﻿40 
  

  

  Prof. 
  C. 
  W. 
  Thomson 
  on 
  the 
  

  

  [Nov. 
  26, 
  

  

  depth 
  of 
  the 
  sound, 
  with 
  absolute 
  certainty, 
  for 
  the 
  Atlantic 
  and 
  the 
  

   Southern 
  Sea, 
  we 
  had 
  perhaps 
  the 
  best 
  opportunity 
  of 
  observing 
  it 
  in 
  our 
  

   first 
  section 
  across 
  the 
  Atlantic, 
  between 
  Teneriffe 
  and 
  St. 
  Thomas. 
  The 
  

   first 
  four 
  stations 
  on 
  this 
  section 
  (PI. 
  IV.), 
  at 
  depths 
  from 
  1525 
  to 
  2220 
  

   fathoms, 
  show 
  " 
  Globigerina-ooze." 
  Prom 
  the 
  last 
  of 
  these, 
  which 
  is 
  about 
  

   300 
  miles 
  from 
  Teneriffe, 
  the 
  depth 
  gradually 
  increases 
  to 
  2740 
  fathoms, 
  

   at 
  500, 
  and 
  2950 
  fathoms, 
  at 
  750 
  miles 
  from 
  Teneriffe. 
  The 
  bottom 
  in 
  

   these 
  two 
  soundings 
  might 
  have 
  been 
  called 
  " 
  grey 
  ooze 
  for 
  although 
  its 
  

   nature 
  has 
  altered 
  entirely 
  from 
  the 
  " 
  Globigerina-ooze" 
  the 
  red 
  clay 
  into 
  

   which 
  it 
  is 
  rapidly 
  passing 
  still 
  contains 
  a 
  considerable 
  admixture 
  of 
  car- 
  

   bonate 
  of 
  lime. 
  

  

  The 
  depth 
  goes 
  on 
  increasing, 
  to 
  a 
  distance 
  of 
  1150 
  miles 
  from 
  Tene- 
  

   riffe, 
  when 
  it 
  reaches 
  3150 
  fathoms 
  ; 
  there 
  the 
  clay 
  is 
  pure 
  and 
  smooth, 
  

   and 
  contains 
  scarcely 
  a 
  trace 
  of 
  lime. 
  Prom 
  this 
  great 
  depth 
  the 
  bottom 
  

   gradually 
  rises, 
  and, 
  with 
  decreasing 
  depth, 
  the 
  grey 
  colour 
  and 
  the 
  cal- 
  

   careous 
  composition 
  of 
  the 
  ooze 
  return. 
  Three 
  soundings 
  in 
  2050, 
  1900, 
  

   and 
  1950 
  fathoms 
  on 
  the 
  " 
  Dolphin 
  Pise," 
  gave 
  highly 
  characteristic 
  

   examples 
  of 
  the 
  Globigerina 
  formation. 
  Passing 
  from 
  the 
  middle 
  plateau 
  

   of 
  the 
  Atlantic 
  into 
  the 
  western 
  trough, 
  with 
  depths 
  a 
  little 
  over 
  3000 
  

   fathoms, 
  the 
  red 
  clay 
  returns 
  in 
  all 
  its 
  purity 
  : 
  and 
  our 
  last 
  sounding, 
  in 
  

   1420 
  fathoms, 
  before 
  reaching 
  Sombrero, 
  restored 
  the 
  Globigerina-ooze 
  

   with 
  its 
  peculiar 
  associated 
  fauna. 
  

  

  This 
  section 
  shows 
  also 
  the 
  wide 
  extension 
  and 
  the 
  vast 
  geological 
  

   importance 
  of 
  the 
  red-clay 
  formation. 
  The 
  total 
  distance 
  from 
  Tenerrffe 
  

   to 
  Sombrero 
  is 
  about 
  2700 
  miles. 
  Proceeding 
  from 
  east 
  to 
  west, 
  we 
  have 
  

   About 
  80 
  miles 
  of 
  volcanic 
  mud 
  and 
  sand. 
  

   350 
  „ 
  „ 
  " 
  Globigerina-ooze" 
  

   1050 
  „ 
  „ 
  " 
  red 
  clay," 
  

   330 
  „ 
  „ 
  " 
  Globigerina-ooze" 
  

   850 
  „ 
  „ 
  " 
  red 
  clay," 
  

   40 
  ,, 
  „ 
  " 
  Globigerina-ooze" 
  

   giving 
  a 
  total 
  of 
  1900 
  miles 
  of 
  red 
  clay 
  to 
  720 
  miles 
  of 
  Globigerina-ooze. 
  

  

  The 
  following 
  Table, 
  taken 
  from 
  the 
  chart, 
  gives 
  a 
  good 
  general 
  idea 
  

   of 
  the 
  distribution 
  of 
  the 
  two 
  formations 
  with 
  respect 
  to 
  depth. 
  It 
  can- 
  

   not 
  of 
  course 
  be 
  taken 
  as 
  exact 
  ; 
  the 
  indications 
  were 
  jotted 
  down 
  from 
  

   the 
  impression 
  of 
  colour 
  given 
  at 
  the 
  time, 
  and 
  there 
  is 
  no 
  hard 
  and 
  

   fast 
  line 
  between 
  Globigerina-ooze 
  and 
  grey 
  ooze 
  on 
  the 
  one 
  hand, 
  and 
  

   between 
  red 
  clay 
  and 
  grey 
  ooze 
  on 
  the 
  other. 
  The 
  Table 
  gives 
  an 
  

   average 
  depth 
  of 
  1800 
  fathoms 
  for 
  our 
  soundings 
  in 
  the 
  Globigerina- 
  

   ooze. 
  This 
  is 
  a 
  datum 
  of 
  no 
  value 
  ; 
  for 
  we 
  only 
  rarely 
  sounded 
  in 
  shallow 
  

   water, 
  and 
  we 
  know 
  that 
  this 
  formation 
  covers 
  large 
  areas 
  at 
  depths 
  

   between 
  300 
  and 
  400 
  fathoms 
  ; 
  but 
  the 
  mean 
  maximum 
  depth 
  at 
  which 
  it 
  

   occurs 
  is 
  important, 
  and 
  that 
  may 
  be 
  taken 
  from 
  the 
  Table 
  as 
  about 
  

   2250 
  fathoms. 
  The 
  mean 
  depth 
  at 
  which 
  we 
  find 
  the 
  transition 
  grey 
  

   ooze 
  is 
  2400 
  fathoms 
  j 
  and 
  the 
  mean 
  depth 
  of 
  the 
  red-clay 
  soundings 
  is 
  

  

  