vanhise.]  THE    CORDILLERAS.  319 
chean  continent,  or  what  its  character  was.  From  the  fact  that  in  the 
Grand  Canyon  of  the  Colorado  similar  rocks  are  fonnd  below  the  Pots- 
dam, and  from  the  profundity  of  their  metamorphism  it  is  believed  that 
these  crystalline  rocks  are  Archean. 
LITERATURE   OF   THE   QUARTZITE   MOUNTAINS. 
Endlich,64  in  1876,  describes  the  Quartzite  mountains.  Near  the 
northern  border  and  toward  the  middle,  qnartzites  and  schists  pre- 
dominate, while  granite  appears  toward  the  east  and  south.  The 
quartzites  are  mostly  of  a  white  or  gray  color,  gradually  becoming  filled 
with  mica  or  chlorite,  thus  turning  into  schists.  The  relations  of  the 
quartzites  are  extremely  varied  and  complicated.  Granites  change 
into  quartzites  between  stations  21  and  22.  The  schists  have  a  less 
horizontal  extent  but  are  just  as  distinct  as  the  quartzites.  They  also 
show  great  variations  in  strike  and  dip.  As  a  rule  they  seem  to  be 
older  than  the  granite,  but  it  was  not  possible  to  establish  this  point 
beyond  doubt.  The  schists  were  nowhere  found  except  in  the  quartz- 
ite group.  All  the  granite  shows  a  remarkable  regular  stratification, 
not  an  apparent  one  only,  produced  by  the  main  cleavage  plane  of  the 
feldspar  or  mica  lying  in  one  direction.  The  dip  of  the  strata  is  con- 
formable with  those  of  the  quartzites  and  schists  and  away  from  the 
anticlinal  axis  toward  the  south.  Generally  the  dip  is  not  very  marked 
but  still  reaching  from  7°  to  10°.  All  along  the  Animas  the  junction 
of  the  sedimentaries  with  the  granite  was  not  observed.  The  latter 
was  exposed  in  the  valley,  while  the  former  appeared  in  steep  bluffs  on 
both  sides.  From  the  dips  observed  it  became  evident  that  the  two 
were  conformable. 
As  to  the  origin  of  the  metamorphic  group  of  rocks  it  is  said  that 
the  Devonian  strata  were  deposited  on  the  granitic  strata  conformably. 
Also  that  from  the  quartzite  into  granite  the  transition  is  perfect, 
although  often  small  specimens  can  be  found  showing  on  the  one  side 
granite  and  on  the  other  granular  red  quartzite.  Near  the  top  of  a 
bluff  the  latter  is  white  or  yellowish,  becoming  red  and  brown  lower 
down.  Finally  some  mica  is  observed  in  it,  and  the  feldspar  appears 
as  such,  until  the  coarse  grained  granite  is  reached.  The  metamor- 
phosis is  very  thorough,  and  can  be  admirably  studied  at  this  point. 
go  far  as  could  be  decided,  the  granite  was  formed  out  of  a  partly  argil- 
laceous sandstone,  containing  some  iron  in  an  oxidized  state,  while  the 
purer  sandstones  were  turned  into  quartzites.  Probably  the  process  of 
metamorphosis  was  a  very  slow  one,  and  lasted  a  long  time.  Through- 
out the  stratification  is  well  preserved  in  all  the  rocks  of  that  group, 
but  particularly  so  in  the  granite  of  the  locality  just  described.  Even 
the  thicknesses  of  the  various  strata  which  have  been  altered  into 
granite  correspond  approximately  to  those  at  present  exhibited  by  the 
Superincumbent  beds.  At  a  short  distance  north  of  station  48,  the 
granite  overlies  the  dark  schists,  which  in  turn  seem  to  be  younger 
