186  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
Occurrence  of  the  ores. — The  iron  ores  of  this  district  are  brown  ores,  occurring  in  bed- 
shaped  deposits,  continuous  in  length  on  the  outcrop  for  considerable  distances. 
The  ore  bodies  usually  outcrop  on  the  southeast  flanks  of  the  ridges,  from  200  to  400  feei 
above  the  valley  bottoms.  Near  the  outcrop  they  are  overlain  either  by  sandstones  o: 
Oriskany  age  or  else  directly  by  the  Devonian  black  shale.  They  are  immediately  underlaii 
in  most  cases  by  a  bed  of  cherty  clay,  which  in  turn  rests  upon  "Clinton"  sandstone  Oi 
shale.  As  the  ore  bodies  are  followed  deeper  it  is  found  that  they  thin  somewhat  and  tha 
limestone  appears  in  one  or  both  walls  of  the  deeper  workings.  It  is  to  be  expected  tha 
finally  the  ores  will  entirely  disappear  in  depth,  their  place  being  taken  by  continuous  bedi 
of  limestone. 
When  for  any  reason  the  Lewistown  ("llelderberg")  limestones  appear  in  several  paralle 
outcrops,  the  ore  bodies  are  likely  to  be  similarly  duplicated. 
At  the  lower  or  southwest  end  of  the  Dolly  Ann  property  "northeast  of  Covington,  fo 
example,  the  ore  beds  are  seen  to  occur  in  three  parallel  synclinal  basins,  thus  giving  si: 
distinct  lines  of  outcrop  of  the  ore.  Farther  northeast  only  the  easternmost  of  these  basin 
persists,  the  other  two  dying  out  owing  to  cross  folding.  Similarly,  to  the  southwest  tfo 
easterly  basin  is  cut  off  by  limestone  near  Jackson  River,  but  occurs  again  south  of  th 
river,  while  the  two  westerly  basins  are  cut  off  some  distance  north  of  the  river  and  do  no 
reappear.  The  ore  in  this  area  varies  from  3  to  32  feet  in  thickness,  probably  avcragin: 
about  12  feet  over  the  entire  property.  It  lies  on  a  foot  wall  of  loose  chert  or  cherty  clay 
which  is  usually  about  1  foot  thick,  but  in  places  5  to  6  feet.  In  most  of  the  openings  th 
ore  is  capped  by  10  to  20  feet  of  yellow  sandstone,  which  is  in  turn  overlain  by  the  blac. 
Devonian  shale. 
Opposite  the  company  store  the  remains  of  the  old  Dolly  Ann  furnace  stand  on  an  or 
bank  which  shows  the  following  section: 
Section  at  ore  bank  near  Covington,  Va. 
Feet. 
Pebbles,  gravels,  etc 6 
Bluish  to  black  shale 4 
Yellow-brown  crumbling  sandstone 18 
Brown  ore 10  + 
Origin  of  the  ores. — The  Oriskany  ores  have  been  usually  described  as  being  original  depof 
its  or  as  having  originated  through  the  weathering  and  hydration  of  carbonates  which  wei 
deposited  with  the  limestones  and  sandstones  that  now  inclose  the  brown  ores. 
In  the  final  report  on  these  ores  the  question  of  origin  will  be  taken  up  in  some  detail  an 
the  reasons  for  the  writer's  conclusions  will  be  stated  more  fully.  Here  it  is  possible  onl 
to  state  the  main  results  briefly. 
The  workable  ores  are  undoubtedly  of  much  later  origin  than  the  rocks  which  no 
inclose  them;  and  the  ore  deposits  occupy  spaces  formerly  filled  by  Lewistown  and  OriskaJ 
limestones  and  sandstones. 
There  seems  to  be  little  reason  to  believe  that  much  of  the  ore  lias  originated  by  tr 
replacement  of  limestone  by  iron  carbonates  and  the  subsequent  hydration  of  this  carbonai 
It  is  true  that  iron  carbonate  has  been  found  at  several  points  in  the  deeper  portions  • 
the  Longdale  mines  and  it  may  be  found  in  other  mines  of  the  district.  But  in  gener 
it  seems  certain  that  the  ore  was  deposited  directly  as  brown  hematite.  The  depositic 
was  in  part  simply  a  filling  of  cavities  in  the  limestone,  but  most  of  the  deposition  piobah 
followed  the  solution  of  the  limestone  so  closely  as  to  amount  practically  to  a  replaccmei 
process. 
Character  of  the  ores. — The  ores  usually  range  from  32  to  36  per  cent  of  metallic  ire 
and  are  commonly  very  high  in  silica. 
An  analysis  of  the  Dolly  Ann  ore,  by  H.  L.  Morris,  follows.  It  is  typical  of  the  mated 
shipped  to  Lowmoor  furnace,  and  is  fairly  representative  of  the  Oriskany  ores  in  genera 
