416  DR.  c.  CALLAWAY  ON  THE  ORIGIN  OE  THE  [Aug.  1 893, 
‘  Yes’ ;  but  where  the  maximum  of  metamorphism  has  taken  place, 
I  should  sometimes  be  obliged  to  reply  in  the  negative.  Take  the 
sericite-schists  of  Bagged  Stone  Hill.  Some  of  these  schists  are 
formed  from  diorite,  some  from  felsite.  Yet,  under  the  microscope, 
both  are  sometimes  seen  to  consist  of  apparently  1  the  same  mate¬ 
rials  arranged  in  a  similar  manner.  The  presence  of  a  small  pro¬ 
portion  of  iron  oxide  and  epidote  or  chlorite  does  not  help  us,  for 
those  minerals  are  sometimes  infiltrated  into  the  shear-planes  of  the 
felsite.  The  schist  produced  from  diorite  is  often  more  or  less 
veined  with  calcite,  which  is  not  the  case  with  the  other  variety ; 
but  slides  of  the  former  sometimes  show  hardly  any  calcite.  How¬ 
ever,  even  in  the  perfectly  formed  schist,  there  is  often  a  residuum 
of  the  shearing-process  in  the  form  of  a  crystal  or  fragment  of 
felspar,  crushed,  and  tapering  at  each  end  in  water-clear  mosaic. 
This  would  seem  to  mark  an  origin  from  diorite,  for  the  felsite  of 
the  locality  never  contains,  so  far  as  the  writer  has  observed,  a 
porphyritic  crystal  of  felspar. 
The  case  just  selected  is  an  extreme  one,  in  so  far  as  Malvern  is 
concerned.  I  do  not  think  there  is  any  other  schist  in  the  district 
which,  in  a  hand-specimen  or  a  micro-slide,  cannot  be  referred  to 
its  origin.  A  few  of  the  chief  types  will  be  taken  in  illustration. 
Banded  Biotite-gneiss. — The  granite-veins  are,  of  course,  easily 
recognizable.  The  micaceous  seams  also  usually  betray  signs  of 
their  dioritic  origin.  There  may  he  slides  in  which  most  of  the 
felspar  has  been  invaded  by  water- clear  granules,  and  in  which  the 
mica  is  arranged  in  parallel  seams ;  but  a  large  proportion  of  the 
specimens  examined  contain  patches  of  the  kersantite-structure 
which  have  resisted  the  metam orphic  forces.  In  these  patches  very 
little  quartz  has  been  generated,  and  the  crystals  of  biotite  are 
sprinkled  among  the  felspars  just  as  in  the  kersantite  formed 
directly  from  diorite  (Ho.  II.,  pi.  xvi.  fig.  1). 
Simple  Biotite-gneiss. — The  structure  of  the  original  diorite  is 
fairly  evident,  the  place  of  the  hornblende  amidst  the  felspar- 
crystals  being  taken  by  biotite,  and  the  felspar  being  more  or  less 
invaded  by  quartz. 
Muscovite- gneiss  formed  from  Granite. — This  variety  often  shows 
the  4  eyes  ’  of  orthoclase  so  well  seen  in  the  aw/eft-gneisses,  de¬ 
scribed  by  Lehmann,  Lapworth,  Bonney,  Teall,  and  others.  Where 
these  are  absent,  the  rock  may  usually  be  differentiated  from  similar 
rocks  which  have  been  formed  from  diorite  by  the  absence  of  plagio- 
clase-felspar  and  of  any  trace  of  diorite-structure. 
Chlorite-gneiss. — The  remarks  of  the  last  paragraph  will  apply 
here,  the  infiltrated  films  of  chlorite  being  interfoliated  with  the 
other  minerals. 
Gneissoid  Quartzite. — I  should  have  little  hesitation  in  recognizing 
the  derivation  of  this  rock  within  the  Malvern  area.  The  marks  of 
origin  are  the  presence  and  arrangement  of  scraps  of  biotite,  the 
1  Quartz  and  felspar  being  undistinguishable  when  in  minute,  water-clear 
granules. 
