an  msE.j  THE    CORDILLERAS.  317 
LITERATURE   OF   THE   ELK  MOUNTAINS. 
Hayden,57  in  1874,  describes  the  Elk  mountains  as  composed  of  an 
pthrust  of  igneous  granite,  which  carries  portions  of  the  sedimentary 
eds  on  its  summits  or  tilting  away  from  the  sides  at  various  angles, 
'he  lowest  group  of  sedimentary  rocks  is  Lower  Silurian.  In  some 
ases  there  is  complete  overturn  of  immense  groups  of  beds,  so  that 
>r  several  miles  there  is  a  double  series  from  the  Silurian  up  to  the 
Iretaceous,  inclusive,  as  at  the  head  of  East  river  and  near  Snow 
lass  peak.  Northeast  of  Snow  Mass  the  sedimentary  beds  may  be 
een  resting  on  the  granite,  on  these  a  great  thickness  of  red  beds, 
nd  on  the  top  of  the  latter  masses  of  irregular  thickness  of  erup- 
[ve  granite  from  100  to  400  feet  thick,  and  at  both  ends  the  red  beds 
gain  resting  upon  the  eruptive  mass,  so  that  the  granite  now  appears 
ke  an  interstratified  rock.  Gothic  mountain  and  Crested  butte  are 
egarded  as  immense  dikes,  the  melted  matter  being  pushed  up  through 
tie  superincumbent  matter  so  as  not  to  disturb  to  any  great  extent  the 
bickness  of  yielding  Cretaceous  shales  and  clays.  On  Eagle  river  are 
eds  of  sandstones  and  quartzites,  the  fragments  of  which  indicate 
hat  they  have  been  derived  from  gneissic  and  granitic  rocks. 
Peale,42  in  1874,  describes  the  entire  mass  of  granite  of  the  Elk 
lountains  as  having  been  either  in  a  plastic  or  melted  condition.  The 
levation  of  the  range  was  post-Cretaceous.  The  mountains  are  cut 
y  numerous  dikes,  which  are  in  part  trachytic,  but  which  are,  how- 
ver,  believed  to  be  connected  with  the  eruptive  granite.  On  the  south- 
ast  side  of  Elk  mountains  are  chloritic  schists,  quartzites,  and  sand- 
fcones,  all  very  much  metamorphosed. 
Holmes,60  in  1876,  gives  the  geology  of  the  northwestern  portion  of 
lie  Elk  range  and  describes  in  detail  the  character  of  the  folding,  fault- 
lg  and  relations  of  the  crystallines  to  the  sedimentary  rocks.  On  the 
ast  side  the  sedimentary  strata  lie  up  against  the  granite  of  the  Sawatch 
ange,  and  on  the  west  they  have  been  carried  high  up  on  the  arch  of 
tie  Elk  mountains,  leaving  the  synclinal  depression  between  the  ranges, 
'he  axes  of  the  two  ranges  are  not  parallel,  but  approach  each  other 
oward  the  south  and  separate  toward  the  north,  giving  an  included 
ngle  of  some  30°.  In  the  vicinity  of  Italian  peak  the  granites  of  the 
wo  ranges  are  in  contact,  or  nearly  so,  being  totally  distinct  in  appear- 
nce  and  in  reality.  The  sedimentary  beds  of  Sopris  and  Eock  creeks 
how  a  considerable  amount  of  metamorphism  and  lateral  crushing, 
lie  Dakota  sandstones  of  the  latter  being  changed  to  hard,  flinty 
uartzites.  A  great  fault,  combined  with  a  fold,  runs  from  the  north 
art  of  the  Elk  group,  i.  e.,  Snow  Mass  mountains,  to  its  south  part, 
^hite  Eock  mountains.  In  the  sections  the  granitic  rocks  are  repre- 
ented  in  places  as  being  above  the  sedimentary  and  in  other  places  as 
itr tiding  themselves  among  the  layers. 
Lakes,61  in  1885,  describes  the  stratified  rocks  adjacent  to  the  Elk 
lountains  as  riddled  with  dikes  and  baked  and  metamorphosed  in 
