vanhise.]  THE    CORDILLERAS.  311 
rock  resembles  a  gneiss.  Besting  immediately  upon  the  granite  is  the 
Silurian,  characterized  by  but  a  few  fossils,  and  the  well  known  quartz- 
itic  formations.  The  granite  of  this  area  is  the  oldest  found  in  the 
region. 
Stevenson,44  in  1875,  states  that  metamorphic  rocks  occur  in  the 
Front  range.  On  the  North  fork  of  the  South  Platte  the  schists  are 
much  contorted.  The  schists  near  Baileys  ranch  contain  rudely  oval 
nodules  of  quartz  and  feldspathic  granite  which  in  several  localities  are 
observed  in  layers.  In  many  instances  the  large  masses  of  gneissoid 
granite  string  out  like  veins  on  all  sides  from  the  center,  and  these  vein- 
like  projections  break  up  into  these  nodules  and  thus  finally  disappear. 
It  is  sufficiently  evident,  then,  that  these  are  not  metamorphosed  peb- 
bles, but  concretions,  the  result  of  segregation,  which  marks  the  forma- 
tion of  the  separate  layers  of  quartz,  feldspar,  and  mica  in  gneiss,  and 
of  the  great  masses  of  coarse  granite,  which  occur  so  frequently  in  the 
gneisses  and  schists.  Gneissoid  granite  is  exceedingly  common.  It  often 
occurs  in  the  gneiss  as  great  included  masses  of  irregular  shape  or  in 
elongate-vein  form,  spreading  from  a  center  and  throwing  out  seams 
which  become  exceedingly  thin  before  they  disappear.  In  each  instance 
the  deposit  seems  to  bear  no  relation  to  the  bedding  of  the  including 
rock.  For  the  most  part,  however,  it  is  found  entirely  displacing  the 
gneiss  and  forming  the  prevailing  rock  for  miles.  In  every  such  instance, 
however,  it  occasionally  changes  into  gneiss  for  short  distances.  ISTot 
unfrequently  seams  of  granite  are  found  along  the  planes  of  cleavage. 
This  granite,  which  may  be  termed  segregated  granite  to  distinguish 
it  from  the  granite  which  many  regard  as  eruptive,  is  coarsely  crystal- 
line, with  the  feldspar  in  great  quantity,  while  the  proportion  of  mica 
is  very  small.  The  feldspar  varies  in  color  from  white  to  red,  and  the 
rock  as  a  whole  yields  readily  under  the  influence  of  the  weather.  The 
gneissoid  granite  of  Taylor  river  exhibits  granite  of  both  the  eruptive 
and  metamorphic  varieties,  one  passing  into  the  other  with  no  line  of 
separation.  There  is  then  no  room  to  doubt  that  they  are  of  common 
origin  and  that  the  whole  is  metamorphic. 
The  gneiss  of  Ten-Mile  creek  is  compact  and  might  be  mistaken  for 
a  quartzite.  Below  the  junction  is  an  immense  segregation  of  granite, 
thoroughly  veinlike,  interlacing  and  running  across  the  bedding  in 
every  conceivable  way,  but  not  persistent,  as  each  of  the  veins  tapers 
off'  until  it  disappears.  In  the  canyon  of  the  Arkansas,  above  the  junc- 
tion with  Tennessee  creek,  is  a  gneiss  which  has  very  close  affinities 
to  the  granites  usually  called  eruptives.  It  passes  gradually  into  a 
micaceous  schist.  On  Trout  creek  is  syenite  and  granite,  which  grad- 
ually assumes  a  gneissoid  structure  and  contains  fragments  of  gneiss 
from  6  to  20  inches  in  diameter  which  are  fragmental  in  shape.  Their 
presence  is  difficult  to  account  for.  If  the  granite  is  eruptive  these 
might  be  included  fragments,  but  there  is  no  reason  to  assign  any  such 
origin  to  it,  for  its  gradual  passage  into  the  gneiss  is  easily  traced.   On 
