﻿ii6 
  

  

  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  were 
  bent 
  upward 
  until, 
  the 
  elastic 
  limit 
  being 
  exceeded, 
  the 
  fold 
  

   snapped 
  along 
  the 
  crest, 
  furnishing 
  relief 
  to 
  the 
  bent 
  flanks 
  and 
  per- 
  

   mitting 
  them 
  to 
  straighten. 
  In 
  the 
  rock 
  here 
  only 
  a 
  single 
  set 
  of 
  

   good 
  joints 
  appears, 
  and 
  this 
  runs 
  at 
  right 
  angles 
  to 
  the 
  axis 
  of 
  the 
  

   fold 
  separating 
  it 
  into 
  a 
  series 
  of 
  transverse 
  blocks. 
  On 
  bending, 
  

   these 
  seem 
  to 
  have 
  fractured 
  individually 
  instead 
  of 
  collectively, 
  so 
  

   that 
  the 
  axial 
  fracture 
  does 
  not 
  coincide 
  in 
  the 
  different 
  blocks, 
  but 
  

   departs 
  from 
  the 
  median 
  line, 
  now 
  on 
  one 
  side 
  and 
  again 
  on 
  the 
  

   other, 
  as 
  illustrated 
  in 
  figure 
  lo, 
  giving 
  rise 
  to 
  the 
  dovetailing 
  of 
  

   slabs 
  along 
  the 
  crest, 
  so 
  well 
  shown 
  in 
  the 
  photograph. 
  

  

  Fig. 
  lo 
  Plan 
  of 
  fold 
  in 
  Potsdam 
  sandstone, 
  j-j-j=joints; 
  f-f=fracture 
  along 
  crest, 
  illus- 
  

   trating 
  the 
  manner 
  in 
  which 
  the 
  fracture 
  shifts 
  laterally 
  in 
  the 
  different 
  joint 
  blocks, 
  caus- 
  

   ing 
  overlap 
  of 
  the 
  rock 
  edges 
  along 
  the 
  crest. 
  

  

  One 
  view 
  of 
  one 
  of 
  the 
  folds 
  in 
  the 
  Lowville 
  iimestone 
  is 
  shown 
  

   in 
  plate 
  30. 
  The 
  greater 
  part 
  of 
  this 
  fold 
  is 
  covered 
  with 
  soil, 
  but 
  

   centrally 
  it 
  has 
  been 
  stripped 
  and 
  a 
  small 
  amount 
  of 
  rock 
  removed 
  

   for 
  local 
  use. 
  It 
  seems 
  to 
  have 
  about 
  the 
  same 
  length 
  as 
  the 
  previous 
  

   one, 
  and 
  to 
  be 
  buckled 
  up 
  about 
  the 
  same 
  amount. 
  Its 
  axis 
  trends 
  

   to 
  the 
  northwest. 
  The 
  rock 
  is 
  more 
  closely 
  jointed 
  than 
  in 
  the 
  Pots- 
  

   dam 
  fold, 
  and 
  with 
  two 
  good 
  sets 
  present, 
  one 
  of 
  which 
  trends 
  north- 
  

   west 
  with 
  the 
  fold, 
  as 
  the 
  view 
  clearly 
  shows. 
  Fracture 
  then 
  was 
  

   unnecessary 
  in 
  this 
  case 
  and 
  readjustment 
  took 
  place 
  by 
  utilization 
  

   of 
  these 
  northwest 
  joints, 
  and 
  instead 
  of 
  being 
  actually 
  folded, 
  as 
  

   might 
  be 
  judged 
  from 
  the 
  photographs, 
  the 
  displacement 
  really 
  has 
  

   the 
  character 
  shown 
  in 
  figure 
  1 
  1 
  , 
  as 
  sketched 
  on 
  the 
  spot. 
  

  

  20** 
  sw 
  

  

  Fig. 
  II 
  Diagram 
  to 
  illustrate 
  the 
  arrangement 
  of 
  the 
  joint 
  blocks 
  in 
  the 
  Lowville 
  fold 
  

   shown 
  in 
  plate 
  30 
  The 
  central 
  block 
  lies 
  nearly 
  horizontally, 
  the 
  adjacent 
  ones 
  tipped 
  in 
  

   the 
  directions 
  and 
  by 
  the 
  amounts 
  indicated. 
  

  

  ; 
  Small 
  postglacial 
  folds 
  of 
  similar 
  type 
  have 
  been 
  described 
  by 
  a 
  

   number 
  of 
  authors 
  and 
  from 
  various 
  localities, 
  and 
  they 
  have 
  re- 
  

   sulted 
  from 
  several 
  different 
  causes. 
  Gilbert, 
  after 
  ^eeifig 
  some.of 
  

  

  