﻿SPECIMENS 
  OF 
  SHROPSHIRE 
  ROCKS. 
  125 
  

  

  The 
  browner 
  spots 
  remain 
  dark, 
  but 
  contain 
  many 
  extremely 
  minute 
  

   (felspar 
  ?) 
  microliths. 
  In 
  places 
  the 
  devitrined 
  structure 
  occupies 
  the 
  

   whole 
  of 
  irregular 
  zones 
  in 
  the 
  slide 
  ; 
  in 
  others 
  there 
  is 
  a 
  con- 
  

   siderable 
  amount 
  left 
  of 
  the 
  apparently 
  unaltered 
  base. 
  This 
  closely 
  

   resembles 
  a 
  nuidal 
  structure. 
  On 
  the 
  whole, 
  therefore, 
  I 
  consider 
  

   this 
  a 
  fragment 
  of 
  rhyolitic 
  lava, 
  parts 
  of 
  which 
  may 
  still 
  remain 
  in 
  a 
  

   glassy 
  state. 
  

  

  (59) 
  West 
  of 
  Gatten 
  Lodge. 
  — 
  A 
  sedimentary 
  rock, 
  with 
  the 
  structure 
  

   characteristic 
  of 
  the 
  argillites 
  or 
  whetstones 
  which, 
  occur 
  in 
  parts 
  

   of 
  Charnwood 
  Forest, 
  the 
  rock 
  being 
  made 
  up 
  of 
  innumerable 
  minute 
  

   granules, 
  probably 
  of 
  quartz, 
  and 
  specks 
  of 
  f 
  errite. 
  Larger 
  fragments 
  

   are 
  also 
  present 
  : 
  some 
  resemble 
  bits 
  of 
  a 
  rather 
  similar 
  rock 
  ; 
  others 
  

   may 
  be 
  only 
  patches 
  where 
  the 
  staining 
  is 
  more 
  pronounced 
  ; 
  many 
  

   are 
  quartz, 
  subangular 
  in 
  form 
  ; 
  and 
  two 
  or 
  three 
  much 
  resemble 
  bits 
  

   of 
  rhyolite. 
  

  

  (60) 
  North 
  end 
  of 
  Knolls 
  Ridge. 
  — 
  A 
  rather 
  coarsely 
  crystalline 
  rock, 
  

   consisting 
  to 
  a 
  large 
  extent 
  of 
  a 
  plagioclastic 
  felspar. 
  This 
  is 
  evidently 
  

   decomposed 
  ; 
  and 
  the 
  crystals 
  enclose 
  numerous 
  microliths 
  of 
  epidote 
  

   (of 
  secondary 
  formation); 
  some 
  exhibit 
  a 
  micrographic 
  structure 
  

   with 
  quartz, 
  such 
  as 
  is 
  common 
  in 
  the 
  syenites 
  of 
  Charnwood 
  Forest. 
  

   Grains 
  of 
  viridite 
  are 
  also 
  enclosed. 
  Larger 
  patches 
  of 
  viridite 
  are 
  

   present, 
  though 
  not 
  numerous, 
  with 
  a 
  little 
  quartz 
  (this 
  has 
  more 
  

   resemblance 
  to 
  an 
  original 
  constituent), 
  some 
  ilmenite 
  and 
  perhaps 
  

   magnetite, 
  and 
  some 
  apatite. 
  Under 
  the 
  circumstances 
  it 
  is 
  difficult 
  

   to 
  decide 
  whether 
  the 
  rock 
  should 
  be 
  called 
  a 
  diorite 
  or 
  a 
  diabase 
  ; 
  

   perhaps 
  the 
  former 
  name 
  is 
  the 
  safer, 
  though 
  it 
  is 
  by 
  no 
  means 
  a 
  

   typical 
  example. 
  

  

  (61) 
  West 
  of 
  Linley 
  Hall. 
  — 
  In 
  parts 
  of 
  this 
  slide 
  a 
  very 
  decided 
  

   fragmental 
  structure 
  is 
  visible. 
  In 
  these 
  older 
  rocks 
  it 
  is 
  necessary 
  

   to 
  be 
  always 
  on 
  one's 
  guard 
  to 
  avoid 
  mistaking 
  the 
  result 
  of 
  brec- 
  

   ciation 
  in 
  situ 
  (due 
  to 
  crushing, 
  especially 
  near 
  faults) 
  for 
  an 
  original 
  

   clastic 
  structure. 
  I 
  think, 
  however, 
  that 
  there 
  is 
  here 
  sufficient 
  

   evidence 
  of 
  the 
  latter. 
  Minute 
  crystals 
  of 
  epidote 
  are 
  not 
  unfrequent, 
  

   especially 
  in 
  the 
  intervals 
  between 
  the 
  apparent 
  fragments. 
  With 
  

   ordinary 
  light 
  the 
  ground-mass 
  is 
  clear 
  and 
  contains 
  numerous 
  

   specks 
  of 
  filmy 
  golden-green 
  mineral, 
  and 
  clotted 
  spots 
  of 
  a 
  dusty- 
  

   grey 
  or 
  brownish 
  mineral 
  : 
  part 
  of 
  the 
  former 
  is 
  epidote 
  ; 
  but 
  some 
  

   may 
  be 
  a 
  variety 
  of 
  mica 
  or 
  chlorite, 
  or 
  possibly 
  hornblende. 
  With 
  

   crossed 
  Nicols 
  the 
  ground-mass 
  exhibits 
  a 
  very 
  minute 
  devitrined 
  

   structure. 
  In 
  this 
  respect 
  it 
  has 
  (except 
  that 
  distinct 
  crystals 
  of 
  

   quartz 
  or 
  felspar 
  are 
  absent) 
  a 
  remarkable 
  resemblance 
  to 
  some 
  of 
  

   the 
  rocks 
  from 
  the 
  Sharpley 
  and 
  Bardon 
  districts 
  in 
  Charnwood 
  

   Forest, 
  especially 
  to 
  the 
  more 
  compact 
  felstone-like 
  varieties 
  of 
  the 
  

   the 
  latter*. 
  I 
  am 
  disposed 
  therefore 
  to 
  regard 
  it 
  as, 
  like 
  these, 
  an 
  

   indurated 
  somewhat 
  altered 
  tuff. 
  

  

  * 
  Quart. 
  Journ. 
  Greol. 
  Soc. 
  vol. 
  xxxiv. 
  p. 
  209, 
  vol. 
  xxxvi. 
  pp. 
  341-347. 
  

  

  