﻿OCEANOGRAPHY 
  — 
  STETSON 
  237 
  

  

  Hvorslev, 
  of 
  the 
  Harvard 
  Engineering 
  School, 
  has 
  recently 
  com- 
  

   pleted 
  extensive 
  sampling 
  experiments 
  for 
  the 
  Committee 
  on 
  Sam- 
  

   pling 
  and 
  Testing, 
  American 
  Society 
  of 
  Civil 
  Engineers, 
  in 
  varved 
  

   clays 
  with 
  different 
  types 
  of 
  coring 
  tubes. 
  He 
  finds 
  (personal 
  

   communication) 
  — 
  

  

  that 
  the 
  layers 
  in 
  the 
  upper 
  parts 
  of 
  the 
  cores 
  are 
  often 
  subjected 
  to 
  an 
  increase 
  

   in 
  thickness 
  clue 
  to 
  plastic 
  flow 
  of 
  additional 
  soil 
  into 
  the 
  tube 
  caused 
  by 
  the 
  

   pressure 
  of 
  the 
  cutting 
  edge. 
  With 
  increasing 
  depth 
  of 
  penetration, 
  and 
  thereby 
  

   increasing 
  friction 
  between 
  the 
  sample 
  and 
  the 
  tube, 
  the 
  general 
  load 
  on 
  the 
  soil 
  

   becomes 
  so 
  great 
  that 
  it 
  now 
  becomes 
  squeezed 
  out 
  from 
  under 
  the 
  sampler 
  and 
  

   the 
  thickness 
  of 
  any 
  given 
  layer 
  is 
  thereby 
  reduced. 
  Finally, 
  at 
  a 
  certain 
  critical 
  

   depth, 
  internal 
  wall 
  friction 
  becomes 
  so 
  great 
  that 
  no 
  more 
  soil 
  can 
  enter, 
  and 
  

   the 
  core 
  and 
  tube 
  are 
  driven 
  as 
  a 
  solid 
  pile, 
  pushing 
  a 
  cone 
  of 
  sediment 
  ahead 
  

   of 
  them. 
  There 
  is, 
  therefore, 
  for 
  each 
  particular 
  type 
  of 
  sampler, 
  and 
  for 
  each 
  

   type 
  of 
  soil, 
  a 
  maximum 
  length 
  of 
  sample 
  that 
  can 
  be 
  obtained 
  in 
  a 
  single 
  drive. 
  

   When 
  the 
  soil 
  consists 
  of 
  alternating 
  layers 
  of 
  firm 
  and 
  soft 
  material 
  a 
  further 
  

   complication, 
  originally 
  observed 
  by 
  Pratje, 
  arises 
  in 
  that 
  the 
  soft 
  layers 
  may 
  

   be 
  squeezed 
  out 
  partly 
  or 
  completely 
  while 
  the 
  firm 
  layers 
  still 
  enter 
  the 
  tube 
  

   without 
  any 
  change 
  in 
  thickness. 
  

  

  This 
  behavior 
  of 
  the 
  material 
  introduces 
  a 
  serious 
  factor 
  of 
  error 
  into 
  

   all 
  attempts 
  to 
  determine 
  rates 
  of 
  sedimentation 
  from 
  linear 
  measure- 
  

   ments. 
  

  

  SHALLOW-WATER 
  SEDIMENTS 
  

  

  Like 
  organisms, 
  sediments 
  are 
  the 
  resultants 
  of 
  the 
  long 
  sequence 
  of 
  

   factors 
  to 
  which 
  they 
  have 
  been 
  exposed 
  : 
  current 
  action, 
  wave-gener- 
  

   ated 
  and 
  otherwise, 
  distance 
  from 
  shore 
  and 
  depth 
  of 
  water, 
  the 
  type 
  of 
  

   material 
  supplied 
  and 
  its 
  availability, 
  plus 
  their 
  combined 
  effect 
  in 
  the 
  

   past. 
  These 
  environmental 
  forces 
  have 
  acted 
  on 
  the 
  sediments 
  at 
  their 
  

   source, 
  during 
  the 
  period 
  of 
  transportation, 
  and 
  at 
  their 
  place 
  of 
  depo- 
  

   sition. 
  Many 
  inferences 
  have 
  been 
  drawn 
  in 
  regard 
  to 
  the 
  conditions 
  

   of 
  marine 
  deposition 
  from 
  the 
  study 
  of 
  sedimentary 
  rocks, 
  but 
  insofar 
  

   as 
  present-day 
  marine 
  sediments 
  are 
  concerned 
  very 
  few 
  observational 
  

   data 
  have 
  been 
  accumulated. 
  Of 
  the 
  sediments 
  in 
  the 
  geologic 
  column 
  

   those 
  laid 
  down 
  in 
  the 
  neritic 
  zone 
  bulk 
  the 
  largest, 
  but 
  our 
  knowledge 
  

   of 
  them 
  is 
  still 
  very 
  elementary. 
  The 
  earlier 
  oceanographers 
  were, 
  as 
  

   we 
  have 
  seen, 
  more 
  interested 
  in 
  the 
  deposits 
  of 
  the 
  deep 
  sea, 
  and 
  they 
  

   added 
  but 
  little 
  information 
  concerning 
  those 
  sediments 
  which 
  to 
  the 
  

   geologist 
  are 
  the 
  most 
  important. 
  Chiefly 
  by 
  increasing 
  our 
  knowl- 
  

   edge 
  of 
  present-day 
  marine 
  sediments 
  and 
  the 
  environments 
  under 
  

   which 
  they 
  are 
  being 
  deposited 
  will 
  we 
  be 
  able 
  to 
  reconstruct 
  with 
  any 
  

   degree 
  of 
  certainty 
  the 
  conditions 
  which 
  governed 
  the 
  formation 
  of 
  

   ancient 
  sediments. 
  With 
  this 
  purpose 
  in 
  view, 
  detailed 
  regional 
  stud- 
  

   ies 
  are 
  now 
  being 
  carried 
  out 
  off 
  the 
  Atlantic 
  and 
  Pacific 
  coasts, 
  by 
  the 
  

   Woods 
  Hole 
  and 
  Scripps 
  Institutions, 
  based 
  on 
  traverses 
  of 
  closely 
  

   spaced 
  surface 
  samples 
  as 
  well 
  as 
  long 
  cores. 
  In 
  addition, 
  some 
  ap- 
  

  

  