.0 
0  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
29,  T.  48  N.,  R.  25  W.,  Mich.;  in  Sec.  20,  T.  48  K,  R.  27  W.,  Mich.;  in 
Sec.  17,  T.  48  K,  R.  26  W.,  Mich.;  in  Sec.  21,  T.  48  N.,  R.  27  W.,  Mich.; 
and  at  various  points  in  T.  49  N.,  R.  28  W.,  Mich. 
From  these  occurrences  it  does  not  appear  possible  to  escape  the 
conclusion  that  the  greenstone  schists,  together  with  the  granite,  are 
greatly  older  than  the  detrital  rocks,  and  before  the  latter  were  formed 
had  already  suffered  disturbance  and  deep  denudation.  This  is  cer- 
tainly true  if  the  underlying  rocks  are  fragmental,  and  the  conclusion  can 
not  be  escaped  if  they  are  eruptive,  for  both  the  greenstone  schists  and 
the  gneissoid  granite  must  have  received  their  schistosity  before  yielding 
the  fragments;  and,  moreover,  their  character  is  such  that  it  is  gener- 
ally believed  that  they  must  have  crystallized  in  depth,  and  must 
therefore  have  had  removed  from  them  great  masses  of  material  before 
yielding  the  discovered  fragments  to  wave  action.  There  are  evi- 
dently granitic  rocks  of  two  different  ages  in  the  Marquette  district, 
because  dikes  of  a  fine  grained  reddish  granite  frequently  cut  the 
other  granite.  This  later  granite,  of  relatively  small  extent  compared 
with  the  main  masses,  may  have  perhaps  been  later  in  time  of  forma- 
tion than  the  detrital  rocks  themselves,  as  indicated  by  the  presence  of 
rare  quartz  porphyry  dikes  and  rare  granitic  dikes  in  the  Felch  moun- 
tain district  intersecting  a  ferruginous  schist  of  the  iron-bearing  series. 
The  above  conclusions  are  further  confirmed  by  the  fact  that  the] 
later  greenstones  interstratified  with  sedimentary  layers,  as  shown  by 
Prof.  Williams,  are  precisely  like  the  corresponding  dikes  in  the  green- 
stone schist  area,  which  were  evidently  intruded  subsequent  to  the 
production  of  a  schistosity.    Also  the  schistosity  of  the  greenstone 
schists  corresponds  at  times  with  the  bedded  structure  of  the  iron  series,  I 
while  at  other  times  there  is  no  such  correspondence.     A  similar  ex- ; 
animation  of  the  facts  in  the  Menominee  district  leads  to  identical 
conclusions;  that  is,  that  the  granite  both  south  and  north  of  the  iron- 
bearing  series  and  the  associated  green  schists  and  gneisses  consti- 
tute a  complex  upon  which  the  newer  series  was  deposited. 
Irving  and  Van  Hise,205  in  1890  and  1892,  give  a  detailed  descrip- 
tion of  the  Penokee  series  of  Michigan  and  Wisconsin,  of  the  complex 
of  rocks  south  of  this  series,  and  discuss  the  relations  which  the  Pen- 
okee rocks  bear  to  the  underlying  and  overlying  series,  as  well  as  to 
the  Eastern  sandstone. 
South  of  the  Penokee  series  is  the  Southern  Complex,  an  area  of  fine 
grained  green  hornblende-schists  and  mica-schists,  gneisses,  and  gran- 
ites. There  is  often  no  proper  contact  between  the  granite,  gneiss,  and 
schist,  but  an  apparent  gradation  through  a  considerable  distance 
from  one  to  the  other,  while  the  granite  often  also  cuts  the  schist, 
playing  the  part  of  a  later  intrusive.  Distant  from  the  lines  of  contact 
the  schists  occupy  considerable  areas.  In  none  of  these  rocks  is  dis- 
covered any  evidence  of  clastic  origin.  If  the  massive  granites  and! 
syenites  are  regarded  as  eruptive,  it  must  be  concluded  that  many  oil 
