vanhise.]  LAKE    SUPERIOR    REOJON.  73 
Locke/4  in  1844,  describes  the  rocks  of  Copper  harbor  as  well  as  the 
whole  of  Keweenaw  peninsula  as  decidedly  metamorphic,  showing 
every  degree  of  change  produced  by  igneous  action,  from  unchanged 
sandstone  to  compact  greenstone.  The  original  stratification  is  gener- 
ally more  or  less  evident;  some  layers  bear  evidence  of  semifusion  with 
a  corresponding  degree  of  induration,  while  others  seem  scarcely  to 
have  been  altered. 
Cunningham,45  in  1845,  Sanders,46  in  1845,  Campbell,47  Sanders,48 
Gray,49  in  1845,  Gray,50  in  1846,  give  various  detailed  observations  as 
to  the  mineral  regions  of  lake  Superior,  but  give  little  or  nothing  of 
structural  interest. 
Bog-ers,51  in  1846,  describes  the  red  sandstones  and  conglomerates  of 
lake  Superior  as  resting  unconformably  upon  highly  inclined  slate  rocks 
undoubtedly  Primal,  and  the  Potsdam  sandstone  of  the  New  York  sur- 
vey at  Chocolate  and  Carp  rivers,  and  therefore  of  post-Paleozoic  age. 
Owen,52  in  1847,  finds  the  horizontal  sandstone  to  overlap  the  crys- 
talline and  metamorphic  formations  at  the  southern  portion  of  the 
Chippewa  land  district  near  the  falls  of  the  streams  flowing  into  the 
Mississippi.  Tb*e  region  to  the  north  is  based  upon  crystalline,  gra- 
nitic, and  other  intrusive  rocks.  North  of  the  summit  levels  of  the 
Chippewa  land  district  the  peculiar  formations  of  the  lake  Superior 
country  commence.  These  are  red  sandstones,  marls,  and  conglomer- 
ates, occasionally  penetrated  by  iutrusive  ranges  of  hornblende,  green- 
stone, trap,  and  amygdaloid  similar  in  their  general  aspect  to  the  con- 
temporaneous ranges  of  igneous  rocks  which  occur  in  the  mining  dis- 
trict of  .Michigan.  Besides  this  trap  formation,  there  is  an  entirely 
distinct  trap  system  in  immediate  juxtaposition  with  which  strata  have 
been  discovered  which  are  as  old  as  if  not  older  than  the  Lingula  beds  of 
the  Potsdam  sandstone  of  New  York. 
Locke,53  in  1847,  speaks  of  the  relation  of  the  trap  rock  and  sand- 
stone at  Presque  isle,  and  submits  a  drawing  of  it. 
Whitney,54  in  1847,  describes  the  wide  band  of  trappean  rocks  com- 
mencing at  the  extremity  of  Keweenaw  point  as  continuing  its  course 
uninterruptedly  as  far  as  the  Montreal  river.  Its  distance  from  the 
lake  between  Portage  and  Ontonagon  is  generally  from  8  to  10  miles. 
The  highest  and  most  imposing  cliffs  are  found  north  and  east  of  Ago- 
gebic  lake.  Beyond  Agogebic  lake  the  trap  range  widens  and  forms 
several  ridges,  between  which  it  is  not  impossible  that  there  may  be 
sandstone.  The  Porcupine  mountains  embrace  a  system  of  trappose 
rocks  in  three  tolerably  distinct  ranges.  All  the  country  north  of  the 
northern  edge  of  the  trap  range  from  the  Ontonagon  to  the  Montreal, 
with  the  exception  of  the  trappose  rocks  of  the  Porcupine  mountains,  is 
covered  by  the  red  sandstone  of  lake  Superior. 
Owen,55  in  1847,  gives  many  details  of  the  formations  of  the  interior 
of  the  Chippewa  land  district,  and  of  the  formation  of  lake  Superior. 
In  the  first  district  are  seen  many  varieties  of  granite,  syenite,  green- 
