78  PRE-C  AM  BRIAN    ROCKS    OF    NORTH    AMERICA.  [bull,  86, 
Burt  69  finds  on  Keweenaw  point  and  along  the  south  shore  of  lake 
Superior  to  the  mouth  of  Carp  river  and  in  the  Porcupine  mountains 
five  principal  groups  of  rocks :  Primary,  Slates,  Trap,  Conglomerate, 
and  Sandstone.  With  the  Primary  rocks  are  placed  syenite  and  gran- 
ite. Flanking  the  Primary  rocks  is  argillaceous  slate 5  flanking  the 
slates  and  resting  upon  them  are  red  and  variegated  sandstones,  and 
these  also  flank  the  Primary  rocks.  The  Trap  rocks  have  a  much  higher 
angle  on  the  southeast  than  on  the  northwest  side  of  the  range,  which 
runs  from  the  northeast  end  of  Keweenaw  point  and  extends  in  a  course 
generally  to  the  southwest.  The  Conglomerate  flanks  the  trap  range 
on  the  northwest,  and  is  made  up  of  sand,  pebbles,  and  small  bowlders 
principally  derived  from  the  rooks  of  the  trap  family.  Resting  con- 
formably upon  the  conglomerate  rock  are  a  series  of  alternating  strata 
of  sandstone  and  conglomerate. 
Hubbard  70  finds,  in  the  district  south  of  lake  Superior,  Primary  and 
Metamorphic  regions,  consisting  of  granite  rocks,  between  which  are 
metamorphic  rocks  which  graduate  into  clay- slate. 
Burt71  finds  in  the  area  bounded  on  the  north  by  the  Fifth  Correc- 
tion line  and  south  by  the  Fourth  Correction  line  and  the  Brule  river, 
between  ranges  23  and  37,  granite  and  syenite,  talcose  and  argillaceous 
slates,  greenstone  and  hornblende- slate,  mica-slates,  coarse  sandstone, 
calciferous  sand  rock,  encrinal  limestone,  red  sandstone  and  red  clay, 
and  magnetic  iron  ore  beds. 
Foster  and  Whitney,72  in  1850,  give  a  systematic  report  on  the 
geology  and  topography  of  the  copper  lands.  On  Keweenaw  point  these 
consist  of  trappean  rocks  associated  with  conglomerates  and  sandstones 
On  this  point  are  two  trap  ranges,  the  southern  known  as  the  Bohe 
mian  range.     The  conglomerates  are  volcanic  friction  rocks  rather  than 
the  result  of  erosion.     The  pebbles  may  have  received  their  rounded 
shape  by  being  projected  from  fissures  through  water.     The  only  in- 
stance in  the  district  in  which  trap  occurs  remote  from  the  lines  of  fissure 
is  in  the  northeast  corner  of  T.  49  K.  R,  36  W.,  where  Silver  mountain  rises 
as  an  isolated  and  dome-shaped  mass  to  the  height  of  1,000  feet.     The 
summit  of  the  rock  consists  of  labrador  and  hornblende,  while  the  sur 
rounding  plain  is  covered  with  clay,  resting  on  sandstone  in  a  nearly 
horizontal  position.     The  sandstones  and  interbedded  traps  of  Kewee 
naw  point  and  isle  Royale  dip  in  opposite  directions  and  form  a  synclinal 
trough.     Near  L'Anse  is  a  limited  patch  of  limestone  which  has  a  dip 
to  the  eastward  from  25°  to  30°,  the  limestone  being  distinctly  stratified. 
The  sandstone  about  a  quarter  of  a  mile  to  the  north  is  horizontal,  and 
it  seems  evident  that  the  limestone  overlies  the  sandstone,  although  the 
position  of  the  inclined  beds  of  the  more  southerly  portion  of  the  lime 
stone  is  difficult  to  explain,  since  the  surrounding  country  is  low  and: 
level  and  underlain  by  sandstone  and  horizontal  beds.    It  seems  evident 
that  at  this  point  the  country  has  been  disturbed  and  upheaved  by- 
igneous  action  beneath,  which  has  raised  the  strata  without  any  ap- 
