bain.]  LEAD   AND    ZINC    RESOURCES    OF    UNITED    STATES.  269 
In  Virginia  the  important  producing  mines  of  recent  years  have 
been  the  Bertha,  situated  about  30  miles  southwest  of  Pulaski;  the 
Wythe,  at  Austinville,  and  the  Clark,  at  Allisonia.  Of  these  the 
Wythe  only  is  now  producing  zinc.  The  Bertha  is  being  worked 
for  iron.  In  Tennessee  the  mines  are  near  Knoxville,  McMillan, 
Mascott,  Newmarket,  Jefferson  City,  and  New  Tazewell.  They  have 
been  described  by  Mr.  Keith." 
The  Virginia  deposits  have  never  been  described  in  detail,  though 
Boyd,''  McCreath,c  Kemp,fZ  and  Ingalls  e  have  each  published  gen- 
eral notes  upon  the  district  and  many  briefer  references  are  to  be 
found.  These  are  mainly  cited  by  Kemp.  A  report  upon  the  dis- 
trict is  now  being  prepared  by  State  Geologist  Watson,  who  has 
kindly  furnished  in  advance  the  following  notes: 
The  ores  occur  in  the  Shenandoah  Valley  in  a  magnesian  limestone 
of  Cambro-Ordovician  age.  In  Virginia  from  Roanoke  to  Scott 
County  this  formation  contains  scattered  bodies  of  lead  and  zinc. 
The  ores  first  worked  were  residual  concentrations  made  up  of  cala- 
mine, with  minor  amounts  of  cerussite  and  smithsonite.  At  the 
Bertha  mine  they  are  covered  by  a  heavy  mantle  of  residual  clay, 
which  is  now  washed  for  the  sake  of  the  limonite  which  it  contains. 
Blende  is  found  in  irregular  deposits  in  the  underlying  limestones 
and  here,  as  elsewhere,  is  presumed  to  represent  the  original  mode  of 
occurrence.  The  Wythe  deposit  is  the  most  important  of  those  yet 
developed  in  the  sulphide  zone. 
In  Tennessee  the  ore  occurs  in  the  Knox  dolomite,  which  represents 
a  portion  of  the  Shenandoah,  particularly  near  the  base  and  at  the 
contact  with  the  underlying  Conasauga  shale.^  It  is  associated  with 
fault  planes  and,  as  in  Virginia,  the  lean  sulphides  seem  to  have  been 
reconcentrated  in  the  form  of  carbonates  and  silicates. 
The  district  as  a  whole  has  not  been  acth^ely  prospected,  though 
considerable  ore  has  been  shipped  and  prospecting  is  now  going  on  at 
several  points.  In  considering  its  relations  to  possible  future  produc- 
;ion  its  favorable  situation  as  regards  high-grade  fuel,  low  labor  cost, 
ind  ease  of  transportation  of  product  to  the  seaboard  must  not  be  lost 
sight  of. 
The  Albemarle  County,  Va.,  occurrence  of  lead  and  zinc  now  being 
xploited  is  particularly  interesting.  The  deposit  occurs  in  mica- 
schist  of  probably  pre-Cambrian  age  and  near  a  diorite  dike  of  pre- 
sumably more  recent  age.     During  the  civil  war  it  was  worked  for 
"  Keith,  Arthur,  Recent  zinc  mining  in  East  Tennessee  :  Bull.  U.  S.  Geol.  Survey  No. 
>25,  pp.  208-213. 
"Boyd,  C.  R.,  Resources  of  Southwest  Virginia,  1881,  321  pp. 
f  McCreath,  A.  S.,  Mineral  Wealth  of  Virginia,  1884,  pp.  101-103. 
rfKemp,  J.  F.,  Ore  Deposits  of  the  United  States  and  Canada,  1903,  pp.  247-24!). 
I     e  Ingails,  W.  R.,  Production  and  Properties  of  Zinc,  1902,  pp.  197-203. 
f  See  Morristown,  Maynardsville,  and  Cleveland  folios,  U.  S.  Geol.  Survey. 
