Vol.  49.]  CRYSTALLINE  SCHISTS  OF  THE  MALVERN  HILLS. 
405 
Quartz  is  in  very  minute  proportion.  Calcite  is  abundant,  either 
in  crystalline  aggregates  enclosed  in  other  minerals,  or  forming 
venules,  which  sometimes  occupy  long  irregular  cracks,  that  also 
contain  opaque  matter  and  occasionally  epidote.  There  can  be 
little,  if  any,  dolomite  in  the  rock,  for  it  effervesces  freely  with 
acids,  and  under  the.  microscope  we  can  often  recognize  the 
polysynthetic  twinning  parallel  to  faces  of  the  rhombohedron 
—  so  characteristic  of  calcite. 
Fig.  1  (Slide  456). 
Diorite  No.  3.  The  hornblende  crushed  and  distorted,  and  the  felspar  moulded 
upon  it.  The  hornblende  is  partly  decomposed  into  chlorite,  epidote, 
calcite,  and  iron  oxide.  Unshaded  portions  are  spaces  where  the  rock 
has  been  torn  away  in  grinding. 
The  felspar  requires  special  notice.  It  is  certainly  secondary,  for 
it  is  moulded  to  the  jagged  and  frayed  edges  of  crushed  hornblende- 
crystals,  and  encloses  shreds  of  that  mineral.  It  is  also  moulded 
to  and  sometimes  encloses  chlorite  and  opaque  black  matter,  pre¬ 
sumably  iron  oxide,  both  of  which  have  been  derived  by  decompo¬ 
sition  from  the  hornblende.  The  species  of  this  felspar  cannot  be 
determined.  It  is  slightly  decomposed,  preserving  in  ordinary 
light  a  somewhat  dingy  appearance.  Here  and  there,  traces  of 
multiple  striping  are  faintly  visible  ;  but  many  of  the  forms,  though 
clear  enough  to  show  twinning,  if  it  were  present,  display  a  uniform 
colour  under  crossed  nicols. 
No.  466. — This  slide  is  from  the  rock  a  few  feet  above  that  from 
which  the  last  set  were  taken.  There  is  a  slight  approach  to¬ 
wards  a  parallel  arrangement  of  the  constituents.  All  the  horn¬ 
blende  has  disappeared.  Calcite,  epidote,  and  fragments  of  felspar 
are  scattered  in  a  groundmass  of  chlorite,  and  the  slide  is  very 
