CHAPTER  XII. 
ISOLATED  AREAS  IN  THE  MISSISSIPPI  VALLEY. 
SECTION  1.     WISCONSIN. 
BARABOO. 
SUMMARY   OF  LITERATURE. 
Shumard,1  in  1852,  mentions  the  quartzite  ranges  of  Sauk  County, 
near  Bamboo.  The  quartzites  are  surmounted  by  sandstone,  and  all 
are  included  in  the  great  sandstone  formation  of  southern  Wisconsin. 
Percival,2  in  1&56,  describes  the  quartzite  ridges  of  Baraboo  and 
Portland.  The  rock  is  a  hard  granular  quartz,  which  has  more  or 
less  distinct  lines  of  stratification,  and  resembles  much  a  Primary 
granular  quartz.  In  the  Baraboo  rock  are  layers  more  or  less  filled 
with  rounded  pebbles  of  quartz,  resembling  layers  of  the  same  kind 
in  the  lower  sandstone,  and  oblique  cross  lines  between  the  regular 
lines  of  stratification,  which  occurrences  appear  to  connect  it  with 
the  lower  sandstone.  The  dip  of  these  ranges  is  at  a  moderate  angle 
to  the  north,  and  if  the  rock  is  formed  from  the  sandstone  by  igneous 
action  from  beneath,  the  metamorphic  change  has  not  been  accom- 
panied by  much  disturbance  of  the  strata.  The  localities  in  which 
Primary  rocks  are  found  are  all  within  the  limits  of  the  lower  sand- 
stone, and  most  of  them  occur  at  the  falls  of  the  northern  rivers. 
These  rocks  are  mainly  hornblendic  and  syenitic,  although  trap  rocks 
resembling  the  intrusive  traps  of  Connecticut  are  seen,  but  these  are 
believed  to  be  rather  Primary  greenstones.  Descriptions  are  given 
of  the  rocks  of  Marquette  and  Waushara  counties  and  of  those  of 
Black,  Wisconsin,  St.  Croix,  and  other  rivers.  On  Black  River  the 
rocks  are  syenite,  greenstone,  and  chlorite  slate,  the  latter  accom- 
panied by  iron  ores. 
Daniels,3  in  1858,  states  that  in  the  lower  part  of  the  Baraboo 
Valley  are  lofty  ranges  of  hard  quartzite  which  are  the  soft,  crum- 
bling Potsdam  sandstone  violently  disturbed  and  changed. 
Hall,4  in  18G2,  concludes  that  the  quartzite  ranges  of  Baraboo  and 
Necedah  hold  the  same  position  relative  to  the  Potsdam  sandstone  as 
the  Huronian  system  of  the  Canadian  Survey. 
Irving,5  in  1872,  maintains  that  the  quartzites  of  Sauk  County  arc 
unconformably  below  the  Potsdam,  because  they  are  uptilted  at   a 
717 
