﻿Appalachian 
  Geosyncline. 
  439 
  

  

  manent 
  water 
  bodies, 
  either 
  lakes 
  or 
  seas. 
  The 
  deposit 
  there- 
  

   fore 
  comes 
  not 
  from 
  the 
  direction 
  of 
  the 
  land, 
  but 
  from 
  the 
  

   direction 
  of 
  the 
  sea. 
  The 
  cracking 
  goes 
  on 
  between 
  the 
  

   extreme 
  levels 
  of 
  high 
  and 
  low 
  water 
  and 
  the 
  slight 
  shifting 
  

   of 
  level 
  is 
  not 
  a 
  tidal 
  but 
  at 
  least 
  a 
  seasonal 
  phenomenon. 
  

   Such 
  mud-cracking 
  of 
  limestones 
  is 
  a 
  playa 
  phenomenon, 
  and 
  

   especially 
  in 
  certain 
  earlier 
  ages 
  when 
  the 
  lands 
  were 
  base- 
  

   leveled 
  and 
  lay 
  awash 
  with 
  the 
  sea, 
  broad 
  areas 
  seem 
  to 
  have 
  

   been 
  at 
  times 
  marine 
  playas. 
  Marine 
  fossils, 
  often 
  of 
  depau- 
  

   perated 
  facies, 
  occur 
  sometimes 
  in 
  mud-cracked 
  limestones. 
  

   The 
  nearest 
  approach 
  in 
  the 
  modern 
  world 
  is 
  found, 
  doubtless, 
  

   in 
  the 
  Kunn 
  of 
  Cutch, 
  an 
  area 
  of 
  10,'000 
  square 
  miles 
  flooded 
  

   by 
  the 
  sea 
  for 
  a 
  part 
  of 
  the 
  year, 
  during 
  the 
  period 
  of 
  onshore 
  

   monsoon 
  winds. 
  

  

  In 
  the 
  detection 
  of 
  mud-cracks 
  in 
  ancient 
  formations, 
  reason- 
  

   able 
  care 
  must 
  be 
  used 
  to 
  avoid 
  mistaking 
  for 
  them 
  a 
  poly- 
  

   gonal 
  cracking 
  of 
  the 
  rock 
  arising 
  after 
  its 
  solidification. 
  The 
  

   two, 
  however, 
  are 
  readily 
  distinguished.. 
  True 
  mud-cracks 
  

   always 
  have 
  a 
  filling, 
  the 
  polygons 
  are 
  irregular 
  but 
  do 
  not 
  

   show 
  an 
  irregularity 
  constant 
  in 
  one 
  direction. 
  True 
  mud- 
  

   cracks, 
  although 
  easily 
  separated 
  from 
  simulated 
  features, 
  are, 
  

   however, 
  often 
  very 
  difficult 
  to 
  detect, 
  as 
  the 
  tilling 
  may 
  be 
  

   identical 
  in 
  nature 
  with 
  the 
  original 
  stratum 
  and 
  weathering 
  

   furthermore 
  destroys 
  such 
  strata 
  very 
  rapidly 
  unless 
  the 
  shales 
  

   are 
  interlaminated 
  with 
  sandstones. 
  Kainprints 
  must 
  be 
  sepa- 
  

   rated 
  from 
  the 
  pits 
  made 
  by 
  escaping 
  marsh 
  gas 
  and 
  are 
  more 
  

   usually 
  marked 
  by 
  a 
  spattered 
  surface 
  of 
  the 
  mud 
  than 
  by 
  a 
  

   few 
  concave 
  depressions. 
  Rootmarks 
  should 
  show 
  a 
  branch- 
  

   ing 
  pattern 
  and 
  finer 
  tendrils 
  given 
  off 
  from 
  the 
  larger 
  marks. 
  

   Footprints 
  may 
  be 
  very 
  obscure, 
  but 
  the 
  test 
  in 
  that 
  case 
  is 
  the 
  

   regularity 
  of 
  recurrence 
  upon 
  the 
  stratum 
  owing 
  to 
  the 
  stride 
  

   of 
  the 
  animal. 
  

  

  Finally, 
  a 
  criterion 
  of 
  special 
  application 
  to 
  the 
  outlying 
  syn- 
  

   cline 
  of 
  Upper 
  Devonian 
  to 
  the 
  east 
  of 
  the 
  main 
  area 
  is 
  found 
  

   in 
  the 
  nature 
  of 
  the 
  conglomerates. 
  

  

  Conglomerates 
  now 
  forming 
  which 
  are 
  both 
  thick 
  and 
  wide- 
  

   spread 
  are 
  observed 
  to 
  be 
  of 
  fluviatile 
  and 
  not 
  littoral 
  origin. 
  

   This 
  is 
  because 
  rivers 
  are 
  able 
  to 
  carry 
  gravels 
  far 
  out 
  over 
  a 
  

   subsiding 
  river 
  plain, 
  but 
  the 
  waves, 
  on 
  the 
  contrary, 
  tend 
  to 
  

   keep 
  gravel 
  banked 
  along 
  the 
  shore. 
  During 
  an 
  advance 
  or 
  

   retreat 
  of 
  the 
  sea, 
  basal 
  conglomerates 
  may 
  be 
  widely 
  spread, 
  

   but 
  they 
  are 
  thin, 
  and 
  often 
  wanting, 
  reaching 
  their 
  greatest 
  

   development 
  among 
  islands 
  or 
  along 
  an 
  irregular 
  rocky 
  shore 
  

   able 
  to 
  withstand 
  the 
  waves 
  for 
  some 
  time 
  during 
  a 
  rising 
  sea. 
  

   A 
  maximum 
  limit 
  to 
  widespread 
  basal 
  marine 
  conglomerates 
  

   seems 
  to 
  be 
  one 
  hundred 
  feet 
  and 
  therefore 
  broad 
  conglomerate 
  

   formations 
  of 
  greater 
  thickness 
  are 
  evidences 
  of 
  terrestrial 
  

  

  