808  PBE-CAMBEIAN    GEOLOGY    OF   NORTH    AMERICA. 
analogy  with  the  unconformable  contacts  at  Coal  Creek  and  South 
Boulder  Creek  canyons,  however,  where  metamorphism  is  less  intense, 
it  is  believed  that  the  quartzite  of  this  era  merely  rests  unconformably 
upon  the  gneisses. 
In  the  Koyal  Gorge  of  Arkansas  River,  from  the  mouth  of  the 
canyon  up  the  river  to  Parkdale,  there  were  observed  a  set  of  old 
gray  gneisses,  red  gneisses,  and  black  amphibolites  intricately  inter- 
mingled, all  cut  by  Pikes  Peak  granite  and  other  igneous  rocks.  The 
complex  probably  contains  Archean  schists  and  Algonkian  granites, 
but  it  would  be  difficult  to  separate  them. 
South  Boulder  and  Coal  Creek  canyons  were  again  visited,  and  it 
was  concluded  that  the  Algonkian  quartzite  rests  unconformably, 
with  basal  conglomerate,  upon  the  granite  of  this  area,  and  that  the 
conformable  gradation  between  quartzite  and  granite  reported  by 
Marvine  and  Lakes  is  an  apparent  one  only,  due  to  development  of 
schistosity  through  readjustment  along  the  contact  plane.  In  both 
places  it  was  possible  to  determine  sharply  the  plane  separating  the 
schists  derived  from  the  metamorphism  of  the  quartzite  and  conglom- 
erate from  that  derived  from  the  metamorphism  of  the  granite.  At 
South  Boulder  Creek  pegmatite  dikes  cut  the  granite,  but  were  not 
observed  cutting  the  quartzite.  At  Coal  Creek  pegmatite  cuts  also 
the  quartzite.  Here  also  quartzite  was  found  to  reappear  west  of  the 
basal  granite,  suggesting  isoclinal  folding  or  faulting,  probably  the 
latter. 
Smith  (W.  N.),74  in  1901,  made  a  section  across  the  belt  mapped 
as  Algonkian  by  Cross  on  Felchs  Creek.  The  southwest  contact  of 
the  quartzites  was,  so  far  as  observed,  always  with  intrusive  granite, 
but  on  the  northeast  the  contact  is  with  the  schist  and  is  sharp  and 
distinct.  The  contact  is  parallel  to  the  bedding  of  the  quartzite. 
Both  quartzite  and  schist  are  cut  by  pegmatite  and  the  quartzite  by 
granite.  The  schist  50  yards  away  from  the  quartzite  contact 
weathers  in  such  a  manner  as  to  give  it  a  conglomerate  appearance. 
About  one-quarter  of  a  mile  away,  in  the  bed  of  Potato  Creek, 
separated  from  the  quartzite  by  intrusive  granite,  appear  rusty 
schists,  biotitic  granites,  and  an  intricate  mixture  of  amphibolitic  ( ?) 
schists,  granites,  and  gneisses,  cut  by  pegmatite,  which  have  the  ap- 
pearance of  belonging  to  the  Basement  Complex. 
On  Burnt  Mountain  south  of  Felchs  Creek  essentially  the  same 
facts  were  observed.  In  the  bed  of  Ute  Creek,  which  cuts  this  mass 
of  quartzite  almost  in  the  middle,  a  black  schist,  or  amphibolite  ( ?), 
was  found  which  had  the  same  Basement  Complex  appearance  as 
that  found  in  the  bed  of  Potato  Creek.  This  was  not  far  from  the 
exposure  of  quartzite,  and  apparently  below  it. 
Ball  and  Spurr,75  in  1005,  describe  the  pre-Cambrian  rocks  of  the 
Georgetown  quadrangle,  situated  in  the  center  of  the  north  half  of 
