﻿36 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  the 
  Precambric 
  surface 
  between 
  Glenfield 
  and 
  East 
  Martinsburg 
  is 
  

   due 
  to 
  the 
  settling 
  of 
  the 
  mass 
  on 
  the 
  south 
  side 
  of 
  the 
  fault. 
  

  

  Extensive 
  folding 
  of 
  the 
  Paleozoic 
  rocks 
  nowhere 
  occurs, 
  Local 
  

   folds 
  are 
  sometimes 
  developed 
  but 
  even 
  these 
  are 
  rare. 
  Such 
  small 
  

   folds 
  are 
  best 
  seen 
  ^ 
  mile 
  above 
  the 
  mouth 
  of 
  Mill 
  creek 
  (north 
  

   of 
  Boonville) 
  ; 
  near 
  Denley; 
  and 
  where 
  the 
  railroad 
  crosses 
  Sugar 
  

   river. 
  At 
  the 
  latter 
  place 
  a 
  syncline 
  in 
  the 
  Trenton 
  is 
  perhaps 
  tho 
  

   best 
  example 
  of 
  folding 
  in 
  the 
  district. 
  

  

  The 
  folded 
  structure 
  of 
  the 
  Precambric 
  rocks 
  will 
  be 
  dealt 
  with 
  

   under 
  the 
  heading 
  " 
  Gneissic 
  structure." 
  

  

  Ripple 
  marks 
  

  

  Small 
  ripple 
  marks 
  are 
  frequently 
  present 
  in 
  the 
  Paleozoic 
  forma- 
  

   tions. 
  Thus 
  at 
  several 
  horizons 
  within 
  the 
  Pamelia, 
  Lowville 
  and 
  

   Trenton 
  limestones 
  there 
  are 
  ripple 
  marks 
  which 
  measure 
  i 
  or 
  2 
  

   inches 
  from 
  crest 
  to 
  crest 
  and 
  about 
  ^ 
  inch 
  from 
  trough 
  to 
  crest. 
  

   Special 
  attention, 
  however, 
  is 
  called 
  to 
  certain 
  ripple 
  marks 
  of 
  un- 
  

   usual 
  interest 
  in 
  the 
  Trenton. 
  They 
  are 
  of 
  unusual 
  interest 
  both 
  

   because 
  of 
  their 
  large 
  size 
  and 
  their 
  occurrence 
  in 
  limestone. 
  

   These 
  marks 
  occur 
  about 
  25 
  or 
  30 
  feet 
  above 
  the 
  base 
  of 
  the 
  

   Trenton 
  and 
  are 
  finely 
  shown 
  in 
  the 
  south 
  bank 
  of 
  Sugar 
  river 
  a 
  

   short 
  distance 
  above 
  the 
  railroad 
  bridge. 
  The 
  ripples 
  measure 
  

   from 
  24 
  to 
  56 
  inches 
  from 
  crest 
  to 
  crest, 
  and 
  4 
  to 
  7 
  inches 
  from 
  

   trough 
  to 
  crest. 
  They 
  strike 
  about 
  n. 
  30° 
  e. 
  The 
  ripple 
  marked 
  

   layer 
  varies 
  in 
  thickness 
  from 
  2 
  to 
  9 
  inches 
  and 
  is 
  a 
  crystalline 
  

   and 
  very 
  fossiliferous 
  limestone. 
  Shale 
  occurs 
  immediately 
  above 
  

   and 
  below 
  the 
  marked 
  stratum 
  and 
  the 
  shale 
  above 
  thickens 
  or 
  

   thins 
  according 
  to 
  whether 
  it 
  rests 
  upon 
  the 
  troughs 
  or 
  crests 
  of 
  

   the 
  ripples. 
  The 
  limestone 
  layers 
  both 
  above 
  and 
  below 
  rapidly 
  

   thicken 
  and 
  thin 
  and 
  are 
  certainly 
  of 
  shallow 
  water 
  origin. 
  

  

  Gneissic 
  structure 
  

  

  The 
  precambric 
  rocks, 
  which 
  are 
  metamorphosed, 
  igneous 
  and 
  

   sedimentary 
  masses, 
  all 
  exhibit 
  the 
  gneissic 
  structure. 
  This 
  struc- 
  

   ture 
  is 
  best 
  developed 
  in 
  the 
  old 
  Grenville 
  sediments 
  and 
  least 
  in 
  

   the 
  syenite. 
  In 
  the 
  areas 
  of 
  mixed 
  gneisses 
  it 
  is 
  also 
  clearly 
  shown. 
  

   The 
  strike 
  of 
  the 
  gneissic 
  bands 
  varies 
  from 
  north-south 
  to 
  almost 
  

   east-west, 
  but 
  the 
  most 
  common 
  range 
  is 
  from 
  n. 
  40° 
  to 
  70° 
  e. 
  The 
  

   direction 
  of 
  dip 
  of 
  the 
  foliation 
  planes 
  is 
  either 
  northward 
  or 
  

   southward 
  but 
  prevailingly 
  northward. 
  The 
  angle 
  of 
  dip 
  is 
  usually 
  

   high, 
  varying 
  from 
  50 
  to 
  80 
  degrees 
  although 
  just 
  north 
  of 
  Lyons 
  

  

  