lkith]  IRON    ORES    IN    SOUTHERN    UTAH.  235 
(h)  There  are  no  clastic  grains  or  sedimentary  structures,  such  as 
bedding,  which  ought  to  appear  in  the  ore  if  it  is  sedimentary  or 
secondary  to  a  sedimentary  formation,  as  they  invariably  do  in  the 
Lake  Superior  ranges.  None  of  the  characteristic  banding  of  ferru- 
ginous cherts  or  jaspers,  and  none  of  the  interstratified  fragmental 
ferruginous  slates  or  paint  rock,  are  to  be  observed  in  the  deposits 
under  discussion. 
(c)  The  long,  high,  steep-sided  masses  in  which  the  ore  occurs  are 
not  characteristic  of  sedimentary  deposits,  and  there  is  no  evidence 
that  folding,  either  in  the  rocks  themselves  or  in  the  rocks  of  the 
adjacent  areas,  has  brought  about  the  present  configuration  of  the 
deposits  from  an  original  flat-lying  sediment. 
(d)  Ore  is  occasionally  in  veins  in  the  foot-wall  rock.  This  vein  ore 
has  identically  the  same  character  and  association  with  quartz  and 
apatite  as  the  ore  in  the  large  ridges  elsewhere  in  the  area,  and  there 
is  no  reason  to  believe  that  the  vein  ore  in  the  andesite  differs  in  origin 
from  that  along  the  contact  of  the  andesite  and  the  limestone.  Further, 
the  little  projections  and  stringers  of  iron  oxide  running  a  few  feet  into 
the  limestone,  as  well  as  the  apparently  isolated  masses  of  ore  a  few 
feet  from  the  contact,  are  not  characteristic  of  an  original  sedimentary 
contact. 
(e)  The  ores  follow  the  contact  of  the  limestone  and  andesite. 
There  is  no  evidence  that  this  contact  follows  any  one  horizon  in  the 
limestone;  indeed,  it  is  probable  from  the  manner  of  the  andesite 
intrusion  that  the  contact  cuts  diagonally  across  the  layers  of  the 
limestone.  If  the  ore  represents  an  original  sedimentary  formation, 
its  inclination  to  the  bedding  of  the  limestone  would  mean  an  erosion 
unconformity  between  the  limestone  and  the  ore.  Of  this  there  is  no 
evidence. 
(f)  The  ore  masses  alternately  widen  and  pinch  out  along  the  strike. 
If  they  represent  an  original  iron  formation  at  a  definite  horizon  and 
conformable  with  the  limestone,  the  horizon  ought  to  appear  in  more 
continuous  and  uniform  belts.  The  narrowing  and  widening  and  the 
discontinuity  along  the  strike  of  a  sedimentary  formation  could  be 
explained  by  an  erosion  unconformity  at  the  base  of  the  limestone, 
but,  as  above  noted,  there  is  no  evidence  of  this. 
It  is  believed  that  the  ore  is  a  secondary  replacement  and  vein 
deposit,  through  the  agency  of  percolating  water,  mainly  along  the 
contact  of  the  andesite  and  limestone,  but  with  veins  extending  into 
the  footwall  andesite,  and  perhaps  also  into  the  overlying  limestone, 
for  the  following  reasons: 
(a)  The  ore  occurs  for  the  most  part  along  the  contact  of  intrusive 
andesite  and  limestone,  a  favorable  zone  for  the  action  of  replacing 
solutions. 
(b)  The  contact  apparently  to  some  extent  cuts  diagonally  the  bed- 
