vAMiisK]  LAKE    SUPERIOR    REGION.  169 
detrital  beds  were  deposited,  although  Ik*  nowhere  stales  whether  this 
is  considered  Laureirtian  or  riot.  Irving- excludes  from  the  Huronian 
on  the  south  shore  large  areas  of  green  crystalline  hornblende  schists, 
chlorite- schists  and  green  schist-conglomerates  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,  the  metamorphic  mica-schists, 
etc.  In  his  Huronian  he  included  the  Animikie  on  the  north  shore, 
placed  above  the  Huronian  by  the  Canadian  geolgists. 
Lawson  abandons  the  term  Huronian  and  divides  the  schistose  rocks 
included  under  this  term  by  the  earlier  Canadian  geologists  into  two  se- 
ries the  Coutchiching  and  Keewatin.  The  Contchiching  includes  the 
lowest  rocks  in  contact  with  the  Lauren tian  gneisses  and  granites  and 
comprises  mica-schists  and  line  grained,  evenly  laminated  gneisses;  that 
is,  thoroughly  crystalline  finely  laminated  rocks.  The  Keewatin  includes 
tine  grained  green  schists,  both  basic  and  acidic,  with  volcanic  tuffs,  ag- 
glomerates, peculiar  altered  conglomerates  with  intersecting  eruptives, 
and  jaspery  iron  ore  beds.  It  does  not  include  the  unaltered  slates, 
gray  wackes  and  ferruginous  beds  of  the  Animikie.  The  position  of  the 
Profs.  AVinchell  is  practically  the  same  as  that  of  Lawson,  except  that 
instead  of  using  Coutchiching,  Vermilion  is  used,  and  both  the  Kee- 
watin and  Coutchiching  are  held  to  be  inferior  to  all  of  the  Huronian. 
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. 
Belonging  to  the  series  designated  by  the  foregoing  terms  are  recog- 
nized by  all  writers  interbedded  and  cutting  basic  and  acid  eruptives 
of  various  sorts,  only  in  the  Animikie  and  in  the  Huronian  of  living  the 
acid  eruptives  are  insignificant  in  amount.  Many  of  the  fine  grained 
green  schists,  with  some  exceptions,  in  early  days  regarded  as  much 
metamorphosed  sedimentary  Huronian  rocks,  are  now  considered  by  all  to 
be  much  altered  eruptives,  either  of  surface  or  deep  seated  origin,  their 
present  structure  being  due  to  secondary  causes.  That  acid  eruptive 
material  should  be  found  plentifully  cutting  the  elastics  series  is  Dotal 
all  surprising.  Acid  eruptions  were  abundant  and  widespread  in  the 
lake  Superior  region  as  late  as  Keweenawau  time,  as  is  attested  by  the 
original  acid  rocks  of  the  copper-bearing  series,  ami  still  more  emphat- 
ically by  the  vast  amount  of  debris  from  felsites,  quartz-porphyries,  etc., 
found  in  the  interlaminated  detrital  beds.  That  so  few  acid  dikes  are 
found  in  the  upper  Huronian  of  the  south  shore  can  be  explained  only 
by  the  fact  that  the  acid  eruptives  of  the  Keweenawau  are  mostly  re- 
mote from  the  Marquette,  Menominee,  and  Penokee  series.  A  closer 
study  in  the  future  will  probably  show  in  these  districts  a  greater 
abundance  of  acid  eruptives  than  has  been  supposed.  The  deep-seated 
pipes  and  bosses  formed  by  the  eruptions  of  the   Keweenawau   felsites 
