THE   CORDILLERAS.  807 
It  is  believed  that  such  an  even  contact  plane  between  the  Cambrian 
and  pre-Cambrian  series  is  widespread  and  characteristic  in  North 
America.  It  appears  to  be  the  case  in  the  valley  of  the  Eagle  River 
and  in  the  canyon  of  the  Grand  River  above  Glenwood,  Colo. ;  in  the 
Black  Hills  of  South  Dakota,  examined  by  the  writer ;  in  the  Grand 
Canyon  of  the  Colorado,  described  by  Walcott;  and  in  Wisconsin, 
described  by  Irving. 
In  the  Manitou,  Eagle  River,  and  Black  Hills  areas,  throughout 
the  Rocky  Mountains,  and  eastward  to  Champlain  Valley  and  beyond, 
the  Cambrian  has  a  nonarkose  character;  it  has  been  thoroughly 
sorted  and  washed  by  water,  a  fact  which  indicates  that  the  incursion 
of  the  sea  was  an  extremely  slow  one.  It  is  believed  that  the  plane 
surface  of  the  Archean  has  resulted  from  the  incursion  of  the  sea 
due  to  the  subsidence  of  the  land,  and  not  from  the  action  of  sub- 
aerial  agents,  for  in  the  latter  case  only  an  approximate  plane  could 
have  resulted  because  of  differential  erosion. 
Mathews,72  in  1900,  gives  a  detailed  petrographic  description  of 
the  granites  of  the  Pikes  Peak  quadrangle,  in  Colorado.  They  are 
referred  to  the  late  Algonkian  period. 
Van  Hise,73  in  1901,  visited  the  northwest  end  of  Blue  Mountain, 
west  of  Florissant.  Fibrolitic  quartzite  is  found  to  be  intricately  in- 
truded by  granite. 
About  2  miles  northwest  from  Rocky  the  belt  which  Cross  mapped 
as  pure  quartzite  beds  passing  into  quartzitic,  micaceous,  and  fibro- 
litic schists  was  found  to  consist  almost  wholly  of  schists,  gneisses, 
and  granites  of  very  great  variety.  By  far  the  larger  mass  con- 
sisted of  ancient  gray  and  reddish  banded  gneisses  and  dark-colored 
pyroxenic  and  amphibolitic  schists,  cut  through  and  through  and 
injected  in  a  parallel  fashion  by  granite  of  a  later  age,  and  especially 
by  pegmatite.  So  far  as  lithology  is  concerned,  this  mass  seems  to 
be  identical  with  the  Basement  Complex. 
Directly  north  of  the  road  at  Rocky  post-office  is  quartzite  inter- 
bedded  with  schist  and  cut  and  injected  with  granite,  precisely  as  on 
Blue  Mountain.  Probably  some  of  the  schists  associated  witli  the 
quartzite  are  sedimentary,  but  it  is  difficult,  if  not  impossible,  to  out- 
line them.  A  small  amount  of  limestone  also  is  observed,  making  it 
possible  that  the  quartzite  observed  has  limestone  f  acies. 
If  one  were  to  examine  the  rocks  adjacent  to  Rocky  and  consider 
the  phenomena  without  reference  to  any  other  locality,  lie  would 
doubtless  conclude  that  all  the  schists,  limestones,  quartzites,  and 
the  banded  gneisses,  amphibolites,  etc.,  belonged  to  the  same  series. 
Indeed,  in  this  era  there  is  no  evidence  to  the  contrary.  However, 
all  these  rocks  are  intruded  and  metamorphosed  by  the  Pikes  Peak- 
granite,  and  it  would  not  he  expected  that  unconformable  relations 
between  the  Quartzite  and  the  gneisses  could  he  observed.     From 
