318  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
places  almost  past  recognition.    The  huge  volcanic  masses  are  some 
of  them  dikes,  while  others  may  be  laccolites. 
Lakes,59  in  1886,  describes  the  Elk  mountain  eruptions  as  having 
occurred  under  an  enormous  pressure  of  superincumbent  strata  not  less 
than  10,000  feet  thick.  The  Elk  mountains  are  diorite  instead  of  being 
eruptive  granite  as  called  in  Hay  den's  reports. 
LITERATURE  OF  THE  GRAND  AND  GUNNISON  RIVERS. 
Schiel,38  in  1855,  states  that  along  Coochetopa  creek  and  Grand 
river  valleys  are  granite,  gneiss,  shale  and  mica-slate. 
Peale,42  in  1874,  states  that  adjacent  to«the  Gunnison  a  section  has 
at  its  base  rust-colored  granite,  above  which  is  mica-shist,  and  over 
this  quartzite  and  sandstone. 
Stevenson,44  in  1875,  states  that  at  several  localities  along  the 
Grand  and  Gunnison  is  a  peculiar,  regularly  laminated  gneiss  which 
resembles  a  micaceous  sandstone.  It  always  occurs  directly  under  the 
sedimentary  rocks  and  no  similar  formation  occurs  lower  down.  It  is 
clearly  unconformable  to  the  great  mass  of  schist  and  gneiss,  though 
precisely  like  them  in  its  changes.  In  consideration  of  all  the  circum- 
stances, one  can  not  resist  the  temptation  of  regarding  it  as  belonging 
to  a  later  series. 
Peale,62  in  1876,  describes  Archean  rocks  as  occurring  along  and 
near  the  gorges  of  Eagle  and  Gunnison  rivers.  The  rocks  of  the  Eagle 
river  are  known  to  be  pre-Potsdam?  because  at  the  head  of  the  stream 
such  rocks  rest  upon  them.  On  the  Gunnison  river  the  Archean  rocks 
are  gneisses  and  schists.  The  presence  of  Dakota  beds  here  resting 
upon  the  Archean  is  supposed  to  prove  that  in  pre-Oretaceous  times 
this  area  was  above  sea  level. 
Peale,63  in  1877,  describes  the  Archean  rocks  of  the  Grand  river, 
These  occur  in  limited  areas  throughout  the  district  between  parallels 
37°  52'  and  39°  15'  and  meridians  107°  and  109°  30'.  They  are  gener- 
ally confined  to  the  courses  of  streams  flowing  in  canyons.  In  many 
places  the  schistose  character  is  very  distinct  and  the  bedding  clearly 
seen,  but  in  most  cases  no  traces  of  bedding  wero*seen,  the  rocks  being 
granitoid.  Erom  the  number  of  exposures  noticed  it  is  evident  thai 
the  rocks  underlie  the  entire  district,  although  from  the  limited  and 
isolated  exposures  it  was  not  possible  to  trace  connections  from  one 
place  to  another.  The  oldest  sedimentary  beds  resting  upon  these 
rocks  are  Carboniferous  or  pre-Carboniferous,  showing  that  they  are 
at  least  pre-Carboniferous,  but  it  is  believed  that  they  are  pre- 
Silurian.  Along  the  Gunnison  outcrops  of  quartzitic  layers  occur 
with  softer  red  and  gray  gneissic  layers.  On  the  Little  Dolores  are 
mica- schists  and  quartzites  dipping  northeast  at  angles  of  60°  to  70°, 
As  to  the  origin  of  these  rocks  it  is  said:  They  were  once  deposited  as 
sediments.  Whence  were  their  materials  derived?  We  have  no  data 
from  which  we  are  able  even  to  guess  what  was  the  extent  of  the  Ar- 
