﻿Ticenlwfel 
  — 
  Wreford 
  and 
  Foraker 
  Limestones. 
  411 
  

  

  4. 
  One 
  bed 
  of 
  intimately 
  intergrown 
  yellowish- 
  gray 
  limestone 
  

   and 
  pale 
  bine 
  chert 
  2 
  feet, 
  2 
  inches. 
  

  

  3. 
  Thin 
  white 
  limestone 
  with 
  an 
  abundance 
  of 
  silicified 
  

   (chert) 
  Composita 
  subtil 
  it 
  a 
  and, 
  more 
  rarely, 
  Derbya, 
  fenestel- 
  

   loid 
  bryozoa 
  and 
  other 
  fossils 
  2 
  feet, 
  4 
  inches. 
  

  

  2. 
  AYhite, 
  somewhat 
  chalky 
  limestone. 
  Contains 
  silicified 
  

  

  (chert) 
  echinoderm 
  spines 
  (Archceocidaris) 
  and 
  bryozoa 
  

  

  6 
  inches. 
  

  

  1. 
  Thin, 
  compact, 
  gray 
  limestone 
  with 
  poorly 
  defined 
  bedding 
  

   planes 
  1 
  foot, 
  .3 
  inches. 
  

  

  Relation 
  of 
  the 
  Cherts 
  to 
  the 
  Limestones. 
  

  

  The 
  sections 
  show 
  that 
  the 
  chert 
  occurs 
  in 
  four 
  more 
  

   or 
  less 
  distinct 
  relations. 
  

  

  In 
  the 
  Foraker 
  limestone 
  it 
  is 
  present 
  as 
  isolated 
  nod- 
  

   ules, 
  of 
  wdiich 
  the 
  average 
  is 
  about 
  five 
  or 
  six 
  inches 
  in 
  

   diameter. 
  These 
  nodules 
  commonly, 
  but 
  not 
  ahvays, 
  

   have 
  their 
  longest 
  axes 
  parallel 
  to 
  the 
  bedding 
  planes 
  and 
  

   in 
  places 
  the 
  chert 
  and 
  limestone 
  are 
  quite 
  intimately 
  

   intergrovm. 
  

  

  The 
  first 
  zone 
  of 
  the 
  AYref 
  ord 
  which 
  contains 
  chert 
  has 
  

   it 
  only 
  in 
  the 
  fossils. 
  The 
  main 
  body 
  of 
  the 
  zone 
  consists 
  

   of 
  limestone. 
  

  

  The 
  second 
  zone 
  which 
  carries 
  chert 
  has 
  it 
  intergrown 
  

   with 
  the 
  limestone 
  in 
  an 
  exceedingly 
  intricate 
  and 
  laby- 
  

   rinthine 
  way, 
  so 
  that 
  in 
  any 
  one 
  mass 
  of 
  rock 
  the 
  chert 
  is 
  

   essentially 
  one 
  piece, 
  which 
  is 
  also 
  true 
  of 
  the 
  limestone. 
  

   On 
  weathered 
  surfaces 
  the 
  division 
  between 
  the 
  chert 
  and 
  

   the 
  limestone 
  is 
  extremely 
  sharply 
  defined 
  and 
  no 
  diffi- 
  

   culty 
  exists 
  in 
  stating 
  where 
  the 
  chert 
  begins 
  and 
  the 
  lime- 
  

   stone 
  ends. 
  Freshly 
  fractured 
  surfaces, 
  however, 
  show 
  

   that 
  there 
  is 
  a 
  zone 
  of 
  about 
  one-half 
  inch 
  in 
  width 
  

   between 
  the 
  chert 
  and 
  the 
  limestone, 
  in 
  which 
  there 
  is 
  a 
  

   minute 
  intergrowth 
  of 
  calcite 
  and 
  silica. 
  

  

  The 
  third 
  chert 
  of 
  the 
  Wreford 
  occurs 
  in 
  large 
  irregu- 
  

   larly 
  shaped 
  nodules 
  of 
  marked 
  concentric 
  structure, 
  the 
  

   nodules 
  in 
  considerable, 
  and 
  probably 
  greater, 
  part 
  

   being 
  elongated 
  parallel 
  to 
  the 
  bedding. 
  There 
  are 
  many 
  

   nodules 
  of 
  a 
  spherical 
  shape 
  in 
  which 
  no 
  longest 
  axis 
  

   exists, 
  and 
  there 
  are 
  numerous 
  others 
  which 
  have 
  their 
  

   longest 
  axes 
  transverse 
  to 
  the 
  bedding. 
  The 
  nodules 
  are 
  

   not 
  sharply 
  delimited 
  from 
  the 
  enclosing 
  limestone. 
  

  

  A 
  fourth 
  chert 
  zone 
  is 
  known 
  to 
  occur 
  in 
  the 
  Wreford, 
  

   and 
  there 
  mav 
  be 
  others. 
  This 
  has 
  the 
  chert 
  in 
  lenticular 
  

  

  