Yol.  49.]  CRYSTALLINE  SCHISTS  OE  THE  MALVERN  HILLS.  415 
Survey  regard  those  observed  by  them  in  the  Highlands  as  segrega¬ 
tions  and  of  contemporaneous  origin. 
6.  The  view  expounded  in  the  present  series  of  papers.  It 
approximates  to  the  preceding  explanation,  but  concludes  that  the 
veins  are  intrusive  and  posterior.  How  far  this  theory  applies  to 
regions  outside  Malvern  the  writer  does  not  presume  to  suggest. 
7.  There  are  suggestions  in  the  preceding  pages  and  in  Ho.  II. 
that  segregation  during  the  shearing-process  has  sometimes  pro¬ 
duced  a  banded  structure. 
Gneissoid  Quartzite. — There  is  not  much  to  add  to  the  explana¬ 
tion  of  the  origin  of  this  rock  given  in  Ho.  II.  (pp.  485,  486).  I 
there  stated  that  it  was  an  extreme  phase  of  alteration  in  diorite. 
Since  it  is  formed  from  the  gneiss  just  described,  I  have  included 
it  under  ‘  injection-schists,’  although  I  by  no  means  affirm  that 
injection  is  necessary  to  its  production.  It  is  not  very  conspicuous 
at  Malvern,  occurring  only  (so  far  as  I  know)  in  a  few  narrow 
bands  near  the  southern  end  of  Swinyard’s  Hill.  Sometimes  it  con¬ 
stitutes  small  patches  and  seams  in  the  biotite-gneiss,  and  wherever 
I  have  seen  it  there  is  a  gradation  between  it  and  the  gneiss.  In  it 
the  biotite  has  almost  disappeared,  muscovite  is  in  equally  small 
proportion,  and  we  have  little  left  but  dull-looking  felspar-crystals 
invaded  by  rounded  granules  of  quartz  or  water-clear  felspar,  or 
entirely  replaced  by  them.  As  there  is  little  parallelism  of 
structure,  the  rock  approximates  to  a  rather  felspathic  quartzite. 
Indeed,  it  is  very  similar  under  the  microscope  to  the  rock  which 
in  Connemara  has  been  usually  described  as  a  ‘  quartzite.’ 
This  theory  of  the  origin  of  the  Swinyard’s  Hill  quartzite  receives 
important  confirmation  from  a  paper 1  by  Mr.  W.  S.  Bayley,  of  the 
Geological  and  Hatural  History  Survey  of  Minnesota.  Mr.  Bayley 
concludes  that  a  certain  quartzite  of  the  Animikie  group,  “  though 
a  completely  crystallized  quartzite,  is  nothing  more  nor  less  than  an 
extreme  phase  of  gabbro,”  or  “  a  completely  altered  gabbro.” 
This  rock  will  be  again  considered  under  Section  YIII.  of  the 
present  paper. 
( b )  Schists  of  Secondary  Injection. 
These  are,  I  suspect,  rather  common  at  Malvern,  but  sections  in 
which  the  process  of  infiltration  can  be  demonstrated  are  rare.  In 
Ho.  II.  (p.  496)  I  referred  to  a  shear-zone  at  the  Wych,  in  which 
a  chlorite-gneiss  was  formed  by  the  infiltration  of  chlorite  (and  iron 
oxide)  from  a  decomposed  diorite  into  the  cracks  and  shear-planes 
of  an  adjacent  mass  of  granite.  The  mineralogical  changes  were 
then  briefly  described,  but  the  limits  of  the  present  paper  preclude 
fuller  details. 
Y.  HOW  EAR  THE  SCHISTS  INDICATE  THEIR  ORIGIN. 
Is  it  possible  among  the  Malvern  rocks  to  determine  the  origin  of 
a  schist  from  its  structure  and  composition  ?  The  answer  is  usually 
1  Nineteenth  Annual  Beport,  Geol.  &  Nat.  Hi&t.  Surv.  Minnesota,  1892. 
