THE    CORDILLERAS.  801 
Hayden,61  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-southeast,  or  nearly  so.  The 
Azoic  rocks  have  two  planes  of  cleavage,  one  of  them  with  a  strike 
northeast-southwest,  and  the  other  at  right  angles.  Besides  these 
cleavage  planes  there  are  in  most  cases  distinct  lines  of  bedding.  At 
Golden  the  sandstones  lie  close  to  the  metamorphic  rocks,  inclining 
30°  to  51°. 
Marvine,02  in  1874,  describes  fully  the  metamorphic  crystalline 
rocks  of  the  Front  Range.  The  rocks  of  this  great  area  are  mostly 
composed  of  schists,  gneisses,  and  granites.  Disregarding  unimpor- 
tant occurrences  of  undoubted  ancient  eruptives,  as  well  as  some  minor 
granite  areas  of  uncertain  nature,  the  series  as  a  whole  must  be  re- 
garded as  a  system  of  ancient  sedimentary  rocks  which  have  under- 
gone the  most  profound  metamorphism,  the  result  of  which  over 
large  areas  has  reached  the  last  term — structureless  granite.  Con- 
sidering its  extent  and  antiquity,  the  formation  as  a  whole  is  remark- 
ably simple  and  uniform,  running  from  quartzite  through  siliceous 
and  mica  schists  to  very  simple  varieties  of  gneisses  and  granites  in 
which  the  mica  is  wholly  subordinate.  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  irregu- 
lar schists,  intercalated  together.  Gneissic  and  granitic  strata  are 
frequent,  while  below  is  a  great  granite  mass  which,  though  there  are 
but  few  remnants  of  bedding  left,  is  apparently  conformable  with 
the  series  above.  A  similar  succession  was  observed  near  the  Little 
Thompson,  quartzites  being  found  at  the  top  and  granites  at  the 
base.  On  South  Saint  Vrains  and  at  the  mouth  of  South  Boulder 
Canyon  is  found  quartzite  resting  upon  zoned  but  structureless  gran- 
ite. The  Triassic  shales  rest  unconformably  upon  the  mica  schists 
on  Little  Thompson.  The  dominant  rocks  are  granitic  and  gneissic, 
although  schists  are  found  over  large  areas,  and  of  these  the  tendency 
is  toward  a  binary  granite  to  which  the  name  aplite  might  apply. 
That  the  characters  noted  above  arc1  evidence  of  a  structure  that 
once  existed  throughout  the  whole  mass;  that  the  inclosed  -ehi>i<>-e 
patches  and  areas  are  neither  remnants  of  foreign  schists  inclosed  in 
an  eruptive  granite  mass  nor  accidental  lamination  developed  by 
crystallization  or  motion  in  a  plastic  rock',  is  abundantly  proved  by 
the  fact  that,  whenever  over  a  continuous  area  a  great  many  of  the 
55721— Lull.  oGO— 01) 51 
