140  PBE-CAMBRIAN    GEOLOGY   OF    NOBTH   AMEBICA. 
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  certainly  true  if  the  underlying  rocks  are  fragmental,  and  the  con- 
clusion can  not  be  escaped  if  they  are  eruptive,  for  both  the  green- 
stone schists  and  the  gneissoid  granite  must  have  received  their  schis- 
tosity  before  yielding  the  fragments;  and,  moreover,  their  character 
is  such  that  it  is  generally  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  evidently  granitic  rocks  of  two  ages  in  the  Mar- 
quette district,  because  dikes  of  a  fine-grained  reddish  granite  fre- 
quently cut  the  other  granite.  This  later  granite,  of  relatively  small 
extent  compared  with  the  main  masses,  may  perhaps  have  been  later 
in  time  of  formation  than  the  detrital  rocks  themselves,  as  indicated 
by  the  presence  of  rare  quartz  porphyry  dikes  and  rare  granitic  dikes 
in  the  Felch  Mountain  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 
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,  while  at  other  times  there  is  no  such  correspondence.  A  similar 
examination  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  constitute 
a  complex  upon  which  the  newer  series  was  deposited. 
Irving  and  Van  Hise/5  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 
granites.  There  is  often  no  proper  contact  between  the  granite, 
gneiss,  and  schist,  but  an  apparent  gradation  through  a  consider- 
able 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  discovered  any  evidence  of  clastic  origin.  If  the  mas- 
sive granites  and  syenites  are  regarded  as  eruptive,  it  must  be  con- 
