232  CONTRIBUTIONS    TO   ECONOMIC    GEOLOGY,  1904.        [bull.  2G0. 
above  the  contact  between  the  Algonkian  and  underlying  crystalline 
schist.  As  seen  through  the  glass  it  had  the  appearance  of  an  intru- 
sive sheet,  and  the  occurrence  of  a  seam  of  asbestos  at  its  contact  with 
the  limestone  seemed  to  favor  this  idea.  Mr.  Walcott,  who  has  actu- 
ally examined  the  bed,  says,  however,  that  it  is  of  effusive  origin 
and  must  have  been  poured  out  at  the  bottom  of  the  sea.  In  either 
case  it  could  not  have  had  any  connection  with  the  ore  deposition, 
since  it  was  apparently  truncated  by  pre- Cambrian  erosion  and  the 
Tonto  (Cambrian)  beds  are  deposited  unconformable  over  its  edges. 
The  only  other  eruptives  in  the  region  are  the  effusive  basalts  of 
the  San  Francisco  Mountain,  Avhich  are  of  very  recent  origin  and 
Avere  poured  out  after  the  removal  by  erosion  of  the  Permian  cover- 
ing of  the  plateau. 
Thus  all  the  facts  I  was  able  to  determine  in  my  visit  that  bear  upon 
the  genesis  of  the  deposit  favor  the  idea  that  the  ore  has  been  leached 
down  from  above  and  is  of  secondary  origin,  rather  than  that  it  is  an 
original  deposit  from  uprising  solutions. 
As  regards  the  processes  of  deposition  which  have  prevailed  in 
these  deposits,  the  applicability  of  what  is  known  as  "  adsorption  " 
lias  recently  been  advocated  by  Dr.  Ernest  Kohler."  This  process  de- 
pends upon  a  selective  property  exercised  by  certain  clay  substances 
which  enables  them  to  separate  out  copper  from  its  dilute  solutions. 
It  has  been  practically  tested  in  the  laboratory  of  the  Survey  by  Doc- 
tor Sullivan  at  the  suggestion  of  Mr.  Waldemar  Lindgren.  Certain 
kaolin-like  clays  from  the  Clifton-Morenci  district  when  agitated 
in  a  dilute  solution  of  sulphate  of  copper  were  found  after  a  brief 
period  to  adsorb  all  the  copper  contained  in  the  solution.  Doctor 
Kohler  states  that  most  of  the  copper  deposits  in  the  Permo-Triassic 
beds  in  Europe  are  associated  more  or  less  intimately  with  finely 
divided  clays,  and  suggests  that  even  in  the  case  of  the  association 
of  copper  with  organic  remains  it  was  a  thin  film  of  clay  around 
them  that  induced  the  precipitation. 
In  the  case  of  the  Grand  View  deposits  of  the  Colorado  Canyon 
the  decomposed  limestone  in  the  chert  zone  would  seeni  to  be  of  suffi- 
cient clayey  consistency  to  have  removed  the  copper  from  dilute  per- 
colating solutions. 
°  Jour,  fur  prakt.  Geol.,  February,  1901,  pp.  49-59. 
