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  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  seen 
  in 
  the 
  Helderberg 
  mountain 
  and 
  in 
  the 
  vicinity 
  of 
  Clarks. 
  

   ville. 
  Between 
  Oniskethau 
  and 
  Callanan's 
  Corners 
  it 
  is 
  in 
  greater 
  

   part 
  covered 
  by 
  drift. 
  It 
  comes 
  out 
  again 
  in 
  the 
  creek 
  bed 
  just 
  

   south 
  of 
  Callanan's 
  Corners 
  and 
  at 
  various 
  other 
  points 
  in 
  the 
  

   vicinity. 
  South 
  of 
  South 
  Bethlehem 
  it 
  extends 
  over 
  a 
  consider- 
  

   able 
  area 
  in 
  the 
  flexures 
  which 
  traverse 
  that 
  district, 
  particularly 
  

   along 
  the 
  base 
  of 
  the 
  steep 
  ridges 
  of 
  Esopus 
  shales. 
  Its 
  relations 
  

   in 
  this 
  region 
  are 
  shown 
  on 
  the 
  section 
  in 
  plate 
  5. 
  

  

  Shaly 
  limestone. 
  — 
  The 
  Becraft 
  limestones 
  are 
  underlaid 
  by 
  

   a 
  series 
  of 
  thin-bedded, 
  very 
  impure, 
  highly 
  fossiliferous 
  lime- 
  

   stones, 
  containing 
  many 
  shaly 
  intercalations, 
  and 
  varying 
  in 
  color 
  

   from 
  gray 
  to 
  gray 
  brown. 
  As 
  is 
  the 
  case 
  with 
  the 
  Esopus 
  shales, 
  

   they 
  are 
  regularly 
  bedded 
  westward, 
  but 
  in 
  the 
  flexures 
  south 
  of 
  

   South 
  Bethlehem 
  they 
  are 
  traversed 
  by 
  more 
  or 
  less 
  slaty 
  cleav- 
  

   age, 
  and 
  become 
  considerably 
  harder. 
  In 
  the 
  Helderberg 
  moun- 
  

   tains 
  and 
  westward 
  they 
  constitute 
  the 
  slopes 
  or 
  gently 
  rolling 
  

   plateaus 
  above 
  the 
  Pentamerus 
  ledges, 
  but 
  to 
  the 
  southward 
  they 
  

   give 
  rise 
  to 
  sharp 
  ridges 
  covered 
  with 
  rugged 
  ledges, 
  in 
  some 
  

   cases 
  closely 
  resembling 
  the 
  lighter-colored 
  outcrops 
  of 
  Esopus 
  

   shales. 
  In 
  the 
  high 
  ridge 
  between 
  Clarksville 
  and 
  Stony 
  Hill 
  

   there 
  are 
  several 
  outliers 
  of 
  the 
  formation. 
  The 
  thickness 
  of 
  

   the 
  Shaly 
  limestone 
  averages 
  100 
  feet 
  throughout. 
  

  

  Pentamerus 
  limestone. 
  — 
  This 
  is 
  the 
  most 
  conspicuous 
  member 
  

   of 
  the 
  Helderberg 
  formation, 
  for 
  its 
  outcrop 
  is 
  marked 
  by 
  

   extended 
  lines 
  of 
  prominent 
  cliffs, 
  in 
  most 
  cases 
  surmounting 
  

   long 
  slopes 
  of 
  the 
  underlying 
  formations. 
  In 
  the 
  few 
  valleys 
  by 
  

   which 
  it 
  is 
  crossed 
  it 
  gives 
  rise 
  to 
  falls. 
  The 
  formation 
  consists 
  

   of 
  hard, 
  very 
  massively 
  -bedded 
  limestone 
  of 
  bluish-gray 
  color, 
  

   weathering 
  to 
  a 
  somewhat 
  lighter 
  tint. 
  The 
  beds 
  are 
  traversed 
  

   by 
  vertical 
  jointing, 
  and 
  tbis 
  character, 
  together 
  with 
  the 
  pres- 
  

   ence 
  of 
  softer 
  underlying 
  beds, 
  gives 
  rise 
  to 
  the 
  cliffs 
  which 
  

   characterize 
  its 
  outcrop. 
  Besides 
  the 
  thick 
  regular 
  bedding 
  there 
  

   is 
  also 
  an 
  irregular 
  sub-bedding 
  into 
  flat, 
  interlocking 
  lenses 
  and 
  

   corrugations, 
  the 
  outlines 
  of 
  which 
  are 
  brought 
  out 
  by 
  weather- 
  

   ing. 
  Occasional 
  shale 
  partings 
  occur, 
  and 
  also 
  nodules 
  and 
  thin 
  

   lenses 
  of 
  chert. 
  The 
  thickness 
  averages 
  sixty-five 
  feet 
  through- 
  

   oat 
  Albany 
  county. 
  Owing 
  to 
  its 
  hardness 
  the 
  formation 
  is 
  

   almost 
  everywhere 
  exposed, 
  but 
  the 
  finest 
  exhibition 
  is 
  in 
  the 
  

   northern 
  and 
  eastern 
  face 
  of 
  the 
  Helderberg 
  mountains, 
  where 
  it 
  

   presents 
  the 
  appearance 
  represented 
  in 
  plate 
  1. 
  

  

  