THE    CORDILLERAS.  813 
These  are  associated  with  granites  and  gneissoid  schists,  associated 
with  which  are  hornblendic,  chloritic,  and  micaceous  schists.  Near 
Trinchera  the  sedimentary  strata  stand  nearly  on  end  and  lie  tipped 
up  against  the  granite.  At  other  places  the  granite  protrudes 
through  the  Carboniferous.  It  is  concluded  that  the  metamorphics 
of  the  lower  Sangre  de  Cristo  are  altered  Silurian  rocks.  North  of 
Arkansas  River  the  Silurian  formation  occurs.  From  here  it  crosses 
the  river  toward  the  south  and  is  last  seen  as  such  near  the  northern 
end  of  the  Sangre  de  Cristo  Range.  In  its  stratigraphical  relations 
it  is  conformable  with  the  overlying  younger  formations  wherever 
it  has  been  there  seen. 
Endlich,81  in  1878,  states  that  while  in  the  Sangre  de  Cristo  the 
eruptive  granite  is  the  cause  of  the  upthrow  of  the  Carboniferous 
strata,  nowhere  in  the  sedimentary  beds  is  found  any  case  of  intru- 
sion.    These  granites  are  regarded  as  post-Carboniferous. 
Emmons  (S.  F.),66  in  1890,  states  that  quartzites  have  been  noticed 
connected  with  the  Archean  of  the  southern  end  of  the  Sangre  de 
Cristo  Range,  which  may  be  assumed  to  be  the  remnants  of  some 
Algonkian  beds. 
Cross,82  in  180G,  describes  the  geology  of  Silver  Cliff  and  the  Rosita 
Hills,  Colorado.  Gneisses  and  granites  form  the  core  of  the  Wet 
Mountains,  on  the  west  flank  of  which  the  district  lies.  The  granites 
were  first  referred  to  the  Archean,  but  are  now  believed  to  be  Algon- 
kian because  of  similarity  to  the  granites  of  the  Front  Range  in  the 
Pikes  Peak  district,  where  similar  granites  are  in  part  at  least  later 
than  the  Algonkian  quartzites.  The  gneisses  may  be  Archean.  The 
gneisses  strike  northeast-southwest,  with  a  northwest  dip  of  between 
45°  and  90°.  Neither  top  nor  bottom  of  the  series  is  determined. 
Volcanic  rocks  occupy  a  considerable  area  on  the  slopes  of  the  Wet 
Mountains.     No  sedimentary  rocks  occur  in  the  region. 
Across  the  valley  to  the  west  the  Sangre  de  Cristo  Range  is  com- 
posed mainly  of  Carboniferous  sandstones  and  conglomerates.  At  the 
east  base  is  a  profound  fault,  which  has  not  been  examined  in  detail. 
Gilbert,815  in  1897,  maps  and  describes  the  geology  of  the  Pueblo 
quadrangle,  including  part  of  Pueblo  County  and  the  southeast  cor- 
ner of  Fremont  County,  Colo.  Archean  rocks  of  the  Wet  Mountain 
core  occupy  two  small  tracts  in  the  southwestern  part  of  the  quad- 
rangle. The  more  abundant  kinds  of  Archean  rocks  are  mica  schist, 
mica  gneiss,  and  granite.  The  schists  and  gneisses  strike  north  to 
northwest,  and  arc  nearly  vertical.  Their  origin  is  not  known.  The 
granite  is  intrusive  in  the  M'hists  and  gneisses. 
The  Archean  rocks  are  overlain  unconformably  by  Paleozoic  and 
Mesozoic  sediments. 
Hills,84  in  1900.  describes  the  geology  of  (he  Walsenburg  quad- 
rangle, in  Colorado.     The  principal  mass  of  the  Greenhorn    (Wet) 
