LAKE    SUPERIOR   REGION.  Ill 
tides  of  quartz  and  feldspar  with  masses  of  ore  intermingled  like  the 
pebbles  of  a  conglomerate. 
Iron  ore  and  marble  were  observed  along  the  Menominee,  as  well  as 
various  other  kinds  of  rocks,  including  granite,  hornblende  slate,  tal- 
cose  slate,  etc.  At  Sandy  portage,  on  the  Menominee,  is  a  class  of  plu- 
tonic  rocks  older  than  the  traps  of  Keweenaw  Point,  which  were  pro- 
truded among  the  slates  and  then  denuded  before  the  deposition  of  the 
sandstone;  for  the  slates  are  intercalated  among  the  igneous  rocks 
with  a  vertical  inclination,  while  the  sandstone  rests  horizontally  or 
nearly  so  upon  them.  This  sandstone  is  regarded  as  the  oldest  of  the 
Paleozoic  rocks  and  is  the  equivalent  of  the  sandstone  on  the  northern 
slope  of  the  Upper  Peninsula.  Resting  upon  this  sandstone  is  a  lime- 
stone which  is  sparingly  fossiliferous. 
Whitney,9  in  1849,  describes  the  iron  ore  of  the  Upper  Peninsula 
of  Michigan  as  existing  in  the  form  of  solid  ridges  and  knobs  inter- 
stratified  with  banded  jasper,  the  whole  evidently  of  igneous  origin. 
Jackson,10  in  1849,  describes  the  sandstone  of  Keweenaw  Point  re- 
mote from  the  trap  as  horizontal  or  but  slightly  waving,  while  near 
the  trap  rock  it  is  as  high  as  30°.  The  conglomerate  is  limited  to  the 
borders  of  the  trap  and  is  of  the  same  age  as  the  finer  grained  sand- 
stone with  which  it  alternates.  At  the  line  of  junction  of  the  trap 
rocks  and  sandstone  the  two  are  interfused,  producing  the  met  amor- 
phic rock  amygdaloid,  which  resembles  the  vesicular  lavas  of  vol- 
canoes, but  has  its  cavities  filled  with  a  great  variety  of  curious  and 
interesting  minerals.  On  Isle  Royal  about  one-quarter  of  the  area 
is  sandstone  and  conglomerate  and  the  remainder  trap,  which  forms 
ridges  extending  the  whole  length  of  the  island. 
Jackson,11  Dickenson,  McIntyre,  Barnes,  Locke,  Foster  and 
Whitney,  Gibbs,  Hill,  Burt,  and  Hubbard,  in  1850,  report  upon 
the  mineral  lands  south  of  Lake  Superior  in  Michigan. 
Jackson,12  in  1850,  describes  the  red  sandstones  and  conglomerates 
of  Keweenaw  Point  as  existing  there  anterior  to  the  elevation  of  the 
trap  rocks,  being  derived  from  the  deposition  of  fine  sand  and  peb- 
bles from  preexisting  Primary  rocks,  such  as  granite,  gneiss,  or  mica 
slate.  Porphyry  furnishes  a  large  portion  of  the  debris,  but  it  is 
doubtful  if  this  is  not  a  semifused  sandstone.  There  is  no  reason  to 
believe  that  igneous  agencies  had  anything  to  do  with  the  origin  of 
the  pebbles  of  the  conglomerate,  for  they  are  rounded  by  the  action 
of  water.  From  the  circumstance  that  the  conglomerate  borders  the 
trappean  rocks  it  is  supposed  an  ancient  shore  may  have  existed  along 
that  line.  It  is  certain  that  the  finer  sandstone  is  more  remote  from 
the  trap  than  the  conglomerate  is,  and  that  it  is  less  uplifted  and  in- 
clined as  it  recedes  from  the  trap  band.  Near  the  junction  of  the  two 
rocks  the  strata  dip  25°  or  30°,  while  remote  from  it  the  sandstone 
is  nearly  horizontal.     The  mineral  composition,  association,  and  con- 
