vanhise.]  LAKE    SUPERIOR    REGION.  105 
The  Gogebic  region  is  described  and  the  rocks  are  divided  into  gran- 
itic, dioritic,  iron  ore,  and  upper  slate  groups,  which  are  analogous  to 
the  similar  groups  in  the  Marquette  country.  G  ranite  seams  were  found 
here  cutting  across  the  dioritic  schists,  but  were  not  found  to  cut  the 
truly  sedimentary  strata.  Locally,  in  contiguity  with  the  granite,  are 
heavy  quartzite  strata  which  are  often  conglomeratic,  and  are  filled  with 
rounded  granite  pebbles.  The  dioritic  rocks  above  the  granite  often 
have  a  brecciated  or  conglomeratic  structure,  the  fragments  being  vari- 
ous kinds  of  diorite  cemented  by  the  same  material.  The  diorite  is  of 
eruptive  character,  as  is  shown  by  the  occurrence  of  belts  of  it  cutting 
transversely  through  the  ore-bearing  series.  Limestones  are  also  found , 
which  occupy  the  same  position  as  the  limestones  below  the  ore-bearing 
strata  in  the  Menominee  district. 
The  succession  in  the  Felch  mountain,  from  the  base  upward,  is  (1) 
granitic  or  dioritic  rocks ;  (2)  quartzite  beds;  (3)  fissile  quartz  schists; 
(4)  micaceous  argillite;  (5)  crystalline  limestone  with  siliceous  seams; 
(6)  ferruginous  quartzites,  containing  the  ore  beds. 
SECTION  IV.  WORK  OF  THE  WISCONSIN  GEOLOGISTS  AND  ASSOCIATES. 
Percival,118  in  1856,  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  stratifi- 
cation, which  occurrences  appear  to  connect  it  with  the  lower  sand- 
stone. 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  accompanied  by  much 
disturbance  of  the  strata.  The  localities  in  which  Primary  rocks  are 
found  are  all  within  the  limits  of  the  lower  sandstone,  and  most  of  them 
occur  at  the  falls  of  the  northern  rivers.  These  rocks  are  mainly  horn- 
blendic  and  syenitic,  although  trap  rocks  resembling  the  intrusive  traps 
of  Connecticut  are  seen,  but  these  arebelieved  to  berather  Primary  green- 
stones. Descriptions  are  given  of  the  rocks  of  Marquette  and  Wau- 
shara counties,  of  those  of  Black,  Wisconsin,  St.  Croix  and  other  rivers. 
On  Black  river  the  rocks  are  syenite,  greenstone  and  chlorite  slate,  the 
latter  accompanied  by  iron  ores. 
Daniel,119  in  1858,  describes  the  iron  ores  of  Black  river  falls  as  as- 
sociated with  the  chloritic  and  micaceous  slates  of  the  Azoic  system. 
Syenite  is  also  found  adjacent.  The  fossiliferous  horizontal  sandstone 
rests  upon  the  upturned  edges  of  the  Azoic  slates,  and  at  the  base  of 
it  is  a  brecciated  conglomerate  consisting  of  sand,  ore  and  slate.  In 
the  lower  part  of  the  Baraboo  valley  are  lofty  ranges  of  hard  quartzite 
which  are  the  soft  crumbling  Potsdam  sandstone  violently  disturbed 
and  changed. 
