270 
CONTRIBUTIONS    TO    ECONOMIC    GEOLOOY,    l'HMJ,   PART    I. 
Table  1. —  Mint  nils  likely  to  be  found  in  fuller's  earth     Continued. 
CLAY  MINERALS. 
Name. 
Kaolin. 
Pholeritc . 
Hailoysite. 
RectoVitc. . 
Newtonite . 
Allophane . 
Smectite . . 
Specific 
gravity 
2.60 
2.00 
2.40 
1.90 
Malthacite 
Passau     porcelain 
clay. 
RazoumotTskinc  . . . 
Montmorillonite  . . . 
ne£?~  Crystallization. 
Effect  of  acids. 
2.00     Monoclinic Insoluble  in  HC1;  decomposed  by 
ll,s<>,. 
2.  00    do Insoluble  in  HNOj 
Amorphous Decomposed  by  acids 
Monoclinic 
Rhombohedral 
3.00      Amorphous Soluble  in  dilute  acids 
Author 
it  v." 
Pyrophyllite . 
Ahauxite. 
Cimolite 
<  !lagerite 
Koilvrite 
Not  decomposed  by  HC1;  decom- 
posed by  IbjSn,. 
2.90       i.  ."(I     Monoclinic Not  decomposed  by  HjSO< 
>sed  by  all  acids  and  1 1  _■<  > 
A.  IS. 
Name 
Formuli 
(  omposil  ion. 
Silica.     Alumina.    Water. 
Kaolin UjOa.2SiOj.2HjO 
Pholerite 2Alj(  »s.3Si«  >j,4Hj<  > 
Hailoysite Uj0».2Si0«.3Hj0 
Rectorite UjO».2SiOj.HjO 
Newtonite Uj0j.2Si0j.5Hj0 
AJlophane \\ ■■<  >8.Si<  >j.5Hj<  I 
I  ite 
Malthacitc 
Passau  porcelain  clay 
Ka/.oimioiTskinc 
Montmorillonite  .... 
Pyrophyllite 
Anauvitc 
Cimohte 
-  ite 
Kollyrite .  3  UjO   BiOj  9HjO. . 
Schrotterite 
\l,().t.7Si<).J.l,|-_'ll,(» 
Uj0j.7Si0j.ll6Hj0 
A  UjO«.9SiOj.ljl2HjO 
VijOj  4Si< »   T 1 1  ■<  I 
1  '.  3Hj(  i 
.  ...  HjO 
UjOs.4SiOj.3HjO 
2AljOj  9Si(  li  6HjO 
2  UjOi  38iOj  6HjO 
12.0 
4< i.  3 
36  2 
■  v     Eakle,  A.  S.,  Mineral  rabies    L904.     B    Comey,  I.  M.,  Dictionary  of  Solubilities,  1896. 
When  the  rocks  From  which  fuller's  earth  is  derived  are  kepi  in 
view,  ii  seems  to  me  thai  the  inference  may  be  fairly  drawn  thai  it 
results  from  the  decomposition  of  the  hornblendes  and  augites,  rather 
than  of  the  feldspars,  as  is  the  case  with  ordinary  clays.  This  view 
is  also  supported  by  the  fact  thai  magnesia  is  almost  invariably  a 
prominent  constituenl  of  fuller's  earth,  in  which  it  averages  much 
higher  than  in  ordinary  clays.     (See  Table  2.) 
Now,  it  is  well  known  that  the  decomposition  of  the  feldspars  tends 
toward  the  production  of  kaolin  and  the  crystalline  aluminum  hydro- 
silicates,  and  it  seems  possible  that  the  hornblendes  and  augites,  on 
the  other  hand,  may  have  a  tendency  to  decompose  into  the  amor- 
phous silicates.  I  will  endeavor  to  show  later  that  fuller's  earth 
contains  these  amorphous  aluminum  hydrosilicates,  and  if  the  truth 
of  this  theory  could  be  proved  much  light  would  be  thrown  on  the 
whole  question  of  the  origin  of  fuller's  earth  and  its  relation  to  the 
clays. 
The  literature  on  this  subject  is  so  fragmentary  and  so  widely  dis- 
tributed that  references  having  a  direct  bearing  on  it  are  difficult  to 
