﻿Geology 
  and 
  Natural 
  History. 
  153 
  

  

  the 
  region 
  of 
  the 
  international 
  boundary 
  is 
  recognized 
  only 
  in 
  a 
  

   tentative 
  way. 
  

  

  Upon 
  the 
  Animikie 
  rests 
  the 
  Keweenawan, 
  and 
  in 
  the 
  discussion 
  

   of 
  this 
  series 
  certain 
  new 
  propositions 
  of 
  interest 
  are 
  advanced. 
  

   It 
  may 
  be 
  said 
  in 
  general 
  that 
  the 
  Keweenawan 
  of 
  Minnesota 
  is 
  

   almost 
  wholly 
  made 
  up 
  of 
  volcanics 
  and 
  the 
  intrusives 
  which 
  

   traverse 
  them, 
  with 
  but 
  a 
  small 
  admixture 
  of 
  sedimentary 
  strata. 
  

   The 
  series 
  is 
  thus 
  in 
  strong 
  contrast 
  to 
  the 
  underlying 
  Animikie. 
  

   A 
  formation 
  of 
  conglomerate 
  with 
  sandstone 
  or 
  quartzite 
  has 
  long 
  

   been 
  recognized 
  in 
  the 
  Thunder 
  Bay 
  region 
  as 
  the 
  base 
  of 
  the 
  

   Keweenawan 
  (Nipigon 
  series). 
  The 
  Minnesota 
  Survey 
  finds 
  that 
  

   Duluth 
  gabbro, 
  the 
  "red 
  rock" 
  and 
  certain 
  lavas, 
  e. 
  g., 
  the 
  

   Beaver 
  Bay 
  diabase, 
  all 
  of 
  which 
  have 
  been 
  referred 
  to 
  as 
  

   Keweenawan, 
  seem 
  to 
  antedate 
  the 
  conglomerate 
  (Puckwunge). 
  

   It 
  therefore 
  divides 
  the 
  Keweenawan 
  into 
  two 
  parts, 
  viz 
  : 
  The 
  

   Cabotian 
  which 
  includes 
  all 
  that 
  precedes 
  the 
  conglomerate 
  and 
  

   the 
  Manitou 
  including 
  the 
  conglomerate 
  and 
  later 
  formations. 
  

   In 
  making 
  this 
  discrimination 
  Mr. 
  Winchell 
  is 
  evidently 
  in 
  a 
  

   quandary 
  whether 
  to 
  put 
  his 
  Cabotian 
  in 
  the 
  Animikie 
  or 
  keep 
  it 
  

   in 
  the 
  Keweenawan. 
  He 
  expresses 
  his 
  opinion 
  that 
  the 
  Animikie 
  

   graded 
  gradually 
  into 
  Keweenawan, 
  and 
  that 
  in 
  the 
  Keweenawan 
  

   there 
  was 
  a 
  profound 
  erosion 
  interval 
  represented 
  by 
  the 
  Puck- 
  

   wunge 
  conglomerate. 
  This 
  seems 
  to 
  the 
  writer 
  an 
  indefensible 
  

   position 
  to 
  assume. 
  The 
  logical 
  thing 
  to 
  do 
  is 
  to 
  place 
  anything 
  

   that 
  grades 
  into 
  the 
  Animikie 
  and 
  antedates 
  such 
  an 
  unconformity 
  

   into 
  the 
  Animikie. 
  . 
  But 
  it 
  is 
  not 
  at 
  all 
  clear 
  that 
  any 
  such 
  recon- 
  

   struction 
  of 
  the 
  Animikie 
  is 
  necessary. 
  It 
  does 
  not 
  seem, 
  for 
  

   instance, 
  to 
  be 
  at 
  all 
  satisfactorily 
  established 
  that 
  the 
  Duluth 
  

   gabbro 
  antedates 
  the 
  conglomerate. 
  No 
  pebbles 
  of 
  the 
  gabbro 
  

   have 
  apparently 
  been 
  found 
  in 
  the 
  conglomerate. 
  The 
  fact 
  that 
  

   the 
  gabbro 
  is 
  inferior 
  in 
  position 
  to 
  the 
  conglomerate 
  is 
  of 
  no 
  

   weight, 
  since 
  the 
  gabbro 
  is 
  admittedly 
  intrusive. 
  The 
  " 
  red 
  

   rock" 
  pebbles 
  are 
  not 
  necessarily 
  derived 
  from 
  gabbro 
  contacts. 
  

   Mr. 
  Winchell 
  assumes 
  that 
  the 
  Logan 
  sills 
  and 
  dikes 
  in 
  the 
  

   Animikie 
  are 
  offshoots 
  from 
  the 
  gabbro 
  intrusion, 
  but 
  this 
  is 
  shown 
  

   to 
  be 
  improbable 
  on 
  petrographic 
  grounds 
  by 
  Dr. 
  Grant; 
  and 
  

   some 
  of 
  these 
  sills 
  and 
  dikes 
  have 
  " 
  red 
  rock 
  " 
  contacts. 
  The 
  

   Duluth 
  gabbro 
  cannot 
  be 
  earlier 
  than 
  the 
  Puckwunge 
  conglom- 
  

   erate 
  and 
  at 
  the 
  same 
  time 
  the 
  equivalent 
  of 
  the 
  Logan 
  sills; 
  for 
  

   the 
  latter 
  are 
  intrusive 
  in 
  abundance 
  not 
  only 
  in 
  the 
  Animikie 
  but 
  

   also 
  in 
  Keweenawan 
  (Nipigon) 
  strata 
  overlying 
  the 
  conglomerate 
  in 
  

   the 
  Thunder 
  Bay 
  district. 
  It 
  seems, 
  moreover, 
  that 
  another 
  incon- 
  

   sistency 
  lies 
  in 
  the 
  fact 
  that 
  the 
  conglomerate 
  is 
  stratigraphically 
  

   beneath 
  the 
  Beaver 
  Bay 
  diabase 
  as 
  mapped 
  on 
  the 
  Cook 
  County 
  

   Plate, 
  while 
  the 
  diabase 
  is 
  throughout 
  the 
  report 
  regarded 
  as 
  the 
  

   surface 
  equivalent 
  of 
  the 
  gabbro. 
  Is 
  it 
  not 
  entirely 
  possible, 
  for 
  

   anything 
  that 
  Mr. 
  Winchell 
  knows 
  to 
  the 
  contrary, 
  that 
  the 
  

   Duluth 
  gabbro 
  was 
  intrusive 
  in 
  late 
  Keweenawan 
  time 
  and 
  that 
  

   some 
  of 
  the 
  "red 
  rock" 
  of 
  Cook 
  County 
  is 
  due 
  to 
  the 
  contact 
  

   action 
  of 
  the 
  gabbro 
  against 
  the 
  Puckwunge 
  sandstone 
  ? 
  It 
  is 
  

   certainly 
  remarkable, 
  in 
  view 
  of 
  Mr. 
  Winchell's 
  contention, 
  that 
  

   neither 
  the 
  geological 
  mapping 
  of 
  Cook 
  County 
  nor 
  the 
  more 
  

  

  