vanhise.]  LAKE    SUPERIOR    REGION.  145 
discovered  in  the  case  of  the  ordinary  quartzites  and  graywaekes,  and 
is  therefore  of  chemical  origin.  Associated  with  the  iron-bearing  beds 
is  often  a  considerable  quantity  of  carbonaceous  or  graphitic  schists. 
It  is  concluded,  (1)  That  the  original  form  of  the  iron-bearing  beds  of 
the  lake  Superior  region  was  that  of  a  series  of  thinly  bedded  carbon- 
ates, interstratilied  with  carbonaceous  shaly  layers  in  places,  which 
were  more  or  less  highly  ferriferous.  (2)  That  by  a  process  of  silicifi 
cation  these  carbonate-bearing  layers  were  transformed  into  the  various 
kinds  of  ferruginous  rocks  now  met  with.  (3)  The  iron  thus  removed 
from  the  rock  at  the  time  of  siiicification,  passed  into  solution  in  the 
percolating  waters,  was  redeposited  in  various  places,  and  thus  formed 
the  ore  bodies  and  bands  of  pure  oxide  of  iron.  (4)  That  in  other 
places,  instead  of  leaching  oat,  the  iron  has  united  with  the  silicifying 
waters  to  form  the  silicates  uoav  fouud,  such  as  actinolite.  (5)  That 
some  of  the  silicifying  process  went  on  before  the  folding,  but  some 
afterwards,  and  to  the  latter  period  belong  probably  the  larger  bodies 
of  crystalline  ore. 
Willis,198  in  1886,  describes  the  rock  occurrences  at  several  iron  dis- 
tricts in  northeastern  Minnesota.  At  Pokegama  falls  on  tke.Mississippi 
ire  found  outcrops  of  red  quartzite,  coarse  grained  sandstone,  some- 
times metamorphosed  to  a  quartzite  and  irregularly interstratified  with 
tiard  specular  ore.  On  Prairie  river  is  found  granite,  southeast  of 
which  are  quartzites,  sandstone,  and  ore. 
At  Vermilion  lake  the  iron-bearing  series  has  a  dip  of  between  85° 
ind  90°,  the  structure  being  regarded  as  an  anticline,  upon  the  north 
side  of  which  is  the  Vermilion  range  and  on  the  south  side  that  of  Two 
rivers.  The  succession  from  the  base  upward  is  as  follows:  (1)  Light 
preen,  thinly  laminated,  chloritic  schist.  (2)  Jasper  of  white,  gray, 
3rown,  and  bright  red  colors,  interstratilied  with  layers  of  hard  bine 
Specular  ore,  which  also  occurs  in  ore-bodies  of  considerable  extent  run- 
ling  across  the  bedding;  thickness  200  to  000  feet  or  more.  (3)  Chlor- 
tic  schist,  similar  to  1 ;  original  thickness  probably  about  150  feet.  (4) 
Quartzite,  dark  gray,  white,  or  black,  of  sac  char  oidal  text  are,  contain- 
ng  grains  of  magnetite  which  make  it  a  readily  recognized  magnetic 
formation;  probable  thickness  200  feet,  (5)  Conglomerate,  consisting 
of  sandstone  pebbles  and  traces  of  black  slate  inclosed  in  siliceous 
Ihloritic  schist.  (6)  Compact  homogeneous  rock,  composed  of  quartz 
grains,  chlorite,  hornblende,  plagioclase  feldspar,  and  calcite.  This 
rock  may  be  an  eruptive  quartz-diorite,  but  is  considered  a  metamor- 
phosed sedimentary  transition  bed  between  5  and  7.  (7)  Black  clay 
slate,  fissile  and  sonorous.  It  occupies  a  broad  area  north  of  Vermilion 
range.  In  section  28  huge  masses  of  jasper  form  the  crown  of  the  arch 
and  are  imbedded  in  green  schist,  with  which  they  agree  in  strike  and 
ftip.  The  jasper  blocks  are  rectangular  and  several  hundred  feci  long; 
the  ends  of  the  bands  come  out  squarely  fco  the  contact  with  the  schist 
las  to  a  fault. 
Bull.  86—10 
