718  PRE-CAMBRIAN    GEOLOGY   OF    NORTH   AMERICA. 
high  angle,  while  the  Potsdam  is  horizontal,  and  the  horizontal  sand- 
stone abuts  against  the  quartzite  and  holds  fragments  derived  from 
it.    These  quartzites  are  either  Laurentian  or  Huronian. 
Eaton,0  in  1872  and  1873,  maps  the  quartzites  of  the  Baraboo  River. 
At  Ableman's  the  highly  tilted  quartzites  are  flanked  on  both  sides  by 
horizontal  sandstone  and  conglomerate,  the  latter  having  angular 
fragments  of  the  quartzite  of  varying  magnitudes.  The  overlying 
sandstone  is  exactly  like  that  described  by  Irving  at  Devils  Lake  as 
containing  Potsdam  fossils.  The  sandstone  is  above  horizontal  lime- 
stone containing  Pleurotomaria.  The  quartzite  is,  then,  an  old  Azoic 
reef  of  tilted  rocks,  which  suffered  enormous  erosion  before  it  was 
washed  by  the  waves  of  the  Potsdam  sea. 
Mtjrrish,7  in  1873,  describes  the  quartzite  ranges  of  Baraboo  as  a 
metamorphic  sandstone  of  Potsdam  age. 
Chamberlin,8  in  1873,  discusses  cleavage  and  fissility  phenomena 
in  the  softer  layers  of  the  Baraboo  quartzite,  and  concludes  that  they 
are  evidence  of  dynamic  metamorphism  of  the  series. 
Chamberlin,9  in  1873,  discusses  the  post-Huronian  history  of  the 
Baraboo  quartzite  ranges. 
Irving,10  in  1877,  describes  in  some  detail  the  geology  of  the  Bara- 
boo quartzite  ranges,  and  concludes  that  the  quartzites  of  the  two 
ranges  appear  to  be  parts  of  a  continuous  series  dipping  to  the  north 
at  angles  as  low  as  15°  on  the  south  range  and  as  high  as  55°  to  90° 
on  the  north  range.  Quartz  porphyry  beds  on  the  north  flank  of  the 
north  range  constitute  the  uppermost  layers.  Unconformable  con- 
tacts of  the  Potsdam  sandstone  on  the  quartzite  are  figured  and 
described. 
Van  Hise,11  in  1893,  considers  the  dynamic  phenomena  shown  by 
the  Baraboo  quartzite  ranges  of  central  Wisconsin.  These  rocks,  in- 
durated by  cementation,  exhibit  all  stages  from  massive  quartzite 
showing  microscopically  little  evidence  of  interior  movement,  through 
a  rock  having  in  turn  fracture  and  cleavage,  to  one  which  is  ap- 
parently a  crystalline  schist,  but  in  thin  section  still  giving  evidence 
of  its  fragmental  origin.  The  schistosity  produced  by  the  movement 
of  the  layers  over  one  another  is  parallel  to  the  bedding.  In  places 
Reibungs  breccias  have  developed.  At  one  point  minor  faulting  was 
noticed.  These  phenomena  are  more  marked  in  the  North  Range 
than  in  the  South  Range,  and  thus  bear  in  favor  of  Irving's  explana- 
tion of  the  structure  as  a  part  of  a  single  great  fold  in  a  set  of  layers 
12,000  feet  thick,  the  North  Range  being  on  the  leg  of  the  fold,  and 
thus  requiring  greater  readjustment  of  the  beds  than  those  on  the 
South  Range,  which  are  near  the  crown  of  the  anticline. 
Weidman,12  in  1895,  describes  the  igneous  rocks  of  the  lower  nar- 
rows of  Baraboo  River.  These  are  in  a  belt  from  one-eighth  to  one- 
half  mile  wide,  running  for  4  miles  in  an  east-west  direction.     Chemi- 
