﻿24 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  At 
  a 
  timiC 
  or 
  at 
  times 
  not 
  accurately 
  determined, 
  but 
  which 
  prob- 
  

   ably 
  began 
  not 
  later 
  than 
  the 
  Upper 
  Silurian, 
  and 
  may 
  have 
  contin- 
  

   ued 
  at 
  intervals 
  to 
  the 
  end 
  of 
  the 
  Palaeozoic, 
  these 
  horizontal 
  strata 
  

   by 
  lateral 
  pressure 
  were 
  thrown 
  into 
  parallel 
  folds 
  throughout 
  a 
  

   broad 
  belt 
  of 
  country 
  having 
  a 
  general 
  northeasterly 
  trend 
  and 
  with 
  

   the 
  Palaeozoic 
  beds, 
  the 
  underlying 
  rocks 
  of 
  greater 
  age 
  were 
  also 
  

   folded. 
  As 
  the 
  cross 
  sections 
  show, 
  the 
  folds 
  are 
  closely 
  compressed 
  

   and 
  in 
  many 
  cases 
  are 
  overthrown 
  to 
  the 
  eastward 
  and 
  westward, 
  so 
  

   that 
  frequently 
  the 
  rocks 
  on 
  both 
  sides 
  of 
  the 
  fold 
  dip 
  in 
  the 
  same 
  

   direction. 
  Associated 
  with 
  the 
  longitudinal 
  folding 
  of 
  these 
  rocks 
  

   was 
  a 
  transverse 
  folding, 
  the 
  general 
  result 
  of 
  which 
  was 
  elevation 
  at 
  

   the 
  northward, 
  so 
  that 
  the 
  parallel 
  ridges 
  with 
  their 
  intervening 
  

   valleys 
  as 
  a 
  rule, 
  pitch 
  or 
  slope 
  very 
  gently 
  to 
  the 
  southwest. 
  There 
  

   are 
  local 
  variations 
  from 
  this 
  general 
  condition 
  and 
  some 
  of 
  the 
  folds 
  

   have 
  locally 
  a 
  northward 
  pitch, 
  but 
  the 
  general 
  condition 
  may 
  be 
  

   noticed 
  in 
  the 
  western 
  ridges 
  of 
  Fordham 
  gneiss 
  which 
  in 
  the 
  town 
  of 
  

   Yonkers 
  attain 
  a 
  height 
  of 
  300 
  feet, 
  and 
  on 
  Manhattan 
  Island 
  pass 
  

   below 
  the 
  sea 
  level 
  and 
  do 
  not 
  reappear. 
  

  

  As 
  already 
  stated 
  these 
  rocks 
  may 
  be 
  classified 
  in 
  the 
  following 
  

  

  manner: 
  

  

  CRYSTALLINE 
  ROCKS. 
  

   Ordovician 
  : 
  

  

  1 
  Manhattan 
  schist, 
  containing 
  garnet 
  fibrolite, 
  kyanite 
  and 
  

  

  staurolite. 
  

  

  2 
  Inwood 
  limestone, 
  crystalline 
  dolomite, 
  containing 
  diopside 
  

  

  and 
  tremolite. 
  

   Cambrian 
  : 
  

  

  Lowerre 
  quartzite 
  

  

  f 
  Algonkian? 
  Fordham 
  gneiss 
  

  

  § 
  « 
  I 
  

  

  *>'_§!,, 
  ( 
  Gneisses 
  

  

  ^ 
  Archaean 
  I 
  ^ 
  

  

  I 
  < 
  Granites 
  

  

  . 
  For 
  detailed 
  examination 
  of 
  these 
  formations, 
  it 
  has 
  been 
  neces- 
  

   sary 
  to 
  depend 
  largely 
  on 
  the 
  exposures 
  along 
  the 
  east 
  shore 
  of 
  the 
  

   Hudson 
  river 
  and 
  those 
  in 
  southern 
  Westchester 
  county 
  and 
  on 
  

   New 
  York 
  Island. 
  In 
  central, 
  eastern 
  and 
  northern 
  Westchester 
  

   county, 
  the 
  quaternary 
  deposits 
  of 
  stratified 
  and 
  unstratified 
  drift 
  

  

  