Yol.  49.] 
Or  3IFSCOVTTE-BIOTITE  GXEISS. 
331 
the  schists  in  every  direction.  In  one  part  of  the  area  the  gneiss 
occurs  as  thin  bands,  permeating  the  other  rocks,  and  an}'  crag-  or 
scar-face  will  show  clearly  its  intrusive  nature.  The  foliation  of 
the  larger  masses  is  rudely  parallel  to  that  of  the  surrounding  schists, 
and  their  intrusive  nature  is  not  so  obvious;  but  it  is  proved  by 
detailed  mapping,  for  these  masses  traverse  different  bands  of  the 
schists,  the  latter  ending  off  against  the  igneous  rock  much  in  the 
same  manner  as  in  any  ordinary  case  of  intrusion. 
The  great  crags  at  the  head  of  Glen  Clova  are  seen  to  be  more  or 
less  permeated  by  small  tongues  or  thin  bands  of  a  grey  gneiss.  In 
some  cases  this  intrusive  rock  nearly  equals  in  total  bulk  the 
surrounding  metamorphic  rocks,  and  to  the  district  in  which  this  is 
the  case  we  have  applied  the  term  ‘  permeation-area.’  This  area 
commences  at  the  north-western  end  of  Glen  Clova  and  stretches 
in  a  north-easterly  direction  for  about  6  miles,  Ho.  1  in  the  Map, 
Pl.  XV.  Xo  strict  boundary  can  be  drawn  to  such  an  area,  for, 
especially  at  its  north-eastern  end,  it  tails  away  by  a  continual 
decrease  in  the  number  of  small  intrusions,  and  consequently  in  the 
proportion  of  igneous  material  to  the  surrounding  rocks. 
Some  distance  to  the  south-east  of  this  area  the  intrusion  is  met 
with  again  as  a  distinctly  foliated  granite.  It  is  no  longer  minutely 
subdivided,  but  forms  rather  a  continuous  mass  with  many  in¬ 
clusions.  The  two  types  of  igneous  rock  are  connected  by  a  narrow 
band,  in  which  the  decreasing  proportion  of  the  surrounding  schists 
and  the  thickening  of  the  separate  intrusions  may  be  fairly  well 
made  out,  in  spite  of  the  covering  of  peat. 
The  mass  (No.  2  in  the  Map,  PI.  XV. )  which  is  thus  connected 
with  the  permeating  gneiss  is,  on  the  whole,  much  less  foliated  and 
weathers  more  like  a  granite,  especially  towards  its  edges.  '  Inclu¬ 
sions  are  more  numerous  on  the  western  than  on  the  eastern  side, 
the  latter  edge  being  often  fringed  with  pegmatite. 
The  next  mass  (No.  3  in  the  Map)  is  very  irregular  in  shape.  The 
appearance  of  the  rock  of  which  it  is  composed  is  that  of  a  slightly 
foliated  granite ;  but  the  most  marked  feature  of  the  mass  is  the 
enormous  fringe  of  pegmatite  on  its  southern  and  eastern  edges. 
There  is  also  a  slight  fringe  on  the  other  edges. 
Another  outcrop  (No.  4  in  the  Map)  forms  part  of  the  high 
ground  drained  by  the  eastern  branch  of  Rottal  Burn.  The  foliation 
is  always  slight,  and  the  rock  passes  insensibly  on  its  south-eastern 
margin  into  a  mass  of  aplite.  Of  the  two  masses  shown  in  the 
Map  on  the  western  side  of  Glen  Clova,  No.  5  is  identical  with 
No.  3 ;  while  No.  6  is  an  inextricably-confused  mass  of  foliated 
granite,  pegmatite,  and  inclusions. 
There  are  in  the  North  Esk  area,  that  is,  north  and  east  of  these 
larger  masses,  many  smaller  patches  of  gneiss,  granite,  and 
pegmatite.  The  gneissose  structure,  never  so  well  seen  as  in  the 
permeation-area,  is  developed  only  when  the  outcrops  have  a  breadth 
of  100  yards  or  more,  and  in  all  the  more  easterly  patches  the 
foliation  is  not  easily  seen  in  a  hand-specimen.  These  small 
patches  are,  however,  invariably  accompanied  by  a  fringe  of 
z  2 
