﻿268 
  

  

  PROCEEDINGS 
  

  

  OF 
  

  

  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  POSTPONED 
  PAPERS. 
  

  

  Expeeimental 
  Reseaeches 
  on 
  the 
  Geanites 
  of 
  Ieeland. 
  Paet 
  IY. 
  

   On 
  the 
  Geanites 
  and 
  Syenites 
  of 
  Donegal 
  ; 
  with 
  some 
  Remarks 
  

   on 
  those 
  of 
  Scotland 
  and 
  Sweden. 
  By 
  the 
  Rev. 
  Samuel 
  Haugh- 
  

   ton, 
  M.D., 
  F.R.S., 
  Fellow 
  of 
  Trinity 
  College, 
  and 
  Professor 
  of 
  

   Geology 
  in 
  the 
  University 
  of 
  Dublin. 
  

  

  [Bead 
  December 
  16, 
  1863.*] 
  

  

  Contents. 
  

  

  I. 
  Mineralogical 
  Composition 
  of 
  the 
  Donegal 
  Granites. 
  

   II. 
  The 
  Syenites 
  of 
  Donegal. 
  

   III. 
  Comparison 
  of 
  the 
  Granites 
  of 
  Donegal 
  with 
  those 
  of 
  Scotland 
  

   and 
  Sweden. 
  

  

  § 
  I. 
  Mineralogical 
  Composition 
  of 
  the 
  Donegal 
  Granites. 
  

  

  In 
  Part 
  III. 
  of 
  these 
  researches 
  f 
  I 
  gave 
  the 
  analyses 
  of 
  fifteen 
  

   Donegal 
  granites, 
  and 
  an 
  account 
  of 
  their 
  constituent 
  minerals, 
  so 
  

   far 
  as 
  I 
  am 
  acquainted 
  with 
  them 
  ; 
  and 
  at 
  the 
  close 
  of 
  the 
  paper 
  

   I 
  endeavoured 
  to 
  calculate 
  the 
  mineral 
  composition 
  of 
  the 
  Doo- 
  

   charry 
  Bridge 
  granite, 
  on 
  the 
  hypothesis 
  that 
  it 
  is 
  composed 
  of 
  the 
  

   four 
  minerals 
  observed 
  to 
  occur 
  in 
  many 
  of 
  the 
  Donegal 
  granites, 
  

   namely, 
  1, 
  Quartz 
  ; 
  2, 
  Orthoclase 
  ; 
  3, 
  Oligoclase 
  ; 
  4, 
  Black 
  Mica. 
  

   I 
  now 
  propose 
  to 
  discuss 
  in 
  detail 
  the 
  mineralogical 
  composition 
  of 
  

   each 
  of 
  these 
  fifteen 
  granites, 
  and 
  in 
  so 
  doing 
  to 
  bring 
  under 
  the 
  

   notice 
  of 
  the 
  Society 
  the 
  method 
  which 
  I 
  usually 
  employ 
  in 
  the 
  in- 
  

   vestigation 
  of 
  such 
  problems 
  ; 
  and 
  from 
  the 
  results 
  of 
  this 
  method 
  of 
  

  

  * 
  For 
  the 
  other 
  communications 
  read 
  at 
  this 
  Evening-meeting, 
  see 
  p. 
  116. 
  

   t 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xviii. 
  p. 
  403. 
  

  

  