ORISKANY    AND    CLINTON    IRON    ORES    OF    VIRGINIA. 
185 
tipping  of  several  adjoining  areas.  Prof.  II.  D.  Campbell,  of  Lexington,  Va.,  kindly  gave 
E  use  of  his  geologic  maps  of  the  district,  and  in  addition  exercised  general  supervision 
mi  the  areal  work  of  Mr.  Grasty. 
\General  geology  of  the  district. — The  rocks  exposed  in  this  district  arc  of  Devonian  and 
ilurian  age,  the  ores  being  associated  with  the  uppermost  Silurian  and  basal  Devonian 
Srmations.     The  formations  are  as  follows: 
Geologic  formations  in  Oriskany  district. 
Devonian  black  shales 
Oriskany  sandstone  and  siliceous  limestone. . 
Lewistown  ("  Heldcrberg")  limestone 
Rockwood  ('  Clinton")  sfoale  and  sandstone. 
Clinch  ("Medina")  quartzite 
Thickness 
in  feet. 
1,000-2,000 
50-     250 
300-    800 
300-    GOO 
50-     150 
above  generalized  section  will  cover  the  variations  in  thickness  shown  in  different 
>f  the  district.     It  may  profitably  be  compared  with  a  carefully  measured  section 
aown  at  a  point  near  the  middle  of  the  ore-beari 
iooo  feet 
Fig. 
-Generalized  section  at  Iron  Gate,  Va. 
The  following  section  was  measured  in  1905  by  E.  O.  Ulrich  at  Iron  Gate,  Va. 
Rockwocd  ("Clinton"). 
,152 
Section  at  Iron  Gate,  Va. 
Thickness 
in  feet. 
Devonian  black  shales (?) 
fa.  Calcareous  sandstone 50 j 
b.  Siliceous  limestone,  with  many  beds  of  chert. .     54 
Oriskany \c.  Bluish-gray  limestone,  with  sandy  beds  in  up-        (209 
per  part „ 65 
Id.  Quartzitic  sandstone,  with  two  shaly  beds 4ol 
Lewistown  ("Helderberg"). Thin-bedded  shaly  limestone  shal«s 322 
,a .  Heavy  sandstone 42 
b.  Alternating  sandstone  and  shale 125 
c.  Sandstones  and  shales,  overlying  a  red  and 
white  mottled  shale;  with  a  heavy  ferrugi- 
nous sandstone  ("block  ore")  near  base 115 
Id.  Shales,  with  fossil  ore  bed  near  top 170 
Clinch  ("Medina").. Hard,  massive  white  sandstone 50 
Structure  of  the  district. — In  the  Oriskany  district  the  rocks  above  described  have  been 
hrown  into  a  series  of  parallel  folds,  trending  about  N.  35°  E.  These  folds  are  not  syni- 
netrical,  for  they  show  low  dips  (5°  to  25°)  toward  the  southwest,  while  the  northeastward 
lips  are  steep — from  60°  to  vertical,  and  sometimes  even  overturned  slightly.  After  (his 
olding  erosion  removed  the  less  resistant  beds  from  the  more  exposed  portions,  so  that  now 
he  crests  of  the  ridges  are  made  up  of  the  hard  "Clinton"  and  "Medina"  quartzites  and 
andstones,  while  the  "Helderberg"  and  Oriskany  beds  outcrop  on  the  slopes  and  in  the 
'alleys  are  covered  by  the  Devonian  shale.  These  structural  conditions,  as  will  be  seen 
ater,  exercised  a  very  marked  influence  on  the  localization  of  the  ore  bodies. 
