﻿446 
  J. 
  D. 
  Dana 
  — 
  The 
  Upturning 
  of 
  

  

  or 
  three 
  miles 
  of 
  the 
  crust, 
  but 
  those 
  below, 
  where 
  Archaean 
  

   rocks 
  and 
  those 
  subjacent 
  to 
  the 
  Archaean 
  exist. 
  For 
  the 
  frac- 
  

   tures 
  were 
  begun 
  below, 
  and 
  in 
  these 
  nether 
  rocks 
  foliation 
  has 
  

   probably, 
  as 
  a 
  consequence 
  of 
  Archaean 
  pressure 
  or 
  tension, 
  

   much 
  greater 
  uniformity 
  than 
  in 
  those 
  of 
  the 
  surface. 
  Still 
  the 
  

   more 
  superficial 
  foliation 
  would 
  have 
  its 
  influence. 
  

  

  Again, 
  the 
  direction 
  of 
  planes 
  of 
  fracture, 
  or 
  of 
  faulting, 
  would 
  

   have 
  depended 
  largely 
  on 
  the 
  direction 
  of 
  the 
  lateral 
  thrust 
  or 
  

   pressure 
  in 
  the 
  earth's 
  crust 
  producing 
  the 
  strain, 
  whether 
  

   normal 
  or 
  oblique, 
  to 
  the 
  plane 
  of 
  easiest 
  cleavage 
  ; 
  an 
  idea 
  

   which, 
  under 
  large 
  extension 
  has 
  been 
  applied 
  by 
  the 
  writer 
  in 
  

   an 
  explanation 
  of 
  the 
  origin 
  of 
  the 
  courses 
  in 
  the 
  feature-lines 
  

   of 
  the 
  globe. 
  

  

  The 
  production 
  of 
  an 
  eastward 
  slope 
  in 
  the 
  upper 
  surface 
  of 
  

   the 
  faulted 
  blocks 
  by 
  compression 
  and 
  molecular 
  transfer, 
  

   sufficient 
  by 
  the 
  hypothesis 
  to 
  produce 
  the 
  dip 
  in 
  the 
  sand- 
  

   stone, 
  may 
  be 
  questioned 
  ; 
  and 
  also 
  the 
  view 
  that 
  the 
  horizon- 
  

   tal 
  force 
  concerned 
  would 
  make, 
  in 
  gneiss, 
  and 
  in 
  other 
  rocks 
  

   equally 
  firm, 
  faulting 
  along 
  foliation-planes 
  of 
  the 
  high 
  east- 
  

   ward 
  dip 
  of 
  60° 
  to 
  80°, 
  instead, 
  for 
  the 
  most 
  part, 
  of 
  fractures 
  

   oblique 
  to 
  these 
  planes. 
  To 
  obtain 
  a 
  clip 
  of 
  20° 
  in 
  the 
  top- 
  

   surface 
  of 
  the 
  westernmost 
  slab 
  or 
  block 
  (and 
  the 
  sandstone 
  

   over 
  it), 
  the 
  displacement 
  a 
  mile 
  down 
  would 
  have 
  to 
  amount 
  

   to 
  1800 
  feet 
  ; 
  and 
  to 
  render 
  the 
  westward 
  shove 
  below, 
  to 
  

   this 
  distance, 
  possible, 
  the 
  compression 
  would 
  have 
  to 
  take 
  

   much 
  from 
  the 
  thickness 
  of 
  this 
  western 
  block 
  on 
  its 
  western 
  

   side, 
  and 
  much 
  from 
  the 
  rock 
  next 
  west, 
  a 
  part 
  from 
  each. 
  

   This 
  would 
  be 
  required 
  whether 
  the 
  other 
  blocks 
  were 
  com- 
  

   pressed 
  or 
  not. 
  When 
  done, 
  it 
  would 
  suffice 
  to 
  give 
  the 
  same 
  

   dip 
  to 
  the 
  top-surface 
  of 
  all 
  the 
  blocks 
  in 
  the 
  series 
  without 
  

   their 
  compression 
  ; 
  but 
  these 
  would 
  also 
  be 
  compressed, 
  and 
  

   the 
  result 
  would 
  be 
  a 
  large 
  increase 
  eastward 
  of 
  dip 
  — 
  a 
  con- 
  

   dition 
  which 
  does 
  not 
  accord 
  with 
  observation. 
  

  

  But 
  suppose 
  the 
  blocks 
  to 
  be 
  so 
  displaced, 
  and 
  pushed 
  up 
  

   thereby 
  nearly 
  to 
  verticality, 
  or 
  beyond 
  it, 
  then 
  they 
  would 
  

   have 
  had 
  little 
  or 
  no 
  westward 
  thrust 
  against 
  the 
  sandstone, 
  

   and 
  accordingly 
  none 
  is 
  appealed 
  to 
  in 
  the 
  statement 
  of 
  the 
  

   hypothesis. 
  Yet, 
  a 
  pitch 
  of 
  10° 
  to 
  25° 
  in 
  the 
  sandstone 
  im- 
  

   plies 
  much 
  diminution 
  in 
  the 
  width 
  of 
  the 
  area. 
  If 
  the 
  mean 
  

   dip 
  is 
  18° 
  the 
  diminution 
  would 
  be, 
  theoretically, 
  5 
  per 
  cent, 
  

   equivalent 
  to 
  1 
  foot 
  in 
  20; 
  or 
  if 
  14°, 
  3 
  per 
  cent.* 
  The 
  effect 
  

   should 
  have 
  been 
  manifested 
  in 
  wide 
  longitudinal 
  fissures 
  if 
  

   this 
  were 
  not 
  prevented 
  by 
  a 
  westward 
  thrust 
  of 
  the 
  sandstone. 
  

  

  * 
  The 
  sandstone 
  in 
  some 
  portions 
  is 
  nearly 
  horizontal, 
  as 
  in 
  the 
  region 
  of 
  the 
  

   Portland 
  quarries, 
  on 
  its 
  eastern 
  border; 
  and 
  occasionally 
  the 
  dip 
  is 
  westerly. 
  

   Hence 
  a 
  mean 
  dip 
  of 
  14° 
  is 
  probably 
  most 
  correct 
  Small 
  flexures 
  also 
  occur 
  but 
  

   only 
  locally. 
  

  

  