130  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  Lbull.225. 
quartz  and  the  encompassing  schist  are  heavily  impregnated  with 
pyrite,  which  at  the  surface  is  completely  oxidized.  The  ore  is 
1  rented  in  a  stamp  mill  and  amalgamates  readily. 
Besides  these  gold-bearing  lodes,  deposits  of  tin  occur  in  rocks  of 
Algonkian  age,  notably  in  the  southern  portion  of  the  hills  and  in  the 
region  to  the  west  of  Spearfish  Canyon,  known  as  Nigger  Hill.  The 
country  rock  in  which  these  deposits  occur  is  apparently  a  coarse 
muscovite-granite,  and  the  cassiterite  or  tin  oxide  is  scattered  through 
this  rock  in  irregular  patches,  increasing  and  decreasing  in  amount 
with  little  or  no  regularity.  At  the  time  of  survey  none  of  the  deeper 
workings  were  accessible.  In  the  earlier  days  of  mining  in  the  Black 
Hills,  the  tin  ore  attracted,  as  is  well  known,  considerable  interest, 
but  the  unfortunate  character  of  the  enterprises  which  were  connected 
with  its  exploitation  have,  much  retarded  its  development.  The  cas- 
siterite occurs  also  in  placers  as  stream  gravels  which  have  beer 
derived  from  the  disintegration  of  the  country  rock  containing  the  tin, 
The  cassiterite  in  these  gravels  is  but  little  rounded,  and  differs  in  ith 
black  color  from  the  usual  reddish-brown  type  of  stream  tin  so  com 
monly  found  in  the  vicinit}^  of  tin-bearing  lodes. 
A  few  small  prospects  of  copper  have  been  found  at  different  place* 
in  the  schist  areas  of  the  northern  Hills,  but  the}r  have  not  yet  provec; 
of  sufficient  size  or  regularity  to  attract  serious  attention. 
MISCELLANEOUS    DEPOSITS    IN    THE    ALGONKIAN    ROCKS. 
At  several  localities  within  the  productive  mining  region  ores  hav<| 
been  found  which  may  proper ly  be   described  with  the  Algonkiarl 
lodes.     They  are  partial^  in  eruptive  rocks  and  partially  in  brecciateol 
material  composed  of  schist  and  porphyry,  while  at  times  they  fornl 
veins  which  pass  from  schist  into  porphyry;  at  other  points  tney  pasl 
from  porphyry  into  Cambrian  rocks.     While  none  of  these  have  ye  I 
attained  any  great  importance,  there  are  two  that  deserve  special  men  j 
tion.     The  first  is  in  Strawberry   Gulch,   where  a  large  number  of 
small  mines  have  been  intermittently  worked.     Much  of  the  ore  occur 
in  a  decomposed  porphyry  in  the  form  of  thin  auriferous  limonite  fill 
ings  in  small  fractures,  or  of  impregnations  in  the  country  rock.     I 
general,  these  pass  downward  into  unoxidized  pyrite,  while  in  a  fell 
cases  sphalerite  and  galena  have  been  reported.     The  porphyry  masi 
in  which  these  ores  are  found  is  extremely  large  and  so  irregularif 
intruded  into  the  schists  that  its  relation  to  them  can   not  readily  b 
made  out.     Some  of  the  ore  obtained  from  the  mines  is  reported  1 1 
have  been  very  rich,  but  it  has  so  far  been  too  irregular  in  its  occuij 
rence  to  form  the  basis  of  extensive  mining.     The  second  locality  wherl 
ore  has  been  found,  which  is  chiefly  in  porphyry,  is  the  Old  Ironside 
mine,  near  the  mouth  of  Squaw  Creek.     Here,  at  the  side  of  the  creek,  if 
