292  PRE-CAMBRIAN    ROCKS    OF   NORTH   AMERICA.  [bull. 86. 
rock  at  Clayton's  peak  possesses  the  physical  habit  of  a  truly  eruptive 
granite  and  has  been  the  center  of  local  metamorpkisin,  but  the  evi- 
dence points  to  the  belief  that  it  is  of  Archean  age.  In  the  Cotton- 
wood canyon  there  is  no  sharp  division  between  the  structureless  gran- 
ite and  the  bedded  gneissoid  form.  In  the  neighborhood  of  Clayton's 
peak  are  bodies  of  granite-porphyry  which  are  probably  a  dependent 
of  the  granite.  West  of  the  granite  body  of  Little  Cottonwood  canyon 
is  a  belt  of  Archean  schists  and  quartzites  having  a  thickness  of  2,000 
or  3,000  feet  and  dipping  at  a  high  angle  to  the  northeast.  In  the  Lit- 
tle Cottonwood  canyon  the  quartzites  are  in  junction  with  the  granite, 
while  at  the  mouth  of  Big  Cottonwood  canyon,  in  direct  contact  with 
the  granite  is  mica  schist.  Between  the  Archean  granite  and  the  crys- 
talline schists  there  are  no  transitions  such  as  to  lead  to  the  belief  that 
the  granite  is  a  more  highly  metamorphic  form  of  the  schist.  The  con- 
tact is  clearly  denned,  the  rocks  mineralogically  dissimilar,  and  the 
granite  is  either  an  intrusive  mass,  or  else  an  original  boss  over  which 
the  Archean  sedimentary  materials  were  deposited.  The  absence  of 
granite  dikes  in  the  schists  strengthens  the  belief  that  the  granite  is 
older.  The  Cambrian  rocks  are  in  such  a  position  as  to  indicate  that 
the  granites  and  schists  alike  antedate  them,  although  in  some  in- 
stances intrusive  dikes  do  cut  the  marbleized  limestone,  but  they  are 
middle-age  porphyries,  not  to  be  confounded  with  the  Archean  crystal- 
line rocks. 
In  the  next  Archean  mass  to  the  north — the  Farmington  area — in 
Sawmill  canyon,  there  seems  to  be  two  distinct  series.  The  later  series 
consists  of  conformable  beds  of  gneiss,  quartzite,  and  hornblende- 
schist,  which  dip  west  at  angles  from  15°  to  40°  ,  and  rest  unconform- 
ably  upon  an  intensely  metamorphosed  material  composed  of  quartz, 
orthoclase,  and  muscovite.  In  reference  to  the  Farmington  gneisses  it 
is  said:  A  mica-schist  passing  into  a  hornblende-schist,  or  a  horn- 
blende-schist into  a  granite,  or  a  gneiss  rock  into  an  argillite,  along 
the  line  of  their  longitudinal  extensions,  are  phenomena  which  fail  to 
appear  on  the  fortieth  parallel.  The  small  granitoid  body  in  Sawmill 
canyon  is  referred  to  the  Laurentian,  while  the  second  series  of  meta- 
morphic rocks,  comprising  the  gneisses  and  schists,  12,000  or  14,000 
feet  thick,  are  referred  to  the  Huronian,  as  are  also  the  argillites  of 
Salt  lake  islands. 
The  Paleozoic  series  of  the  Wasatch,  although  30,000  feet  in  thick- 
ness, show  in  their  lowest  portions  only  a  very  slight  tendency  to  become 
crystalline  schists.  The  pre-Cambrian  topography  of  the  northern  part 
of  the  Wasatch  was  that  of  dome-like  peaks  with  gently  inclined 
sides.  The  Cottonwood  canyons,  however,  presented  an  almost  pre- 
cipitous face  of  30,000  feet  to  the  westward.  The  height  of  the  range 
was  then,  therefore,  from  17,000+  feet  to  30,000-f  feet. 
Passing  upward  from  the  Archean,  at  the  base  of  the  Paleozoic 
slates  are  Lower  Cambrian  slates  and  dark  argillites  and  intercalated 
