TRATHPEFFER  is  situated  on  the  Old  Red
Sandstone  beds,  a  geologic  formation  laid  down
in  salt  seas  abounding  in  fish.  The  larger
hills,  Ben  Wyvis  to  the  north,  and  the  mountains  of
Ross  to  the  west,  are  composed  of  the  more  ancient
Primary  Rocks — Gneiss  (whinstone),  with  Mica  and
Quartz.  From  Craig  Ulladaile,  north-west  of  the  Spa^
eastwards  to  the  Cat's  Back  and  Knock  Farril,  the
beds  of  the  "  Old  Red  "  appear  in  ascending  order —
that  is,  those  nearer  the  earth's  surface  to  the  eastward
— forming  parallel  strips  at  the  outcrop,  with  a  general
dip  E.S.E.  Conglomerate  caps  the  series,  forming  a
sharp  ridge  or  knife-edge  south  of  the  valley,  and
terminated  by  the  two  abrupt  summits  known  as  Knock
Farril  and  the  Cat's  Back.  On  the  south  aspect  of  the
last-named  hill,  the  cliffs  of  Brahan,  with  the  broken
masses  at  their  base,  admirably  exhibit  the  pudding-like
formation  of  this  rock.  To  the  west,  the  limit  of  the
conglomerate  formation  extends   as  far  as  Tor  Achilty.
I40  STRATHPEFFER  SPA.
It  is  well  exposed  in  the  precipitous  eastern  face  of  this
hill.
