﻿364 
  miss 
  c. 
  a. 
  raisin 
  on 
  the 
  petrology 
  [Aug. 
  1897, 
  

  

  II. 
  Petrology. 
  

   By 
  Miss 
  C. 
  A. 
  Raisin, 
  B.Sc. 
  

  

  The 
  collection 
  of 
  specimens 
  sent 
  by 
  Capt. 
  Lyons 
  includes 
  many 
  

   rocks 
  of 
  similar 
  class, 
  but 
  I 
  have 
  given 
  short 
  notes 
  of 
  all, 
  as 
  they 
  

   represent 
  a 
  district 
  on 
  which 
  no 
  penological 
  information 
  is 
  available, 
  

   and 
  they 
  show 
  some 
  variations. 
  I 
  have 
  to 
  thank 
  Prof. 
  Bonney 
  for 
  

   much 
  kind 
  help 
  in 
  my 
  investigation. 
  

  

  In 
  order 
  to 
  avoid 
  repetition, 
  the 
  specimens 
  have 
  been 
  grouped 
  

   petrologically. 
  Those 
  in 
  Groups 
  vii 
  & 
  ix 
  come 
  from 
  the 
  ' 
  schistose 
  ' 
  

   area, 
  but 
  the 
  majority 
  are 
  from 
  the 
  areas 
  marked 
  by 
  Capt. 
  Lyons 
  as 
  

   ' 
  crystalline 
  rocks,' 
  among 
  which 
  only 
  one 
  specimen 
  (Group 
  viii) 
  is 
  

   sedimentary. 
  The 
  ' 
  crystalline 
  ' 
  districts 
  may 
  be 
  described 
  as 
  (1) 
  

   the 
  ' 
  Southern 
  ' 
  (around 
  Murrat), 
  and 
  the 
  ' 
  Western 
  ' 
  (around 
  Jebel 
  

   Raft) 
  separated 
  by 
  the 
  southern 
  tract 
  of 
  ' 
  schistose 
  ' 
  rocks 
  ; 
  (2) 
  an 
  

   ' 
  Eastern 
  ' 
  district 
  beyond 
  the 
  schistose 
  outcrops 
  just 
  mentioned, 
  

   extending 
  over 
  the 
  watershed 
  to 
  the 
  head 
  of 
  the 
  Wadi 
  Allaki. 
  Of 
  the 
  

   crystalline 
  rocks, 
  those 
  which 
  bear 
  most 
  distinct 
  signs 
  of 
  modification 
  

   are 
  treated 
  first. 
  

  

  (i) 
  Gneiss. 
  

  

  (18 
  * 
  : 
  Murrat, 
  from 
  the 
  Southern 
  area). 
  Of 
  this 
  only 
  one 
  specimen 
  

   occurs 
  ; 
  it 
  is 
  jointed, 
  and 
  has 
  a 
  rather 
  fragmental 
  aspect. 
  — 
  Microsc. 
  

   The 
  original 
  constituents 
  are 
  often 
  reconstituted. 
  The 
  quartz 
  forms 
  

   a 
  clear 
  mosaic 
  enclosing 
  minute 
  zircons 
  and 
  other 
  prisms. 
  The 
  

   clustered 
  felspar-crystals 
  or 
  grains 
  (sometimes 
  plagioclase 
  and 
  

   somewhat 
  idiomorphic) 
  are 
  altered, 
  and 
  may 
  be 
  bordered 
  by 
  minute 
  

   mica 
  ; 
  and 
  a 
  small 
  amount 
  of 
  a 
  green, 
  rather 
  dichroic, 
  altered 
  

   biotite 
  occurs 
  with 
  some 
  ferrite. 
  The 
  rock 
  is 
  a 
  fine-grained 
  biotite- 
  

   gneiss, 
  which 
  appears 
  to 
  be 
  granitic 
  in 
  its 
  origin, 
  probably 
  somewhat 
  

   pressure-modified, 
  but 
  it 
  possibly 
  bears 
  traces 
  of 
  a 
  slight 
  original 
  

   banding. 
  

  

  (ii) 
  Hornblendite. 
  

  

  (7 
  : 
  Abu 
  Sinaiyat, 
  in 
  the 
  Southern 
  area,) 
  A 
  greyish-green 
  

   schistose 
  rock 
  of 
  rather 
  friable 
  actinolitic 
  hornblende. 
  — 
  Microsc. 
  

   The 
  crystals 
  are 
  pale 
  green, 
  often 
  iron-stained, 
  scarcely 
  dichroic, 
  

   well 
  cleaved, 
  and 
  resemble 
  the 
  small 
  prisms 
  of 
  secondary 
  hornblende 
  

   in 
  many 
  of 
  the 
  other 
  rocks. 
  The 
  mineral 
  is 
  orientated. 
  The 
  macro- 
  

   scopic 
  aspect 
  suggests 
  pressure-modification, 
  and 
  the 
  microscopic 
  

   would 
  accord 
  with 
  it. 
  

  

  (iii) 
  Altered 
  Gabbro 
  or 
  Dolerite, 
  Diabase, 
  etc. 
  

  

  (a) 
  Altered 
  Gabbro. 
  — 
  Several 
  rocks, 
  all 
  coming 
  from 
  the 
  southern 
  

   area, 
  are 
  evidently 
  altered 
  forms 
  of 
  gabbro 
  (11, 
  15 
  : 
  Murrat 
  ; 
  10, 
  

   19 
  : 
  Abu 
  Sinaiyat). 
  In 
  three 
  specimens 
  (11, 
  10, 
  19) 
  the 
  mineral 
  

   constituents 
  are 
  almost 
  entirely 
  changed 
  into 
  an 
  actinolitic 
  aggregate 
  

   and 
  a 
  mass 
  of 
  zoisite 
  with 
  some 
  epidote, 
  but 
  diallage 
  can 
  be 
  recog- 
  

   nized 
  in 
  one 
  rock 
  (11). 
  In 
  this 
  the 
  hand-specimen 
  shows 
  abundant 
  

  

  1 
  The 
  numbers 
  are 
  those 
  attached 
  to 
  the 
  specimens 
  by 
  Oapt. 
  Lyons. 
  

  

  