vanhtse.]  LAKE    SUPERIOR    REGION.  187 
districts.  The  percentage  of  iron  is  so  great  in  certain  localities  that 
the  material  is  tyeing  mined  for  an  ore.  For  placing  these  rock  series 
with  the  Keweenawan,  as  has  sometimes  been  done,  there  is  neither 
lithological  nor  structural  grounds.  In  the  character  of  the  material  of 
which  they  are  composed,  in  the  presence  of  iron  formations  in  certain 
localities  and  in  their  induration,  they  differ  profoundly  from  any  of 
the  rocks  known  to  belong  with  the  Keweenawan. 
No  one  has  placed  these  series  lower  in  the  geological  column  than 
Upper  Huronian,  so  perhaps  it  is  not  necessary  to  give  evidence  that 
they  are  not  Lower  Huronian.  The  occurrence  of  chert  and  jasper 
fragments  in  the  ChippeAva  quartzites,  mentioned  by  Sweet,  and  the 
presence  of  abundant  identical  material  in  the  quartzites  of  southern 
Minnesota  and  southeastern  Dakota,  at  least  show  that  before  the  for- 
mation of  these  series  there  was  a  prior  series  bearing  chert  and  jasper. 
Such  a  series  is  the  Lower  Huronian.  These  series  then  in  degree  of 
induration,  amount  of  folding  and  in  lithological  character  are  like  the 
Upper  Huronian. 
SUCCESSION  AND  EQUIVALENTS  OF  THE    PENOKEE  AND  ANIMIKIE    DISTRICTS    SE1UES. 
In  the  Penokee  district  of  Michigan  and  Wisconsin  is  the  following 
succession:  At  the  base  is  a  granite-gneiss-schist  complex.  The  schists 
are  always  completely  crystalline,  although  often  finely  laminated  or 
foliated.  The  granites,  with  granite-gneisses,  and  the  hue  grained  green 
hornblende-schists,  mica-schists,  and  chlorite-schists  occupy  large  sep- 
arate areas,  with  a  debatable  ground  along  their  borders.  The  contacts 
of  the  granites  and  granite-gneisses  with  the  crystalline  schists  are 
eruptive  ones,  the  former  being  clearly  the  intrusives.  Above  this  com- 
plex, and  separated  from  it  by  a  great  unconformity,  is  a  Cherty  Lime- 
stone member  which  in  places  is  300  feet  thick.  While  it  extends  east 
and  west  many  miles,  it  is  not  longitudinally  continuous.  Above  this 
Cherty  Limestone,  separated  by  an  unconformity,  is  the  Penokee  series 
proper,  which  consists  of  a  Quartz-Slate  member,  the  upper  horizon  of 
which  is  a  vitreous  quartette,  an  Iron-bearing  member,  and  an  Upper 
Slate  member.  Above  the  Penokee  series,  separated  by  another  very 
considerable  unconformity,  is  the  Keweenawan.  The  parallelism  be- 
tween this  district  and  the  Marquette  already  described  is  at  once  man 
ifest.  The  Penokee  series  proper  is  the  equivalent  of  the  Upper  Origi- 
nal Huronian,  Upper  Marquette  and  their  equivalents;  the  Cherty 
Limestone  member  stands  as  the  only  known  equivalent  of  the  Lower 
Marquette;  for  in  the  Penokee  district  the  upper  members  of  the  equiv- 
alent of  the  Lower  Marquette  have  not  been  found  or  have  been  removed 
by  erosion.  That  the  latter  is  not  improbable  is  indicated  by  the  very  con 
siderable  thickness  in  some  places  of  the  cherty  limestone  and  its  ab- 
sent ,  in  others,  while  numerous  fragments  of  it  are  found  in  the  basal 
men  >er  of  the  Penokee  series  proper.  These  fragments  are  so  abun- 
dai?'/  in  places  as  to  constitute  a  true  basal  conglomerate.     They  are  well 
