356 
ME.  G.  BAEEOW  OX  AX  IXTEUSIOX 
[Aug.  1893, 
Plate  XVI. 
Fig.  1  (Slide  No.  4540).  Sillimanite-needles  in  quartz.  X  40  diameters. 
Fig.  2  (Slide  No.  4531).  Sillimanite  associated  with  mica.  Close  to  the  Lee 
Water,  North  Esk.  x  40  diameters. 
Fig.  3  (Slide  No.  4547).  Cyanite-schist  or  gneiss.  In  the  centre  of  the  field  is 
a  crystal  of  cyanite  enclosing  a  small  garnet.  The  cj’anite  shows  the 
planes  of  easiest  cleavage,  and  the  gliding-planes  parallel  to  the  base. 
The  garnets  are  very  similar  to  those  shown  in  pi.  xxiii.  vol.  xlvi.  of 
this  Journal,  which  have  been  developed  by  the  contact-metamorphism 
of  the  Galloway  Granite.  X  20  diameters. 
Fig.  4.  Iron-ore  inclusions  in  cyanite.  ‘  Contact-structure.’  Bulg,  North 
Esk.  X  20  diameters. 
Fig  5  (Slide  No.  5101).  Staurulite  surrounded  by  ‘ shimmer  ’-aggregate.  X  20 
diameters. 
Fig.  6.  Brown  contact-mica,  in  the  position  of  maximum  and  minimum  absorp¬ 
tion  of  light.  One  half  shows  the  pleochroic  spots  in  the  most 
marked  manner,  in  the  other  half  the  spots  are  almost  invisible. 
Some  cyanite  (glassy-white  mineral)  is  also  jmesent,  showing  the 
typical  high  refractive  index  by  its  strongly-marked  borders. 
Discussion1-. 
The  Peesidext  said  that  it  was  of  great  advantage  to  the  Society 
to  have  communications  from  the  Officers  of  the  Geological  Survey  now 
engaged  in  the  work  of  mapping  the  Highlands  of  Scotland.  In  this 
paper  the  Author  suggested  solutions  of  some  geological  puzzles. 
He  (the  speaker)  asked  for  fuller  information  as  to  the  relations  be¬ 
tween  the  oligoclase-  and  microcline-bearing  portions  of  the  intrusive 
masses ;  as  to  the  effects  of  the  later  granite ;  and  as  to  the  nature 
of  the  original  rocks.  Why  was  sillimanite  found  in  one  area, 
cyanite  in  a  second,  and  staurolite  in  a  third? 
Prof.  Judd  called  attention  to  the  circumstance  that  the  district 
described  by  the  Author  of  the  paper  is  near  Kmnordy,  the  birthplace 
and  home  of  the  late  Sir  Charles  Lyell.  A  year  or  two  before  Lyell’s 
death,  the  speaker  had  spent  some  days  in  Glen  Clova,  in  company 
with  the  veteran  geologist,  examining  the  geological  structure  of  the 
district,  and  they  had  been  greatly  impressed  by  the  intricacy  as 
well  as  the  suggestiveness  of  that  structure.  He  complimented  the 
Author  of  the  paper  on  the  thoroughness  and  excellence  of  his  work 
in  the  district,  and  was  pleased  to  find  that  the  Officers  of  the  Geo¬ 
logical  Survey,  in  carrying  on  their  important  studies  of  the  High¬ 
land  rocks,  were  ready  to  accept  and  weigh  all  evidence,  without  any 
reference  to  preconceived  opinions.  He  remarked,  in  conclusion, 
that  the  paper  constituted  a  splendid  vindication  of  the  principles 
so  long  ago  enunciated  by  Lyell  concerning  the  mode  of  formation 
of  the  ‘  hypogene  rocks.’ 
Mr.  Euiley  fully  endorsed  the  statements  of  the  last  speaker  with 
reference  to  the  value  of  the  paper.  He  considered  that  some  of 
the  rocks  exhibited  bore  a  resemblance  to  those  met  with  in  the 
Malvern  range,  and  that  the  latter  had  probably  been  altered  under 
conditions  similar  to  those  which  the  Author  had  indicated.  He 
thought  it  likely  that  both  sillimanite  and  cyanite  might  be  deve¬ 
loped  in  the  same  rock,  but  that  staurolite  would  be  formed  in  a 
