﻿AGE 
  OF 
  THE 
  TACONIC 
  SYSTEM. 
  407 
  

  

  for 
  that 
  of 
  Massachusetts 
  from 
  my 
  own 
  observations. 
  The 
  maps 
  of 
  

   Vermont 
  and 
  Massachusetts 
  could 
  be 
  much 
  improved 
  by 
  a 
  more 
  

   thorough 
  survey 
  ; 
  but 
  the 
  changes 
  that 
  would 
  be 
  thus 
  introduced 
  

   would 
  not 
  alter 
  the 
  general 
  facts 
  bearing 
  on 
  the 
  Taconic 
  question. 
  

  

  A 
  word 
  further 
  with 
  regard 
  to 
  the 
  paragraph 
  cited 
  in 
  the 
  early 
  

   part 
  of 
  this 
  paper 
  from 
  the 
  Proceedings 
  of 
  the 
  Geological 
  Society. 
  

  

  This 
  paragraph 
  makes 
  the 
  stratigraphical 
  evidence 
  doubtful, 
  be- 
  

   cause 
  it 
  says, 
  " 
  where 
  newer 
  strata 
  are 
  in 
  unconformable 
  contact 
  

   with 
  older 
  ones, 
  the 
  effect 
  of 
  lateral 
  movements 
  of 
  compression, 
  in- 
  

   volving 
  the 
  two 
  series, 
  is 
  generally 
  to 
  cause 
  the 
  newer 
  and 
  more 
  

   yielding 
  strata 
  to 
  dip 
  towards 
  and 
  even 
  beneath 
  the 
  edges 
  of 
  the 
  

   older 
  rock." 
  

  

  The 
  fact 
  here 
  alleged 
  may 
  be 
  questioned. 
  But 
  letting 
  it 
  stand 
  

   that, 
  under 
  the 
  conditions 
  stated, 
  the 
  newer 
  and 
  more 
  yielding 
  

   strata 
  are 
  generally 
  made 
  to 
  dip 
  toward 
  the 
  older 
  rock, 
  it 
  has 
  no 
  

   bearing 
  here 
  ; 
  for 
  there 
  is 
  no 
  such 
  general 
  dip 
  along 
  the 
  Taconic 
  

   range. 
  The 
  limestone 
  of 
  its 
  eastern 
  side, 
  here 
  claimed 
  to 
  be 
  the 
  

   newer, 
  does 
  not 
  generally 
  dip 
  toward 
  the 
  older 
  rock^ 
  that 
  is, 
  toward 
  

   the 
  Taconic 
  schists, 
  which 
  are 
  claimed 
  to 
  be 
  the 
  older. 
  Through 
  

   nine 
  tenths 
  of 
  the 
  length 
  of 
  the 
  belt, 
  the 
  dip, 
  as 
  all 
  observers 
  have 
  

   found, 
  and 
  as 
  recognized 
  above, 
  is 
  eastward 
  for 
  both 
  the 
  eastern 
  

   limestone, 
  the 
  schists, 
  and 
  the 
  western 
  limestone, 
  the 
  westward 
  dip 
  

   of 
  the 
  eastern 
  limestone 
  occurring, 
  as 
  has 
  been 
  stated, 
  in 
  the 
  region 
  

   of 
  the 
  higher 
  peaks. 
  Hence 
  the 
  point 
  insisted 
  upon 
  by 
  the 
  pro- 
  

   pounder 
  of 
  the 
  doubt, 
  if 
  true 
  in 
  fact, 
  has 
  no 
  application 
  to 
  the 
  region 
  

   of 
  the 
  Taconic 
  schists. 
  

  

  The 
  stratigraphical 
  and 
  palseontological 
  demonstration 
  of 
  the 
  

   Lower 
  Silurian 
  age 
  of 
  the 
  Taconic 
  and 
  associated 
  rocks 
  leads 
  us 
  to 
  

   conclusions 
  of 
  lithological 
  interest. 
  It 
  enables 
  us 
  to 
  decide 
  defi- 
  

   nitely 
  what 
  are 
  some 
  of 
  the 
  kinds 
  of 
  metamorphic 
  rocks 
  that 
  may 
  

   be 
  of 
  Lower 
  Silurian 
  age, 
  and 
  of 
  the 
  closing 
  period 
  of 
  the 
  Lower 
  

   Silurian 
  ; 
  for 
  the 
  Taconic 
  schists, 
  which 
  are 
  in 
  part 
  roofing-slates 
  

   at 
  the 
  northern 
  extremity 
  of 
  the 
  range 
  in 
  Vermont, 
  where 
  the 
  meta- 
  

   morphic 
  changes 
  were 
  slight, 
  are, 
  a 
  little 
  to 
  the 
  south, 
  hydromica- 
  

   schist 
  ; 
  and 
  further 
  south, 
  chloritic 
  hydromica-schist 
  and 
  chlorite- 
  

   schist, 
  as 
  well 
  as 
  ordinary 
  hydromica-schist, 
  each 
  kind 
  often 
  granati- 
  

   ferous 
  ; 
  and 
  then, 
  still 
  further, 
  mica-schist, 
  generally 
  granatiferous 
  

   and 
  in 
  some 
  places 
  staurolitic 
  ; 
  and 
  at 
  the 
  southern 
  extremity 
  they 
  

   are 
  in 
  part 
  mica- 
  schist 
  and 
  gneiss. 
  Such 
  facts 
  bear 
  weightily 
  on 
  the 
  

   lithological 
  criterion 
  of 
  geological 
  age 
  in 
  its 
  application 
  to 
  meta- 
  

   morphic 
  rocks 
  ; 
  and 
  perhaps 
  some 
  will 
  recognize 
  in 
  this 
  a 
  reason 
  

   for 
  the 
  expression 
  of 
  that 
  doubt 
  remarked 
  upon 
  above. 
  

  

  I 
  leave 
  the 
  lithological 
  branch 
  of 
  the 
  subject 
  with 
  this 
  single 
  

   remark, 
  referring 
  to 
  my 
  papers 
  on 
  the 
  limestone 
  and 
  associated 
  rocks 
  

   of 
  the 
  Green 
  Mountains 
  for 
  further 
  details. 
  

  

  