THE  BROWN  ORES  OF  THE  NEW  RIVER-CRIPPLE 
CREEK  DISTRICT,  VIRGINIA." 
By  R.  J.  Holden. 
Location.  The  New  River  Cripple  Creek  area  includes  most  of  the  limonites  of  the  vallei 
region.  The  area  in  which  ores  are  now  mined  lies  chiefly  in  the  southwestern  pari  of 
Pulaski  County  and  the  southern  part  of  Wythe  County.  It  is  a  narrow  strip  of  territory 
aboul  3  miles  wide  and  55  miles  long  and  lies  on  the  southeastern  side  of  the  Great  Valley 
near  the1  foot  of  the  mountains. 
Geology. — The  rocks  with  which  most  of  these  ores  are  associated  are  of  Cambrian  and 
Ordovician  age.  The  chief  rock  is  the  Cambro-Ordovician  limestone,  which  is  here  dolo- 
mitic  through  many  of  its  phases  and  which  contains  considerable  interbedded  red  shales. 
While  in  ;i  major  way  this  formation  conforms  to  the  structure  described  later,  in  a  minor 
way  it  is  complexly  folded  and  somewhat  faulted,  SO  that  its  thickness  is  difficult  to  deter- 
mine. Its  southeastern  horder  is  only  a  few  hundred  feet  thick,  while  toward  the  center 
of  (he  valley  it  attains  a  great  thickness.  This  formation  furnishes  the  chief  surface  rock 
of  the  valley,  which  is  here  from  6  to  12  miles  wide.  Underlying  the  limestone  is  a  Cam- 
brian quartzite  and  under  t  his  in  t  urn  a  shale.  These  latter  format  ions  ate  probably  to  be* 
correlated,  respectively,  with  the  En*  in  quartzite  and  the  Hampton  shale  of  the  (Van  berry 
folio.  They  form  the  main  portion  of  the  mountains  to  the  southeast  and  appear  in  the' 
valley  in  a  few  places  as  anticlinal  ridges. 
Structure. — Structurally  the  region  is  characterized  by  thrust  faults,  with  the  fault  planes 
dipping  to  the  southeast.  These  faults  ate  apparently  not  very  closely  spaced,  yet  are* 
sufficiently  so  to  give  to  the  strata  their  prevailing  southeastward  dip.  The  most  com 
spicuous  faults  are  those  at  the  margins  of  the  valley.  On  the  southeast  side  the  quartzite 
is  locally  faulted  over  onto  the  limestone.  On  the  northwest  side  the  limestone  is  thrust 
over  onto  the  Devonian  and  Lower  Carboniferous  sediments.  While  faulting  has  been  the 
dominant  type  of  deformation,  folding  has  not  been  unimportant.  The  Cambrian  shows  a 
number  of  anticline-,.  The  mountain  to  the  southeast  is  in  the  main  anticlinal,  as  is  also 
Lick  Mountain,  a  valley  ridge.  There  are  a  number  of  anticlinal  ridges  which  extendi 
into  the  valley  as  spurs  of  the  main  mountain.  I  lowever,  these  anticlines  show  a  tendency 
toward  faulting  on  their  northern  sides. 
Relief. — The  region  in  which  the  ore  territory  lies  is  one  of  considerable  relief.  The 
crests  of  the  ridges  are  from  500  to  1,500  feet  a  hove  the  valley  floor  and  New  River  and  its 
branches  have  cut  down  200  to  300  feet  belowr  the  general  level  of  the  valley.  The  topog- 
raphy is  controlled  by  the  rock  structure,  the  southeastward  dips  having  produced 
northeast-southwest  ridges  and  valleys.  The  exception  to  this  is  the  modifying  influence 
of  New  River,  which  is  an  antecedent  stream,  cutting  directly  across  the  trend  of  the 
mountains.  In  the  valley,  while  the  streams  have  cut  down  several  hundred  feet,  erosion 
has  cut  back  from  the  stream  courses  in  the  softer  strata,  making  the  valley  surface  a 
series  of  oval  domes. 
a  This  report  is  the  result  of  cooperative  work  carried  on  in  1!»05  by  the  Virginia  and  United  States 
Geological  Surveys,  and  is  here  presented  by  permission  of  Mr.  T.  F.  Watson,  State  geologist  of  Vir- 
ginia. The  relations  of  this  particular  area  arid  report  to  the  general  problem  are  discussed  on  pp.  183-184 
E.  C.  E. 
190 
