﻿OCEANOGRAPHY 
  — 
  STETSON 
  239 
  

  

  continued 
  action 
  producing 
  the 
  present 
  topography 
  largely 
  by 
  solution. 
  

   Before 
  introducing 
  his 
  new 
  theory, 
  Johnson 
  (1939) 
  gives 
  an 
  excellent 
  

   account 
  of 
  the 
  whole 
  canyon 
  problem 
  to 
  date. 
  2 
  

  

  Whatever 
  their 
  origin, 
  these 
  submerged 
  canyons 
  offer 
  the 
  only 
  

   available 
  opportunities 
  for 
  getting 
  at 
  the 
  older 
  formations 
  beneath 
  

   the 
  mantle 
  of 
  Recent 
  veneer, 
  for 
  in 
  places 
  their 
  walls 
  stand 
  as 
  cliffs, 
  

   steeper 
  than 
  the 
  angle 
  of 
  repose 
  of 
  unconsolidated 
  sediment. 
  The 
  

   fossiliferous 
  fragments 
  broken 
  from 
  the 
  outcropping 
  ledges 
  indicate 
  

   that 
  these 
  valleys 
  are 
  comparatively 
  young. 
  This 
  adds 
  to 
  the 
  com- 
  

   plexity 
  of 
  the 
  problem, 
  because 
  we 
  cannot 
  retreat 
  into 
  the 
  security 
  

   of 
  the 
  distant 
  past 
  when 
  called 
  upon 
  for 
  an 
  explanation 
  of 
  their 
  

   origin. 
  Heavy 
  iron 
  scraper 
  dredges 
  have 
  been 
  successfully 
  employed, 
  

   in 
  comparatively 
  deep 
  water, 
  both 
  by 
  Woods 
  Hole 
  and 
  Scripps, 
  off 
  

   the 
  east 
  and 
  west 
  coasts, 
  for 
  obtaining 
  samples 
  from 
  these 
  outcrops. 
  

   Where 
  the 
  beds 
  are 
  nearly 
  horizontal 
  it 
  is 
  even 
  possible 
  to 
  work 
  out 
  

   roughly 
  the 
  stratigraphic 
  succession. 
  This 
  serves 
  the 
  double 
  pur- 
  

   pose 
  of 
  not 
  only 
  giving 
  some 
  information 
  as 
  to 
  the 
  rocks 
  constituting 
  

   the 
  continental 
  shelves 
  but 
  also 
  of 
  fixing 
  at 
  least 
  the 
  maximum 
  age 
  

   of 
  the 
  canyons. 
  On 
  the 
  east 
  coast 
  the 
  formations 
  are 
  all 
  sedimentary, 
  

   ranging 
  from 
  Upper 
  Cretaceous 
  through 
  the 
  late 
  Plioecne. 
  In 
  texture 
  

   the 
  different 
  beds 
  vary 
  from 
  indurated 
  sandstones 
  to 
  friable 
  green- 
  

   sands 
  and 
  compacted 
  silts 
  and 
  clays 
  (Stetson 
  et 
  al., 
  1936). 
  Cores 
  

   taken 
  from 
  the 
  bottom 
  of 
  the 
  canyons 
  show 
  a 
  clay, 
  with 
  Arctic 
  For- 
  

   aminifera, 
  presumably 
  deposited 
  during 
  the 
  last 
  stage 
  of 
  the 
  Wis- 
  

   consin. 
  The 
  time 
  of 
  canyon 
  excavation 
  can 
  thus 
  be 
  bracketed 
  with 
  

   fair 
  exactness, 
  and 
  further 
  work 
  will 
  doubtless 
  narrow 
  this 
  span. 
  

   Mollusks 
  and 
  echinoderms 
  have 
  proved 
  useful 
  in 
  some 
  cases 
  as 
  guide 
  

   fossils, 
  but 
  Foraminifera 
  have 
  been 
  by 
  far 
  the 
  most 
  valuable. 
  Al- 
  

   though 
  the 
  shelf 
  is 
  the 
  submerged 
  extension 
  of 
  the 
  Coastal 
  Plain, 
  the 
  

   fauna 
  of 
  the 
  sediments 
  at 
  the 
  continental 
  margin 
  differs 
  from 
  that 
  

   of 
  the 
  emerged 
  portion, 
  and 
  the 
  formations 
  evidently 
  belong 
  to 
  differ- 
  

   ent 
  facies. 
  In 
  some 
  cases 
  there 
  is 
  a 
  curious 
  parallelism 
  with 
  the 
  

   warm-water 
  fauna 
  of 
  the 
  Mississippi 
  Embayment. 
  The 
  walls 
  of 
  

   the 
  west 
  coast 
  canyons 
  likewise 
  consist, 
  for 
  the 
  most 
  part, 
  of 
  sedi- 
  

   mentary 
  formations, 
  the 
  youngest 
  of 
  which 
  are 
  Pliocene, 
  although 
  in 
  

   the 
  upper 
  part 
  of 
  Monterey 
  Canyon 
  Shepard 
  has 
  reported 
  granite. 
  

   Any 
  theory 
  which 
  is 
  put 
  forward 
  to 
  explain 
  the 
  much-disputed 
  ques- 
  

   tion 
  of 
  origin 
  of 
  these 
  extraordinary 
  topographic 
  features 
  must 
  take 
  

   into 
  account 
  the 
  data 
  which 
  this 
  dredging 
  has 
  afforded, 
  namely, 
  their 
  

   age 
  and 
  the 
  type 
  of 
  rock 
  into 
  which 
  they 
  are 
  cut. 
  Similar 
  work 
  in 
  

   the 
  canyons 
  of 
  other 
  continents 
  is 
  much 
  to 
  be 
  desired, 
  in 
  order 
  that 
  

  

  2 
  Since 
  the 
  manuscript 
  has 
  been 
  completed 
  yet 
  another 
  theory 
  has 
  been 
  added 
  to 
  the 
  list. 
  

   Bucher 
  (1940) 
  considers 
  that 
  the 
  erosive 
  effect 
  of 
  tsunamis 
  spending 
  their 
  energy 
  against 
  

   the 
  continental 
  slope 
  may 
  be 
  the 
  most 
  important 
  single 
  factor 
  in 
  producing 
  this 
  maturely 
  

   dissected 
  submarine 
  topography. 
  

  

  