﻿352 
  A. 
  W. 
  Giles 
  — 
  Niagara 
  Limestone 
  at 
  Rochester. 
  

  

  ence 
  of 
  these 
  cavities 
  has 
  made 
  possible 
  the 
  greater 
  part 
  

   of 
  the 
  brecciation 
  of 
  the 
  rock. 
  

  

  The 
  breccia 
  is 
  of 
  the 
  endolithic 
  type, 
  both 
  crackle 
  and 
  

   mosaic 
  patterns 
  being 
  represented. 
  All 
  of 
  the 
  fragments 
  

   are 
  angular 
  and 
  small, 
  the 
  largest 
  having 
  major 
  dimen- 
  

   sions 
  of 
  a 
  few 
  inches 
  only, 
  while 
  many 
  measure 
  but 
  an 
  

   inch 
  or 
  even 
  less 
  in 
  their 
  longest 
  directions. 
  The 
  brec- 
  

   ciation 
  has 
  originated 
  from 
  a 
  number 
  of 
  causes. 
  Some 
  

   of 
  it 
  is 
  undoubtedly 
  expansion 
  breccia. 
  The 
  Lockport 
  

  

  Fig. 
  2. 
  

  

  Fig. 
  2. 
  — 
  Breccia 
  fragments 
  of 
  Niagara 
  limestone 
  in 
  selenite. 
  Note 
  the 
  

   rhombs 
  of 
  dolomite 
  in 
  the 
  extreme 
  right 
  at 
  the 
  top 
  and 
  the 
  crystals 
  of 
  

   sphalerite 
  just 
  to 
  the 
  left 
  of 
  the 
  center. 
  

  

  limestone 
  carries 
  a 
  great 
  deal 
  of 
  both 
  gypsum 
  and 
  anhy- 
  

   drite, 
  especially 
  in 
  the 
  central 
  and 
  upper 
  portions 
  of 
  the 
  

   formation. 
  In 
  altering 
  to 
  gypsum 
  anhydrite 
  expands 
  

   greatly, 
  the 
  increase 
  in 
  volume 
  being 
  60-30 
  per 
  cent 
  

   according 
  to 
  Van 
  Hise. 
  3 
  The 
  force 
  resulting 
  from 
  this 
  

   expansion 
  repeatedly 
  fractured 
  the 
  containing 
  limestone, 
  

   the 
  portions 
  of 
  the 
  rock 
  adjacent 
  to 
  the 
  cavities 
  being 
  

   especially 
  affected, 
  for 
  the 
  stresses 
  found 
  easy 
  relief 
  by 
  

   forcing 
  the 
  cavity 
  walls 
  inward. 
  

  

  8 
  A 
  Treatise 
  on 
  Metamorphism, 
  U. 
  S. 
  Geol. 
  Surv. 
  Mon. 
  47, 
  p. 
  357, 
  1904. 
  

  

  