﻿80 
  J. 
  D. 
  Dana 
  — 
  Features 
  of 
  non-volcanic 
  Igneous 
  Ejections. 
  

  

  on 
  the 
  west.) 
  The 
  map 
  shows 
  the 
  positions 
  of 
  the 
  four 
  trap 
  

   ridges 
  — 
  more 
  strictly 
  trap-and-sandstone 
  ridges 
  — 
  West 
  Eock, 
  

   Pine 
  Rock, 
  Mill 
  Rock 
  and 
  East 
  Rock, 
  and 
  gives 
  their 
  heights 
  

   above 
  mean 
  tide. 
  These 
  rampart-like 
  elevations 
  are 
  now 
  two 
  

   to 
  three 
  miles 
  from 
  New 
  Haven 
  Bay; 
  but 
  they 
  bear 
  evidence 
  

   of 
  having 
  been 
  for 
  a 
  time 
  the 
  headlands 
  of 
  a 
  much 
  larger 
  bay. 
  

  

  The 
  ridges 
  are 
  part 
  of 
  the 
  Jura-Trias 
  Mountain-range 
  of 
  the 
  

   Connecticut 
  Valley. 
  (1) 
  East 
  Rock 
  and 
  West 
  Rock 
  are 
  like 
  

   the 
  other 
  north-and-south 
  ridges 
  of 
  the 
  range 
  in 
  their 
  form, 
  

   structure 
  and 
  direction, 
  and 
  West 
  Rock 
  ridge 
  after 
  a 
  course 
  of 
  

   seventeen 
  miles, 
  dies 
  out 
  just 
  where 
  the 
  higher 
  trap 
  ridges 
  of 
  

   the 
  Mt. 
  Tom 
  line 
  commence, 
  showing 
  an 
  interlocking 
  with 
  the 
  

   rest 
  of 
  the 
  system. 
  (2) 
  They 
  consist 
  of 
  Jura-Trias 
  sandstone 
  

   with 
  an 
  intercalated 
  sheet 
  of 
  trap 
  (as 
  the 
  igneous 
  rock 
  is 
  pop- 
  

   ularly 
  called). 
  (3) 
  The 
  sheet 
  of 
  trap 
  in 
  the 
  ridges 
  has 
  a 
  rising 
  

   inclination 
  westward, 
  or 
  a 
  dip 
  eastward, 
  like 
  the 
  associated 
  

   beds 
  of 
  sandstone, 
  the 
  liquid 
  rock 
  having 
  been 
  extruded 
  from 
  

   a 
  fissure 
  or 
  fissures 
  situated 
  somewhere 
  to 
  the 
  eastward. 
  (4) 
  

   As 
  a 
  consequence 
  of 
  these 
  common 
  features, 
  denudation 
  by 
  

   water 
  and 
  ice 
  has 
  given 
  to 
  the 
  New 
  Haven 
  ridges 
  the 
  features 
  

   typical 
  of 
  the 
  range,* 
  namely, 
  a 
  steep 
  western 
  front, 
  consisting 
  

   of 
  sandstone 
  below 
  and 
  the 
  harder 
  trap 
  above, 
  a 
  top 
  of 
  bare 
  

   trap, 
  and 
  eastern 
  slopes 
  of 
  sandstone, 
  that 
  is 
  of 
  the 
  overlying 
  

   sandstone. 
  

  

  From 
  such 
  common 
  features 
  the 
  inference 
  as 
  to 
  a 
  common 
  

   method 
  of 
  origin 
  is 
  natural. 
  Still, 
  as 
  Professor 
  Davis 
  claims, 
  

   it 
  needs 
  also 
  other 
  support 
  for 
  acceptance. 
  

  

  We 
  note 
  also 
  (4) 
  that 
  these 
  Rocks 
  are 
  situated 
  at 
  the 
  south- 
  

   ern 
  extremity 
  of 
  the 
  Jura-Trias 
  Mountain-range 
  ; 
  for 
  the 
  Con- 
  

   necticut 
  Valley 
  and 
  its 
  Jura-Trias 
  beds 
  do 
  not 
  extend 
  over 
  

   Long 
  Island. 
  Instead 
  of 
  this, 
  Long 
  Island 
  pertains 
  to 
  an 
  east- 
  

   and-west 
  system 
  of 
  mountain-structure. 
  Whether 
  nearness 
  in 
  

   position 
  to 
  this 
  east-and-west 
  range 
  has 
  occasioned 
  any 
  of 
  the 
  

   features 
  of 
  the 
  Rocks 
  is 
  an 
  interesting 
  question 
  for 
  con- 
  

   sideration. 
  

  

  1. 
  Summary 
  of 
  the 
  principal 
  facts 
  and 
  conclusions. 
  

  

  The 
  facts. 
  — 
  The 
  facts 
  relate 
  to 
  the 
  sandstone 
  of 
  the 
  New 
  

   Haven 
  region 
  as 
  well 
  as 
  the 
  trap 
  ; 
  for 
  the 
  sandstone 
  was 
  broken 
  

   through 
  to 
  give 
  exit 
  to 
  the 
  liquid 
  trap, 
  and 
  it 
  broke 
  as 
  such 
  a 
  

   sandstone 
  would 
  break. 
  

  

  (1) 
  The 
  sandstone, 
  as 
  the 
  rock 
  is 
  comprehensively 
  called, 
  

   varies 
  from 
  fine-grained 
  to 
  coarse, 
  and 
  beyond 
  this, 
  to 
  a 
  fine 
  

  

  * 
  In 
  the 
  writer's 
  paper 
  on 
  the 
  Geology 
  of 
  the 
  New 
  Haven 
  region 
  of 
  1869, 
  

   (Trans. 
  Conn. 
  Acad. 
  Sci., 
  ii. 
  4. 
  1870), 
  he 
  observes 
  that 
  "the 
  sandstone 
  mass 
  with 
  

   its 
  intersecting 
  dikes 
  of 
  trap 
  constituted 
  the 
  block 
  out 
  of 
  which 
  the 
  future 
  New 
  

   Haven 
  region 
  was 
  to 
  be 
  carved 
  by 
  various 
  denuding 
  agencies." 
  

  

  