OF  MTTSCOVITE-BIOTITE  GNEISS. 
349 
Yol.  49.] 
are  found  to  contain  little  crystals  of  an  emerald-green  mica.  The 
extreme  purity  of  this  quartzite,  coupled  with  the  presence  of  this 
very  rare  mica,  enables  us  to  recognize  the  rock  instantly.  It  is 
here  quite  close  to  the  rock  containing  the  largest  isolated  crystals 
of  cyanite,  with  ilmenite-inclusions,  that  occur  in  the  whole 
district. 
(c)  The  Stciurolite-zone. 
The  first  staurolite-bearing  rock  was  met  with  on  the  south¬ 
western  side  of  Glen  Clova,  just  where  the  pack-road  to  Glen  Prosen 
reaches  the  crest  of  the  hill.  The  staurolite  weathers  out  of  the 
rock  in  six-sided  crystals,  which  are  frequently  twinned.  The 
crystals  are  embedded  in  a  matrix  of  fine  sericite-schist,  spotted 
over  with  specks  of  brown  mica  similar  to  those  seen  in  the  schist 
close  to  the  limestone.  This  outcrop  is  separated  from  the  main 
mass  of  staurolite-bearing  schist  by  a  great  development  of  the 
pebbly  grits  of  the  Southern  Highlands.  The  pebbles  in  the  grits 
can  still  be  clearly  recognized,  in  spite  of  the  profound  alteration 
which  the  rocks  have  undergone. 
The  main  mass  of  staurolite-schist  commences  on  the  ridge  that 
forms  the  watershed  between  Glen  Elfock  and  the  West  Water 
(Burn  of  Saughs  in  its  upper  part).  A  specimen  taken  from 
the  Cruys  (4862)  is  a  silvery  mica-schist,  with  conspicuous  staurolite- 
crystals  on  the  weathered  surface.  Under  the  microscope  only  a 
few  small  patches  of  staurolite  are  left  as  kernels  to  ‘  shimmer 
aggregates,  which  are  set  in  a  schist-matrix  composed  of  quartz, 
white  mica,  and  chlorite  (?  after  biotite).  Small  garnets  and  iron 
ores  are  scattered  through  the  slide,  while  blue  tourmaline  is  occa¬ 
sionally  seen. 
Following  the  outcrop  of  this  staurolite-schist  along  the  ridge,  the 
crystals  that  weather  out  are  seen  to  diminish  in  size.  They  show 
also  a  tendency  to  aggregate  together,  so  that  several  smaller 
crystals  are  twinned  obliquely  with  a  larger  one. 
Staurolite-bearing  rocks  are  abundant  in  the  north-western  face  of 
Bulg ;  these  are  mostly  compact  schists  with  little  crystals  of 
staurolite  weathering  out  as  small  yellow  projections.  Under  the 
microscope  the  matrix  is  seen  to  be  composed  of  brown  and  white 
mica  and  quartz.  The  latter  occurs  as  evenly-distributed  grains 
with  the  micas, 'and  also  as  clear  patches  in  the  small  segregations. 
These, under  crossed  nicols,  show  the  signs  of  optical  strain  common 
to  nearly  all  the  larger  grains  in  the  contact-rocks.  In  the  schist- 
matrix  are  set  a  great  number  of  what  were  once  staurolite-crystals. 
For  the  most  part  they  are  replaced  by  (  shimmer  ’-aggregates,  in 
some  of  which  cores  of  staurolite  are  still  visible ;  the  boundaries 
of  the  aggregates  are  those  proper  to  the  mineral  replaced.  A 
specimen  from  the  south-east  of  Bulg,  close  to  the  949' bench-mark, 
shows  the  typical  yellow  projections  on  the  surface.  The  matrix 
(5100)  is  composed  of  white  and  brown  mica  and^  a  little 
quartz.  In  this  are  embedded  a  considerable  number  of  quite 
fresh  garnets,  and  still  more  numerous  grains  and  crystals  of 
