204  '  OXTRIBUTIONS    TO   ECONOMIC    GEOLOGY,  1906,  PART    I. 
of  the  pre-Cambrian  iron-ore  body  at  that  point.  Although  large 
amounts  of  this  ore  have  been  shipped,  iron-ore  float  even  now 
occurs  throughout  the  productive  portions  of  the  iron  range. 
Pebbles  of  iron  ore  are  found  in  the  bed  of  Platte  River  some  dis- 
tance below  the  town  of  Guernsey.  At  Guernsey  they  are  1  inch  or 
less  in  diameter  and  increase  gradually  in  size  upstream.  The  peb- 
bles do  not  occur  in  the  Platte  above  the  mouth  of  Hartville  Canyon, 
but  are  found  in  the  canyon  as  far  up  as  Sunrise. 
IRON    IN    OTHER    PRE-CAMBRIAN    ROCKS. 
The  jasper  of  the  second  pre-Cambrian  series  contains  at  many 
places  some  hematite  and  limonite.  Veins  of  hematite  occurring  in 
fractures  cut  it  and  irregular  masses  of  hematite  cement  its  brecciated 
fragments.  The  jasper  itself  is  also  more  or  less  replaced  by  hema- 
tite  and  limonite,  but  no  considerable  body  of  ore  has  yet  been  dis- 
covered in  it,  and  most  of  the  ore  found  in  it  is  probably  too  siliceous 
to  be  of  value.  South  of  Shaws  Pass  a  peculiar  metamorphosed  type 
of  the  pre-Cambrian  schist,  containing  a  large4  amount  of  amphibole, 
is  heavily  iron  stained.  The  matrix  of  the  conglomeratic  phase  of 
the  second  pre-Cambrian  series  contains  at  many  places  considerable 
iron,  but  none  of  the  prospects  in  such  rocks  have  yet  proved  valuable. 
DEPOSITS  ALONG  THE   FAULT  CONTACT  OF  THE  PRE-CAMBRIAN  AND  THE 
GUERNSEY  LIMESTONE. 
Along  a  line  beginning  approximately  one-hall'  mile  north  of  (iiicrn- 
sey  and  extending  eastward  across  low  hills  to  Whalen  Canyon,  the 
Guernsey  formation  and  the  pre-Cambrian  rocks  are  in  fault  contact. 
The  downthrow  n  side  of  this  fault  is  to  the  south  and  appears  to  have 
been  dropped  more  than  200  feet.  The  fault  plane  is  everywhere! 
iron  stained  and  a  number  of  prospects  are  situated  along  it.  Three 
shafts  in  the  south-central  portion  of  sec.  25,  T.  27  N.,  K.  66  W., 
owned  by  Mr.  C.  A.  Guernsey,  are  within  100  feet  of  one  another; 
The  northern  or  hanging  wall  of  the  ore  body  is  smooth,  and  the  con- 
tact between  the  ore  and  the  pre-Cambrian  limestone  is  sharp.  Far- 
ther south  the  ore  passes  gradually  into  iron-stained  Guernsey  lime- 
stone. The  iron  ore  lens,  consisting  of  good  soft  and  hard  grades,  is 
from  2  to  6  feet  wide  upon  the  surface,  and  widens  somewhat  toward 
the  west.  At  the  bottom  of  the  shafts,  which  range  in  depth  from  24 
to  60  feet,  the  lens  is  somewhat  wider  and  apparently  increases  in  thick- 
ness with  depth.  One-quarter  of  a  mile  west  of  this  locality  several 
shafts  and  tunnels  develop  other  ore  bodies  in  breccia  zones  within 
the  pre-Cambrian  limestone,  parallel  to  this  fault.  The  ore  here  is  a 
black  pulverulent  hematite  containing  considerable  calcite  and  siderite. 
The  appearance  of  the  ore  indicates  that  it  contains  manganese.     Not 
