﻿Report 
  of 
  the 
  State 
  Geologist. 
  449 
  

  

  gentle 
  corrugations 
  in 
  a 
  west-dipping 
  monocline, 
  which 
  pitches 
  

   slightly 
  to 
  the 
  southward. 
  It 
  bears 
  a 
  wide 
  area 
  of 
  Esopus 
  

   shales, 
  which 
  dip 
  beneath 
  the 
  Onondaga 
  limestone 
  to 
  the 
  west 
  

   and 
  south. 
  The 
  corrugations 
  flatten 
  southward 
  and 
  extend 
  the 
  

   Onondaga 
  limestone 
  over 
  a 
  wide 
  area 
  in 
  the 
  Hannacrois 
  valley, 
  

   also 
  giving 
  rise 
  to 
  the 
  eastward 
  extension 
  of 
  the 
  Hamilton 
  hills 
  

   in 
  this 
  region. 
  

  

  One 
  of 
  the 
  most 
  noteworthy 
  details 
  of 
  structure 
  in 
  southern 
  

   Albany 
  county 
  is 
  an 
  overthrust 
  of 
  small 
  amount, 
  but 
  with 
  most 
  

   interesting 
  features. 
  It 
  is 
  among 
  the 
  gentle 
  flexures 
  near 
  the 
  

   northern 
  edge 
  of 
  the 
  disturbed 
  area 
  in 
  the 
  Helderberg 
  rocks. 
  

   Its 
  general 
  relations 
  are 
  represented 
  in 
  the 
  following 
  section 
  : 
  

  

  Fig. 
  6. 
  — 
  Cross-section 
  southwest 
  of 
  South 
  Bethlehem, 
  showing 
  relations 
  of 
  the 
  overthrust. 
  

   S., 
  Beeraft 
  limestone; 
  SL., 
  Shaly 
  limestone; 
  P., 
  Pentamerus 
  limestone; 
  T., 
  Tentaculite 
  lime- 
  

   stone 
  and 
  Salina 
  waterlime; 
  HE,, 
  Hudson 
  river 
  formation. 
  Looking 
  north-northeast. 
  Hori- 
  

   zontal 
  scale, 
  one 
  mile 
  to 
  one 
  inch. 
  Vertical 
  scale 
  exaggerated 
  two 
  and 
  one-half 
  times. 
  This 
  

   section 
  is 
  at 
  5 
  A., 
  on 
  figure 
  4. 
  

  

  The 
  characteristics 
  of 
  this 
  overthrust 
  are 
  an 
  " 
  underturned 
  " 
  

   flexure 
  in 
  the 
  thin-bedded 
  underlying 
  limestones, 
  also 
  involving 
  

   the 
  soft 
  slate 
  of 
  the 
  Hudson 
  river 
  formation, 
  and 
  a 
  fault 
  which 
  

   offsets 
  the 
  flexure 
  and 
  traverses 
  the 
  hard, 
  massive 
  overlying 
  beds 
  of 
  

   Pentamerus 
  limestone. 
  The 
  overthrust 
  is 
  exposed 
  only 
  on 
  Spray 
  t 
  

   creek, 
  which 
  it 
  crosses 
  at 
  an 
  old 
  mill 
  about 
  three-quarters 
  of 
  a 
  

   mile 
  west-southwest 
  of 
  the 
  village. 
  Its 
  trend 
  is 
  north 
  and 
  

   south, 
  but 
  it 
  does 
  not 
  appear 
  to 
  extend 
  for 
  any 
  great 
  distance. 
  

   The 
  principal 
  features 
  of 
  the 
  exposure 
  at 
  the 
  mill 
  are 
  shown 
  in 
  

   plate 
  6, 
  in 
  which 
  the 
  enclosed 
  wedge 
  of 
  slate 
  is 
  shown 
  in 
  the 
  

   lower 
  left-hand 
  corner, 
  the 
  flat 
  arch 
  of 
  the 
  enclosing 
  limestones 
  

   in 
  the 
  middle 
  of 
  the 
  view, 
  mainly 
  far 
  to 
  the 
  right. 
  The 
  massive 
  

   overlying 
  series 
  is 
  the 
  Pentamerus 
  bed. 
  

  

  The 
  relations 
  at 
  the 
  mill 
  and 
  their 
  interpretation 
  are 
  further 
  

   illustrated 
  in 
  the 
  following 
  figures, 
  in 
  which 
  the 
  features 
  above 
  

   57 
  

  

  