﻿440 
  J. 
  D. 
  Dana 
  — 
  PercivaVs 
  Map 
  of 
  the 
  Jura-Trias. 
  

  

  The 
  Map 
  : 
  some 
  of 
  the 
  Features 
  of 
  the 
  area, 
  and 
  facts 
  con- 
  

   nected 
  with 
  its 
  Southern 
  termination. 
  

  

  As 
  Percival's 
  Report 
  is 
  little 
  known 
  among 
  geologists 
  I 
  in- 
  

   troduce 
  a 
  photo-engraved 
  copy 
  of 
  the 
  middle 
  portion 
  of 
  his 
  

   chart, 
  which 
  includes 
  the 
  larger 
  part 
  of 
  the 
  Jura-Trias 
  area, 
  

   along 
  with 
  borders 
  of 
  the 
  eastern 
  and 
  western 
  metamorphic 
  

   regions 
  of 
  the 
  State. 
  It 
  makes 
  Plate 
  XVI. 
  

  

  The 
  Jura-Trias 
  area, 
  or 
  that 
  of 
  the 
  Connecticut 
  valley 
  sand- 
  

   stone, 
  is 
  the 
  colored 
  portion. 
  The 
  length 
  from 
  the 
  Sound 
  to 
  

   the 
  northern 
  limit, 
  8 
  miles 
  north 
  of 
  Hartford, 
  is 
  about 
  37^ 
  

   miles. 
  It 
  contains 
  all 
  of 
  the 
  more 
  complicated 
  portion 
  of 
  the 
  

   trap-region 
  of 
  Connecticut, 
  the 
  part 
  omitted 
  having 
  only 
  the 
  

   continuation 
  of 
  the 
  two 
  western 
  belts 
  and 
  another 
  smaller 
  on 
  

   the 
  western 
  margin 
  of 
  the 
  area. 
  

  

  The 
  narrow 
  linear 
  areas 
  on 
  the 
  map 
  are 
  the 
  trap-belts. 
  They 
  

   include, 
  according 
  to 
  Percival, 
  simple 
  trap-dikes 
  and 
  dikes 
  

   with 
  outflows 
  between 
  layers 
  of 
  sandstone. 
  The 
  breaks 
  in 
  

   the 
  trap-belt 
  of 
  a 
  range 
  generally 
  correspond 
  to 
  actual 
  intervals 
  

   in 
  the 
  extrusions 
  of 
  trap. 
  But 
  in 
  some 
  cases, 
  as 
  in 
  the 
  body 
  

   of 
  Mt. 
  Carmel, 
  they 
  indicate 
  only 
  abrupt 
  depressions 
  in 
  the 
  

   ridge, 
  Percival 
  appearing 
  to 
  regard 
  them 
  as 
  a 
  consequence 
  of 
  

   partial 
  interruptions 
  in 
  the 
  outflow; 
  and 
  in 
  the 
  southern 
  end 
  

   of 
  West 
  Rock, 
  where 
  the 
  bay 
  of 
  sandstone 
  just 
  north 
  (Plate 
  YI) 
  

   evidently 
  suggested 
  a 
  similar 
  supposition. 
  

  

  About 
  New 
  Haven 
  the 
  figures 
  1, 
  2, 
  3, 
  4, 
  mark 
  successively 
  

   East 
  Rock, 
  Mill 
  Rock, 
  Pine 
  Rock 
  and 
  the 
  West 
  Rock 
  Ridge. 
  

   The 
  long 
  southern 
  part 
  of 
  the 
  latter 
  is 
  lettered 
  W 
  S 
  I, 
  and 
  the 
  

   northern 
  W 
  S 
  1 
  1. 
  North 
  of 
  North 
  Haven 
  at 
  6 
  is 
  Mt. 
  Carmel. 
  

   In 
  the 
  northern 
  part 
  of 
  the 
  town 
  of 
  Meriden 
  are 
  the 
  " 
  Hanging 
  

   Hills" 
  ; 
  and 
  3, 
  4, 
  5, 
  6, 
  7, 
  8, 
  9, 
  and 
  others 
  beyond 
  are 
  parts 
  of 
  

   the 
  longest 
  and 
  most 
  elevated 
  trap-range 
  of 
  the 
  valley 
  ; 
  it 
  con- 
  

   tinues 
  to 
  Mt. 
  Tom 
  in 
  Massachusetts, 
  nearly 
  56 
  miles, 
  and 
  has 
  a 
  

   height 
  of 
  996 
  feet 
  at 
  its 
  southern 
  end 
  according 
  to 
  Guyot's 
  

   barometric 
  observations. 
  

  

  To 
  the 
  east 
  of 
  New 
  Haven 
  and 
  New 
  Haven 
  Bay, 
  in 
  East 
  

   Haven, 
  the 
  bow-shaped 
  trap-ridge, 
  E 
  I, 
  is 
  the 
  Saltonstall 
  

  

  his 
  death 
  it 
  was 
  sold 
  for 
  $20,000. 
  Such 
  was 
  the 
  man 
  that 
  made 
  the 
  remarkable 
  

   survey 
  of 
  the 
  trap-belts 
  of 
  Connecticut. 
  He 
  received 
  but 
  small 
  pay 
  from 
  the 
  

   State, 
  and 
  at 
  last 
  had 
  to 
  content 
  himself 
  with 
  a 
  very 
  insufficient 
  sum 
  for 
  the 
  pub- 
  

   lication 
  of 
  his 
  Report 
  — 
  "not 
  exceeding 
  $1,500, 
  for 
  printing 
  and 
  superintending." 
  

   The 
  Report 
  is 
  therefore 
  but 
  an 
  abstract, 
  as 
  he 
  says 
  in 
  his 
  Preface, 
  of 
  what 
  with 
  

   more 
  generous 
  treatment 
  he 
  would 
  have 
  published. 
  

  

  His 
  geological 
  science 
  was 
  not 
  altogether 
  that 
  of 
  the 
  present 
  day 
  ; 
  for 
  he 
  be- 
  

   lieved 
  that 
  the 
  crystalline 
  formations 
  were 
  segregations 
  out 
  of 
  a 
  world-wide 
  

   magma: 
  but 
  he 
  still, 
  as 
  he 
  says, 
  recorded 
  in 
  his 
  notebook 
  more 
  than 
  8,000 
  dips 
  

   and 
  strikes, 
  realizing 
  their 
  value 
  in 
  investigation 
  far 
  better 
  than 
  many 
  a 
  recent 
  

   student 
  of 
  such 
  rocks. 
  It 
  is 
  greatly 
  to 
  be 
  regretted 
  that 
  a 
  full 
  Report 
  was 
  not 
  

   published. 
  

  

  Percival 
  was 
  born 
  in 
  1795 
  and 
  died 
  in 
  1856. 
  

  

  