142  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.«    & 
much  eroded  before  the  deposition  of  the  Eastern  sandstone,  that  tin?06 
latter  was  laid  down  unconforinably  against  and  upon  the  former,  an< ; )) 
that  subsequent  minor  faulting  along  the  old  line  ensued,  disturbin, 
the  contact  edge  of  the  sandstone. 
Irving,195  in  1885,  discusses  the  divisibility  of  the  Archean  in  th 
Northwest.  The  relations  of  the  Penokee-Gogebic  series  to  the  ovei 
lying  Keweenawan  and  to  the  underlying  complex  are  first  discussec 
The  area  south  of  the  Penokee-Gogebic  series  is  found  to  consist  of  crys 
talline  hornblendic,  chloritic  and  micaceous  schists  which  locally  sho^ 
unmistakable  evidence  of  fragmental  origin,  but  which  as  a  whole  ar 
intensely  metamorphosed.  The  granites,  however,  are  considered  as  c 
eruptive  origin  as  they  intersect  intricately  the  associated  schists  a 
their  contacts  with  them,  but  the  granite  is  never  found  to  cut  th 
overlying  slates.  Above  this  granite-gneiss-schist  area  is,  first,  a  be! 
of  slate  500  feet  thick,  over  this  a  belt  of  iron-bearing  rocks  of  variou 
kinds,  and  above  this  quartzites  and  slates,  all  having  a  dip  to  th 
north  and  extending  for  many  miles  east  and  west.  None  of  these  rock 
are  metamorphic. 
North  of  this  succession  of  layers,  the  Penokee  series,  is  the  Kewee 
nawan  series,  which  appears  at  first  to  be  conformable,  but  a  closer  ii 
spection  shows  that  it  is  now  in  contact  with  one  member  of  the  undei 
lying  series  and  now  with  another,  even  lying  against  the  lowest 
member  of  the  Penokee  series.  These  relations  are  taken  to  imply  tha 
between  the  Keweenawan  and  Penokee  series  there  was  a  long  period  c 
erosion.  There  is  also  an  unconformity  between  the  granite-gneiss-schis 
complex  and  the  Penokee  Gogebic  series.  This  is  shown  in  the  man 
ner  in  which  the  regularly  succeeding  belts  of  the  iron  series  travers 
the  courses  of  the  lower;  in  the  strong  contrast  between  the  two  serie 
in  degree  of  crystallization,  the  lower  series  being  nearly  completel 
crystalline  while  the  higher  is  little  altered,*  in  the  highly  folded  an 
contorted  condition  of  the  lower  series  as  contrasted  with  the  unfolde 
condition  of  the  higher;  in  the  contrast  between  the  contacts  of  th 
granite  with  the  lower  schists  and  with  the  higher  slates,  the  forme 
being  invaded  by  it  in  an  intricate  manner,  the  latter  never;  in  th 
discordant  lamination  of  the  two  sets  of  rocks  when  in  contact  or  clos 
proximity;  in  the  occurrence  in  the  upper  series,  not  only  at  horizon 
above  the  base,  but  also  at  points  on  the  contact  line,  of  abundaii 
detrital  material  from  the  lower  series. 
In  the  Marquette  district  is  found  a  slaty  iron-bearing  series  whic 
by  common  consent  is  regarded  as  the  equivalent  of  the  Penoket 
Gogebic  series ;  but  the  two  have  one  point  of  contrast,  the  Marquett 
is  highly  folded.  Here  intervenes  between  the  iron-bearing  slates  an 
the  granites  and  gneisses  a  set  of  greenish  hornblendic  rocks,  calle 
by  Eominger  a  dioritic  group,  which  at  their  contact  with  the  boundin 
granite  are  penetrated  by  them  in  the  most  intricate  manner,  so  that  on 
can  not  resist  the  conclusion  that  the  granite  is  the  more  recently  forme' 
