108  PRE-CAMBRIAN   ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
with  them.  The  Silurian  rocks  in  Ashland  county  are  in  a  horizontal 
position  in  a  trough  between  two  lines  of  highly  tilted  beds  of  the 
( Jopper-bearing  scries.  At  one  place  the  horizontal  sandstone  is  found 
within  a  few  hundred  feet  of  the  copper-bearing  trap  and  within  2  miles 
of  vertical  sandstones  of  the  same  group. 
In  Douglas  county  the  horizontal  sandstone  is  traceable  to  within  a 
short  distance  of  the  trap,  and  sometimes  to  actual  contact,  the  trap 
dipping,  whenever  it  is  observable,  always  to  the  southward,  and 
having  no  tilted  sandstones  and  conglomerates  associated  with  them. 
As  the  Huronian  and  Copper-bearing  series  are  in  apparent  con- 
formity it  is  concluded  that  they  were  once  spread  out  horizontally 
one  over  the  other,  and  owe  their  present  highly  tilted  position  to  one 
and  the  same  disturbance;  and  subsequently,  after  a  long  period  of 
erosion,  the  horizontal  Silurian  sandstones  were  laid  down  over  and 
against  the  upturned  edges  of  the  Copper-bearing  series 5  and  that 
hence  the  Copper-bearing  series  is  more  nearly  allied  to  the  Archean 
than  to  the  Silurian  rocks.  One  fact  is,  however,  difficult  of  explana- 
tion on  this  hypothesis.  In  Douglas  county  at  several  places  the  hor- 
izontal sandstones,  when  traced  to  their  junction  with  the  southward 
dipping  trap,  present  a  remarkable  change;  the  horizontal  layers  are 
suddenly  seen  to  change  from  their  ordinary  position  to  a  confused' 
mass  of  broken  layers,  dipping  in  every  conceivable  direction  and  in- 
creasing in  confusion  as  the  trap  is  approached,  until  finally  the  whole 
changes  to  a  confused  breccia  of  mingled  trap  and  sandstone  fragments. 
It  is  suggested  that  this  appearance  is  due  to  the  movement  of  the  solid 
trail  northward  against  the  sandstone  since  the  deposition  of  the  latter 
rock.  The  great  lake  Superior  synclinal  of  Copper-bearing  rocks  is 
found  to  extend  west  into  northern  Wisconsin. 
Sweet,129  in  1876,  describes  the  junction  of  the  Laurentian  and  Hu- 
ronian rocks  on  Bad  river.  Here  at  the  base  of  the  Huronian  series  is 
a  siliceous  marble  dipping  to  the  northward  at  an  angle  of  66°,  while 
100  feet  to  the  south  is  a  ledge  of  gneissoid  granite  showing  a  well 
defined  dip  of  77°  to  the  south.  There  can  be  no  doubt  of  the  uncon- 
formability  of  these  formations.  The  Penokee  series  is  found  to  be 
aboii^  5,000  feet  thick,  to  be  everywhere  conformable,  and  to  dip  about 
66°  to  the  north. 
On  the  Chippewa  is  found  a  quartzite  which  has  a  layer  the  lowest 
stratum  of  which  is  a  reddish  metamorphic  conglomerate  having  a 
thickness  of  300  feet.  The  pebbles  of  this  conglomerate  are  either 
jasper  or  amorphous  quartz.  The  conglomerate  and  quartzite  are  dis- 
tinctly and  heavily  bedded.  South  of  this  quartzite  are  syenitic  gran- 
ites which  are  assumed  to  be  of  Laurentian  age,  and  the  quartzites 
and  conglomerates  are  assumed  to  overlie  them  unconformably.  A 
short  distance  north  of  the  mouth  of  Snake  river  cupriferous  melaphyres 
and  amygdaloids  are  overlain  by  horizontal  beds  of  light  colored  Pots- 
dam sandstone,  while  a  few  miles  to  the  north  conglomerates  and  shales 
