THE   CORDILLERAS.  817 
of  Taylor  Park  and  the  Sawatch  Range  on  the  east.  The  northern 
part  of  the  area  is  included  in  the  granitic  system  of  the  Sawatch 
Eange.  The  southern  part  is  occupied  by  schists  and  gneisses,  under- 
lain by  coarse  massive  granite.  The  schists  and  gneisses  are  of  pre- 
Cambrian  age,  but  whether  Algonkian  or  older  has  not  been  deter- 
mined. The  contact  of  the  schists  and  gneisses  with  the  underlying 
granite  is  an  eruptive  one,  the  granite  containing  fragments  of  the 
schist,  giving  the  impression  that  the  schists  had  been  floated  up  on 
an  underlying  molten  or  semimolten  sea  of  granite.  Cutting  the 
schists  are  occasional  dikes  of  diabase  and  possibly  basalt  and  andes- 
ite,  and  resting  on  the  eroded  edges  of  the  schists  are  various  later 
overflows  of  andesitic  breccia,  rhyolite,  trachyte,  and  basalt. 
Spurr,94  in  1898,  maps  and  briefly  describes  the  Archean  "  granite 
of  the  Aspen  district  of  Colorado.  This  is  unconformably  below  and 
in  direct  contact  w^ith  sediments  of  upper  Cambrian  age. 
Van  Hise  and  Leith,85  in  1905,  made  a  reconnaissance  along  a  part 
of  the  Sawatch  Range.  On  the  wTest  flank  of  the  Sawatch,  about  '2 
miles  north  of  Tincup,  fine-grained  fissile  mica  schists,  taken  to  be 
altered  sediments,  were  observed.  Some  of  the  schists  have  quartzitic 
aspects.  The  marble  described  by  Cross  in  this  vicinity  was  not  vis- 
ited. Southeast  of  Tincup,  on  the  road  to  St.  Elmo,  typical  ellipsoidal 
basalts  and  green  schists,  similar  to  those  of  the  Keewatin  of  the  Lake 
Superior  region,  were  found  to  extend  nearly  to  the  top  of  the 
Sawatch  divide.  At  the  divide  the  coarse  Sawatch  granite  intrudes 
the  green  schists. 
The  area  about  Salida,  described  by  Cross,  was  examined.  About 
5  miles  southeast  of  Salida,  along  the  Arkansas  River,  Paleozoic  sedi- 
ments may  be  seen  dipping  to  the  southeast,  down  the  river,  and  rest- 
ing upon  a  crystalline  series  taken  to  be  pre-Cambrian.  This  con- 
sists of  fine-grained  novaculitic  quartzite,  intruded  and  interbedded 
by  a  porphyry  with  flow7  structure  and  dark  felsitic  phases,  so  closely 
resembling  the  quartzite  that  it  is  difficult  to  tell  in  some  place-  where 
the  quartzite  ends  and  the  porphyry  begins.  The  quartzite  dips  at 
about  the  same  angle  as  the  Paleozoic  limestones  above.  The  plane 
of  contact  is  apparently  an  even  one,  and  there  is  to  be  seen  no  evi- 
dence of  any  conglomerate  or  structural  unconformity.  However,  the 
porphyry  may  be  traced  within  a  few  yards  of  the  limestone  contact, 
where  it  ends  abruptly.  This  fact,  together  with  the  general  meta- 
morphosed aspect  of  the  quartzite.  is  taken  to  indicate  its  probable 
unconformity  wTith  the  overlying  Paleozoic  sediment-.  However,  it  is 
also  possible  that  the  lower  portion  of  the  Paleozoic  has  been  invaded 
by  acidic  intrusives  which  have1  reached  a  certain  horizon  and  meta- 
morphosed all  rocks  beneath  this  horizon.      In  this  case  the  supposed 
"Tli."  term  Archean  is  evidently  used  in  the  sense  of  pre-Cambrian, 
55721— Bull.  300—00 52 
