422 
DR.  C.  CALLAWAY  ON  THE  ORIGIN  OF  THE  [Aug.  I  893, 
IX.  Secondary  Consolidation. 
One  difficulty  which  hinders  the  acceptance  of  the  new  views  of 
metamorphism  at  Malvern  is  the  sound  condition  of  the  gneissic 
rocks.  It  is  unnecessary  to  repeat  here  what  I  have  said  in  Sec¬ 
tion  III.  on  decomposition  and  reconstruction.  Most  of  the  minerals 
of  the  gneiss  are  sound  and  clear,  because  they  were  newly  formed 
during  the  metamorphism,  and  have  not  since  been  crushed.  Their 
reconstruction  involves  a  more  or  less  complete  fusion  of  the  rock. 
This  is  a  demonstrable  fact  where  the  fragments  of  crushed  felspar 
are  squeezed  out  into  lenticles  and  coalesce  with  each  other,  as  in 
the  sericite-gneiss  of  .Ragged  Stone  Hill  (p.  411),  and  is  a  matter 
of  fair  inference  wherever  there  is  a  clear  passage  between  crushed 
diorite  and  a  sound  gneiss. 
X.  Summary. 
It  will  be  convenient  to  bring  together  the  chief  results  of  my 
live  years’  work  at  Malvern,  as  expounded  in  the  present  series  of 
papers. 
1.  All  the  crystalline  schists  of  Malvern  have  been  elaborated  out 
of  plutonic  igneous  rocks,  chiefly  out  of  a  binary  granite  and 
two  varieties  of  diorite. 
2.  The  schist-making  process  has  been  confined  to  certain  bands 
(shear-zones),  within  which  the  rocks  have  been  subjected  to 
great  compression,  the  mechanical  effects  produced  varying 
between  slight  crashing  and  a  pronounced  shearing-movement 
among  the  constituents,  the  two  extremes  shading  imper¬ 
ceptibly  into  each  other. 
3.  The  bulk  of  the  rocks  had  consolidated  before  the  chief  pressures 
set  in.  During  the  metamorphism,  partial  fusion,  resulting  in 
plasticity,  took  place.  This  effect  is  found  so  often  to  occur 
where  the  shearing  is  at  its  maximum,  while  the  adjacent  rock 
is  merely  a  crushed  solid,  that  the  generation  of  heat  by  the 
shearing-process  becomes  a  probable  inference. 
4.  A  crushed  diorite,  in  course  of  transformation  into  a  mica-gneiss, 
sometimes  passes  through  the  intermediate  state  of  a  laminated 
grit,  which  thus  simulates  a  true  sediment,  the  subsequent 
stages  of  alteration  and  cementation  resembling  the  process  of 
metamorphism  in  some  bedded  rocks. 
5.  The  chief  mineral  and  chemical  changes  took  place  where  diorite 
was  interlaced  with  numerous  granite-veins,  the  effects  pro¬ 
duced  in  the  diorite  being  due  partly  to  the  shearing,  partly 
to  the  action  of  mineral  solutions. 
6.  The  massive  rocks  pass  into  schists  through  a  process  of  decom¬ 
position,  followed  and  partly  accompanied  by  a  process  of 
reconstruction,  the  newly-generated  quartz  and  felspar  in  the 
secondary  consolidation  crystallizing,  the  former  always,  the 
latter  frequently,  in  a  granular  form. 
7.  The  chief  mineral  changes  affecting  the  schist-making  process 
