rant.]  ZINC   AND   LEAD   OF    SOUTHWESTERN    WISCONSIN.  305 
melted  at  North  Chicago,  and  most  of  the  zinc  carbonates  and  the 
3wer  grades  of  the  zinc  sulphides  are  shipped  to  Mineral  Point,  Wis., 
rhere  an  extensive  plant  for  the  manufacture  of  zinc  oxide  and  sul- 
furic acid  is  located.  Within  the  last  year  a  new  railway — the  Min- 
ral  Point  and  Northern — has  been  constructed.  This  furnishes  an 
utlet  by  rail  for  the  ores  from  Highland,  which  is  the  most  import- 
1 1 1  point  in  the  northern  part  of  the  ore-bearing  region.  Recently  a 
iad  furnace  has  been  reopened  at  Dodge ville,  Wis.,  and  plants  for 
fie  manufacture  of  mining  and  concentrating  machine^  have  been 
stablished  at  Galena,  111.,  and  at  Platteville,  Wis. 
GENERAL  GEOLOGY. 
The  outcropping  strata  are  of  early  Paleozoic  age.  Igneous  rocks 
re  not  exposed,  but  underlie  the  Paleozoic  sediments.  The  dip  of  the 
trata  is  at  a  very  low  angle  toward  the  south-southwest,  averaging 
bout  20  feet  per  mile.  Locally  the  rocks  have  been  thrown  into 
entle  folds,  whose  axes  have  a  general  east-west  direction  and  whose 
Duth  limbs  are  long  and  gently  sloping,  while  their  north  limbs  are 
lort  and  steeper.  The  formations  represented  are  shown  on  the 
ccompanying  section,  in  which  the  approximate  average  thickness 
f  each  is  given.  The  important  deposits  of  zinc  and  lead  occur  in 
le  Galena  and  Platteville  limestones,  which  comprise  the  surface 
3cks  over  the  larger  part  of  the  region. 
Formations  of  the  Wisconsin  lead  and  zinc  region. 
Feet. 
Pleistocene:  loess  and  soil 7 
Silurian:  Niagara  limestone 50 
Ordovician  : 
Maquoketa  shale .  100 
Galena  limestone 230 
Platteville  limestone -       55 
St.  Peter  sandstone 70 
"Lower  Magnesian  "  limestone 200 
Cambrian:  "Potsdam  sandstone" 700 
The  Platteville — known  locally  as  the  Trenton — limestone  is  made 
:>  largely  of  nonmagnesian  beds,  although  in  its  lower  part  are  cer- 
in  magnesian  strata.  The  thickness  of  the  Platteville  averages  55 
et.  It  ranges  from  40  to  nearly  70  feet,  being  greatest  toward  the 
stern  part  of  the  region.     A  generalized  section  of  this  formation 
as  follows : 
Generalized  section  of  Platteville  formation. 
Feet. 
Limestone  and  shale 10-20 
■  Thin  and  undulating  bedded  very  fine-grained  limestone 15-25 
*  Heavy-bedded  magnesian  limestone  or  dolomite 15-25 
(Blue    shale 1-5 
Bull.  260—05  m 20 
