﻿230 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  194 
  3 
  

  

  slope 
  and 
  covered 
  an 
  area 
  of 
  1764 
  square 
  statute 
  miles 
  extending 
  more 
  than 
  150 
  

   miles 
  offshore, 
  all 
  of 
  which 
  was 
  precisely 
  controlled 
  by 
  radio 
  acoustic 
  ranging 
  

   and 
  taut 
  wire 
  traverses 
  tied 
  in 
  to 
  the 
  shore 
  triangulation 
  net 
  on 
  North 
  American 
  

   1927-datum. 
  

  

  As 
  a 
  contrast, 
  he 
  cites 
  the 
  504 
  deep-sea 
  soundings 
  made 
  by 
  the 
  

   Challenger 
  and 
  the 
  then 
  remarkable 
  number 
  of 
  3,195 
  made 
  between 
  

   1874 
  and 
  1879 
  by 
  the 
  Blake. 
  Similar 
  work 
  is 
  constantly 
  being 
  carried 
  

   out 
  on 
  the 
  Pacific 
  coast 
  and 
  in 
  the 
  Gulf 
  of 
  Mexico 
  as 
  well 
  as 
  on 
  the 
  

   Atlantic. 
  

  

  Almost 
  as 
  important 
  as 
  the 
  development 
  of 
  the 
  fathometer 
  is 
  the 
  

   new 
  method 
  of 
  determining 
  positions 
  accurately 
  at 
  long 
  distances 
  

   from 
  shore 
  (Geophysical 
  Exploration 
  of 
  the 
  Ocean 
  Bottom, 
  1937, 
  

   pp. 
  9-25). 
  Formerly 
  only 
  the 
  inshore 
  waters 
  within 
  sight 
  of 
  the 
  

   triangulation 
  stations 
  were 
  accurately 
  surveyed. 
  Once 
  out 
  of 
  sight 
  

   of 
  these 
  fixed 
  marks 
  the 
  position 
  of 
  the 
  surveying 
  ship 
  becomes 
  more 
  

   and 
  more 
  doubtful 
  as 
  she 
  proceeds 
  offshore, 
  until 
  at 
  some 
  distance 
  

   from 
  land 
  the 
  positions 
  of 
  individual 
  soundings 
  on 
  the 
  older 
  charts 
  

   are 
  not 
  much 
  more 
  accurate 
  than 
  an 
  ordinary 
  sextant 
  fix. 
  As 
  an 
  

   illustration, 
  on 
  all 
  charts 
  prior 
  to 
  1938 
  the 
  steep, 
  outer 
  part 
  of 
  the 
  

   Hudson 
  Gorge 
  makes 
  a 
  pronounced 
  S-curve. 
  The 
  recent 
  surveys 
  have 
  

   shown 
  that 
  this 
  S-curve 
  is 
  fictitious, 
  and 
  that 
  the 
  head 
  of 
  the 
  Hudson 
  

   Gorge 
  had 
  been 
  connected 
  with 
  the 
  mouth 
  of 
  a 
  smaller 
  neighbor, 
  

   and 
  its 
  own 
  mouth 
  had 
  been 
  missed 
  entirely. 
  When 
  vessels 
  were 
  

   slow 
  a 
  very 
  generalized 
  representation 
  of 
  the 
  continental 
  shelf 
  and 
  

   slope 
  was 
  considered 
  sufficient 
  for 
  all 
  practical 
  navigational 
  purposes 
  ; 
  

   but 
  now, 
  when 
  many 
  liners 
  have 
  cruising 
  speeds 
  of 
  over 
  20 
  and 
  even 
  

   30 
  knots 
  and 
  all 
  are 
  equipped 
  with 
  echo-sounding 
  apparatus, 
  the 
  

   Survey 
  decided 
  that 
  more 
  accurate 
  detail 
  of 
  the 
  offshore 
  bottoms 
  

   would 
  be 
  of 
  considerable 
  assistance 
  to 
  shipping. 
  In 
  thick 
  weather 
  a 
  

   topographic 
  profile 
  could 
  be 
  constructed 
  by 
  taking 
  continuous 
  sound- 
  

   ings 
  and 
  the 
  ship 
  located 
  by 
  comparison 
  with 
  the 
  topography 
  on 
  the 
  

   chart. 
  This 
  decision 
  on 
  the 
  part 
  of 
  the 
  Survey 
  was 
  more 
  far-reaching 
  

   than 
  was 
  at 
  first 
  realized, 
  for 
  in 
  carrying 
  out 
  this 
  work 
  the 
  true 
  

   configurations 
  of 
  the 
  now 
  famous 
  submarine 
  canyons 
  were 
  revealed 
  

   for 
  the 
  first 
  time, 
  far 
  greater 
  numbers 
  of 
  them 
  were 
  discovered 
  

   than 
  had 
  hitherto 
  been 
  dreamed 
  of, 
  and 
  a 
  major 
  geological 
  discussion 
  

   was 
  precipitated 
  which 
  is 
  still 
  far 
  from 
  settled. 
  

  

  To 
  solve 
  this 
  difficulty 
  of 
  accurate 
  positions 
  offshore, 
  the 
  United 
  

   States 
  Coast 
  and 
  Geodetic 
  Survey 
  developed 
  a 
  method 
  which 
  they 
  

   call 
  radio-acoustic 
  ranging 
  (Geophysical 
  Exploration 
  of 
  the 
  Ocean 
  

   Bottom, 
  1937, 
  pp. 
  9-25). 
  Briefly, 
  the 
  system 
  is 
  this: 
  Two 
  or 
  more 
  

   radio 
  stations 
  are 
  equipped 
  with 
  hydrophones, 
  and 
  their 
  positions 
  

   are 
  determined 
  with 
  reference 
  to 
  the 
  triangulation 
  on 
  shore. 
  The 
  

   surveying 
  vessel, 
  out 
  of 
  sight 
  of 
  land, 
  steams 
  along 
  her 
  course, 
  

   sounding 
  continuously 
  with 
  her 
  fathometer. 
  When 
  a 
  position 
  is 
  

  

  