286  PRE-CAMBKIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
gireisses.  Without  more  detailed  examination'  and  search  for  obscure 
folds  it  is  impossible  to  estimate  the  total  thickness,  but  it  is  certainly 
very  great. 
SUMMARY    OF    RESULTS. 
It  is  evident  from  the  literature,  as  well  as  from  Hayden's  own  state- 
ment, that  no  systematic  work  has  been  done  among  the  pre- Cambrian 
rocks,  with  the  exception  of  that  by  Peale  on  the  Three  forks  sheet. 
The  information  at  hand  makes  it  clear  that  this  region  will  yield  re- 
sults of  extreme  interest  when  considerable  areas  arc  mapped.  In  the 
region  are  great  areas  of  intricately  mingled  granitic  and  gneissie  rocks 
which  certainly  belong  to  the  Archean.  Associated  with  this  class  of 
rocks  are  immense  thicknesses  of  regularly  bedded  gneisses,  mica- 
schists,  chlorite-schists,  quartz-schists,  quartzites,  and  limestones. 
Whether  the  regular  lamination  of  the  gneiss  is  due  to  sedimentation 
or  to  other  forces  is  uncertain,  but  the  great  belts  of  inter  stratified 
crystalline  limestone,  quartz-schists,  and  quartzites  are  evidence  that 
here  is  a  series  of  clastic  origin,  although  at  the  present  time  it  has 
become  thoroughly  crystalline.  The  relations  of  this  series  to  the 
granites  and  gneisses  donbtfully  referred  to  the  Archean  have  not  been 
worked  out. 
There  is  also  in  this  region,  as  shown  by  the  work  of  Davis  and 
Peale,  a  great  series  of  unaltered  strata  which  are  probably  Algonkian. 
This  series  is  a  downward  succession  of  barren  slates  below  the  fossil- 
iferous  Cambrian,  and  if  Algonkian,  is  the  uppermost  division  and 
equivalent   to  the  upper  Algonkian  of  the  Wasatch.     Peale's  results 
indicate  that  while  there  is  no  actual  unconformity,  there  is  a  change 
of  physical  conditions,  a  subsidence,  and  perhaps  a,  real  time  break  be 
tween  the  Cambrian  and  Algonkian.     Nowhere  yet  have  the  unaltered 
barren  slates  and  the  more  crystalline  series  of  clastic  origin  been  foim 
in  contact.     Between  the  slates  and  the  Archean  gneisses  is  a  great  un 
conformity,  and  there  is  little  doubt,  when  the  unaltered  series  is  cai 
ried  over  to  the  vertical  limestones,  quartzites,  and  quartz-schists,  tha 
it  will  be  found  to  rest  upon  them  unconfofmably.     There  is,  then,  iu 
this  region  probably  two  series  of  Algonkian  rocks,  one  almost  com 
pletely  unaltered,  the  other  thoroughly  crystalline,  and  both  of  great 
thickness. 
SECTION  IV.      UTAH   AND   SOUTHEASTERN  NEVADA. 
LITERATURE   OF   THE   UINTA  MOUNTAINS. 
Marsh,27  in  1871,  states  that  in  the  Uinta  mountains  is  an  extensivj 
series  consisting  of  reddish  sandstones  and  quartzites,  sometimes  meta 
morphosed  and  apparently  without  fossils.  The  series  is  referred  pro 
visionally  to  the  Silurian  on  the  ground  that  resting  conformably  upoi 
them  are  limestones  bearing  Carboniferous  fossils. 
