﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  

  

  105 
  

  

  set. 
  Figure 
  4 
  is 
  an 
  attempt 
  to 
  illustrate 
  these 
  relations. 
  These 
  two 
  

   joint 
  sets, 
  both 
  having 
  the 
  same 
  strike 
  as 
  the 
  Grenville 
  rocks, 
  are 
  

   much 
  the 
  most 
  prominent 
  of 
  the 
  joints 
  which 
  these 
  rocks 
  show, 
  and 
  

  

  Fig. 
  4 
  Sketch 
  and 
  section 
  of 
  alternating 
  quartzite 
  and 
  amphibolite 
  bands 
  of 
  Gren- 
  

   ville 
  series, 
  the 
  quartzites 
  forming 
  low 
  ridges 
  on 
  the 
  surface. 
  The 
  line 
  A 
  represents 
  the 
  

   direction 
  of 
  the 
  joints 
  which 
  follow 
  the 
  dip, 
  the 
  line 
  B 
  that 
  of 
  those 
  at 
  right 
  angles 
  to 
  the 
  

   first 
  set, 
  and 
  C 
  represents 
  the 
  direction 
  in 
  which 
  both 
  sets 
  cut 
  the 
  surface 
  

  

  conspicuous 
  at 
  every 
  good 
  exposure 
  of 
  the 
  Grenville 
  schists 
  or 
  

   quartzites, 
  though 
  much 
  less 
  conspicuous 
  in 
  the 
  limestones. 
  The 
  

   quarry 
  face 
  in 
  plate 
  2 
  is 
  on 
  the 
  dip 
  joints, 
  here 
  steep, 
  and 
  the 
  other 
  

   set 
  are 
  quite 
  flat 
  and 
  show 
  well 
  in 
  the 
  view, 
  as 
  does 
  also 
  a 
  vertical 
  

   set 
  of 
  northwest 
  joints. 
  So 
  common 
  are 
  they 
  that 
  they 
  soon 
  came 
  to 
  

   be 
  recognized 
  as 
  a 
  matter 
  of 
  course, 
  which 
  it 
  was 
  superfluous 
  

   to 
  chronicle 
  in 
  the 
  notebook. 
  Hence 
  the 
  number 
  of 
  observations 
  

   on 
  joints 
  striking 
  n. 
  40° 
  e.-n. 
  60° 
  e. 
  shown 
  on 
  the 
  diagram 
  [fig. 
  

   5] 
  is 
  misleading 
  as 
  to 
  their 
  abundance 
  and 
  importance. 
  The 
  com- 
  

  

  ,\luii/i/, 
  

  

  Fig. 
  5 
  Diagram 
  to 
  indicate 
  the 
  number 
  of 
  readings 
  on 
  joint 
  directions 
  in 
  the 
  Pre- 
  

   cambric 
  rocks 
  of 
  the 
  district 
  for 
  each 
  5° 
  point 
  of 
  the 
  compass, 
  the 
  outer 
  row 
  of 
  figures 
  

   giving 
  this 
  number, 
  and 
  the 
  inner 
  row 
  the 
  compass 
  degrees, 
  corrected 
  for 
  variation 
  

  

  paratively 
  slight 
  variation 
  in 
  the 
  number 
  of 
  readings 
  for 
  all 
  points 
  

   between 
  n. 
  30° 
  e. 
  and 
  east 
  is 
  however 
  a 
  result 
  of, 
  and 
  indication 
  ^f. 
  

   the 
  swerving 
  of 
  these 
  joints 
  with 
  swerve 
  in 
  the 
  rock 
  strike. 
  

  

  