﻿414 
  Twenhofel 
  — 
  Wreford 
  and 
  Foraker 
  Limestones. 
  

  

  commonly 
  fragments 
  and 
  young 
  shells. 
  Fusulina 
  is 
  

   extremely 
  rare. 
  The 
  fossils 
  have 
  the 
  appearance 
  of 
  

   being 
  most 
  abundant 
  in 
  the 
  outer 
  granular 
  portions 
  

   of 
  the 
  chert, 
  but 
  in 
  reality 
  such 
  is 
  not 
  the 
  case. 
  Many 
  of 
  

   those 
  in 
  the 
  limestone 
  are 
  composed 
  of 
  chert. 
  The 
  pre- 
  

   servation 
  in 
  the 
  chert 
  is 
  as 
  good 
  as 
  in 
  the 
  limestone. 
  

  

  The 
  chert 
  masses, 
  in 
  general, 
  are 
  elongated 
  parallel 
  to 
  

   the 
  bedding 
  but 
  they 
  also 
  cut 
  across 
  the 
  bedding 
  and 
  go 
  

   from 
  slightly 
  lower 
  to 
  slightly 
  higher 
  levels. 
  In 
  addition, 
  

   fingers 
  of 
  chert 
  go 
  out 
  in 
  every 
  possible 
  direction, 
  so 
  that 
  

   each 
  unit 
  — 
  if 
  a 
  unit 
  may 
  be 
  said 
  to 
  be 
  present 
  — 
  is 
  united 
  

   to 
  chert 
  above, 
  below, 
  and 
  laterally. 
  

  

  The 
  groundmass 
  of 
  the 
  chert 
  of 
  this 
  zone 
  consists 
  of 
  

   exceedingly 
  minute 
  grains 
  of 
  chalcedony, 
  quartz, 
  and 
  

   limonite, 
  limonite 
  and 
  limonite 
  staining 
  being 
  quite 
  abun- 
  

   dant. 
  Amorphous 
  silica 
  does 
  not 
  appear 
  to 
  be 
  present. 
  

   In 
  the 
  groundmass 
  are 
  many 
  minute 
  fragments 
  of 
  fos- 
  

   sils 
  of 
  which 
  the 
  most 
  conspicuous 
  are 
  of 
  needle-like 
  

   shape. 
  As 
  these 
  are 
  not 
  parallel 
  in 
  arrangement, 
  it 
  

   results 
  that 
  a 
  thin 
  section 
  shows 
  them 
  with 
  different 
  out- 
  

   lines. 
  Those 
  whose 
  axes 
  are 
  parallel 
  to 
  the 
  surface 
  of 
  

   the 
  thin 
  section 
  have 
  needle-like 
  outlines 
  ; 
  those 
  whose 
  

   axes 
  are 
  perpendicular 
  appear 
  as 
  circles 
  ; 
  while 
  those 
  

   transverse 
  give 
  ellipses. 
  The 
  needle-like 
  structures 
  are 
  

   of 
  light 
  color 
  in 
  thin 
  section 
  and 
  each 
  of 
  them 
  appears 
  to 
  

   have 
  had 
  a 
  central 
  axial 
  canal 
  or 
  filament, 
  which 
  is 
  indi- 
  

   cated 
  by 
  a 
  thread-like 
  portion 
  of 
  different 
  color, 
  a 
  pale 
  

   yellow 
  being 
  most 
  common. 
  These 
  needle 
  structures 
  

   appear 
  to 
  be 
  almost 
  wholly 
  composed 
  of 
  chalcedony, 
  very 
  

   little, 
  if 
  any, 
  quartz 
  being 
  present, 
  and 
  are 
  believed 
  to 
  

   be 
  monaxial 
  sponge 
  spicules. 
  They 
  are 
  about 
  one-tenth 
  

   of 
  a 
  millimeter 
  in 
  diameter 
  and 
  one 
  millimeter 
  long. 
  Bry- 
  

   ozoa 
  have 
  also 
  been 
  recognized 
  among 
  the 
  minute 
  frag- 
  

   ments 
  of 
  other 
  fossils 
  which 
  are 
  present. 
  A 
  cylindrical 
  

   rod-like 
  structure 
  is 
  present 
  in 
  one 
  section 
  which 
  may 
  

   have 
  come 
  from 
  one 
  of 
  the 
  calcareous 
  algae. 
  This 
  is 
  

   peculiar 
  in 
  that 
  it 
  appears 
  to 
  have 
  the 
  remains 
  of 
  a 
  small 
  

   coiled 
  organism 
  in 
  its 
  interior. 
  If 
  Fusulina 
  be 
  present 
  

   in 
  this 
  chert, 
  it 
  is 
  extremely 
  rare. 
  

  

  The 
  chert 
  of 
  the 
  third 
  zone 
  of 
  the 
  Wreford 
  (see 
  fig. 
  1) 
  

   is 
  in 
  the 
  form 
  of 
  lar^e 
  and 
  small 
  nodules 
  of 
  variable 
  and 
  

   peculiar 
  shapes. 
  Maximum 
  diameters 
  equal 
  and 
  perhaps 
  

   exceed 
  four 
  feet. 
  The 
  surfaces 
  are 
  extremely 
  irregular 
  

   by 
  reason 
  of 
  dome-shaped 
  protuberances 
  which 
  appear 
  

  

  