HARTVILLE    IRON-ORE    RANGE,  WYOMING.  195 
quartzite,  or  a  limestone  containing  sand  grains.  The  upper  part  of 
the  formation  is  composed  of  massive  beds  of  gray  limestone.  Prior 
to  the  deposition  of  the  Guernsey  formation  the  pre-Carboniferous 
land  surface  was  reduced  to  "a  peneplain.  The  contact  between  the 
pre-Cambrian  and  Carboniferous  rocks  is  therefore  a  flat  surface  that 
has  been  locally  warped  by  post-Carboniferous  folding.  When  the 
Carboniferous  rocks  are  in  contact  with  the  pre-Cambrian  schist  the 
contact  plane  is  level,  while  the  Carboniferous  extends  down  into 
the  pre-Cambrian  limestone  in  many  ramifying  rounded  bodies.  Evi- 
dently where  the  pre-Carboniferous  peneplain  was  underlain  by  lime- 
stone, solution  formed  caves  with  attendant  cave  galleries,  sink  holes, 
and  irregular  solution  joint  cavities.  Unconformably  upon  the 
Guernsey  lies  the  Hartville  formation,  which  is  at  most  places  650 
feet  thick.  Its  basal  member  is  a  deep  red  sandstone  and  above  this 
is  white  or  gray  limestone.  Some  distance  northwest  of  the  iron 
range  Messrs.  Smith  and  Darton  a  found  a  number  of  Jurassic-Trias- 
sic  and  Cretaceous  sedimentary  formations. 
The  older  rocks  prior  to  late  Tertiary  times  were  deeply  eroded,  and 
the  resulting  older  gulches,  canyons,  and  valleys  have  been  tilled 
by  the  Tertiary  sandstone,  which  in  the  folio  alread}T  mentioned  is 
called  the  Arikaree.  The  Pleistocene  formations  consist  of  terrace 
gravels,  alluvium,  and  wash. 
STRUCTURE. 
The  pre-Cambrian  sedimentary  rocks  have  been  folded  into  a  com- 
plexly folded  trough  or  synclinorium  with  east  and  west  axis.  The 
axis  of  the  synclinorium  passes  through  Sunrise.  The  beds  of  the 
north  arm  near  Sunrise  course  north  of  east.  To  the  northeast  they 
bend  farther  northward  and  at  Frederick  course  east  of  north.  North 
of  Frederick  the  direction  of  the  axis  is  north-south,  its  direction  being 
determined  by  the  contiguous  granite  mass.  Between  Sunrise  and 
Guernsey  the  strike  of  the  beds  is  practically  east-west,  although  in 
the  isolated  hills  south  of  Haystack  Peak,  across  Whalen  Canyon,  the 
strike  is  again  north-south.  Presumably,  therefore,  beneath  Whalen 
Canyon,  east  of  Guernsey,  the  beds  strike  southeastward.  In  the 
main  schist  area  east  of  Sunrise  the  folding  is  probably  close,  since  it 
is  known  that  the  schist  is  repeated  by  folding  at  least  four  times. 
Minor  folds  in  the  synclinorium  are  of  two  kinds — (1)  those  formed 
contemporaneously  with  the  main  folding  of  the  series,  and  (2)  those 
due  to  buckling  caused  by  the  intrusion  of  the  granite. 
Faults,  particularly  those  cutting  the  extension  of  the  beds  of  the 
synclinorium  at  right  angles,  are  common  in  the  pre-Cambrian  com- 
plex. The  greatest  fault  in  the  area,  however,  extends  eastward  from 
a  point  one-half  mile  north  of  Guernsey.     Here  the  pre-Cambrian  and 
a  Description  of  the  Hartville  quadrangle:  Geologic  Atlas  U.  S.,  folio  91,  U.  S.  Geol.  Survey,  1903. 
