﻿626 
  MR. 
  F. 
  RTTTLEY 
  ON 
  TACHYLYTE 
  FROM 
  

  

  38. 
  On 
  Tachylyte 
  from 
  Victoria 
  Park, 
  "Whitelnch, 
  near 
  Glasgow. 
  

   By 
  Prank 
  Rtitley, 
  Esq., 
  F.G.S., 
  Lecturer 
  on 
  Mineralogy 
  in 
  the 
  

   Royal 
  School 
  of 
  Mines. 
  With 
  an 
  Analysis 
  of 
  the 
  Rock, 
  by 
  

   Philip 
  Holland, 
  Esq., 
  F.C.S., 
  P.I.C. 
  (Read 
  June 
  19, 
  1889.) 
  

  

  In 
  a 
  paper 
  published 
  last 
  year 
  in 
  the 
  < 
  Transactions 
  of 
  the 
  Geolo- 
  

   gical 
  Society 
  of 
  Glasgow' 
  by 
  Messrs. 
  John 
  Young, 
  P.G.S., 
  and 
  

   D. 
  Corse 
  Glen, 
  F.G.S.*, 
  an 
  interesting 
  account 
  is 
  given 
  of 
  certain 
  

   intrusive 
  sheets 
  and 
  veins 
  of 
  dolerite 
  passing 
  through 
  Carboniferous 
  

   shales 
  and 
  sandstones, 
  which 
  contain 
  the 
  erect 
  stems 
  of 
  fossil 
  trees, 
  

   determined 
  by 
  Mr. 
  R. 
  Kidston, 
  P.G.S., 
  as 
  those 
  of 
  Lepidodendron 
  

   Veltheimianum 
  t. 
  In 
  one 
  instance 
  a 
  thin 
  vein 
  of 
  the 
  dolerite 
  was 
  

   found 
  to 
  pass 
  completely 
  through 
  one 
  of 
  the 
  trees 
  a 
  little 
  above 
  the 
  

   roots. 
  There 
  can 
  therefore 
  be 
  no 
  doubt 
  that 
  these 
  dolerite 
  veins 
  

   were 
  formed, 
  as 
  the 
  authors 
  point 
  out, 
  subsequently 
  to 
  the 
  growth 
  

   of 
  the 
  trees 
  and 
  the 
  deposition 
  of 
  the 
  surrounding 
  beds. 
  

  

  In 
  the 
  paper 
  already 
  cited 
  the 
  authors 
  duly 
  recognize 
  the 
  tachy- 
  

   lytic 
  character 
  which 
  the 
  margins 
  of 
  the 
  smaller 
  intrusive 
  veins 
  

   present 
  in 
  the 
  following 
  words 
  : 
  — 
  

  

  " 
  In 
  this 
  quarry 
  we 
  have 
  the 
  interesting 
  evidence 
  that 
  along 
  these 
  

   lines, 
  especially 
  in 
  the 
  thinner 
  veins, 
  the 
  dolerite 
  has 
  cooled 
  as 
  a 
  

   vitreous 
  glassy 
  lava, 
  in 
  which 
  a 
  thin 
  layer, 
  showing 
  micro-spheru- 
  

   litic 
  structure, 
  has 
  been 
  developed 
  during 
  the 
  process 
  along 
  the 
  

   surface 
  of 
  both 
  faces 
  of 
  the 
  vein. 
  These 
  veins 
  are 
  now 
  seen 
  to 
  have 
  

   lost 
  their 
  glassy 
  structure 
  through 
  devitrification, 
  and 
  are 
  of 
  a 
  whitish 
  

   colour, 
  but 
  their 
  spherulitic 
  structure, 
  which 
  still 
  remains, 
  clearly 
  

   indicates 
  that 
  they 
  once 
  existed 
  as 
  veins 
  of 
  a 
  glassy 
  tachylyte. 
  This 
  

   is 
  the 
  first 
  instance 
  in 
  which 
  we 
  have 
  found 
  such 
  a 
  structure 
  amongst 
  

   the 
  dolerites 
  of 
  the 
  Glasgow 
  Coal-field." 
  

  

  I 
  am 
  indebted 
  to 
  the 
  kindness 
  of 
  Mr. 
  John 
  Young 
  for 
  the 
  speci- 
  

   mens 
  upon 
  which 
  this 
  paper 
  is 
  based. 
  

  

  Of 
  these 
  the 
  most 
  important 
  is 
  one 
  in 
  which 
  the 
  entire 
  thickness 
  

   of 
  the 
  vein 
  is 
  shown, 
  and 
  to 
  which 
  the 
  shale, 
  forming 
  one 
  of 
  the 
  

   walls, 
  is 
  attached. 
  The 
  total 
  thickness 
  of 
  the 
  vein, 
  with 
  its 
  tachy- 
  

   lyte 
  selvages, 
  is 
  about 
  one 
  inch. 
  The 
  vein 
  itself 
  is 
  of 
  a 
  pale 
  bluish 
  

   grey 
  to 
  brownish 
  grey, 
  becoming 
  greyish 
  white 
  along 
  the 
  margins 
  

   where 
  the 
  spherulitic 
  structure 
  is 
  best 
  developed. 
  A 
  very 
  narrow 
  

   band, 
  or 
  rather 
  film, 
  of 
  a 
  partially 
  vitreous 
  character, 
  lying 
  between 
  

   this 
  and 
  the 
  shale, 
  is 
  of 
  an 
  ashy 
  grey 
  colour. 
  The 
  shale 
  is 
  black 
  or 
  

   dark 
  bluish 
  grey, 
  and 
  the 
  planes 
  of 
  lamination 
  are 
  speckled 
  with 
  

   exceedingly 
  minute 
  scales 
  of 
  mica. 
  

  

  That 
  portion 
  of 
  the 
  section 
  which 
  is 
  most 
  remote 
  from 
  the 
  contacts 
  

   shows 
  a 
  confusedly 
  crystalline 
  structure, 
  together 
  with 
  a 
  small 
  

   quantity 
  of 
  interstitial 
  glass. 
  

  

  * 
  " 
  Notes 
  on 
  a 
  Section 
  of 
  Carboniferous 
  Strata 
  containing 
  Erect 
  Stems 
  of 
  

   Fossil 
  Trees 
  and 
  Beds 
  of 
  Intrusive 
  Dolerite 
  in 
  the 
  old 
  Whinstone 
  Quarry, 
  

   Victoria 
  Park, 
  Lower 
  Balshagrav, 
  near 
  Whiteinch 
  and 
  Partick." 
  

  

  t 
  Ibid. 
  

  

  