124  PRE-CAMBEI AN    GEOLOGY    OF    NORTH   AMERICA. 
Many  details  are  given  as  to  the  Menominee  and  Fetch  Mountain 
districts.  The  rocks  of  these  ranges  are  parallel  with  those  in  the 
Marquette  district.  At  many  places  the  Silurian  rocks  unconform- 
ably  cap  the  iron-bearing  rocks. 
The  Lake  Gogebic  and  Montreal  River  iron  range  is  regarded  as  an 
eastern  prolongation  of  the  Penokee  range  of  Wisconsin.  The  north- 
ern geological  boundary  is  the  south  copper  range,  consisting  of 
massive  and  amygdaloidal  copper-bearing  traps,  the  bedding  of 
which  is  exceedingly  obscure,  with  occasional  beds  of  sandstone  and 
imperfect  conglomerates.  The  strike  of  these  rocks  is  east  and  west, 
with  a  dip  to  the  north  at  a  high  angle,  thus  conforming  with  the 
Huronian  rocks  underneath.  On  the  south  of  the  iron-bearing  rocks 
is  a  series  of  granites,  gneisses,  and  obscure  schists,  which  are  unmis- 
takably Laurentian  in  their  lithological  character,  and  they  are  un- 
conformably  overlain  by  the  Huronian  rocks.  The  horizontal  Lower 
Silurian  sandstones  occupy  a  broad  belt  of  country  north  of  the  cop- 
per range.  Their  actual  contact  with  the  highly  tilted  copper  rocks 
was  not  seen,  but  they  show  not  the  slightest  evidence  of  disturbance 
Avithin  a  few  miles  of  these  steeply  inclined  rocks,  and  are  regarded 
as  unconformably  above  them. 
Pumpelly,34  in  1873,  gives  a  systematic  account  of  the  copper- 
bearing  rocks.  These  on  Keweenaw  Point  consist  of  an  immense 
development  of  alternating  trappean  rocks  and  conglomerates  dip- 
ping to  the  northwest  at  an  angle  running  from  60°  to  23°.  The  red 
sandstone  and  shales  of  Lake  Superior  are  everywhere  nearly  hori- 
zontal on  the  south  shore  of  Lake  Superior  between  the  Sault  Ste. 
Marie  and  Bete  Grise  Bay.  At  the  western  edge  of  this  belt  its 
nearly  horizontal  strata  abut  against  the  steep  face  of  a  wall  formed 
by  the  upturned  edges  of  beds  of  the  cupriferous  series  of  melaphyre 
and  conglomerate,  which  dip  away  from  the  sandstone  at  angles  of 
40°  to  60°.  This  sharp  line  has  been  explained  as  due  to  a  fault,  the 
horizontal  sandstone  being  regarded  as  of  the  same  age  as  the  con- 
formable overlying  sandstone  of  the  cupriferous  series.  One  objec- 
tion to  this  explanation  is  the  enormous  amount  of  dislocation  re- 
quired, amounting  to  several  miles.  Again,  near  Houghton  there  are 
two  patches  of  sandstone  lying  on  the  upturned  melaphyre  beds.  In 
the  horizontal  sandstone  near  the  so-called  fault  are  abundant  pebbles 
of  melaphyre  and  conglomerate  of  the  cupriferous  series.  But  the 
most  decided  facts  found  by  Major  Brooks  and  the  author  are  in  the 
country  between  Bad  River  in  Wisconsin  and  the  middle  branch  of 
the  Ontonagon,  east  of  Lake  Gogebic.  Here  the  quartzites  and  schists 
of  the  Huronian  formation  are  bordered  on  the  south  by  the  Lauren- 
tian gneisses,  and  are  overlain  conformably  by  the  bedded  melaphyres 
and  interstratified  sandstones  of  the  cupriferous  series.  Between 
these  ridges,  forming  the  south  mineral  range  and  the  main  range  of 
