380  PRE-CAMBRIAN"    GEOLOGY   OF    NORTH    AMERICA. 
eluded  in  the  Huronian  all  the  rocks  in  character  like  those  placed  in 
this  system  on  the  north  shore,  with  also  large  areas  of  rocks  the  clas- 
tic character  of  which  is  evident,  such  as  limestones,  ferruginous  beds, 
slates,  graywackes,  etc.,  which  while  always  tilted  or  gently  folded 
have  not  the  schistose  structure  of  the  "  Huronian  "  of  the  north 
shore,  but  rather  resemble  the  Animikie.  Later,  Brooks  placed  as  the 
upper  member  of  the  "  Huronian  "  large  areas  of  gneiss  and  granite 
which  had  earlier  been  regarded  as  Laurentian.  Rominger  went  a 
step  farther  and  recognized  in  his  published  report  on  the  south  shore 
the  "  Huronian  "  only,  seeing  as  he  did  that  a  part  of  the  granite 
gneiss  certainly  cuts  a  portion  of  the  schistose  rocks  which  had  been 
regarded  as  "Huronian."  He  thus  included  in  the  "Huronian"  the 
granite  gneisses  which  are  equivalent  to  Lawson's  "  Laurentian,"  and 
reverted  to  the  position  of  Foster  and  Whitney,  making  his  "  Hu- 
ronian "  the  equivalent  of  their  "Azoic,"  one  indivisible  system.  In 
Rominger's  later  unpublished  manuscript,  however,  he  distinctly 
recognizes  besides  a  later  intrusive  granite  an  earlier  granite  gneiss 
upon  which  the  lowest  detrital  beds  were  deposited,  although  he 
nowhere  states  whether  this  is  considered  Laurentian  or  not.  Irving- 
excludes  from  the  Huronian  on  the  south  shore  large  areas  of  green 
crystalline  hornblende  schists,  chlorite  schists,  and  green  schist  con- 
glomerates cut  by  granite  veins,  heretofore  called  "  Huronian ;  " 
that  is,  he  included  in  the  Huronian  only  those  detrital  rocks  the 
clastic  character  of  which  is  apparent  or  which  can  be  traced  into 
the  clastic  rocks,  such  as  the  quartzites,  limestones,  ferruginous  beds, 
argillaceous  slates,  nietamorphic  mica  schists,  etc.  In  his  Huronian 
he  included  the  Animikie  on  the  north  shore,  placed  above  the  Hu- 
ronian by  the  Canadian  geologists. 
Animikie. — The  Animikie  includes  the  unaltered,  or  little  altered, 
gently  inclined  or  folded  slates,  graywackes,  and  ferruginous  beds  on 
the  north  shore  and  in  northeastern  Minnesota. 
Basic  and  acidic  eruptives. — All  writers  recognize  as  belonging  to 
the  series  designated  by  the  foregoing  terms  interbedded  and  cutting 
basic  and  acidic  eruptives  of  various  sorts,  although  in  the  Animikie 
acidic  eruptives  are  insignificant  in  amount.  Many  of  the  fine-grained 
green  schists,  with  some  exceptions  regarded  in  early  days  as  much 
metamorphosed  sedimentary  "  Huronian  "  rocks,  are  now  considered 
by  all  to  be  much  altered  eruptives,  either  of  surface  or  of  deep- 
seated  origin,  their  present  structure  being  due  to  secondary  causes. 
That  acidic  eruptive  material  should  be  found  plentifully  cutting  the 
clastic  series  is  not  at  all  surprising.  Acidic  eruptions  were  abundant 
and  widespread  in  the  Lake  Superior  region  as  late  as  Keweenawan 
time,  as  is  attested  by  the  original  acidic  rocks  of  the  copper-bearing 
series,  and  still  more  emphatically  by  the  vast  amount  of  debris  from 
f  el  sites,  quartz  porphyries,  etc.,  found  in  the  interlaminated  detrital 
