﻿276 
  

  

  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  From 
  the 
  entire 
  of 
  the 
  preceding, 
  it 
  may 
  he 
  safe 
  to 
  draw 
  the 
  

   following 
  conclusions 
  respecting 
  the 
  granites 
  of 
  Donegal 
  : 
  — 
  

  

  1. 
  That 
  nearly 
  half 
  of 
  them 
  are 
  certainly 
  not 
  composed 
  altogether 
  

   of 
  the 
  four 
  minerals, 
  quartz, 
  oligoclase, 
  orthoclase, 
  and 
  black 
  mica, 
  

   that 
  are 
  found 
  in 
  them 
  in 
  distinct 
  crystals. 
  

  

  2. 
  That 
  the 
  remaining 
  half, 
  even 
  if 
  they 
  be 
  composed 
  of 
  these 
  

   minerals, 
  must 
  have 
  a 
  paste 
  made 
  of 
  quartz, 
  orthoclase, 
  oligoclase, 
  

   and 
  black 
  mica, 
  not 
  having 
  precisely 
  the 
  chemical 
  composition 
  of 
  

   the 
  separate 
  crystals. 
  

  

  § 
  II. 
  On 
  the 
  Syenites 
  of 
  Donegal. 
  

  

  In 
  many 
  parts 
  of 
  the 
  co. 
  Donegal 
  syenites 
  are 
  found, 
  which 
  

   appear 
  to 
  form 
  great 
  bedded 
  masses, 
  rudely 
  stratified 
  like 
  the 
  gra- 
  

   nites 
  ; 
  and, 
  like 
  them, 
  also 
  occasionally 
  penetrating 
  the 
  neighbour- 
  

   ing 
  rocks 
  in 
  dykes, 
  making 
  various 
  angles 
  with 
  the 
  beds 
  of 
  strati- 
  

   fication. 
  The 
  following 
  Table 
  contains 
  the 
  analyses 
  of 
  such 
  as 
  I 
  

   have 
  examined. 
  

  

  

  Table 
  VII.- 
  — 
  Analyses 
  

  

  of 
  Donegal 
  Sy 
  

  

  znitei 
  

  

  

  

  

  d 
  

  

  525 
  

  

  Locality. 
  

  

  os 
  

   o 
  

  

  w. 
  

  

  03 
  

  

  n 
  

   3 
  

  

  •3 
  

  

  Iron, 
  

   peroxide. 
  

   Iron, 
  

   protoxide. 
  

  

  a 
  

   i-3 
  

  

  o8 
  

  

  "co 
  

  

  oS 
  

  

  oS 
  

  

  O 
  

   W. 
  

  

  A 
  

  

  m 
  

   oS 
  

  

  O 
  

  

  Pn 
  

  

  J- 
  r& 
  

  

  OS 
  O 
  

  

  oS 
  

  

  O 
  

  

  H 
  

  

  1. 
  

  

  2. 
  

   3. 
  

  

  4. 
  

  

  Lough 
  Anure 
  . 
  . 
  . 
  

   Kilrean 
  

  

  49-20 
  

   44-40 
  

   50-08 
  

  

  58-05 
  

  

  18-32 
  

   25-00 
  

   18-84 
  

  

  16-08 
  

  

  712 
  1-95 
  

   6-45J2-11 
  

  

  7-05 
  1-03 
  

  

  8-27| 
  0-45 
  

  

  9-72 
  

   10-17 
  

   12-37 
  

  

  6-52 
  

  

  711 
  

   3-51 
  

   6-57 
  

  

  2-94 
  

  

  1-92 
  

  

  2-58 
  

   2-39 
  

  

  4-65 
  

  

  1-72 
  

   2-66 
  

   0-57 
  

  

  2-21 
  

  

  1-00 
  

  

  0-84 
  

   0-88 
  

  

  1-12 
  

  

  1-20 
  

   1-08 
  

   0-80 
  

  

  99-26 
  

  

  98-80 
  

   100-58 
  

  

  100-28 
  

  

  Doonane 
  

  

  Precise 
  locality 
  

   unknown 
  

  

  1. 
  Lough 
  Anure. 
  — 
  A 
  medium 
  -grained 
  syenite, 
  or 
  crystalline 
  greenstone, 
  com- 
  

  

  posed 
  of 
  small 
  plates 
  of 
  black 
  mica, 
  with 
  some 
  hornblende, 
  aggre- 
  

   gated 
  together 
  ; 
  and 
  of 
  a 
  felspar, 
  which 
  seems 
  to 
  be 
  oligoclase. 
  

  

  2. 
  Kilrean. 
  — 
  A 
  coarse-grained 
  syenite, 
  containing 
  — 
  

  

  (a.) 
  Long 
  crystals 
  of 
  green 
  hornblende. 
  

  

  (b.) 
  White 
  felspar 
  (? 
  oligoclase). 
  

  

  (<?.) 
  Specks 
  of 
  iron 
  pyrites. 
  

   In 
  addition 
  to 
  the 
  constituents 
  given 
  in 
  the 
  analysis, 
  this 
  rock 
  contained 
  

   1*078 
  per 
  cent, 
  of 
  sulphur, 
  which, 
  no 
  doubt, 
  was 
  present 
  in 
  the 
  form 
  of 
  the 
  

   bisulphuret 
  of 
  iron. 
  It 
  is 
  one 
  of 
  the 
  toughest 
  rocks 
  I 
  have 
  ever 
  met 
  with. 
  

  

  3. 
  Doonane 
  Hill, 
  near 
  Donegal. 
  — 
  A 
  crystalline, 
  greasy 
  trap-rock, 
  forming 
  a 
  

  

  dyke 
  penetrating 
  the 
  lower 
  arenaceous 
  Carboniferous 
  Limestone, 
  and 
  

   then 
  expanding 
  into 
  a 
  mass 
  on 
  the 
  summit 
  of 
  the 
  hill. 
  It 
  con- 
  

   tains 
  — 
  

  

  (a.) 
  Black 
  hornblende. 
  

  

  (b.) 
  Green 
  felspar. 
  

  

  4. 
  This 
  specimen 
  closely 
  resembles 
  those 
  found 
  in 
  the 
  Black 
  Gap, 
  near 
  Pet- 
  

  

  tigo 
  ; 
  it 
  forms 
  a 
  connecting 
  link 
  between 
  the 
  true 
  granites 
  and 
  the 
  

  

  greenstone-syenites, 
  as 
  it 
  contains 
  — 
  

   (a.) 
  Quartz. 
  

  

  (b.) 
  Oligoclase, 
  pinkish 
  yellow, 
  in 
  large 
  crystals 
  with 
  brilliant 
  cleavage. 
  

   (c.) 
  Hornblende, 
  dark 
  glossy 
  black-green. 
  

   {d.) 
  Occasional 
  facets 
  of 
  sphene 
  in 
  minute 
  crystals. 
  

  

  