vanhise.]  LAKE    SUPERIOR    REGION.  129 
Original  Huronian  convinced  the  author  of  the  parallelism  of  the  great 
quartzite  there  displayed  with  those  of  Wisconsin  and  Minnesota.  But 
things  that  are  equal  to  the  same  thing  are  equal  to  each  other,  hence 
the  Huronian  quartzite  is  no  other  than  the  Potsdam  sandstone  of  New 
York,  the  Eed  sandrock  of  Vermont,  and  the  granular  quartz  of  the 
Taconic. 
Winchell  (N.  H.),178  in  1889,  gives  a  summary  of  the  results  of  work 
on  the  crystalline  rocks  of  northeastern  Minnesota.  In  many  points  the 
conclusions  and  facts  are  the  same  as  in  the  previous  reports.  The 
Laurentian  age  is  made  to  include  the  gneiss,  granite,  and  syenite,  but 
excludes  the  crystalline  schists.  It  is  the  fundamental  gneiss  of  Min- 
nesota. Associated  with  this  fundamental  gneiss  are  areas  of  massive 
eruptive  syenite  which  are  regarded  as  due  to  the  hydrothermal  fusion 
of  the  gneissic  belts.  The  gneisses  grade  into  the  Vermilion  schists, 
which  are  the  equivalent  of  Lawson's  Coutchiching.  Along  their  con- 
tact the  Laurentian  plays  the  part  of  intrusive  rocks,  which  is  indica- 
tive that  the  opening  of  Vermilion  age  was  one  of  violent  volcanic 
action.  The  beds  have  subsequently  been  affected  by  hydrothermal 
fusion,  which  has  tended  to  unify  the  Laurentian  and  Vermilion  sys- 
tems. 
The  Vermilion  group  passes  by  conformable  transition  into  the 
Keewatin.  The  character  of  the  Keewatin  rocks  indicates  that  there 
was  active  volcanic  action  during  the  whole  period  and  that  the  ejecti- 
menta  were  received  and  distributed  by  the  waters  of  the  surrounding 
sea.  This  is  indicated  by  the  alternation  of  breccias  and  volcanic  ma- 
terial with  truly  sedimontary  strata.  The  Keewatin  is  the  iron-bearing 
formation.  The  iron  ore  is  associated  with  the  jaspilite,  which  is  of  a 
sedimentary  origin.  Parallel  with  the  Keewatin  of  Minnesota  is  the 
serpentine  and  dioritic  group  of  Eominger  in  the  Marquette  region. 
Above  this  group  in  both  regions  rs  a  profound  unconformity. 
The  Animikie  series  of  Minnesota,  bearing  iron  at  one  horizon,  is  the 
equivalent  of  the  Marquette  series  bearing  the  iron  group  of  Eominger, 
of  the  Penokee-Gogebic  series  of  Michigan  and  Wisconsin,  of  the  Mesabi 
range  in  Minnesota,  of  the  Black  river  iron-bearing  schists  in  Wiscon- 
sin, and  of  the  quartzites  of  the  Black  hills.  All  are  of  Taconic  age,  for 
the  Lower  Cumbrian  is  equal  to  the  Taconic,  the  Huronian  is  equal  to 
the  Taconic  ;%ierefore  the  Lower  Cambrian  is  equal  to  the  Huronian. 
In  the  PotsciLm  sandstone,  which  is  unconformably  on  the  Taconic, 
is  included  the  upper  quartzites  of  the  Original  Huronian,  certain  of  the 
Quartzites  of  Marquette,  the  Sioux  quartzites  of  Dakota,  and  the 
piartzites  of  Minnesota  and  Wisconsin.  This  is  also  the  age  of  the 
3opper-bearing  rocks,  which  are  an  alternation  of  basic  and  acid  erup- 
tions with  interbedded  sandstones  and  conglomerates.  The  great  gab- 
)ro  eruption  is  later  than  the  beginning  of  the  Potsdam  age.  Uncon- 
brmably  above  the  Potsdam  is  the  St.  Oroix  sandstone. 
Bull.  86 9 
