MR.  G.  BARROW  ON  AN  INTRUSION 
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[Aug.  1893, 
staurolite.  The  latter  mineral  is  a  good  deal  altered  in  the  usual 
manner. 
The  most  southerly  outcrop  of  staurolite-bearing  rock  is  seen  on 
a  narrow  ridge  north-west  of  Cornescorn  Farm,  rather  less  than 
half-a-mile  from  the  house.  Comparing  this  rock  with  a  specimen 
(4862)  from  the  Cruys,  it  is  seen  that  while  the  latter  contains  large 
crystals  of  staurolite  and  the  matrix  is  coarsely  crystalline,  in  the 
former  the  crystals  are  quite  small  and  set  in  a  fine  schist-matrix. 
These  staurolite-bearing  rocks  are  frequently  seen  on  the  ridge 
to  he  close  to  a  mass  of  pebbly  grits,  just  as  in  Glen  Clova.  At 
the  north-western  end  of  the  ridge  the  grits  cannot  be  recognized 
as  such  ;  they  are  here  represented  by  distinctly  coarse  schists  or 
fine  gneisses,  often  garnetiferous.  As  we  recede  from  the  area  of 
intrusion  little  patches  occur,  in  which  the  pebbles  begin  to  be 
recognizable,  and  at  the  great  gap  in  the  ridge  where  it  is  crossed 
by  the  old  road  to  the  West  Water,  the  bulk  of  the  rocks  are  unmis¬ 
takably  of  clastic  origin.  They  are,  of  course,  much  altered,  and 
the  matrix  in  which  the  pebbles  are  set  is  thoroughly  schistose. 
The  pebbles  are  also  granulitized. 
In  addition  to  these  grits  there  is  in  this  zone  a  little  band  of 
very  pure  quartzite,  containing  bright  emerald-green  crystals  of 
mica.  '  This  rock  is  unmistakable  wherever  seen,  and  it  follows  the 
staurolite-schist  continuously  for  some  miles,  after  which  it  is  fre¬ 
quently  met  with  as  small  infolds,  fixing  accurately  the  horizon  of 
the  surrounding  rocks.  It  is  no  exaggeration  to  say  that  this 
quartzite  gives  the  clue  both  to  the  structure  of  the  country  and 
to  the  succession  of  the  rocks,  for  it  is  the  same  rock  as  that  described 
on  Cairn  Caidloch  (see  pp.  348-349)  ;  and  it  follows  that  this  long 
outcrop  of  staurolite-schist  is  the  same  bed  as  the  far  more  highly- 
crystalline  cyanite-gneiss  in  Glen  Effock.  The  latter  rock  is  much 
nearer  the  igneous  gneiss  than  the  former. 
The  area  close  to  the  North  Esk  between  the  staurolite-zone  and 
the  Great  Eault  that  bounds  the  Southern  Highlands  is  chiefly 
composed  of  the  massive  pebbly  grits  and  slates  (or  phyllites)  so  well 
known  along  the  Highland  border.  In  addition  there  are  two  rocks 
occurring  close  to  the  Great  Fault,  not  known  west  of  this  district. 
These  are  the  red-and-yellow  jaspers,  and  a  sill  of  basic  igneous  rock. 
The  sill,  when  uncrushed,  is  a  massive  ophitic  dolerite  or  fine  gabbro, 
in  which  the  augite  is  singularly  fresh.  The  jaspers  are  essentially 
limestone  and  chert,  altered  by  the  contact-action  of  the  sill. 
We  may  ask,  what  further  evidence  is  there  of  the  effects  of  the 
great  intrusion  on  these  rocks  ?  In  the  case  of  the  grits  the  meta¬ 
morphism  is  considerably  greater  in  the  north-western  portion  of 
their  outcrop  than  in  the  south-eastern  ;  but  the  effect  of  contact- 
alteration  on  coarse  grits  has  not  yet  been  sufficiently  worked  out  to 
justify  our  ascribing  the  increased  metamorphism  to  that  cause. 
However,  a  band  of  fine  grey  phyllite,  folded  in  with  the  grits  at  the 
Mooran  Burn,  contains  little  rounded  grains  of  brown  mica  closely 
resembling  the  brown  contact-mica  described  above.  The  only 
