grant.]  ZINC    AND    LEAD    OF    SOUTHWESTERN    WISCONSIN.  307 
About  40  feet  above  the  base  of  this  member — No.  1 — of  the  Galena 
is  a  layer,  1  foot  to  3  feet  in  thickness,  which  carries  numerous  re- 
mains of  Receptaculites  oweni  Hall,  known  locally  as  "  the  sun- 
flower coral  "'  or  "  the  lead  fossil."  Closely  connected  with  this  hori- 
zon, which  marks  the  top  of  No.  1  of  the  above  section,  are  the  first 
of  the  flinty  nodules  and  layers  which  are  so  common  in  No.  2  of  this 
formation. 
THE  ORE  DEPOSITS. 
The  ores  consist  of  galena,  sphalerite,  smithsonite,  and  iron  sul- 
phide; the  last  usually  in  the  form  of  marcasite.  The  ore  deposits 
occur  (1)  in  cracks  or  irregular  openings,  (2)  in  apparently  brec- 
ciated  or  very  porous  parts  of  the  Galena  limestone,  and  (3)  in  small 
particles  in  certain  layers  of  rock.  The  first  class  of  deposits  are 
known  as  crevice  deposits,  the  second  as  honeycomb  deposits,  and  the 
third  as  disseminated  deposits.  These  three  types,  are  frequently 
well  defined,  though  at  other  times  they  grade  into  one  another  and 
can  not  be  regarded  as  genetically  distinct. 
The  crevice  deposits  are  the  most  important.  In  the  upper  half 
of  the  Galena  limestone  these  deposits  commonly  exist  in  vertical 
crevices,  which  are  enlarged  to  small  caves  along  certain  beds  of  rock. 
On  the  walls  of  such  caves  the  ore  frequently  passes  into  honeycomb 
deposits,  which  consist  of  apparently  brecciated  or  semibrecciated 
porous  rock,  the  fragments  of  which  are  surrounded  by  ore.  The 
Hazel  Green  mine,  near  the  town  of  Hazel  Green,  furnishes  a  good 
example  of  the  crevice  deposits  in  the  upper  half  of  the  Galena  lime- 
stone. Deeper  down  in  this  limestone  the  crevices  commonly  become 
inclined  and  also  run  horizontally  along  bedding  planes.  These 
inclined  and  horizontal  crevices  carrying  ore  form  the  well-known 
flats  and  pitches  of  the  Upper  Mississippi  Valley  lead  and  zinc  dis- 
:rict.  The  flats  and  pitches  are  especially  well  developed  in  the 
ower  member  of  the  Galena  limestone  and  in  the  lower  half  of  the 
lext  overlying  member.  At  times  flats  of  ore  are  found  running 
3ack  from  the  foot  wall  of  the  pitch  on  either  side  of  a  deposit,  thus 
mriching  large  blocks  of  ground  so  much  that  the  whole  can  be  sent 
:o  the  concentrating  mill.  The  Hoskins  and  the  Kennedy  mines, 
lear  Hazel  Green,  and  the  Enterprise  mine,  at  Platteville,  are  types 
jf  ore  bodies  in  which  the  additional  flats  just  mentioned  occur. 
Large  flats  at  times  occur  in  and  just  above  the  main  oil-rock  horizon, 
such  deposits  consisting  frequently  of  a  combination  of  the  crevice 
tnd  the  disseminated  deposits.  Such  flats  also  exist  in  connection 
lith.  another  layer  of  oil-rock  material  in  the  upper  part  of  the 
latteville  limestone  just  below  the  glass-rock  horizon.  About 
odgeville  (Williams  mine),  as  described  on  pages  313-314,  and  at 
inden  (Mason  mine)  these  flats  are  well  developed. 
