194  CONTRIBUTIONS    TO   ECONOMIC    GEOLOGY,  1906,  PART    I. 
gray.     They  are  typically  fine  grained  and  pass  from  biotitic  to  mus- 
covitic  varieties  both  along  and  across  the  bedding.     Slaty  schists 
and  siliceous  schists  also  occur.     Interbedded  with  this  old  series  are 
thin  beds  and  lenses  of  gray  quartzose  rock  and  dark-brown  or  blacks 
jaspers. 
In  the  broad  schist  area  east  of  Sunrise  a  second  sedimentary 
series  lies  unconformably  upon  the  uppermost  bed  of  the  series  just 
described.  The  unconformable  character  of  this  series  is  indicated  by 
its  location  in  synclinal  troughs  upon  the  uppermost  beds  of  the  older 
rock  series,  which  is  folded  into  a  s^mcline,  by  a  conglomerate  that  is 
present  in  some  places  at  its  base,  by  the  fact  that  it  slightly  cutss 
across  the  beds  of  the  older  formation,  and  by  its  sharp  contacts  with 
and  lithological  differences  from  the  older  formation.  This  second 
series  of  sedimentary  rocks  is  composed  of  gray,  thoroughly  crystal- 
line quartzose  rocks,  which  are  at  some  places  conglomeratic  and  at! 
others  nonconglomeratic.  Associated  with  these  altered  sandstones 
are  beds  of  jasper,  which  vary  in  color  from  gray  through  browns  an 
reds  into  black.  The  banding  of  the  jaspers  is  at  some  places  close 
Although  most  of  the  exposures  are  too  poor  to  determine  the  younger 
age  of  the  quartzose  rocks  and  jaspers  of  all  the  areas,  there  is  nq» 
doubt  that  two  sedimentary  series  occur  in  the  pro-Cambrian  of  this 
district  and  that  many  of  the  areas  of  siliceous  rocks  arc  younger  than 
the  schist-limestone  series. 
The  next  youngest  pre-Cambrian  rocks  arc  gabbros,  diorites,  and 
allied   porphyries  and  the  same  rocks  mashed  into  hornblende  and 
chloritic    schist.     These   rocks   grade   into   one   another.     At   most 
places  these  igneous  rocks  are  intrusive  in  the  older  pre-Cambrian 
sedimentary  series.     It  is  possible,  however,  that  some  of  the  chloritic  | 
and  hornblende  schists  may  represent  later  basic  lava  flows.     The  age 
relation  of  the  rocks  of  the  third  to  those  of  the  second  pre-Cambi  ian 
series  is  unknown,  since  at  no  place  were  the  two  observed  in  contact, 
although  it  is  believed  from  differences  in  the  amounts  of  folding 
suffered  by  the  two  formations  that  the  sedimentary  is  the  older  1 
series.     The  intrusion  of  the  gabbros  and  the  diorite  was  followed  by 
that  of  a  coarse-grained  pink  biotite  granite,  which  at  many  places  >; 
contains   large   feldspar  crystals.     It   occurs   in   rounded,   intrusive 
masses  characterized  by  but  few  offshoots  and  in  isolated  dikes. 
Aplites  and  pegmatites  allied  in  composition  to  the  granite  followed  I. 
its  intrusion.     The  last  of  the  pre-Cambrian  series  is  a  diabase  which 
occurs  in  dikes  that  are  sparsely  distributed  throughout  a  wide  area. 
The  Carboniferous  series  alone  of  the  Paleozoic  and  Mesozoic  rocks 
occurs  in  the  immediate  vicinity  of  the  ore  deposits.  The  Carbon- 
iferous consists  of  a  basal  member,  the  Guernsey,  and  an  upper  mem- 
ber, the  Hartville  formation.  The  Guernsey  is  normally  150  feet 
thick  and  comprises  at  its  base  either  a  conglomeratic  quartzite,  a 
