vanhise.]  LAKE    SUPERIOR    REGION.  97 
and  limoiiitic  schistose  ores;  (h)  diorite,  hornblende- schist,  and  chlor- 
ite- schist ;"(*)  arenaceous  quartz-schist,  banded  with  micaceous  iron 
and  quartzose  linionitic  ore;  (j)  pure  specular  hematite  and  magnetite, 
with  banded  jaspery  schists  and  interstratified  beds  of  chloritic  and 
hydromica- schist;  (k)  an  arenaceous  quartzite,  often  semischistose  and 
conglomeratic;  (I)  argillaceous  slate;  (m)  quartz-schists;  (n)  autho- 
pliyllitic  schist;  (o)  mica-schist.  Similar  successions  are  given  in  the 
other  regions  mentioned  and  correlated  with  that  in  the  Marquette 
region,  and  all  of  these  successions  are  compared  and  correlated  with 
Logan's  succession  in  Canada. 
The  Huronian  in  the  Marquette,  Menominee,  and  Gogebic  regions  is 
nonconformable  with  the  Lauren tian. 
Pumpelly,108  in  1878,  describes  lake  Superior  as  divided  into  two 
distinct  basins  by  Keweenaw  point,  the  western  basin  being  a  geosyn- 
clinal  trough.  The  southeastern  lip  of  this  trough  consists  of  an  im- 
mense development  of  volcanic  rocks  in  the  form  of  great  beds  and 
flows  associated  with  conglomerates  and  sandstones,  both  of  which  con- 
sist essentially  of  porphyry  detritus.  This  Keweenaw  series  is  more 
nearly  conformable  with  the  underlying  highly  tilted  Huronian  schists 
than  with  the  Potsdam  sandstone.  The  prominent  eruptive  rocks  of 
the  Keweenaw  series  fall  under  the  two  heads,  diabase  and  melaphyre. 
The  changes  which  have  taken  place  in  the  interior  of  the  rock  masses 
since  eruption,  that  is,  the  metasomatic  development  of  these  rocks,  is 
traced  out  in  great  detail. 
Wright,109  in  1879,  describes  the  Laurentian  series  as  consisting  of 
coarsely  crystalline  massive  granites,  passing  into  gneissoid  rocks,  and 
these  graduating  into  mica-schists,  and  the  latter  even  as  imperceptibly 
into  slates.  The  Laurentian  granite  is  regarded  as  a  metamorphic 
sedimentary  rock,  because  the  quartz  grains  contain  cavities  filled 
with  liquid,  while  igneous  granites  never  contain  such  cavities,  but 
rather  those  filled  with  glass  or  stone.  The  lower  Huronian  strata  have 
been  chiefly  derived  from  the  ruins  of  the  Laurentian  rocks.  The  non- 
conformity between  the  Laurentian  and  Huronian  maybe  seen  at  Pen  - 
okee  gap.  Here  the  dip  of  the  gneissoid  granite  is^about  70°  to  the 
south,  Avhile  the  plainly  bedded  Huronian  strata  in  direct  contact  have 
a  dip  of  65°  to  the  north.  At  the  Macomber  mine,  near  Kegaunee,  is 
found  a  bed  of  manganiferous  hematitic  shale  bearing  the  impression 
of  some  fossil  which  Profs.  Brush,  Yerrill,  Dana,  and  Smith  pronounce 
to  belong  to  the  lower  forms  of  life.  The  Lower  Silurian  sandstone 
about  the  city  of  Marquette  is  nearly  horizontally  bedded,  and  rests 
unconformabiy  on  and  against  the  Huronian. 
Rominger,110  in  1881,  gives  a  general  account  of  the  Marquette  and 
Menominee  iron  region,  with  very  voluminous  details  as  to  particular 
localities. 
The  Marquette  region. — In  general  remarks  on  the  geology  of  the  Mar- 
quette district  the  succession  is  (1)  Granitic  group;  (2)  Dioritic  group; 
Bull.  86 7 
