282  PRE-CAMBRlAN   ROCKS    OF    NORTH    AMERICA.  (bull. 86. 
the  various  authors  to  be  metamorphic  because  having  a  lamination  or 
foliation, and  the  more  massive  rocks  are  regarded  as  being  older  because 
more  metamorphic,  and  also  because  they  are  usually  core  rocks.  As 
has  been  seen  in  the  case  of  the  Laramie  hills  and  other  regions,  these 
facts  may  be  equally  well  explained  by  regarding  the  rocks  as  all  an- 
cient igneous  rocks,  parts  of  which  have  been  given  a  laminated  struc- 
ture by  dynamic  action. 
Nowhere  is  anything  said,  as  to  any  unconformable  relations  between 
any  parts  of  the  various  series  referred  respectively  to  the  Huroniau, 
Laurentiau,  or  Prozoic,  as  the  case  may  be.  Consequently  the  only  sure 
structural  conclusion  reached  is  that  there  is  in  these  mountain  ranges 
a  great  complex  of  granites,  gneisses,  and  schists,  thoroughly  crystal- 
line, and  as  yet  undivided,  which  are  of  pre-Cambrian  age. 
SECTION   III.     CENTRAL   AND    SOUTHWESTERN  MONTANA,  WITH   ADJA- 
CENT  PARTS   OF   WYOMINO   AND   IDAHO. 
LITERATURE. 
Hayden,10  in  1861,  describes  along  the  Madison,  one  of  the  forks  of 
the  Missouri,  beds  of  feldspathic  rocks,  and  mica-slates  and  clay-slates 
above  the  eruptive  granites  of  the  region. 
Hayden,19  in  1872,  describes  Archean  rocks  at  many  points  in  south- 
western Montana.  Among  the  localities  mentioned,  the  following  are 
worthy  of  note:  Upon  Black-Tailed  Deer  creek  in  southwestern  Mon- 
tana is  an  immense  thickness  of  alternating  beds  of  quartzites,  true 
gneiss  and  mica-schist,  the  first  predominating,  and  inclining  to  the 
west  from  30°  to  45°.  Old  granite  ridges  are  also  found.  On  the  north 
side  of  this  creek  are  gneissic  beds,  which  incline  to  the  northwest  at 
angles  varying  from  30°  to  60°.  On  the  Stinking  water  are  immense 
thicknesses  of  micaceous  gneiss  underlying  massive  layers  of  quartz- 
jte.  Along  the  Madison  canyon  is  found  granite.  The  rocks  adjacent 
to  Virginia  City  are  clearly  stratified,  wholly  metamorphic,  and  are  I 
regarded  as  below  the  Paleozoic.  Upon  the  Upper  Gallatin  are  gra-  I 
nitic  nuclei,  with  the  unchanged  sedimentary  beds  upon  the  sides  and 
summits  inclining  at  various  angles.  In  the  first  canyon  of  the  Yel- 
lowstone is  true  gneissoid  granite  and  micaceous  gneiss  of  different, 
shades  of  color,  giving  its  sides  a  peculiarly  stratified  appearance.  At 
Cinnabar  mountain  is  a  plainly  metamorphic  reddish  feldspathic  quartz? 
ite,  upon  which  rests  unconforinably  the  Carboniferous  limestone. 
Hell  -Roaring  mountain  consists  of  stratified  gneiss  and  massive  red  or 
gray  feldspathic  granite.  At  Horse  plain  valley  are  quartzites  and 
micaceous  schists,  which  rise  beneath  the  limestones  and  quartzites  of 
Carboniferous  age. 
Peale,20  in  1872,  gives  many  details  with  reference  to  the  lithological 
and  mineralogical  character  of  the  rocks,  the  locations  of  which  are  | 
given  by  Hayden. 
