326  PRE-CAMBRIAN   ROCKS    OF    NORTH   AMERICA.  [bull. 86. 
banded  gneisses,  granitoid  gneisses  and  granites  are  cut  by  foliated 
dikes  of  hornblende- schist,  which  never  penetrate  the  fragmental 
series.  At  one  of  the  places  along  the  Animas  at  which  the  quartz- 
ite  is  separated  by  a  very  short  interval  from  the  granite  complex  there 
is  a  sharp  discordance  in  its  foliation  and  a  series  of  sharply  folded 
anticlines  and  synclines  of  quartzite,  which  with  considerable  certainty 
indicate  the  bedding  of  the  latter  group.  Also,  while  the  quartzite 
series  inclines  at  a  steep  angle  and  is  in  places  sharply  folded,  it  upon 
the  whole  has  not  suffered  any  such  profound  and  repeated  dynamic 
movements  as  are  exhibited  by  the  granite- gneiss  complex.  If  the  lat- 
ter series  be  taken  as  sedimentary  its  complete  metamorphism  argues 
its  greater  age;  and  if  it  be  taken  as  wholly  eruptive  its  present  im- 
plicated character,  with  strongly  developed  schistose  structures,  de- 
noting profound  metamorphism,  indicates  a  history  much  longer  than 
the  one  revealed  by  the  quartzites.  This  great  quartzite  and  slate 
series  can  then  with  a  considerable  degree  of  certainty  be  regarded  as 
much  later  in  age  than  the  granite-gneiss-schist  complex.  Also  it  is 
far  more  ancient  than  the  Carboniferous,  because  near  Ouray  the  Trias 
conformably  above  the  Carboniferous  rests  in.  a  nearly  horizontal  posi- 
tion upon  the  upturned,  nearly  vertical,  truncated  edges  of  the  quartz- 
ite. On  general  structural  and  lithological  grounds  it  may  with  great 
probability  be  referred  to  the  Algonkian.  Of  the  two  other  areas  of 
clastic  rocks  too  little  is  known  to  offer  any  suggestions  as  to  their  age 
or  relations. 
A  part  of  the  so-called  granite  (diorite?)  of  the  Elk  mountains  and  a 
part  of  that  of  the  Sangre  de  Cristo  range  is  plainly  an  eruptive  of  later 
age  than  the  Cambrian,  and  therefore  it  does  not  properly  fall  within 
the  province  of  this  review. 
Whether  there  are  any  pre-Cambrian  rocks  in  the  La  Plata  mountains 
is  uncertain.  The  small  area  of  metamorphosed  rock  bears  such  relations 
to  the  eruptives  as  to  suggest  that  their  present  condition  may  be  due 
to  contact  metamorphism. 
SECTION  VII.    ARIZONA  AND  WESTERN  NEW  MEXICO. 
LITERATURE. 
Powell,28  in  1874,  states  that  below  the  Carboniferous  is  a  succes- 
sion of  nonconformable  shales,  sandstones  and  limestones,  the  greatest 
thickness  of  the  beds  being  a  little  more  than  10,000  feet.  The  beds 
are  traversed  by  dikes  of  trap  or  greenstone  and  irregular  layers  of  \ 
the  same  eruptive  material  are  found  in  places  between  these  noncon- 
formable rocks  and  the  overlying  beds  of  Carboniferous  age.  Pro- 
visionally these  sedimentary  rocks  are  called  Devonian  and  Silurian. 
Still  underlying  these  is  an  extensive  series  of  metamorphic  crystalline 
schists,  in  some  places  yet  showing  faint  traces  of  the  original  stratifi- 
cation,  but  usually  these  are  so  degraded  that  the  total  thickness  of  the 
