﻿90 
  J. 
  D. 
  Dana 
  — 
  Features 
  of 
  non-volcanic 
  Igneous 
  Ejections. 
  

  

  by 
  sea-shore 
  action. 
  Through 
  such 
  means, 
  beyond 
  doubt, 
  the 
  

   part 
  of 
  it 
  extending 
  from 
  Mill 
  River 
  westward 
  for 
  300 
  yards, 
  

   was 
  reduced 
  to 
  a 
  width 
  above 
  ground 
  of 
  40 
  to 
  50 
  feet. 
  This 
  

   narrowing 
  commences 
  just 
  west 
  of 
  the 
  Pumping 
  House 
  of 
  the 
  

   City 
  Water 
  Works 
  (p, 
  fig. 
  5), 
  and 
  continues 
  without 
  inter- 
  

   ruption 
  to 
  the 
  river. 
  It 
  is 
  part 
  of 
  the 
  evidence 
  of 
  a 
  greater 
  

   New 
  Haven 
  Bay 
  at 
  some 
  former 
  time. 
  

  

  Why 
  the 
  range 
  falls 
  gradually 
  to 
  so 
  low 
  a 
  level 
  at 
  Whitney 
  - 
  

   ville, 
  appears 
  to 
  be 
  explained 
  only 
  on 
  the 
  view 
  that 
  less 
  trap 
  

   here 
  came 
  to 
  the 
  surface. 
  I 
  have 
  elsewhere 
  shown 
  that 
  it 
  

   cannot 
  be 
  due 
  to 
  glacial 
  removal. 
  Neither 
  is 
  it 
  probable 
  that 
  

   fluvial 
  or 
  marine 
  waters 
  have 
  produced 
  it. 
  We 
  have 
  to 
  attri- 
  

   bute 
  it 
  to 
  some 
  condition 
  existing 
  or 
  produced 
  in 
  the 
  supply 
  - 
  

   fissures 
  of 
  eastern 
  Mill 
  Rock 
  and 
  Whitney 
  Peak, 
  at 
  the 
  time 
  

   they 
  were 
  opened. 
  

  

  Besides 
  the 
  dikes 
  of 
  Pine 
  Rock 
  and 
  Mill 
  Rock, 
  there 
  is 
  another 
  

   transverse 
  dike 
  of 
  special 
  interest 
  which 
  intersects 
  the 
  West 
  Rock 
  

   ridge 
  just 
  below 
  the 
  margin 
  of 
  Wintergreen 
  Lake, 
  or 
  about 
  one 
  

   and 
  a 
  quarter 
  miles 
  north 
  of 
  the 
  southern 
  termination 
  of 
  the 
  ridge 
  

   and 
  four 
  miles 
  from 
  New 
  Haven 
  Bay. 
  It 
  descends 
  the 
  eastern 
  

   slope 
  of 
  West 
  Rock 
  in 
  an 
  interrupted 
  ridge, 
  forms 
  part 
  of 
  the 
  

   southern 
  bank 
  of 
  Wintergreen 
  Lake, 
  sinks 
  to 
  the 
  level 
  of 
  the 
  

   West 
  Rock 
  surface 
  at 
  the 
  summit, 
  but 
  stands 
  out 
  like 
  a 
  buttress 
  

   along 
  the 
  steep 
  west 
  front 
  of 
  the 
  Rock. 
  From 
  the 
  last 
  feature 
  

   I 
  have 
  called 
  it 
  for 
  the 
  past 
  twenty 
  years, 
  the 
  "Buttress 
  dike." 
  

   It 
  extends 
  south-westward 
  through 
  the 
  metamorphic 
  region 
  

   of 
  the 
  towns 
  of 
  Woodbridge 
  and 
  Orange 
  to 
  the 
  mouth 
  of 
  the 
  

   Housatonic 
  — 
  as 
  long 
  since 
  mapped 
  and 
  described 
  by 
  Pereival. 
  

   This 
  dike 
  has 
  a 
  pitch 
  northward, 
  amounting 
  to 
  25° 
  from 
  a 
  vertical 
  

   in 
  the 
  part 
  of 
  it 
  intersecting 
  West 
  Rock, 
  but 
  in 
  that 
  through 
  

   the 
  metamorphic 
  rocks 
  it 
  is 
  nearly 
  vertical* 
  The 
  strike 
  of 
  

   the 
  inclined 
  columns 
  in 
  the 
  buttress 
  portion 
  is 
  S. 
  30-3*2° 
  E. 
  It 
  

   is 
  an 
  example 
  of 
  a 
  dike 
  made 
  subsequently 
  to 
  the 
  cooling 
  of 
  

   another 
  dike, 
  that 
  of 
  West 
  Rock. 
  It 
  has 
  great 
  importance 
  in 
  

   this 
  connection, 
  since 
  it 
  brings 
  into 
  the 
  Jura-Trias 
  system 
  of 
  

   mountain-movements 
  a 
  dike 
  intersecting 
  the 
  metamorphic 
  rocks 
  

   outside 
  of 
  the 
  Connecticut 
  Valley, 
  and 
  one 
  that 
  branches 
  off 
  from 
  

   the 
  southern 
  or 
  New 
  Haven 
  part 
  of 
  the 
  system. 
  

  

  3. 
  THE 
  EAST 
  ROCK 
  SERIES. 
  

  

  The 
  form 
  of 
  the 
  East 
  Rock 
  area 
  and 
  its 
  position 
  between 
  

   Mill 
  River 
  and 
  the 
  Quinnipiac, 
  are 
  shown 
  on 
  Plate 
  II. 
  Through 
  

  

  * 
  The 
  rock 
  of 
  the 
  dike 
  is 
  sparsely 
  porphyritic 
  ; 
  and 
  the 
  feldspar 
  distributed 
  

   through 
  it 
  in 
  crystals 
  a 
  fourth 
  to 
  a 
  third 
  of 
  an 
  inch 
  Jong 
  is 
  anorthite, 
  as 
  shown 
  

   by 
  G. 
  W. 
  Hawes 
  (this 
  Journal, 
  III, 
  ix, 
  188, 
  1875). 
  This 
  character 
  makes 
  it 
  easy 
  

   to 
  identify 
  the 
  several 
  parts 
  of 
  the 
  dike 
  ; 
  it 
  is 
  the 
  only 
  case 
  in 
  which 
  this 
  mineral 
  

   has 
  thus 
  far 
  been 
  found 
  in 
  the 
  Connecticut 
  Valley 
  trap. 
  

  

  Percival's 
  account 
  of 
  the 
  Buttress 
  dike 
  and 
  its 
  extension 
  southwestward 
  is 
  on 
  

   page 
  399 
  of 
  his 
  Report. 
  

  

  