﻿124 
  PROF. 
  T. 
  G. 
  BONNET, 
  NOTES 
  UPON 
  SOME 
  

  

  Appendix. 
  

  

  Notes 
  upon 
  some 
  Specimens 
  of 
  Shropshire 
  Bocks. 
  

   By 
  Prof. 
  T. 
  GL 
  Bonnet, 
  M.A., 
  E.B.S., 
  Sec. 
  G.S. 
  

  

  (55) 
  Lyd's 
  Hole, 
  Pontesbury. 
  — 
  A 
  rhyolite, 
  with 
  well-marked 
  fluidal 
  

   structure, 
  much 
  stained 
  with 
  ferrite 
  and 
  with 
  occasional 
  patches 
  

   of 
  opacite. 
  The 
  rock 
  exhibits 
  a 
  devitrified 
  structure, 
  the 
  crystallites 
  

   in 
  most 
  parts 
  assuming 
  an 
  acicular 
  form, 
  the 
  majority 
  no 
  doubt 
  

   being 
  felspar 
  ; 
  but 
  some, 
  of 
  a 
  pale 
  golden 
  colour, 
  must 
  be 
  a 
  different 
  

   mineral, 
  possibly 
  a 
  mica 
  allied 
  to 
  sericite. 
  There 
  seems 
  in 
  parts 
  a 
  

   tendency 
  to 
  a 
  microspherulitic 
  and 
  even 
  micrographic 
  structure 
  ; 
  the 
  

   ferruginous 
  constituents 
  assume 
  many 
  forms, 
  from 
  mere 
  specks 
  to 
  

   little 
  rods 
  and 
  granules. 
  There 
  are 
  two 
  or 
  three 
  larger 
  crystals 
  of 
  

   felspar, 
  containing 
  apparently 
  glass 
  inclusions 
  ; 
  the 
  fluidal 
  bands 
  are 
  

   crossed 
  transversely 
  by 
  a 
  much 
  more 
  deeply 
  stained 
  zone. 
  The 
  rock 
  

   has 
  a 
  general 
  similarity 
  to 
  those 
  common 
  in 
  the 
  neighbourhood 
  of 
  

   the 
  Wrekin. 
  

  

  (56) 
  Pontesford 
  Hill, 
  North-End 
  Quarry. 
  — 
  A 
  remarkably 
  beautiful 
  

   specimen. 
  The 
  slide 
  gives 
  a 
  complete 
  section 
  of 
  an 
  elongated 
  cavity 
  

   filled 
  with 
  chalcedony. 
  The 
  enclosing 
  border 
  of 
  rock 
  is 
  a 
  rhyolite 
  ; 
  

   this 
  has 
  a 
  fluidal 
  structure 
  parallel 
  to 
  the 
  longer 
  axis 
  of 
  the 
  concre- 
  

   tion, 
  is 
  deeply 
  stained 
  with 
  ferrite, 
  and 
  exhibits 
  in 
  its 
  crystallites 
  

   indications 
  of 
  radial 
  structure 
  normal 
  to 
  the 
  longer 
  axis 
  ; 
  within 
  this 
  

   is 
  a 
  zone 
  of 
  chalcedony, 
  sometimes 
  containing 
  fragments 
  of 
  the 
  

   rhyolite, 
  the 
  microliths 
  of 
  quartz 
  being 
  grouped 
  in 
  radiating 
  tufts 
  

   like 
  the 
  hairs 
  in 
  a 
  sable-brush, 
  a 
  familiar 
  appearance 
  in 
  agates 
  : 
  in 
  

   places 
  also 
  they 
  form 
  regular 
  spherulites 
  ; 
  within 
  this 
  is 
  an 
  enclo- 
  

   sure 
  of 
  minutely 
  crystalline 
  quartz. 
  These 
  hollow 
  spherulitic 
  con- 
  

   cretions, 
  subsequently 
  partially 
  or 
  wholly 
  filled 
  by 
  infiltrated 
  mine- 
  

   rals, 
  are 
  not 
  uncommon 
  in 
  acid 
  lavas 
  ; 
  and 
  I 
  have 
  been 
  for 
  some 
  

   time 
  engaged 
  upon 
  the 
  study 
  of 
  a 
  somewhat 
  similar 
  group 
  from 
  

   North 
  Wales. 
  The 
  rock 
  of 
  Lea 
  Hill, 
  in 
  the 
  Wrekin 
  district, 
  is 
  

   very 
  similar 
  in 
  structure 
  to 
  this 
  one 
  from 
  Pontesford 
  Hill. 
  

  

  (57) 
  Pontesford 
  Hill 
  (summit). 
  — 
  The 
  ground- 
  mass 
  is 
  full 
  of 
  

   elongated 
  microliths 
  of 
  felspar 
  with 
  a 
  slightly 
  parallel 
  grouping, 
  

   generally 
  plagioclase, 
  but 
  possibly 
  in 
  one 
  or 
  two 
  cases 
  orthoclase, 
  

   with 
  dark 
  granules, 
  probably 
  in 
  many 
  cases 
  haematite, 
  and 
  numerous 
  

   grains 
  (generally 
  rather 
  irregular 
  in 
  outline) 
  of 
  augite. 
  One 
  of 
  more 
  

   definite 
  form 
  is 
  a 
  compound 
  crystal 
  about 
  '02 
  inch 
  in 
  diameter. 
  

   There 
  is 
  a 
  small 
  quantity 
  of 
  a 
  chloritic 
  mineral. 
  The 
  rock 
  is 
  a 
  basalt, 
  

   and 
  more 
  resembles 
  that 
  of 
  a 
  flow 
  than 
  of 
  a 
  dyke. 
  

  

  (58) 
  North 
  ofLyd's 
  Hole, 
  Block 
  in 
  Caradoc 
  Shale. 
  — 
  The 
  structure 
  of 
  

   this 
  rock 
  is 
  a 
  little 
  abnormal. 
  With 
  ordinary 
  light 
  it 
  exhibits 
  a 
  clear 
  

   base 
  containing 
  a 
  multitude 
  of 
  dark 
  specks, 
  evidently 
  ferruginous, 
  some 
  

   being 
  brown 
  (probably 
  the 
  hydrous 
  peroxide 
  of 
  iron) 
  others 
  nearly 
  

   black. 
  These 
  are 
  so 
  arranged 
  as 
  to 
  give 
  a 
  spotted 
  aspect 
  to 
  the 
  slide. 
  

   On 
  using 
  crossed 
  Nicols 
  the 
  spots 
  containing 
  the 
  latter 
  prove 
  to 
  be 
  

   devitrified 
  patches 
  of 
  one 
  or 
  more 
  crystals, 
  very 
  imperfectly 
  developed. 
  

  

  