110  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
upper  or  gray  sand  rock  conforms  to  the  limestone  above  it,  and  rests 
conformably  upon  the  uptilted  edges  of  the  sand  rock  below. 
Locke,3  in  1841,  describes  the  rocks  of  Copper  Harbor  as  well  as 
the  whole  of  Keweenaw  Peninsula  as  decidedly  metamorphic,  show- 
ing every  degree  of  change  produced  by  igneous  action,  from  un- 
changed sandstone  to  compact  greenstone.  The  original  stratification 
is  generally  more  or  less  evident;  some  layers  bear  evidence  of  semi- 
fusion  with  a  corresponding  degree  of  induration,  while  others  seem 
scarcely  to  have  been  altered. 
Rogers,4  in  1846,  describes  the  red  sandstones  and  conglomerates  of 
Lake  Superior  as  resting  unconformably  upon  highly  inclined  slate 
rocks  undoubtedly  Primal  and  upon  the  Potsdam  sandstone  of  the 
New  York  Survey  at  Chocolate  and  Carp  rivers,  and  therefore  re- 
gards them  as  of  post-Paleozoic  age. 
Locke,5  in  1847,  speaks  of  the  relation  of  the  trap  rock  and  sand- 
stone at  Presque  Isle,  and  submits  a  drawing  of  it. 
Whitney,6  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  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 
Agogebic  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  Porcu- 
pine Mountains,  is  covered  by  the  red  sandstone  of  Lake  Superior. 
Whitney,7  in  1848,  finds  in  the  townships  near  L'Anse  fossilifer- 
ous  limestone,  which  seems  to  be  surrounded  by  and  has  been  depos- 
ited on  the  Lake  Superior  sandstone. 
Foster,8  in  1848,  in  passing  front  Copper  Harbor  to  L'Anse,  finds 
that  the  trap,  instead  of  being  forced  through  the  layer  of  sandstone, 
as  on  the  northern  slope  of  Keweenaw  Point,  protrudes  through  a  fis- 
sure in  it,  causing  an  anticlinal  axis.  A  few  miles  farther  south  the 
sandstone  is  nearly  horizontal,  being  in  a  series  of  gentle  undulations. 
At  L'Anse  the  sandstones  overlie  the  talcose,  argillaceous,  and  horn- 
blendic  slates  unconformably,  while  15  miles  southeast  of  L'Anse  the 
granites  protrude  through  these  schists. 
On  Michigamme  River  were  found,  in  order,  beds  of  quartz  and 
feldspar,  hornblende,  and  specular  oxide  of  iron,  associated  with  tal- 
cose and  argillaceous  schists.  On  the  left  bank  of  the  Michigamme 
(sec.  1,  T.  46  N.,  R.  30  W.)  is  a  hill  170  feet  high  which  exposes  a 
very  large  mass  of  nearly  pure  specular  oxide  of  iron.  About  40  feet 
from  the  escarpment  is  a  metamorphic  rock  composed  of  rounded  par- 
