308  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
that  in  the  Ombe  range,  where  inter  stratified  with  the  quartzite  are 
seams  of  mica-schists. 
Upon  general  principles  it  appears  improbable  that  an  equivalent  to 
the  Weber  quartzite  of  the  Wasatch  should  so  widely  be  a  basal  for- 
mation. That  a  quartzite  should  be  the  lowest  formation  adjacent  to 
an  earlier  mountain  range  is  what  one  would  expect,  but  that  in  so 
large  a  proportion  of  the  ranges  should  now  be  found  exposed  as  the 
basal  series  the  same  division  of  a  single  period  is  contrary  to  proba- 
bility. 
SECTION  VI.     COLORADO  AND  NORTHERN  NEW  MEXICO. 
LITERATURE  OF  THE  FRONT  RANGE,  NORTH  AND  EAST  OF  THE  ARKANSAS. 
Long,40  in  1823,  describes  granite  as  succeeding  pudding-stone  or  con- 
glomerate on  Defile  creek.  The  granite  is  coarse  grained  and  rapidly 
disintegrates.  A  high  peak  was  ascended  and  was  found  to  consist  of 
an  indestructible  aggregate  of  quartz  and  feldspar,  with  a  little  horn- 
blende in  small  particles. 
Hayden,3  in  1869,  states  that  all  the  mountains  east  of  the  South 
park  have  a  gneissic  and  granitic  nucleus.  Each  of  the  great  ranges 
of  the  park  are  anticlinal  axes  with  massive  granite  cores  and  gneissic 
granites  inclining  from  each  side  in  the  form  of  ridges.  The  trend  of 
the  ranges  is  in  most  cases  northwest  and  southeast  or  nearly  so.  The 
Azoic  rocks  have  two  planes  of  cleavage,  one  of  them  with  a  strike 
northeast  and  southwest,  and  the  other  at  right  angles.  Besides  these 
cleavage  planes  there  are  in  most  cases  distinct  lines  of  bedding.  At 
Golden  city  the  sandstones  lie  close  to  the  metaniorphic  rocks,  inclin- 
ing 30°  to  54°. 
Mar  vine,41  in  1874,  describes  fully  the  metaniorphic  crystalline  rocks 
of  the  Front  range.  The  rocks  of  this  great  area  are  mostly  composed 
of  schists,  gneisses  and  granites.  Disregarding  unimportant  occur- 
rences of  undoubted 'ancient  eruptives,  as  well  as  some  minor  granite 
areas  of  uncertain  nature,  the  series  as  a  whole  must  be  regarded  as  a 
system  of  ancient  sedimentary  rocks  which  have  undergone  the  most 
profound  metamorphism,  the  result  of  which  over  large  areas  has  reached 
the  last  term,  structureless  granite.  Considering  the  extent  and  an- 
tiquity, the  formation  as  a  whole  is  remarkably  simple  and  uniform, 
running  from  quartzite  through  siliceous  and  mica-schists  to  very  sim- 
ple varieties  of  gneisses  and  granites  in  which  the  mica  is  wholly  subor- 
dinate. The  least  metamorphosed  rocks  observed  were  excessively  hard 
and  compact  quartzites  found  in  the  lower  canyons  of  Coal  and  Ralston 
creeks.  They  here  pass  into  a  series  of  highly  siliceous  schists,  in  places 
ferruginous,  in  which  may  possibly  be  found  workable  deposits  of  iron 
ore.  These  are  associated  with  fine  siliceous  mica  schists,  above  which 
are  very  irregular  schists,  intercalated  together.  Gneissic  and  gran- 
itic strata  are  frequent,  while  below  is  a  great  granite  mass  with  but 
few  remnants  of  bedding  left,  but  which  is  apparently  conformable  with 
