vanhibk.]  THE    CORDILLERAS.  293 
siliceous  schists  800  feet  thick ;  above  this  Cambrian  quartzite,  an  im- 
mense series  of  siliceous  and  arkose  rocks  12,000  feet;  and  above  this 
Cambrian  calcareous  shales  of  variable  thickness,  and  containing  Pri- 
mordial fossils,  75  to  600  feet.  This  great  thickness  is  found  in  the 
Cottonwood  area,  on  the  lower  half  of  Big  Cottonwood  canyon,  and 
from  Big  Cottonwood  canyon  in  a  northeasterly  direction  across  the 
spur  which  divides  the  waters  of  Cottonwood  creek  from  Mill  creek. 
In  other  localities  the  Cambrian  is  far  thinner  or  wholly  absent.  The 
section  in  the  Big  Cottonwood  canyon,  in  passing  upward,  comprises 
black  slates  and  thinly  laminated  ar^illites  800  or  900  feet  in  thickness; 
above  these,  8,000  or  9,000  feet  of  mixed  siliceous  schists  and  argilla- 
ceous schists;  above  these;  3,000  feet  of  true  quartzite  capped  by  200 
feet  of  schistose  rock,  quite  micaceous  toward  the  bottom,  and  at  Twin 
peak  approaching  a  true  mica- schist.  At  the  second  section  the  series 
consists  of  four  members :  the  bottom  slates,  800  feet  thick ;  varying 
siliceous  and  argillaceous  schists,  containing  some  mica-bearing  zones, 
8,000  or  9,000  feet  thick ;  salmon  colored  and  white  quartzites,  inter- 
calated with  dark  schists,  2,500  to  3,000  feet;  and  the  capping  schists 
of  200  feet,  which  are  partly  argillaceous  and  calcareous  rocks  and 
partly  mica-bearing  argillites.  Passing  up  the  Little  Cottonwood,  the 
successively  higher  members  of  the  Cambrian  rest  against  the  granite 
until  the  latter  rises  into  contact  with  the  Silurian  limestone,  which 
conformably  overlies  the  Cambrian.  Although  a  careful  search  was 
made  in  these  schists  no  fossils  were  found. 
Geikie,32  in  1880,  discusses  the  nature  of  the  pre-Cambrian  mountains 
of  the  Wasatch  and  the  eruptive  or  metamorphic  origin  of  the-  Cotton- 
wood granite.  That  this  granite  is  eruptive  is  maintained  on  the 
grounds  of  the  enormous  height  of  the  cliff  which  would  be  required  in 
case  it  was  an  Archean  island ;  that  if  it  were  an  old  shore  line,  some- 
where granite  pebbles  would  be  found  to-day;  that  the  granite  is  said 
by  King  to  be  a  source  of  local  metamorphism;  that  there  are  porphy- 
ries cutting  the  limestones,  probably  dependent  on  the  granite;  and 
that  it  is  exceedingly  improbable  that  there  was  a  cliff*  12  miles  high 
which  has  been  turned  over  on  its  back  as  required  by  the  descriptions 
and  sections  by  King.  All  these  difficulties  are  overcome  by  regarding 
the  granite  as  a  subsequent  intrusive  of  post- Carboniferous  age. 
Waloott,33  in  1886,  describes  the  Big  Cottonwood  canyon  section  of 
Cambrian  rocks,  which  is  found  to  be  12,000  feet  thick.  It  consists  of 
shales,  quartzites,  sandstones,  and  slates.  The  upper  250  feet  of  shale 
bears  the  Oienellus  fauna,  while  other  layers,  although  in  a  most  excel- 
lent condition  for  finding  fossils,  did  not  reveal  any.  The  Oienellus 
horizon  is  placed  at  the  base  of  the  Middle  Cambrian  and  the  great  re- 
maining part  as  Lower  Cambrian. 
Emmons,  (S.  F.),34  in  1886,  discusses  the  possibility  of  the  post-Cam- 
brian eruptive  character  of  the  Cottonwood  granite.  This  body  occu- 
pies an  area  of  about  ,7  by  15  miles,  and  a  thickness  of  some  5  miles  of 
