GILA    RIVER    ALUM    DEPOSITS.  223 
have  been  observed  within  the  area  of  the  alum  basin.  A  few  miles 
distant  up  Gila  Canyon  hot  springs  occur  at  three  separate  points. 
No  analyses  of  the  waters  from  these  springs  are  available,  but  they 
show  no  evidence  of  being  highly  mineralized.  The  only  deposit  at 
these  vents  is  a  very  slight  incrustation  of  the  rocks  over  which  the 
waters  flow,  and  this  is  apparently  silica.  Their  presence,  therefore, 
near  the  breccia-filled  volcanic  vent  is  probably  without  significance. 
UTILIZATION. 
In  Ins  paper  on  these  deposits  Blake  states  that  the  residual  rock 
from  which  the  soluble  sulphates  have  been  leached  consists  essen- 
tially of  hydrated  aluminum  oxide  or  bauxite.  The  analyses  given 
on  page  219  do  not  indicate  the  presence  of  free  aluminum  oxide,  but, 
on  the  contrary,  show  that  the  residual  rock  is  essentially  the  silicate 
of  aluminum,  having  approximately  the  composition  of  kaolin.  The 
value  of  the  deposits  will  therefore  depend  on  the  utilization  of  the 
soluble  sulphates  which  they  contain.  The  present  surface  accumu- 
lations of  alunogen,  though  probably  amounting  to  many  hundreds 
or,  more  probably,  thousands  of  tons,  represent  bui,  an  insignificant 
quantity  compared  with  the  sulphates  still  in  the  rock.  Wherever 
observed  the  rock  is  highly  porous,  and  the  extent  of  its  porosity 
represents  the  amount  of  material  removed.  In  the  higher  and  more 
exposed  ledges  the  rock  is  thoroughly  leached  and  will  yield  nothing 
more.  At  lower  levels  the  rock  still  contains  a  part  of  its  soluble 
constituents,  which  are  coming  to  the  surface  by  the  capillary  circu- 
lation of  surface  waters.  The  extent  of  this  loss  is  shown  in  tunnel 
No.  2,  where  the  average  annual  accumulation  of  halotrichite  is  about 
half  an  inch.  No  test  has  been  made  of  the  rock  below  drainage  level, 
but  it  is  probable  that  here,  where  there  has  been  no  opportunity  for 
leaching,  will  be  found  the  largest  amount  of  soluble  constituents. 
Since  tins  deposit  presents  so  many  unique  characteristics,  it  is 
hazardous  to  venture  a  prediction  as  to  its  future  utilization.  New 
methods  of  mining  and  treatment  must  be  devised  to  meet  the  pecul 
iar  conditions,  and  success  will  depend  largely  on  the  skill  with 
which  the  problem  is  handled.  That  there  exists  here  an  almost 
unlimited  supply  of  aluminum  sulphate  appears,  however,  certain, 
and  in  view  of  the  rapidly  growing  demand  for  this  substance  in  the 
arts,  in  sanitary  engineering,  and  as  a  source  of  the  metal,  there  is 
little  question  that  the  supply  will  in  time  be  fully  utilized.  The 
essentials  for  such  utilization  appear  to  be  transportation  facilities 
and  chemical  engineering  skill. 
