LAKE    SUPERIOR   REGION.  219 
ceeding  5°.  Intrusive  rocks  are  abundantly  present  as  sills  lying  par- 
allel to  the  stratification,  resembling  contemporaneous  beds,  and  as 
vertical  dikes,  some  of  which  have  been  observed  in  continuity  with 
the  sills.  Faulting  is  a  common  occurrence  in  the  Animikie,  many 
scarps  being  due  primarily  to  this  cause. 
The  Archean  shares  the  coast  line  with  the  Animikie  and  Kewee- 
nian  from  the  vicinity  of  Port  Arthur  to  the  eastern  end  of  Nipigon 
Bay,  and  beyond  this  point  to  the  outlet  of  the  lake  is  the  dominant 
series.  This  complex  consists  of  two  divisions:  (1)  A  great  volume 
of  profoundly  altered  sedimentary  and  volcanic  rocks,  character- 
istically schistose  or  in  the  form  of  massive  greenstones,  which  have 
suffered  intense  disturbance,  and  which  correspond  to  what  has  been 
designated  the  Ontarian  system,  and  (2)  immense  batholiths  of  irrup- 
tive  gneiss  and  granite,  which  have  invaded  the  rocks  of  the  Ontarian 
system  from  below  in  the  most  irregular  fashion,  corresponding  to 
that  division  of  the  Archean  which  is  commonly  recognized  as  Lau- 
rentian.  These  Laurentian  rocks  exhibit  only  to  a  very  subordinate 
extent  those  evidences  of  disturbances  and  deformation  which  are 
so  abundantly  apparent  in  the  schists  which  they  have  invaded.  The 
Laurentian  gneisses  and  granites  occupy  much  more  of  the  shore 
than  do  the  metamorphic  and  schistose  rocks  of  the  Ontarian.  Both 
divisions  of  the  formation  are  cut  by  basic  dikes,  which,  as  a  rule,  do 
not  exceed  100  feet  in  width,  and  are  vertical  or  nearly  so.  The 
Archean  forms  the  basement  upon  which  the  Animikie  rests  in  glar- 
ing unconformity,  the  actual  superposition  being  observed  at  several 
points,  with  the  Keweenian  lying  flat  on  the  latter.  In  many  places, 
however,  the  Keweenian  reposes  directly  upon  the  Archean. 
Bayley,183  in  1893,  describes  actinolite-magnetite  schist  from  the 
Mesabi  range  of  Minnesota.  This  rock  differs  from  the  correspond- 
ing schists  of  the  Penokee  series  only  in  that  quartz  is  rare  and  hema- 
tite is  absent. 
Winchell  (H.  V.),184  in  1893,  describes  the  Mesabi  iron  range  of 
Minnesota.  The  range  extends  from  the  Canadian  boundary  a  little 
south  of  west  to  Mississippi  River,  a  distance  of  140  miles  or  more, 
but  is  concealed  for  a  part  of  this  distance  by  the  later  gabbro  over- 
flow.    The  succession  of  the  Mesabi  is,  in  descending  order: 
1.  Gabbro  unconformably  on  all  tbe  following Taconic. 
2.  Black  slates,  Animikie Taconic. 
3.  Greenish  siliceous  slates  and  cherts Taconic. 
4.  Iron-ore  and  taconite  horizon Taconic. 
5.  Quartzite  unconformable  on  6  and  7 Taconic. 
G.  Green  schists  of  the  Keewatin Archean. 
7.  Granite  or  syenite  of  the  Giants  range  Archean. 
The  granite  of  the  Giants  range  is  bounded  on  the  north  by  a  bell  of 
crystalline  mica  schists  and  hornblende  schists,  and  on  the  south  seems 
