﻿A. 
  W. 
  Giles 
  — 
  Niagara 
  Limestone 
  at 
  Rochester. 
  351 
  

  

  nite 
  arrangement 
  but 
  instead 
  occurs 
  in 
  patches. 
  Large 
  

   areas 
  of 
  the 
  rock 
  free 
  from 
  cavities 
  are 
  likewise 
  free 
  

   from 
  brecciation; 
  this 
  is 
  true 
  of 
  the 
  rock 
  occurring 
  

   between 
  the 
  cavities 
  in 
  the 
  same 
  stratum, 
  and 
  also 
  in 
  the 
  

   strata 
  superjacent 
  and 
  subjacent 
  to 
  the 
  cavities. 
  

  

  The 
  cavities 
  have 
  originated 
  in 
  four 
  ways: 
  (1) 
  Pre- 
  

   servation 
  of 
  the 
  original 
  openings 
  in 
  the 
  growing 
  reefs 
  ; 
  

   (2) 
  Jointing 
  and 
  fracturing 
  of 
  the 
  rock 
  during 
  consolida- 
  

   tion 
  and 
  subsequent 
  earth 
  movements; 
  (3) 
  Shrinkage 
  of 
  

   the 
  rock 
  in 
  its 
  transformation 
  from 
  a 
  limestone 
  to 
  a 
  dolo- 
  

  

  FlG. 
  1. 
  

  

  Fig. 
  1. 
  — 
  Niagara 
  limestone 
  breccia. 
  The 
  angular 
  fragments 
  of 
  limestone 
  

   are 
  embedded 
  in 
  a 
  matrix 
  of 
  calcite 
  and 
  dolomite 
  (natural 
  size). 
  

  

  mite 
  ; 
  (4) 
  Solution 
  of 
  the 
  rock 
  by 
  circulating 
  underground 
  

   waters. 
  

  

  The 
  agent 
  involved 
  in 
  the 
  last 
  method 
  of 
  cavity 
  forma- 
  

   tion 
  may 
  enlarge 
  the 
  cavities 
  formed 
  in 
  the 
  first 
  three 
  

   ways 
  mentioned. 
  However 
  the 
  cavities 
  are 
  small, 
  rarely 
  

   exceeding 
  one 
  foot 
  in 
  diameter, 
  and 
  commonly 
  they 
  meas- 
  

   ure 
  but 
  a 
  few 
  inches 
  across. 
  It 
  is 
  believed 
  that 
  the 
  pres- 
  

  

  