86  PRE-CAMBKIAN    ROCKS    OF    NORTH    AMERICA.  [bttll.  80. 
Williams  and  Blandy,90  in  1862,  describe  the  trap  ranges  of  Port- 
age lake  as  being  about  3  miles  wide  and  consisting  of  amygdaloidal 
trap,  occasionally  intercalated  with  sandstones  and  conglomerates. 
The  dips  vary  from  60°  to  75°,  becoming  nearer  horizontal  toward  the 
northwest,  until  finally  the  sandstone  which  succeeds  it  becomes  ab- 
solutely so. 
Kimball,91  in  1805,  divides  the  rocks  of  the  Marquette  region  into 
two  formations,  Laurentian  and  Huronian;  the  former  including  the 
granite  ridges,  while  the  latter  nearly  agrees  with  Foster  and  Whitney's 
limits  for  the  Azoic.  The  crystalline  rocks  south  of  Keweenaw  point 
are  pre-Paleozoic,  while  the  greenstones  of  that  point  are  intercalated 
conformably  with  the  Paleozoic.  The  specular  iron  ore  and  beds  of 
specular  conglomerate  are  heavy  bedded  strata  and  schists  in  which 
none  of  the  phenomena  of  aqueous  deposits  are  wanting.  They  exhibit 
not  only  stratification,  but  anticlinal  and  synclinal  folds.  From  a 
stratigraphical  point  of  view  the  Huronian  greenstones,  schists,  and 
iron  ores  of  Marquette  exhibit  characters  which  render  quite  untenable 
the  theory  of  the  exotic  character  of  any  portion  of  them. 
AdASSiz,92  in  1867,  finds  at  two  ravines  near  Torch  lake — one  the 
Douglass  Houghton — that  the  sandstone  rests  uneonformably  upon 
the  trap.  The  trap  dips  N.  42°,  while  the  sandstone,  100  feet  distant, 
lies  nearly  horizontal,  with -no  trace  of  an  anticlinal  axis  between. 
The  sandstone  contains  wal  er-worn  fragments  of  the  trap.  The  sand- 
stone north  of  the  range  is  conformable  with  the  trap,  but  the  sandstone 
south  is  plainly  of  a  different  age. 
Whittlesey,93  in  1876,  finds  nowhere  on  the  American  side  of  the 
boundary,  except  at  Vermilion  lake,  rocks  which  are  like  the  Laurentian 
of  Canada.  The  great  masses  of  granite  and  syenite  around  which  the: 
Huronian  is  formed  do  not  resemble  the  Laurentian  of  the  Canadian- 
geologists.  Between  the  Canadian  and  American  Huronian  there  is  aj 
very  close  resemblance.  The  conclusion  of  Foster  and  Whitney  that  the 
traps  of  lake  Superior  are  of  Potsdam  age  is  adopted.  The  Bohemian 
range  resembles  more  nearly  the  HurOnian  than  it  does  the  trap  series. 
In  this  range  are  bands  of  friction  conglomerates  with  the  evidences  ofj 
metamorphic  sandstone  passing  into  jasper,  vesicular  trap,  and  brec- 
cia. A  friction  conglomerate  also  occurs  at  Aminicon,  Douglas  county 
Wisconsin. 
Wadsworttt,94  in  1880,  gives  notes  on  the  geology  of  the  iron  and 
copper  districts  of  lake  Superior.  The  contacts  of  the  jasper  and  ore,; 
which  are  interlaminated  and  have  a  common  origin  with  the  asso 
ciated  schists,  are  described,  and  at  numerous  points  the  contacts  are 
found  to  be  those  of  eruptive  and  sedimentary.  The  schistose  struct 
ure  is  regular,  while  the  jasper  and  ore  is  exceedingly  contorted,  breaks 
across  the  schistose  and  other  rocks,  and  contains  fragments  of  th 
schists.  Not  the  slightest  sign  of  plasticity  or  intrusion  of  the  schist) 
relative  to  the  ore  and  jasper  was  seen.     The  present  lamination  of  the 
