﻿A. 
  W. 
  Giles 
  — 
  Niagara 
  Limestone 
  at 
  Rochester. 
  353 
  

  

  Again 
  some 
  of 
  the 
  breccia 
  is 
  to 
  be 
  classified 
  as 
  tectonic. 
  

   Western 
  New 
  York 
  has 
  never 
  experienced 
  severe 
  dynamic 
  

   deformation. 
  However, 
  there 
  are 
  many 
  evidences 
  of 
  

   minor 
  and 
  gentle 
  movements, 
  especially 
  seen 
  in 
  the 
  small 
  

   anticlines 
  and 
  synclines 
  with 
  major 
  dimensions 
  of 
  but 
  a 
  

   few 
  feet, 
  and 
  in 
  the 
  small 
  faults 
  of 
  both 
  normal 
  and 
  thrust 
  

   types 
  with 
  a 
  vertical 
  throw 
  of 
  a 
  few 
  inches. 
  These 
  gentle 
  

   warpings 
  and 
  displacements 
  have 
  effectively 
  brecciated 
  

   the 
  limestone 
  which 
  had 
  been 
  weakened 
  by 
  the 
  numerous 
  

   cavities 
  present. 
  Similar 
  crush 
  breccia 
  originating 
  in 
  

   an 
  analogous 
  fashion 
  is 
  to 
  be 
  seen 
  in 
  the 
  sheet 
  breccias 
  of 
  

   the 
  Joplin 
  district 
  (14). 
  Owing 
  to 
  the 
  limited 
  time 
  at 
  

   the 
  writer's 
  disposal 
  no 
  safe 
  conclusions 
  have 
  been 
  drawn 
  

   as 
  to 
  the 
  precise 
  relations 
  of 
  the 
  areas 
  of 
  brecciation 
  to 
  

   the 
  lines 
  of 
  deformation. 
  

  

  Founder, 
  or 
  solution, 
  breccia 
  is 
  also 
  represented 
  

   although 
  of 
  relative 
  unimportance 
  in 
  comparison 
  with 
  

   the 
  prevalence 
  of 
  the 
  preceding 
  types. 
  The 
  walls 
  of 
  some 
  

   of 
  the 
  larger 
  cavities 
  have 
  collapsed, 
  the 
  fissures 
  being 
  

   healed 
  by 
  calcite, 
  dolomite, 
  barite, 
  strontianite, 
  gypsum 
  

   and 
  many 
  other 
  minerals 
  occurring 
  commonly 
  in 
  the 
  

   Niagara 
  limestone. 
  In 
  fact 
  essentially 
  all 
  of 
  the 
  Niagara 
  

   breccia 
  is 
  held 
  together 
  by 
  these 
  light-colored 
  minerals. 
  

   Such 
  cavity 
  collapse 
  has 
  been 
  directly 
  aided 
  probably 
  by 
  

   the 
  gentle 
  stresses 
  resulting 
  from 
  the 
  slow 
  settling 
  of 
  the 
  

   heavy 
  dolomite 
  into 
  the 
  weak 
  Rochester 
  shale 
  beneath, 
  

  

  Little 
  has 
  been 
  said 
  regarding 
  brecciation 
  in 
  the 
  Niag- 
  

   ara 
  limestone 
  elsewhere. 
  Possibly 
  it 
  is 
  not 
  a 
  common 
  

   characteristic 
  of 
  the 
  formation. 
  Chamberlin 
  mentions 
  

   a 
  "brecciated 
  or 
  conglomeritic 
  dolomite 
  " 
  of 
  Eacine 
  age 
  

   in 
  his 
  Wisconsin 
  report 
  (4), 
  and 
  Alden 
  describes 
  local 
  

   brecciation 
  in 
  the 
  same 
  formation 
  in 
  the 
  Milwaukee 
  area 
  

   (1). 
  Some 
  reference 
  has 
  been 
  made 
  also 
  to 
  brecciation 
  

   in 
  the 
  Niagara 
  limestone 
  of 
  Iowa 
  (2). 
  

  

  It 
  is 
  hoped 
  that 
  these 
  hasty 
  and 
  scanty 
  observations 
  

   will 
  furnish 
  the 
  impetus 
  for 
  a 
  more 
  careful 
  study 
  of 
  the 
  

   Niagara 
  brecciation 
  not 
  only 
  at 
  Rochester, 
  but 
  through- 
  

   out 
  western 
  New 
  York 
  ; 
  a 
  study 
  that 
  might 
  well 
  be 
  under- 
  

   taken 
  in 
  connection 
  with 
  the 
  larger 
  problem 
  of 
  the 
  dolo- 
  

   mitization 
  of 
  the 
  Niagara 
  formation. 
  

  

  BIBLIOGRAPHY. 
  

  

  (1) 
  Alden, 
  W. 
  C: 
  Milwaukee 
  Folio, 
  No. 
  140, 
  Geologic 
  Atlas 
  of 
  the 
  United 
  

  

  States. 
  

  

  (2) 
  Calvin, 
  Sam. 
  and 
  Bain, 
  H. 
  F.: 
  Iowa 
  Geol. 
  Surv., 
  vol. 
  10, 
  pp. 
  447-448, 
  

  

  480, 
  etc., 
  1899. 
  

  

  