﻿20 
  NEW 
  YORK 
  STATE 
  :MUSEUM 
  

  

  and 
  whose 
  present 
  northern 
  margin 
  of 
  outcrop 
  is 
  distant 
  but 
  15 
  

   miles 
  from 
  the 
  map 
  limits^ 
  may 
  also 
  have 
  been 
  somewhat 
  deposited 
  

   within 
  it. 
  Certainly 
  the 
  sandstone 
  extended 
  orginally 
  farther 
  

   north 
  than 
  now, 
  but 
  just 
  how 
  far 
  no 
  one 
  can 
  say. 
  

  

  The 
  deposit 
  of 
  these 
  sands 
  indicates 
  a 
  shallowing 
  of 
  the 
  waters 
  

   over 
  the 
  region, 
  following 
  which 
  it 
  was 
  uplifted 
  above 
  sea 
  level. 
  

   Thenceforth 
  in 
  the 
  main, 
  throughout 
  the 
  millions 
  of 
  years 
  which 
  

   have 
  since 
  elapsed, 
  the 
  district 
  has 
  remained 
  a 
  land 
  area. 
  It 
  is 
  

   quite 
  possible 
  that 
  the 
  succeeding 
  Siluric 
  and 
  Devonic 
  seas, 
  whose 
  

   waters 
  covered 
  central 
  and 
  western 
  New 
  York, 
  may 
  have 
  washed 
  

   over 
  this 
  district, 
  and 
  laid 
  down 
  thin 
  deposits. 
  But 
  if 
  so, 
  every 
  

   trace 
  of 
  such 
  deposits 
  hereabouts 
  has 
  disappeared 
  through 
  erosion, 
  

   so 
  that 
  no 
  certainty 
  can 
  be 
  arrived 
  at 
  in 
  the 
  matter. 
  

  

  As 
  a 
  result 
  of 
  the 
  various 
  oscillations 
  of 
  level 
  which 
  the 
  region 
  

   has 
  undergone 
  the 
  rocks 
  described 
  have 
  been 
  changed 
  from 
  their 
  

   original 
  nearly 
  horizontal 
  position, 
  into 
  a 
  series 
  of 
  low 
  folds. 
  This 
  

   folding 
  seems 
  to 
  have 
  commenced 
  early 
  and 
  to 
  have 
  been 
  continued 
  

   on 
  various 
  occasions, 
  since 
  there 
  is 
  some 
  evidence 
  that 
  the 
  Pots- 
  

   dam 
  and 
  Theresa 
  formations 
  were 
  somewhat 
  folded 
  before 
  Pa- 
  

   melia 
  deposition 
  began. 
  Subsequently 
  more 
  folding 
  took 
  place, 
  in- 
  

   volving 
  the 
  entire 
  series, 
  and 
  though 
  the 
  folding 
  is 
  gentle 
  its 
  topo- 
  

   graphic 
  expression 
  is 
  plain. 
  

  

  The 
  principal 
  folds 
  have 
  axes 
  which 
  trend 
  northeast-southwest, 
  

   but 
  there 
  is 
  also 
  present 
  another 
  set 
  with 
  northwest-southwest 
  trend, 
  

   or 
  at 
  right 
  angles 
  to 
  the 
  first 
  set, 
  whose 
  arches 
  and 
  troughs 
  are 
  

   thus 
  folded 
  up 
  and 
  down, 
  producing 
  gently 
  elevated 
  domes 
  and 
  de- 
  

   pressed 
  basins, 
  the 
  former 
  where 
  the 
  arches 
  of 
  the 
  two 
  sets 
  cross, 
  

   and 
  the 
  latter 
  at 
  trough 
  intersections. 
  Many 
  of 
  the 
  outliers 
  shown 
  

   on 
  the 
  accompanying 
  geologic 
  maps 
  owe 
  their 
  existence 
  and 
  pres- 
  

   ervation 
  to 
  this 
  folding. 
  

  

  Subsequent 
  history 
  of 
  the 
  region 
  

  

  But 
  little 
  that 
  is 
  definite 
  can 
  be 
  said 
  of 
  the 
  history 
  of 
  the 
  district 
  

   during 
  its 
  long 
  existence 
  as 
  a 
  land 
  area 
  following 
  the 
  deposition 
  

   of 
  the 
  rocks 
  previously 
  described. 
  It 
  seems 
  quite 
  certain 
  that 
  the 
  

   amount 
  of 
  reck 
  worn 
  away 
  from 
  the 
  surface 
  during 
  this 
  time 
  is 
  

   slight, 
  considering 
  the 
  length 
  of 
  the 
  time 
  interval, 
  and 
  that 
  there- 
  

   fore 
  the 
  land 
  has 
  seldom 
  had 
  any 
  considerable 
  altitude. 
  Where 
  

   the 
  entire 
  thickness 
  of 
  overlying 
  rocks 
  has 
  been 
  worn 
  away 
  and 
  

   the 
  Precambric 
  exposed 
  at 
  the 
  surface, 
  as 
  is 
  the 
  case 
  on 
  parts 
  of 
  

   the 
  Theresa 
  and 
  Alexandria 
  sheets, 
  it 
  seems 
  quite 
  certain 
  that 
  not 
  

  

  