THE   CORDILLERAS.  833 
CORRELATION  .a 
The  ancient  granites,  gneisses,  and  schists  constituting  the  oldest 
basal  rocks  of  the  mountains  (division  1  of  Cross)  are  referred  to 
the  Archean.  They  are  similar  in  lithology  and  complexity  to  the 
Laurentian  rocks  of  Canada  and  the  Lake  Superior  region,  using  the 
term  in  its  restricted  sense.     (See  p.  325.) 
The  metamorphosed  basic  volcanic  rocks  of  the  Salida  district  and 
of  the  Needle  Mountains  (division  2  of  Cross)  can  not  be  satisfac- 
torily classified.  They  are  older  than  the  Algonkian  sediments  and 
younger  than  the  Archean  granites  and  gneisses.  Cross  and  Howe 
provisionally  refer  them  to  the  early  Algonkian.  This  correlation  is 
here  followed  because  they  are  doubtless  much  more  recent  than  the 
plutonic  granites  and  gneisses  of  the  Archean,  but  their  reference 
to  the  early  Algonkian  rather  than  the  late  Archean  is  largely  one  of 
personal  choice.  These  outcrops  are  similar  to  the  hornblende  schist 
series  at  the  base  of  the  sedimentary  series  in  the  Grand  Encampment 
district  of  Wyoming,  described  by  Spencer,  and  to  the  volcanics  of  the 
southern  Piedmont,  described  by  Keith.  In  the  latter  district  Keith 
has  referred  them  provisionally  to  the  Algonkian  because  of  the 
extended  interval  which  must  have  elapsed  between  their  eruption 
and  the  formation  of  the  plutonic  igneous  granites  and  gneisses  upon 
which  they  rest.  Similar  rocks  are  known  in  both  the  Archean  and 
the  Algonkian  of  the  Lake  Superior  region. 
The  pre-Cambrian  sedimentary  rocks  (division  3  of  Cross)  and  the 
massive  igneous  rocks  intrusive  into  them  (division  4  of  Cross)  are 
referred  to  the  Algonkian.    The  latter  may  be  in  part  post-Algonkian. 
No  attempt  is  made  to  classify  the  basal  gneisses  of  the  George- 
town quadrangle,  believed  by  Spurr  to  be  of  sedimentary  origin.  The 
quartzites  of  the  Needle  Mountains  may  constitute  a  part  of  a  great 
pre-Cambrian  tcrrane*  formerly  continuous  witli  the  quartzites  of 
the  Wasatch  and  Uinta  mountains,  the  Grand  Canyon,  and  the  Belt 
series. 
SECTION  7.     WYOMING. 
SUMMARY  OF  LITERATURE. 
LARAMIE,    MEDICINE    BOW,    AM)    PARK    RANGES    IN    SOUTHERN     WYOMING. 
Stansbury,-"'4  in  1853,  states  that  in  the  Black  Hills  (Laramie)  is 
an  extensive  formation  of  massive  red  feldspathic  granite  with  occa- 
sional outcrops  of  ferruginous  quartz. 
Hayden,107  in  1863,  describes  the  Laramie  Hills  as  consisting  <>!' 
numerous  centers  of  uplifted  granite  upon  the  sides  of  which  the 
Carboniferous   limestones   lie    in    unconformable    patches.      'There    i< 
By  the  authors. 
55721—  P. ui  L.  36< >—<><) 53 
