722  PRE-CAMBKIAN    GEOLOGY   OF    NOKTH   AMERICA. 
FOX  RIVER  VALLEY, 
SUMMARY  OF  LITERATURE. 
Irving,17  in  1877,  describes  the  quartz  porphyry  at  Marcellon,  Ob- 
servatory Hill,  Moundville,  Pine  Bluff,  Marquette,  and  Berlin,  and 
the  granite  at  Montello,  in  Marquette  County,  and  at  Marion,  in 
Washara  County.  All  are  assigned  to  the  Archean,  using  this  term 
to  cover  all  pre-Silurian  rocks.  From  emphasis  placed  on  the  bed- 
ding it  is  apparent  that  the  quartz  porphyries  are  considered  to  be 
sedimentary. 
Chamberlin,18  in  1877,  describes  the  Archean  rocks  which  in  the 
eastern  part  of  Wisconsin  protrude  through  but  are  not  intrusive  in 
the  Paleozoic  formations.  These  are  the  Mukwa  granite,  the  Berlin 
porphyry,  the  Pine  Bluff  quartz  porphyry,  the  Marquette  quartz 
porphyry,  and  the  quartzites  of  Portland  and  Waterloo.  The  por- 
phyries are  found  to  have  obscure  but  distinct  bedding.  The  meta- 
morphosed quartzites  show  ripple  marks  and  contain  conglomeratic 
layers.  The  Potsdam  sandstone  and  Lower  Magnesian  limestone  rest 
in  a  horizontal  position  against,  and  contain  fragments  from,  the 
crystalline  rocks.  The  quartzites  are  regarded  as  originally  sand- 
stones and  conglomerates  which  were  metamorphosed  before  the 
neighboring  horizontal  rocks  were  deposited,  and  were  tilted  and 
eroded  before  the  stratified  rocks  were  deposited.  These  quartzites 
are  regarded  as  a  portion  of  the  Baraboo  quartzite  series. 
Pretts,19  in  1895,  describes  and  maps  the  rocks  of  Marquette  on 
Fox  River.  They  are  acidic  igneous  rocks  with  volcanic  textures, 
cut  by  basic  dikes. 
Leith  and  Hobbs,20  in  1897,  1898,  and  1899,  describe  and  map  the 
rocks  of  Marcellon,  Observatory  Hill,  Taylors  Hill,  Moundville, 
Montello,  and  Marquette.  The  rocks  are  principally  metarhyolites, 
some  of  them  aporhyolites,  showing  a  great  variety  of  surface  vol- 
canic textures  and  cut  by  basic  dikes.  At  Montello  is  a  porphyritic 
granite.  From  their  similarity  to  rhyolites  on  the  north  flank  of  the 
Baraboo  Range,  mapped  by  Weidman  as  Keweenawan,  they  are 
tentatively  asigned  to  the  Keweenawan. 
Weidman,21  in  1898,  describes  the  pre-Cambrian  igneous  rocks  of 
the  Utley,  Berlin,  and  Waushara  areas  in  the  Fox  River  valley  of 
Wisconsin.  They  range  from  volcanic  flows  to  masses  of  deep-seated 
origin,  with  corresponding  textures.  The  rock  of  the  Utley  area  is 
a  metarhyolite,  at  Berlin  a  rhyolite  gneiss,  and  in  the  Waushara  area 
a  granite.  Analyses  of  the  rocks  of  the  three  areas  show  a  close  simi- 
larity in  chemical  composition,  and  it  is  believed  that  the  rocks  rep- 
resent phases  of  a  single  parent  magma.  The  rocks  have  been  meta- 
morphosed to  different  degrees,  and  the  results  of  the  metamorphism, 
particularly  of  the  feldspars,  are  described  in  detail. 
