274  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA  [bull. 80. 
ward  into  the  mountain.  Below  these  are  quartzose  argillites,  which 
are  again  underlain  by  crystalline  schists.  Mill  peak,  north  of  east 
from  Medicine  peak,  has  at  its  base  a  white  quartzite,  which  is  overlain 
by  a  body  of  red  conglomerate  resembling  the  red  jasper  conglomerate 
of  the  Huronian  series  of  lake  Huron.  Above  this  is  amorphous 
quartzite,  and  the  peak  is  capped  by  white  and  gray  siliceous  limestone/; 
The  prevailing  dips  at  Mill  peak  are  to  the  west,  while  those  at  Medi-' 
cine  peak  are  to  the  east,  indicating  that  there  is  a  broad  synclinal  fold; 
between  the  two.  A  striking  characteristic  of  the  entire  series  is  the 
banded  and  laminated  appearance  of  the  constituent  minerals.  The] 
Archean  series  of  the  Medicine  bow  range  present  many  marked  fea- 
tures analogous  to  the  Huronian  formation  on  the  shores  of  lake  Union 
and  Canada,  as  well  as  to  various  localities  throughout  the  Appalachian 
chain;  and  they  are — with  considerable  hesitation,  however — recognized! 
as  of  Huronian  age,  because  they  are  so  widely  separated  from  any] 
beds  distinctly  recognized  as  such,  and  the  reference  is  based  entirely] 
upon  lithological  evidence.  The  rocks  also  present  many  features  in 
contrast  with  Laurentian  rocks  of  the  Colorado  Front  range. 
The  Park  range,  the  third  of  the  great  Archean  uplifts  of  the  Rocky] 
mountains,  is  a  system  of  highly  crystalline  rocks  of  Archean  age.  Th  J 
later  rocks  form  a  very  subordinate  part  of  the  uplift,  rising  not  morel 
than  a  few  hundred  feet  above  the  plain,  where  they  rest  unconfornij 
ably  on  the  older  series.  The  rocks  of  the  Park  range  resemble  morJ 
closely  those  of  the  Colorado  Front  range  than  they  do  the  Medicine] 
bow,  and  are  referred  to  the  Laurentian .  The  range  contains  much  struct 
tureless  granite  overlain  by  gneisses  and  schists  similar  to  the  series  of] 
the  Colorado  range,  but  carrying  more  hornblende-bearing  beds  in  the] 
upper  members.  Oft"  the  other  hand,  there  are  not  wanting  rocks  which! 
are  characteristic  of  the  Medicine  bow  series  and  which  were  referred 
to  the  Huronian  formation.  The  range  has  a  monoClrhal  structure  with' 
the  prevailing  dips  to  the  west,  while  an  outlying  spur  to  the  east- 
indicates  the  existence  of  the  eastern  side  of  the  fold. 
Emmons,6  in  1877,  describes  Rawlings  peak  as  an  outlying  area  ol 
Archean  granite-gneiss  which  shows  distinct  lines  of  bedding,  having 
an  inclination  of  45°  to  the  west,  while  the  overlying  quartzites  and 
sandstones  dip  10°  to  the  east. 
King-,7  in  1878,  describes  the  rocks  which  uncon  form  ably  overlie  thJ 
Archean  of  the  Colorado  range  as  varying  from  the  lowest  Paleozoic  up 
to  the  post-Pliocene.     The  Archean  core  of  the  range  is  a  broad  central 
anticline,  the  arch  having  a  flat  summit  and  the  dip  increasing  rapidly 
as  the  axis  becomes  distant.     In  this  range  complex  faulting,  inetar 
morphism  and  crystallization,  combined  with  widespread  erosion,  took  I 
place  before  the  beginning  of  Cambrian  time.     The  rocks  comprise 
granites  and  granite-gneisses,  above  which,  with  no  apparent  uncoiw 
foriiiity,  are  red  granites  showing  distinct  bedding,  and  above  tliesefl 
great  thickness  of  mica-gneisses,  the  estimated  thickness  of  which  is 
