Yol.  49.] 
OP  MtrSCOYITP-BlOTlTE  GNEISS. 
347 
above  the  farm-steading  of  Alton.  The  gneiss  consists  of  large 
hakes  of  brown  and  white  mica  lying  in  layers  in  a  fine  gneissose 
matrix,  mostly  of  quartz  and  felspar.  In  Bonhard  Corrie,  a  short 
distance  north-west  of  the  Clova  Hotel,  the  weathered  surfaces  of 
some  of  the  finer-grained  rocks  are  coated  with  a  vast  number  of  tiny 
crystals  of  blue  cyanite.  The  same  is  true  of  the  fine  gneisses  at  the 
head  of  Saughs  Bum.  About  Loch  Lee  rather  coarsely-micaceous 
rocks  (fine  gneisses)  frequently  show  cyanite-crystals  on  their 
weathered  surfaces.  A  specimen  (4547)  is  composed  of  quartz, 
muscovite,  and  chlorite,  with  a  little  garnet  and  iron  ores.  In  this 
as  a  matrix  are  set  glassy  crystals  of  cyanite,  the  high  refraction  and 
cross-cleavage  cracks  being  well  shown. 
A  section  was  also  made  of  a  rock-specimen  (4539),  occurring 
close  to  the  last,  in  which  the  cyanite  is  not  so  well  preserved.  The 
matrix  is  composed  of  quartz,  chlorite,  muscovite,  and  a  little  felspar, 
with  iron  ores,  garnet,  and  tourmaline  as  accessories.  In  this  are 
set  a  number  of  vividly-polarizing  aggregates,  in  the  centre  of  which 
small  patches  of  cyanite  may  still  be  recognized.  Comparing  slide 
Ho.  4539,  containing  cyanite,  with  No.  4541,  containing  sillimanite, 
in  what  can  be  clearly  proved  to  have  been  originally  the  same  rock, 
the  transverse  section  shows  that  in  the  latter  a  further  segregation 
of  felspar  has  taken  place,  and  the  rock  is  on  the  whole  more  crystal¬ 
line  and  gneissose.  That  is,  the  development  of  sillimanite  in 
place  of  cyanite  in  the  same  band  is  accompanied  by  a  higher  phase 
of  crystallization  in  the  whole  rock. 
Some  of  the  finest  and  most  interesting  specimens  of  cyanite  are 
seen  on  the  weathered  rock-surfaces  on  the  northern  flank  of  Glen 
Effock,  about  halfway  up  the  hill.  Almost  every  crystal,  and  they 
are  both  numerous  and  large,  shows  in  perfection  the  regular 
dissemination  through  it  of  iron  ore-grains  (ilmenite).  They 
probably  form  about  one  fourth  of  the  whole,  as  seen  under  the 
microscope.  The  structure  is  best  marked  in  thin  cleavage-flakes, 
which  can  be  taken  off  with  a  blunt  knife.  At  the  head  of  Glen 
Effock  (a  little  north  of  the  word  ‘  Cruys ’  on  the  one-inch  Ordnance 
map,  Sheet  66)  there  are  some  rather  coarse  quartz-segregations,  in 
which  are  embedded  the  most  perfect  specimens  of  bright  blue 
cyanite-crystals  to  be  met  with  in  the  whole  district.  On  Bulg, 
a  mountain  close  to  the  main  stream  of  the  North  Esk,  some  way 
below  Keeny  or~  Millden,  a  finely-marked  horizon  of  cyanite-schist 
is  met  with,  striking  E.N.E.  across  the  river.  The  cyanite  here 
occurs  principally  as  ‘  blackleaded  ’  crystals  in  a  fine-grained  schist 
composed  of  felted  mica  cemented  by  little  grains  of  quartz  and 
felspar.  The  amount  of  this  rock  is  very  large,  and  specimens  of 
it  occur  abundantly  as  drifted  boulders  in  the  fields  between  the 
Wood  of  the  Burn  (on  the  North  Esk)  and  Easque.  A  section  of 
such  a  rock  shows  crystals  of  cyanite  full  of  black  inclusions,  set  in 
a  matrix  of  quartz  and  brown  and  white  mica.  The  cyanite  is 
surrounded  by  the  typical  ‘  shimmer  ’-aggregate.  In  addition  to 
these  evenly-distributed  crystals,  cyanite  is  also  to  be  found  on 
Bulg  in  aggregated  masses,  sometimes  as  large  as  a  man’s  head.  A 
2  a  2 
