bain]  FLUORSPAR    DEPOSITS    OF    SOUTHERN    ILLINOIS.  511 
the  ore  bodies.  It  has  been  impossible  to  get  any  data  on  the  character 
of  the  rock  which  occurs  in  this  area  beneath  the  Chattanooga  shale. 
Normally  a  considerable  thickness  of  dolomites  and  limestones  would 
be  expected  to  be  present,  but  they  may  be  absent,  and  it  would  not 
be  impossible  that  the  supposed  igneous  mass  should  occur  below  the 
shale.  In  all  the  mines  so  far  located  in  Illinois,  the  shale  lies  500  to 
1,000  feet  or  more  below  present  workings. 
There  are  no  data  at  hand  for  predictions  as  to  change  in  character 
and  richness  of  the  ores  with  depth.  Changes  in  the  country  rock 
n:my  be  expected  to  have  an  important  influence,  and  so  far  the  Ste. 
Genevieve  and  Chester  formations  have  proved  most  favorable.  In 
the  Illinois  mines  nothing  suggesting  rearrangement  of  the  ores  and 
secondary  enrichment  coincident  with  degradation  of  the  surface  was 
observed.  The  Fairview  and  Rosielare  mines  are  now  working  well 
below  ground- water  level,  and  neither  increase  or  decrease  in  amount 
nor  change  in  character  of  the  sulphides  with  depth  was  observed.  At 
the  Empire  mine  carbonates  gave  place  to  sulphides  within  the  first 
hundred  feet,  and  below  that  level  no  change  was  observed. 
In  the  Kentucky  mines  a  number  of  deposits  of  first-grade  fluorspar 
are  said  to  have  given  out  or  lost  grade  with  depth.  The  significance 
of  this  fact  is  uncertain.  Whether  it  is  to  be  correlated  with  change 
in  wall  rock,  or  indicates  only  the  usual  irregular  distribution  of  ore 
in  depth  as  well  as  along  a  vein,  is  not  clear.  In  no  case  was  develop- 
ment carried  on  to  determine  whether  the  ore  would  come  in  again  at 
lower  levels.  If  it  be  true  that  the  diminution  in  size  of  the  ore 
bodies  was  related  to  topograph}^  rather  than  stratigraphy,  it  can  only 
be  stated  that  the  best  obtainable  evidence  in  Illinois  does  not  warrant 
the  belief  that  the  rule  is  universal.  The  character  and  size  of  the 
ore  bodies  certainly  do  not  bear  any  constant  relation  to  the  present 
land  surface. 
In  the  light  of  these  facts  and  the  wide  prospecting  which  has  been 
going  on  in  the  district,  little  encouragement  is  offered  to  the  hope  of 
finding  important  bodies  of  lead  and  zinc  on  the  northern  side  of  the 
river,  but  it  is  believed  that  the  fluorspar  deposits  afford  the  basis  for 
an  important  and  growing  industry. 
