236  CONTRIBUTIONS    TO    ECONOMIC    OEOLOGY,   1903.  [bull. 225. 
ding  of   the  limestone,  and  there  is  no  evidence  of  an  erosion  uncon- 
formity. 
(c)  There  is  a  generally  sharp  surface  of  demarcation  between  the 
ore  and  the  wall  rocks,  and  especially  between  the  ore  and  the  andesite. 
This,  together  with  the  absence  of  minerals  of  igneous  origin,  shuts 
out  suggestion  of  magmatic  segregation. 
(d)  The  lenticular  shape  of  the  ridges  of  ore.  The  sides  are  usually 
monoclinal  and  steeply  inclined.  In  other  words,  the  shape  is  char- 
acteristic of  contact,  and  vein  deposits.  At  the  narrow  ends  the  vein 
aspect  is  especially  noticeable.  There  is  no  evidence  that  folding  or 
other  secondary  deformation  has  had  an}Tthing  to  do  in  developing  the 
present  configuration  of  the  deposits. 
The  existence  of  veins  of  ore  within  the  andesite,  the  comb  structure 
to  be  observed  where  the  ore  is  associated  with  apatite  in  such  veins, 
the  prevalence  of  mammillary  forms,  and  the  intimate  association  with 
chalcedonic  and  vein  quartz,  might  point  to  original  deposition  of  the 
iron  ore  in  this  form  from  percolating  solutions  or  to  recrystallization 
and  alteration  of  a  previously  deposited  iron  compound.  From  analogy 
with  other  western  contact  and  vein  deposits  it  may  be  suggested  that 
the  original  deposit  may  have  been  an  iron  sulphide.  No  evidence  of 
the  preexistence  of  iron  sulphide  has  yet  appeared,  although  it  may 
develop  at  considerable  depth.  It  may  be  further  suggested,  from 
analogy  with  other  districts,  that  if  sulphides  should  appear  with  depth 
the  sulphides  of  metals  other  than  iron  may  in  time  give  the  property 
its  chief  value. 
The  ores  here  described  have  points  of  similarity  to  iron  ores  at 
Fierro,  N.  Mex.,  at  Iron  Mountain,  Mo.,  in  various  parts  of  Mexico, 
and  in  southeastern  Cuba.  It  is  interesting  to  note  that  explanations 
similar  in  certain  respects  to  those  above  given  have  been  presented 
by  R.  T.  m\\a  for  the  Mexican  deposits  and  by  J.  P.  Kimball6  for 
the  Cuban  deposits. 
The  above  discussion  offers  no  explanation  of  the  ultimate  source  of 
the  iron.  One  first  thinks  of  the  surrounding  limestone  and  andesite, 
and  of  the  masses  of  these  and  other  rocks  which  have  been  removed 
from  above  by  erosion,  and  then  of  rocks  far  beneath  the  surface. 
Neither  the  limestone  nor  andesite  contain  a  large  percentage  of  iron 
to  contribute  to  percolating  waters,  although  it  is  difficult  to  say  how 
small  a  percentage  of  iron  in  rocks  might,  during  a  long  geologic 
period,  furnish  sufficient  iron  to  account  for  the  observed  deposits. 
Partial  analyses  of  the  limestone  are  given  below.  Analyses  1  and  2 
are  by  George  Steiger  and  analysis  3  by  Lerch  Bros. 
a  Hill,  R.  T.,  The  occurrence  of  hematite  and  martite  iron  ores  in  Mexico:  Am.  Jour.  Sci.,  3d  series, 
vol.  45,  1893,  p.  111. 
b Kimball,  J.  P.,  Geological  relations  and  genesis  of  the  specular  iron  ores  of  Santiago  de  Cuba: 
Am.  Jour.  Sci.,  3d  series,  vol.  28,  1884,  p.  416;  also,  The  iron  ore  range  of  the  Santiago  district  of  Cuba: 
Trans.  Am.  Inst,  Min.  Eng.,  vol.  13,  p.  613;  Eng.  Min.  Jour.,  Dec.  20,  1884,  p.  409. 
