LAKE    SUPERIOR   REGION.  211 
low  the  Animikie,  among  other  reasons  because  it  lies  next  to  and 
immediately  south  of  the  gneiss  of  the  Giants  range  without  the 
appearance  of  any  black  slate  between  them,  and  because  bowlders 
of  characteristic  gabbro,  red  syenite,  and  quartz  porphyry  occur 
abundantly  in  the  later  traps  of  the  Cupriferous. 
Winchell  (N.  H.  and  H.  V.),171  in  1891,  give  an  extended  treat- 
ment of  the  iron  ores  of  northeastern  Minnesota  and  the  rocks  in 
which  thej^  are  contained.  Excluding  the  Cretaceous,  the  rocks  here 
found  are  divided  as  follows,  in  descending  order:  Keweenawan— 
trap  rocks,  tuffs,  red  sandstones,  and  conglomerates  (Potsdam?)  ; 
Animikie — black  slates,  gray  feldspathic  sandstones,  and  limestones ; 
Xorian — gabbro  of  the  Mesabi  Hills,  red  granite,  quartz  porphyry, 
and  red  felsite;  Pewabic  quartzite  (granular  quartz,  Potsdam?); 
Keewatin — sericitic  schists,  graywackes,  greenstones,  agglomerates, 
and  jaspilite;  Vermilion — mica  schists  and  hornblende  schists 
(Coutchiching?)  ;  Laurentian — sedimentary,  gneissic  and  eruptive, 
massive  or  porphyritic.  The  Keweenawan  to  the  Pewabic  inclusive 
are  placed  in  the  Taconic,  and  the  Keewatin  to  the  Laurentian  in- 
clusive in  the  Archean  or  Azoic. 
The  jaspilite  and  schist  of  the  Keewatin  are  in  some  places  mi- 
nutely interlaminated ;  at  other  places  the  jasper  is  in  irregular  layers, 
none  of  which  have  any  great  extent  and  all  of  which  finally  pinch 
out;  at  still  other  places  it  is  in  oval  forms,  the  greater  lengths  being 
parallel  with  the  schistose  structure.  Again,  the  jaspilite  is  in  great 
fragments  within  the  green  or  massive  diabasic  schists,  the  masses 
having  in  places  such  relations  with  one  another  as  to  show  that  they 
are  a  broken  continuous  layer.  The  branches  from  the  large  bodies 
of  jaspilite  are  supposed  to  be  caused  by  the  crumpling,  breaking, 
and  squeezing  of  the  entire  rock  structure,  by  which  the  thinner  sheets 
have  been  buckled  out  and  thrust  laterally  among  the  inclosing 
schists.  The  ore  always  occurs  associated  with  the  jaspilite,  the 
forms  of  the  deposits  being  exceedingly  irregular.  The  ore  and 
jasper  are  regarded  as  a  direct  chemical  deep-sea  precipitate,  accom- 
panied and  interrupted  by  repeated  ejections  of  basic  volcanic  rocks, 
from  which  the  iron  for  the  ore  is  extracted. 
The  rocks  of  the  Animikie  equivalent  to  the  Huronian  and  included 
in  the  Taconic  consist  chiefly  of  carbonaceous  and  argillaceous  slates 
with  siliceous  slates,  fine-grained  quartzites,  and  gray  limestones.  At 
the  bottom  of  the  series  is  a  fragmental  quartz  sandstone  300  feet  in 
thickness,  which  is  named  the  Pewabic  quartzite.  The  slates,  con- 
glomerates, and  quartzites  are  profoundly  affected  and  intermingled 
with  eruptive  material  similar  to  that  found  so  abundantly  in  the 
Keewatin.  These  beds  have  the  appearance  of  consolidated  beds  of 
basic  lava  or  of  porous  tuff,  but  where  this  prevails  there  is  a  sensible 
gradation  from  the  dark,  trap-looking  beds  to  thin  beds  of  slate.    At 
