
granular  limestone — the  Upper  Coal  Measures  limestone  of  the  For- 
tieth Parallel  Survey.  The  upper  part  of  this  formation  consists  of 
yellow  sandstone  and  sandy  limestones  which  grade  into  a  blue-gray 
compact  limestone  just  beneath  the  phosphate  beds.  In  these  blue 
and  gray  limestones  indistinct  fossils  weather  out  on  the  surface, 
but  arc  difficult  of  determination.  This  portion  of  the  section  varies 
considerably  in  the  character  of  sediments. 
PHOSPHATE-BEARING    SERIES. 
The  phosphate  series  consists  of  alternating  layers  of  black  or 
brown  phosphatic  material,  shale,  and  hard  blue  or  gray  compact 
limestones.  The  limestones  are  in  the  main  very  fossiliferous,  con- 
taining well-preserved  forms  of  RTxynchonella,  Chonetes,  Omphalo- 
trochus,  and  Productus,  which  are  apparently  the  characteristic  fos- 
sils of  this  horizon.     The  shales  contain  Lingula  and  lamellibranchs. 
The  phosphate  series  is  in  places  about  90  feet  thick.  The  beds 
vary  in  thickness  from  a  few  inches  to  about  10  feet,  but  where  of 
this  extreme  width  are  in  general  broken  by  thin  layers  of  shaly 
material  poorer  in  P205.  At  the  base  the  series  begins  with  lime- 
stone, and  as  a  rule  6  to  8  inches  of  soft  brown  shale  overlies  this 
basal  limestone.  Above  is  the  main  phosphate  bed,  5  to  6  feet 
thick.  This  is  almost  entirely  oolitic  in  structure  and  high  in  P205. 
Several  other  beds,  varying  in  thickness  from  a  few  inches  to  about 
10  feet,  separated  by  6  inches  to  2  feet  of  limestone  or  shah1,  occur 
in  the  series.  The  beds  of  extreme  thickness,  as  already  mentioned, 
contain  seams  of  shaly  material,  itself  phosphatic,  too  thin  to  be 
separated  from  the  pure  oolitic  material  in  mining.  All  the  sections 
that  have  been  examined  show  one  and  some  of  them  two  beds 
which  are  of  commercial  value.  The  other  beds  are  not  of  sufficient 
thickness,  nor  of  a  grade  which  will  pay  to  mine  at  present. 
The  phosphate  series  is  overlain  by  a  coarse-grained,  locally  brec- 
ciated  limestone,  for  the  most  pari  in  massive  outcrops.  Above  this 
limestone  is  sometimes  found  100  feet  or  more  of  nearly  white  lime- 
stone, but  as  a  rule  it  is  succeeded  by  a  series  of  blue  and  gray  lime- 
stones containing  large  spirifers  and  Productus.  Next  above  is  a 
series  of  red  sandstones  and  shales  containing  brachiopods  and  lamel- 
libranchs. Still  higher  in  the  section  is  a  considerable  thickness  of 
blue,  gray,  and  greenish  limestones,  which  form  the  upper  part    of 
