vAMiisr..]  LAKE    SUPERIOR    REGION.  95 
ceased  toact  over  extended  areas  during  the  time  of  the  formation  of 
the  sandstones  and  conglomerates.   The  abundance  of  acid  rocksamong 
the  conglomerates  was  noted,  and  opposite  Calumet  the  former  pres 
ence  of  predominant  quartz  -porphyry  was  inferred. 
Rominger,104  in  1873,  places  the  lake  Superior  sandstone  as  Potsdam, 
finding  it  directly  overlapped  by  the  calciferous  formation.  At  Presque 
isle  and  Granite  point  the  horizontal  sandstones  arc  found  resting 
upon  the  crystalline  rocks,  there  being  at  the  former  place  a  conglom- 
erate which  rests  unconformably  upon  the  dolomite  of  Presque  isle. 
The  sandstones  on  the  eastern  shore  of  Keweenaw  point  retain  their 
horizontal  position  and  lithological  character  to  such  a  degree  that  the 
different  strata  can  be  parallelized  without  difficulty  with  those  of  the 
more  eastern  localities.  Near  the  center  the  horizontal  sandstones  are 
found  abutting  against  the  uplifted  edges  of  a  different  rock  series,  the 
copper-bearing  rocks.  The  abrupt  edges  of  the  strata  look  to  the  south- 
east, and  their  dip  is  in  the  opposite  direction  under  angles  varying 
from  70°  to  40°.  The  unconformable  abutment  of  the  sandstones  against 
the  trappean  series  is  plainly  observed  at  several  places  near  Houghton, 
on  the  property  of  the  Isle  Royale  company,  near  the  stamp  works  of 
the  Calumet  and  Hecla  mines,  on  the  railroad  coming  down  from  the 
mines  to  the  stamp  works,  and  on  the  Sheldon  and  Columbia  property. 
KominCtER,105  in  1870,  describes  the  red  lake  Superior  sandstone  as 
unconformably  abutting  against  or  overlapping  the  trap  rock  with  hori- 
zontally disposed  layers.  On  the  western  slope  of  the  ridge  the  trap 
rocks  are  conformably  overlain  by  sandstones,  conglomerates,  and  slates, 
the  age  of  which  is  intermediate  between  the  trap  and  the  horizontal 
sandstone,  but  bet  ween  all  three  there  are  such  great  lithological  affinities 
that  it  is  natural  to  regard  them  as  consecutive  products  of  one  and 
the  same  epochs.  The  absence  of  trappean  rocks  distinguishes  the 
upper  division  from  the  lower. 
The  Huron  mountains  nre  a  crystalline  granitic  and  dioritic  Lauren 
tian  rock  series.  These  granitic  rocks  are  surrounded  by  a  narrow  belt 
of  the  horizontal  red  sandstone  of  lake  Superior,  which  abuts  uncon- 
formably against  them.  The  Huronian  rock  series,  with  uplifted  beds 
alternating  with  slate  rocks,  quartzites,  diorites,  and  jaspery  strata, 
with  seams  of  iron  ore,  lean  unconformably  against  the  granitic  series. 
Brooks,106  in  1876,  places  granite  as  the  youngest  Huronian  rock 
south  of  lake  Superior.  This  granite  occurs  as  the  uppermost  member  oi 
the  Menominee  and  Penokee  series,  but  in  the  latter  it  thins  out  and  <lis 
appears  before  reaching  the  Gogebic  region.  The  lithological  character 
of  this  granite  belt  bears  a  general  resemblance  to  the  Lauren  I  ian 
rocks.  This  granite,  from  the  fact  that  it  does  not  give  off  dikes  cut- 
ting the  copper-bearing  series,  is  believed  i<>  be  earlier  than  the  latter. 
Although  there  is  approximate  conformability  in  strike  and  clip,  there 
is  probably  an  unconformity  between  the  copper-bearing  rocks  and  the 
