tanhism.]  LAKE    SUPERIOR    REGION.  103 
ing  Silver  mountain,  wliich  are  composed  of  lava  flows.  These  traps 
sometimes  have  a  dip  not  higher  than  9°  to  20°.  In  Sees.  11,  13  and 
14,  T.  40  "8. ,  R.  31  W.,  sandstone  is  found  overlying  the  lava  flows.  The 
Eastern  sandstone  on  Traverse  island,  in  Keweenaw  bay,  is  said  to 
have  an  inclination  of  from  5°  to  14°,  while  in  the  vicinity  of  Torch  lake 
it  has  a  dip  of  from  5°  to  23°.  It  is  concluded  that  the  above  observa- 
tions go  to  show  that  the  lava  flows  of  the  South  Trap  range  east  of 
lake  Gogebic  do  not  dip  at  a  high  angle,  as  has  been  generally  asserted, 
and  further  that  the  Eastern  sandstone  is  not  horizontal,  as  has  been 
generally  stated,  but  that  the  two  dip  at  a  low  angle,  generally  5°  to 
20°.  These  observations  also  indicate  that  the  Eastern  sandstone  and 
the  lava  flows  of  the  South  Trap  range  are  one  formation,  and  are  as 
conformable  as  eruptions  of  lava  can  be  with  a  contemporaneous 
sedimentary  deposit. 
Rominger,117  in  unpublished  manuscript  of  the  Michigan  Survey  for 
1881  to  1884,  further  reports  upon  the  complex  described  in  the  former 
volume  as  the  Huronian  system.  The  lower  granite  and  gneissoid  por- 
tion of  the  rock  groups  in  the  Marquette  region  exhibits  the  characters 
of  an  eruptive  and  not  of  an  altered  sedimentary  rock.  Generally  a 
solid  crust  of  granite  probably  served  as  a  substratum  on  which  the 
Huronian  sediments  were  laid  down,  but  an  opportunity  is  not  often 
afforded  to  see  the  rocks  in  contiguity  well  enough  exposed  to  allow  a 
discrimination  as  to  whether  such  contact  is  an  original  primary  one  or 
resulted  from  dislocation.  The  existence  of  granite  as  a  surface  rock  at 
the  time  the  Huronian  sediments  formed  is  proved  by  the  occurrence  of 
belts  of  granite,  conglomerate  and  breccia  in  different  horizons  of  the 
series. 
A  large  belt  of  conglomerate  formed  of  rounded  weather-worn  granite 
pebbles  and  schistose  rock  fragments,  cemented  by  a  matrix  of  similar 
schistose  material,  is  seen  in  contact  with  a  granite  belt  in  the  south 
half  of  Sec.  2,  T.  48  N.,  R.  26  W.  j  in  the  SE.  \  Sec.  22,  T.  47  K,  B.2<>  W. ; 
and  in  the  north  half  of  Sec  29,  T.  48  ST.,  E.  25  W.  In  the  first  of  these 
localities  the  fragments  are  different  from  the  underlying  granite.  The 
second  locality  furnishes  a  better  proof  of  the  deposition  of  Huronian 
sediments  on  a  base  of  granite.  Here  several  knobs  centrally  com- 
posed of  massive  granite  are  surrounded  by  a  mantle  of  coarse  granite 
breccia,  with  a  well  laminated  quartzose  material  as  a  cement.  This 
breccia  is  conformably  succeeded  by  hydromica-slates,  interlaininated 
with  heavy  belts  of  compact  quartzite.  At  the  third  locality  granite 
3onglomeraJ:e  is  interlaininated  with  dioritic  schists,  but  is  remote  from 
granite  outcrops.  The  gradation  of  the  quartzite  formation  into  the 
granite,  described  in  the  previous  report  as  occurring  in  the  north  part 
}f  T.  47  K,  Rs  25  W.,  is  now  considered  as  a  recemented  mixture  of 
granite  fragments  mingled  with  arenaceous  material,  although  it  is  sin- 
gular that  the  orthoclase  crystals  copiously  found  in  the  mass  have  all 
sharp  outlines  and  are  quite  fresh. 
