vanhisb.]  LAKE    SUPERIOR    REGION.  67 
any,  is  so  complex  that  no  attempt  was  made  to  work  it  out,  and,  while 
parts  of  the  granite  seem  to  belong  to  the  Lanrentian  proper,  it  is  cer- 
tain that  granitic  eruptions  have  occurred  in  this  series  after  the  main 
mass  of  the  rock  had  solidified.  The  belts  of  Keewatin  rocks  which 
encircle  the  Lanrentian  areas  are  anastomosing  or  confluent,  forming  a 
continuous  retiform  area,  the  meshes  being  occupied  by  the  Lanrentian 
gneiss.  At  their  nodes  or  points  of  confluence,  these  belts  have  their 
greatest  width.  The  Ooutchiching  schists  dip  away  from  the  Lau- 
rentian  bosses  in  all  directions,  so  that  the  general  anticlinal  struc- 
ture of  the  belt  is  made  up  of  three  anticlinal  domes.  These  relations 
are  taken  to  mean  that  the  surrounding  schistose  rocks  represent  sedi- 
mentary beds  which  have  been  thrust  aside  by  the  entering  granite. 
Along  the  contacts  of  the  Lanrentian  and  Ooutchiching  are  found  such 
minerals  as  andalusite,  staurolite,  and  garnet.  Besides  the  granite 
masses,  which  cut  all  three  of  the  previous  series  and  thus  are  later  than 
all,  are  also  numerous  diabase  and  trap  dikes,  which  cut  the  series 
mentioned  and  the  granite  besides. 
Ingall,30  in  1888,  in  describing  the  mines  and  mining  of  lake  Superior, 
finds  the  rocks  to  consist  of  Laurentian  gneisses  and  granite,  within 
which  are  found  considerable  areas  of  plutonic  and  volcanic  rocks  and 
metamorphic  slates,  considered  to  be  Huronian,  while  overlying  these, 
chiefly  about  Thunder  bay  and  lake  Mpigon,  are  the  sedimentary  and 
volcanic  rocks  of  the  Animikie,  Mpigon,  and  Keweenian  groups,  which 
are  in  approximately  a  horizontal  position  and  contrast  markedly  with 
the  steeply  inclined  or  almost  vertical  older  rocks.  The  Animikie  for- 
mation is  divisible  into  an  upper  and  lower  portion.  The  chief  charac- 
ter of  the  lower  division  is  the  preponderance  of  siliceous. rock,  such  as 
chert  and  jasper,  which  are  often  accompanied  by  ferruginous  dolomite 
with  magnetite  j  while  the  upper  division  is  formed  for  the  most  part  of 
black,  soft  argillaceous  argillites,  which  are  occasionally  dolomitic  and  fer- 
ruginous,  and  sometimes  contain  silica  in  such  proportion  as  to  approach 
the  character  of  the  lower  division.  The  thickness  of  the  Animikie  is 
placed  at  12,000  feet.  The  traps  of  the  Animikie  are  concluded  to  be 
intrusive,  frequently  breaking  as  they  do  across  the  beds.  In  one  case  a 
sheet  is  seen  to  divide  into  three  tongues.  The  dark  color  of  the  upper 
division  of  the  Animikie  is  due  to  the  presence  of  carbon.  Patches  of 
basal  conglomerates  are  occasionally  found  at  the  base  of  the  Animikie, 
lying  in  hollows  in  the  old  Arcbean  sea  bottom,  the  fragments  consisting 
in  general  of  granitic  material. 
Selwyn,37  in  1890,  announces  the  discovery  by  Ingall  of  traces  of  a 
fossil  in  the  Animikie  rocks.  A  part  of  the  impressions  are  pronounced 
by  Matthew  to  be  similar  to  Eophyton,  while  for  others  the  names 
Taonichnites  and  Otenichnites  are  proposed.  A  part  of  them  arc  of 
similar  origin  with  characteristic  tracks  of  the  Cambrian  rocks  of  the 
St.  John  group  of  New  Brunswick. 
