﻿crystalline 
  rocks 
  of 
  the 
  malvern 
  hills. 
  501 
  

  

  Summary. 
  

  

  1. 
  All 
  the 
  crystalline 
  rocks 
  of 
  the 
  Malvern 
  Chain 
  are 
  of 
  igneous 
  

   origin. 
  

  

  2. 
  The 
  gneisses 
  and 
  schists 
  are 
  produced 
  out 
  of 
  igneous 
  rocks 
  by 
  

   secondary 
  action. 
  

  

  3. 
  The 
  chief 
  mineral 
  and 
  chemical 
  changes 
  have 
  taken 
  place 
  in 
  

   bands 
  of 
  rock 
  (shear-zones) 
  which 
  have 
  been 
  subjected 
  to 
  a 
  shearing- 
  

   movement, 
  so 
  that 
  the 
  metamorphism 
  may 
  be 
  described 
  as 
  " 
  zonal." 
  

   The 
  maximum 
  of 
  alteration 
  has 
  been 
  produced 
  in 
  diorite 
  which 
  has 
  

   been 
  sheared 
  in 
  proximity 
  to 
  granite-veins. 
  Contact-effects 
  are 
  

   here 
  combined 
  with 
  dynamic 
  metamorphism. 
  

  

  4. 
  The 
  most 
  important 
  chemical 
  changes 
  are 
  the 
  removal 
  of 
  

   bases 
  and 
  the 
  combination 
  of 
  potash 
  with 
  some 
  of 
  the 
  constituents 
  

   of 
  diorite. 
  

  

  5. 
  The 
  chief 
  mineral 
  changes 
  are 
  the 
  reconstruction 
  of 
  felspar, 
  

   and 
  the 
  production 
  of 
  biotite 
  (from 
  chlorite), 
  white 
  mica 
  (from 
  

   orthoclase, 
  plagioclase, 
  black 
  mica, 
  and 
  chlorite), 
  granular 
  quartz, 
  

   sphene, 
  and 
  actinolite. 
  

  

  EXPLANATION 
  OF 
  PLATE 
  XVI. 
  

  

  Figs. 
  1, 
  2, 
  3. 
  Series 
  showing 
  the 
  conversion 
  of 
  kersantite 
  through 
  mica-gneiss 
  

   into 
  gneissoid 
  quartzite. 
  (Shear-zone 
  at 
  Swinyard's 
  Hill, 
  p. 
  482. 
  > 
  

  

  Fig. 
  1 
  (313, 
  p. 
  485). 
  Kersantite, 
  being 
  diorite 
  (275, 
  276) 
  altered 
  at 
  contact 
  

   of 
  granite-vein, 
  which 
  appears 
  at 
  the 
  upper 
  part 
  of 
  the 
  slide. 
  Some 
  

   aggregation 
  of 
  the 
  mica 
  is 
  seen 
  at 
  the 
  junction. 
  

  

  2 
  (277, 
  p. 
  486). 
  Eiotite-gneiss 
  from 
  the 
  shear-zone. 
  Structure 
  similar 
  to 
  

  

  last, 
  but 
  more 
  aggregation 
  of 
  the 
  mica 
  in 
  continuous 
  folia. 
  Passing, 
  

   in 
  the 
  same 
  slide, 
  insensibly, 
  both 
  transversely 
  and 
  longitudinally, 
  into 
  

   the 
  gneissoid 
  quartzite 
  of 
  fig. 
  3. 
  

  

  3 
  (277, 
  p 
  486). 
  Gneissoid 
  quartzite. 
  Most 
  of 
  the 
  felspar 
  has 
  been 
  re- 
  

  

  placed 
  by 
  quartz, 
  and 
  much 
  of 
  the 
  mica 
  has 
  disappeared. 
  

  

  4 
  (322, 
  p. 
  496). 
  Diorite, 
  with 
  granite 
  vein 
  at 
  the 
  upper 
  side. 
  To 
  show 
  

  

  aggregation 
  and 
  enlargement 
  of 
  the 
  hornblende 
  at 
  the 
  contact. 
  

  

  5 
  (396, 
  p. 
  496). 
  Biotite-gneiss, 
  with 
  granite-vein. 
  To 
  show 
  similar 
  effects 
  

  

  with 
  mica. 
  

  

  6 
  (403, 
  p. 
  480). 
  One 
  of 
  the 
  later 
  slides 
  of 
  the 
  diorite-series 
  at 
  the 
  shear-zone 
  

  

  at 
  West 
  Malvern. 
  Along 
  the 
  line 
  a 
  .... 
  a 
  fragments 
  of 
  hornblende 
  

   crystals 
  are 
  arranged 
  in 
  an 
  irregular 
  folium. 
  In 
  the 
  upper 
  square 
  

   a 
  cluster 
  of 
  biotite 
  crystals 
  is 
  moulded 
  on 
  the 
  hornblende. 
  The 
  line 
  

   h 
  . 
  . 
  . 
  .b 
  indicates 
  the 
  position 
  of 
  a 
  band 
  of 
  biotite 
  interlaminated 
  with 
  

   chlorite. 
  In 
  the 
  lower 
  square 
  the 
  biotite 
  encloses 
  a 
  crystal 
  of 
  epidote. 
  

   The 
  rest 
  of 
  the 
  slide 
  is 
  mainly 
  white 
  mica 
  and 
  epidote. 
  

  

  Discussion. 
  

  

  The 
  President 
  observed 
  that 
  the 
  gist 
  of 
  the 
  question 
  lay 
  in 
  the 
  

   evidence. 
  

  

  Mr. 
  Kutley 
  said 
  that 
  the 
  Malvern 
  Hills 
  offer 
  comparatively 
  small 
  

   and 
  interrupted 
  exposures 
  of 
  rock. 
  He 
  went 
  there 
  with 
  no 
  pre- 
  

   conceived 
  opinion, 
  and 
  concluded 
  that 
  a 
  certain 
  number 
  of 
  the 
  rocks 
  

   were 
  eruptive, 
  although 
  he 
  considered 
  that 
  a 
  large 
  proportion 
  con- 
  

   sisted 
  of 
  the 
  detritus 
  of 
  eruptive 
  rocks, 
  while, 
  towards 
  the 
  south 
  

  

  