142  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
some  time  ago.  Both  these  shafts,  when  visited,  wen1  filled  with  water.  The  more  recent, 
on  the  R.  A.  Martin  tract,  was  sunk  to  a  depth  of  70  feet  by  Mr.  S.  M  Boyd,  of  Philadel- 
phia. It  was  worked  intermittently  during  1903  and  1904,  work  having  been  suspended 
at  the  end  of  the  latter  year.  The  older  of  the  shafts  is  situated  on  the  F.  C.  Hartley 
estate,  below  and  southwest  of  the  Boyd  shaft.  According  to  report  it  was  worked  over 
thirty  years  ago. 
At  the  mines  of  the  High  Top  Copper  Company,  near  High  Knob,  about  7  miles  south- 
east of  Elkton,  considerable  development  work  lias  be<  n  done.  In  addition  to  several 
prospects  scattered  about  the  property  a  shaft  has  been  sunk  to  a  depth  of  90  feet  and 
about  300  feet  farther  down  the  hill  a  level  has  been  run  in  about  50  £e<  t.  It  is  the  inten- 
tion of  the  company  to  sink  the  shaft  and  continue  work  in  the  level  until  the  two  intersect, 
as  well  as  to  sink  other  shafts  and  run  other  levels  on  them  on  the  company's  property  to 
the  northwest.  At  the  present  time  the  machinery  on  the  ground  aggregates  200  horse- 
power, with  compressors  and  air  drills  lor  facilitating  the  work.  It  is  the  intention  of  the 
management  to  add  largely  to  the  equipment  in  the  near  future.  Unfortunately,  at  the 
time  of  the  writer's  visit  to  the  region  (February,  1906)  the  shaft  was  Idled  with  water, 
hence  the  copper-bearing  rock  in  it  could  not  !>:■  studied. 
Occurrence. — The  ore  deposits  seen  at  all  of  these  points  are  similar  in  character.  The  ore 
usually  occurs  along  joint  planes  and  in  fissures  and  is  most  frequently  accompanied  by 
quartz.  It  may  accompany  shear  zones,  which  are  a  very  conspicuous  structural  feature 
in  the  localities  visited.  At  the  mines  of  the  Virginia  Consolidated  Copper  Company  near 
Ida,  where  development  has  reached  the  maximum  in  the  region  under  discussion,  it  was 
noted  that  these  shear  zones  correspond  to  a  system  of  joint  planes  in  the  country  rock 
varying  in  direction  within  the  limits  S.  4°  W.  and  S.  2f>°  YV.  A  similar  though  not  so  close 
a  relationship  between  the  strike  of  these  shear  zones  and  a  prominent  system  of  joints  was 
observed  at  the  property  of  the  High  Top  Mining  Company.  Usually  the  alteration  of  the 
country  rock  has  reached  its  maximum  in  close  proximity  to  these  shear  zones,  or  accompa- 
nying them.  Similar  zones  of  alteration  were  seen  at  the  Blue  Ridge  Copper  Company's 
workings  near  Fishers  (lap,  but  development  had  not  proceeded  far  enough  to  systematize 
them. 
Xear  these  shear  zones  the  country  rock  is  decidedly  epidot  ized.  Chlorite  has  also  forma 
as  well  as  quartz  and  feldspar,  an  association  in  the  case  of  the  last  two  minerals  indicating 
the  action  of  ascending  thermal  agencies.  Some  chalcopyrite  and  bornite  may  be  found 
accompanying  the  quartz  and  feldspar  The  copper  sulphides  are  not  confined  to  the  veins 
neai  or  in  these  shear  zones,  however,  but  occur  in  the  mass  of  the  basalt  as  well.  The  sum 
face  indications  in  the  region  lead  to  the  conclusion  that  the  ore  deposits  are  irregular  in| 
occurrence,  that  the  alteration  of  the  country  rock  has  been  rather  general,  and  that, 
all  hough  it  may  prove  to  be,  as  a  ride,  more  marked  along  the  major  joint  planes  and  in  the 
shear  zones,  it  also  probably  occurs  along  the  minor  joints  and  the  innumerable  cracks  in 
the  rock. 
Origin. — Besides  the  altera!  ion,  the  weathering  of  the  rocks  has  resulted  in  the  production 
of  quartz  and  calcite,  which  occur  as  fillings  along  the  joint  planes,  sometimes  as  mere  films, 
locally  swelling  into  lenticular  masses,  which  may  end  abruptly  or  zigzag  in  the  most  irreg- 
ular fashion  through  the  rock.  The  main  masses  of  copper  ore  are  found  generally  asso- 
ciated with  these  secondary  minerals  which  have  resulted  from  weathering.  This  ore  is 
in  the  form  chiefly  of  native  copper  and  cuprite,  with  small  amounts  of  malachite  and 
a zu rite.  From  their  mode  of  occurrence  these  fillings  and  lenses  are  believed  to  be  veins. 
At  the  Virginia  Consolidated  Copper  Company's  mine  they  appear  to  be  developed  on  a 
larger  scale  comparatively  near  the  surface  and  to  diminish  in  extent  with  depth.  From 
the  fact  that  the  mines  near  Ida  tend  to  become  dry  with  depth,  it  is  believed  that  the  mois- 
ture in  the  workings  is  chiefly  of  meteoric  origin  and  moreover  has  been  instrumental  in 
producing  the  main  ore  deposits.  The  disseminated  sulphides  have  probably  furnished 
much  of  the  ore,  which  has  been  segregated  along  the  fissures  and  joint  planes  in  the  rock 
