﻿62 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  calcareous 
  in 
  all 
  cases. 
  The 
  angular 
  form 
  of 
  the 
  pebbles 
  is 
  due 
  

   to 
  the 
  close 
  jointing 
  of 
  the 
  quartzite 
  bands 
  and 
  granite 
  dikes 
  in 
  

   the 
  limestone, 
  and 
  the 
  trifling 
  amount 
  of 
  wear 
  exhibited 
  points 
  

   to 
  residual 
  accumulation 
  in 
  the 
  hollows, 
  whereby 
  they 
  were 
  pro- 
  

   tected 
  from 
  abrasion. 
  The 
  very 
  small 
  supply 
  of 
  such 
  material, 
  

   taken 
  in 
  conjunction 
  with 
  the 
  small 
  amount 
  of 
  decay 
  shown 
  by 
  the 
  

   underlying 
  rocks, 
  is 
  a 
  factor 
  of 
  much 
  significance. 
  

  

  On 
  the 
  Alexandria 
  quadrangle^ 
  both 
  on 
  the 
  mainland 
  and 
  on 
  

   Wellesley 
  and 
  Grindstone 
  islands, 
  a 
  more 
  extensive 
  and 
  bulky 
  con- 
  

   glomerate 
  occurs, 
  which 
  has 
  already 
  been 
  described 
  by 
  Smyth 
  [see 
  

   pi. 
  14].^ 
  The 
  most 
  impressive 
  display 
  of 
  this 
  conglomerate 
  known 
  

   to 
  us 
  is 
  that 
  in 
  the 
  clifif 
  along 
  the 
  St 
  Lawrence 
  in 
  the 
  extreme 
  north- 
  

   east 
  corner 
  of 
  the 
  Alexandria 
  sheet 
  where, 
  rising 
  sharply 
  from 
  the 
  

   river 
  level 
  it 
  reaches 
  a 
  hight 
  of 
  20 
  feet 
  above 
  it. 
  Here, 
  as 
  usual, 
  

   the 
  deposit 
  has 
  a 
  calcareous 
  cement 
  which 
  dissolves 
  away, 
  loosening 
  

   the 
  cobbles, 
  and 
  giving 
  an 
  exterior 
  resemblance 
  to 
  a 
  cobbly 
  mo- 
  

   raine, 
  while 
  the 
  adjacent 
  river 
  bottom 
  is 
  solidly 
  paved 
  with 
  the 
  

   material 
  which 
  has 
  already 
  weathered 
  out. 
  The 
  deposit 
  is 
  every- 
  

   where 
  very 
  coarse, 
  a 
  cobble 
  deposit 
  rather 
  than 
  a 
  gravel. 
  In 
  the 
  

   exposure 
  here 
  the 
  cobbles 
  run 
  up 
  to 
  a 
  foot 
  in 
  diameter, 
  and 
  average 
  

   probably 
  3 
  inches. 
  They 
  are 
  round 
  to 
  subangular 
  and 
  consist 
  ex- 
  

   clusively 
  of 
  Grenville 
  quartzite. 
  Smyth 
  notes 
  the 
  presence 
  of 
  a 
  

   few 
  small 
  pebbles 
  from 
  the 
  tourmalin 
  contact 
  zones, 
  but 
  agrees 
  

   in 
  asserting 
  the 
  entire 
  absence 
  of 
  granite 
  and 
  schist 
  material, 
  

   though 
  several 
  of 
  the 
  conglomerate 
  outcrops 
  rest 
  on 
  these 
  rocks. 
  

  

  In 
  addition 
  many 
  of 
  the 
  exposures 
  show 
  that 
  the 
  conglomerate 
  

   is 
  not 
  strictly 
  basal, 
  but 
  has 
  pebbleless 
  sandstone 
  beneath, 
  up 
  to 
  a 
  

   thickness 
  of 
  at 
  least 
  10 
  feet; 
  and 
  in 
  all 
  cases 
  the 
  abrupt 
  transition 
  

   from 
  sand 
  to 
  coarse 
  cobble 
  at 
  both 
  upper 
  and 
  lower 
  contacts 
  is 
  one 
  

   of 
  the 
  most 
  interesting 
  features 
  of 
  the 
  deposit. 
  Its 
  coarseness, 
  its 
  

   abruptness, 
  its 
  horizon, 
  and 
  the 
  lack 
  of 
  variety 
  in 
  material 
  ^^ 
  ^-^p 
  

   cobbles 
  render 
  it 
  an 
  exceedingly 
  difficult 
  deposit 
  to 
  explain. 
  

  

  There 
  occur, 
  in 
  a 
  few 
  localities 
  on 
  the, 
  Theresa 
  quadrangle 
  ;, 
  c-, 
  

   patches 
  of 
  a 
  dark 
  red, 
  very 
  thoroughly 
  indurated 
  and 
  vitrcojs 
  

   sandstone 
  which 
  thus 
  differs 
  from 
  the 
  general 
  run 
  of 
  the 
  sand- 
  

   stone 
  of 
  the 
  district, 
  though 
  similar 
  rock 
  occurs 
  in 
  the 
  formcit:>,i! 
  

   elsewhere, 
  as 
  in 
  the 
  Clarkson 
  quarry 
  at 
  Potsdam. 
  As 
  it 
  occurs 
  here 
  

   it 
  seems 
  to 
  be 
  distinctly 
  older 
  than 
  the 
  general 
  formation. 
  All 
  seen 
  

   of 
  it 
  was 
  absolutely 
  basal, 
  nowhere 
  was 
  the 
  thickness 
  as 
  gre^t 
  as 
  i 
  

   foot 
  and 
  it 
  is 
  only 
  visible 
  at 
  actual 
  exposures 
  of 
  the 
  Pnt^darn 
  

   contact 
  on 
  the 
  Precambric. 
  But 
  all 
  the 
  sand-filled 
  cracks 
  ^^^'^--n 
  'in 
  

  

  1 
  op. 
  cit. 
  p. 
  rgg. 
  

  

  