﻿[27] 
  ON 
  DEEP-SEA 
  DEPOSITS 
  785 
  

  

  chalk 
  where 
  Pelagic 
  conditions 
  are 
  indicated 
  nmst 
  bo 
  regarded 
  as 
  hav- 
  

   ing 
  been 
  laid 
  down 
  rather 
  along 
  the 
  border 
  of 
  a 
  continent 
  than 
  in 
  a 
  

   true 
  oceanic 
  area. 
  On 
  the 
  other 
  hand, 
  the 
  argillaceous 
  and 
  calcareous 
  

   rocks 
  recently 
  discovered 
  by 
  Dr. 
  Guppy 
  in 
  the 
  upraised 
  coral 
  islands 
  in 
  

   the 
  Solomon 
  group 
  are 
  nearly 
  identical 
  with 
  the 
  Pteropod 
  and 
  Globi- 
  

   gerina 
  oozes 
  of 
  the 
  Pacific. 
  

  

  Regions 
  situated 
  similarly 
  to 
  inclosed 
  and 
  shallow 
  seas 
  and 
  the 
  bor- 
  

   ders 
  of 
  the 
  present 
  continents 
  appear 
  to 
  have 
  been, 
  throughout 
  all 
  geo- 
  

   logical 
  ages, 
  the 
  theater 
  of 
  the 
  greatest 
  and 
  most 
  remarkable 
  changes 
  ; 
  

   in 
  short, 
  all, 
  or 
  nearly 
  all, 
  the 
  sedimentary 
  rocks 
  of 
  the 
  continents 
  would 
  

   seem 
  to 
  have 
  been 
  built 
  up 
  in 
  areas 
  like 
  those 
  now 
  occupied 
  by 
  the 
  ter- 
  

   rigenous 
  deposits, 
  which 
  we 
  may 
  designate 
  the 
  transitional 
  or 
  critical 
  

   area 
  of 
  the 
  earth's 
  surface. 
  This 
  area 
  occupies, 
  we 
  estimate, 
  about 
  two- 
  

   eighths 
  of 
  the 
  earth's 
  surface, 
  while 
  the 
  continental 
  and 
  abysmal 
  areas 
  

   occupy 
  each 
  about 
  three-eighths. 
  

  

  During 
  each 
  era 
  of 
  the 
  earth's 
  history 
  the 
  borders 
  of 
  some 
  lands 
  have 
  

   sunk 
  beneath 
  the 
  sea 
  and 
  been 
  covered 
  by 
  marine 
  sediments, 
  while 
  in 
  

   other 
  parts 
  the 
  terrigenous 
  deposits 
  have 
  been 
  elevated 
  into 
  dry 
  land, 
  

   and 
  have 
  carried 
  with 
  tbem 
  a 
  record 
  of 
  the 
  organisms 
  which 
  flourished 
  

   in 
  the 
  sea 
  of 
  the 
  time. 
  In 
  this 
  transitional 
  area 
  there 
  has 
  been 
  through- 
  

   out 
  a 
  continuity 
  of 
  geological 
  and 
  biological 
  phenomena. 
  

  

  From 
  these 
  considerations 
  it 
  will 
  be 
  evident 
  that 
  the 
  character 
  of 
  a 
  

   deposit 
  is 
  determined 
  much 
  more 
  by 
  distance 
  from 
  the 
  shore 
  of 
  a 
  conti- 
  

   nent 
  than 
  by 
  actual 
  depth, 
  and 
  the 
  same 
  would 
  appear 
  to 
  be 
  the 
  case 
  

   with 
  respect 
  to 
  the 
  fauna 
  spread 
  over 
  the 
  floor 
  of 
  the 
  present 
  oceans. 
  

   Dredgings 
  near 
  the 
  shores 
  of 
  continents, 
  in 
  depths 
  of 
  1,000, 
  2,000, 
  or 
  

   3,000 
  fathoms, 
  are 
  more 
  productive 
  both 
  in 
  species 
  and 
  individuals 
  than 
  

   dredgings 
  at 
  similar 
  depths 
  several 
  hundred 
  miles 
  seawards. 
  Again, 
  

   among 
  the 
  few 
  species 
  dredged 
  in 
  the 
  abysmal 
  areas 
  furthest 
  removed 
  

   from 
  land 
  the 
  majority 
  show 
  archaic 
  characters, 
  or 
  belong 
  to 
  groups 
  

   which 
  have 
  a 
  wide 
  distribution 
  in 
  time 
  as 
  well 
  as 
  over 
  the 
  floor 
  of 
  the 
  

   present 
  oceans. 
  Such 
  are 
  the 
  HexaCtinellida, 
  Brachiopoda, 
  Stalked 
  

   Crinoids, 
  and 
  other 
  Echinoderms, 
  &c. 
  

  

  As 
  already 
  mentioned, 
  the 
  transitional 
  area 
  is 
  that 
  which 
  now 
  shows 
  

   the 
  greatest 
  variety 
  in 
  respect 
  to 
  biological 
  and 
  physical 
  conditions, 
  

   and 
  in 
  past 
  time 
  it 
  has 
  been 
  subject 
  to 
  the 
  most 
  frequent 
  and 
  the 
  great- 
  

   est 
  amount 
  of 
  change. 
  The 
  animals 
  now 
  living 
  in 
  this 
  area 
  may 
  be 
  

   regarded 
  as 
  the 
  greatly 
  modified 
  descendants 
  of 
  those 
  which 
  have 
  lived 
  

   in 
  similar 
  regions 
  in 
  past 
  geological 
  ages, 
  and 
  some 
  of 
  whose 
  ancestors 
  

   have 
  been 
  preserved 
  in 
  the 
  sedimentary 
  rocks 
  as 
  fossils. 
  On 
  the 
  other 
  

   hand, 
  many 
  of 
  the 
  animals 
  dredged 
  in 
  the 
  abysmal 
  regions 
  are 
  most 
  

   probably 
  also 
  the 
  descendants 
  of 
  animals 
  which 
  lived 
  in 
  the 
  shallower 
  

   water 
  of 
  former 
  geological 
  periods, 
  but 
  descended 
  into 
  deep 
  water 
  to 
  

   escape 
  the 
  severe 
  struggle 
  for 
  existence, 
  which 
  must 
  always 
  have 
  ob- 
  

   tained 
  in 
  those 
  depths 
  affected 
  by 
  light, 
  heat, 
  motion, 
  and 
  other 
  condi- 
  

   tions. 
  Having 
  found 
  existence 
  possible 
  in 
  the 
  less 
  favorable 
  and 
  deeper 
  

   S. 
  Mis. 
  70 
  50 
  

  

  