132  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
as  follows:  (1)  The  hematites  and  liraonites  of  the  Mesabi  range,  the 
equivalents  of  the,hematites  of  the  Penokee- Gogebic  range  in  Wiscon- 
sin ;  (2)  the  gabbro  titaniferous  magnetites  near  the  bottom  of  the  rocks 
of  the  Mesabi  range ;  (3)  Olivinitic  magnetites,  just  below  the  gabbro 
in  the  basal  portion  of  the  Mesabi  rocks;  (4)  the  hematites  ami  mag- 
netites of  the  Vermilion  range  in  the  Keewatin  formation;  (5)  the  mag- 
netites of  the  crystalline  schists  of  the  Vermilion  formation.  It  is  main- 
tained that  the  upper  iron  deposits  of  the  Mesabi  and  those  of  the 
Penokee- Gogebic  are  the  equivalents  of  the  Taconic  ores  of  western  New 
England. 
Winchell  (N.  H.)187,  In  1891,  gives  numerous  additional  field  obser- 
vations. The  relations  of  the  jaspilite,  argillite,  and  green  schist  are 
considered,  and  the  argillite  at  least  is  regarded  as  a  sedimentary 
rock.  The  position  of  the  Pewabic  quartzite  is  left  uncertain.  It  is 
considered,  however,  to  overlie  the  Animikie  black  slate,  unless  there 
are  two  great  quartzites.  This  quartzite  has  heretofore  been  made  the 
parallel  of  the  great  quartzite  that  overlies  the  Animikie  unconform- 
able, but  it  is  possible  that  it  runs  below  it  conformably.  In  the  Stuntz 
conglomerate  is  found  a  large  bowlder  which  contains  pebbles  of  chal- 
cedonic  quartz  and  quartzose  felsite  and  the  porphyrel  at  Kekekabik 
lake.  A  study  of  the  ore  formation  leads  to  the  conclusion  that  al 
three  of  the  known  agencies  for  rock-forming  were  intermittently  at 
work  and  concerned  in  the  formation  of  the  iron  ore,  viz :  Eruption,  to 
afford  the  basic  eruptive  material;  sedimentation,  to  arrange  it  (in  the 
main),  and  chemical  precipitation  in  the  same  water,  to  give  the  pure 
hematite  and  the  chalcedonic  silica.  The  great  gabbro  of  the  Cuprifer- 
ous formation  is  regarded  as  lying  below  the  Animikie,  among  other 
reasons,  because  it  lies  next  to  and  immediately  south  of  the  gneiss  of 
the  Giant  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),188  in  1891,  give  an  extended  treatment 
of  the  iron  ores  of  northeastern  Minnesota  and  the  rocks  in  which  they 
are  contained.  Excluding  the  Cretaceous,  the  rocks  here  found  are 
divided  in  descending  order,  as  follows :  Keweenawan — trap  rocks,  tuffs, 
red  sandstones,  and  conglomerates  (Potsdam?);  Animikie — black  slates, 
gray,  feldspathic  sandstones  and  limestones;  Norian — gabbro  of  the 
Mesabi  hills,  red  granite,  quartz-porphyry,  red  felsite ;  Pewabic  quartz- 
ite (Granular  quartz,  Potsdam?);  Keewatin — sericitic  schists,  gray- 
wackes,  greenstones,  agglomerates,  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  inclusive  in  the  Archean  or  Azoic. 
The  jaspilite  and  schist  of  the  Keewatin  are  found  to  occur  some- 
times minutely  interlaminated;  at  other  times  the  jasper  is  in  irregular 
layers,  which  never  have  any  great  extent  and  always  finally  pinch 
