^  ol.  49.]  LLANDOVERY  AND  ASSOCIATED  ROCXS  OF  CORWEN.  431 
the  stream  which  runs  down  near  Ty-isaf.  Thence  it  is  continued 
past,  and  a  little  above,  the  Rectory,  for  a  considerable  distance 
towards  the  east,  and  it  here  forms  a  well-marked  vertical  cliff. 
Relow  this  band  of  grit  are  found  Rala  Reds,  while  above  it  come 
the  greyish  slates  with  grit-bands,  which  extend  southward  as  far 
as  the  fault  (fig.  3). 
Fig.  3. — Section  500  yards  east  of  Ty-isaf. 
s. 
[For  explanation  of  lettering,  see  fig.  1.] 
Retween  the  27ant  Cawrddu  and  Nant  Llechog  Faults,  therefore, 
the  beds  which  form  the  Rerwyn  dome  are  thrown  into  a  series  of 
east-and-west  folds  which  follow  one  another  from  north  to  south, 
and  these  folds  are  faulted  along  the  crests  of  the  anticlinals.  The 
southerly  dips  are  short  and  steep,  and  the  northerly  dips  are  long 
Fig.  4. — Diagrammatic  section  of  the  northern  slope  of  the  Berwyn 
Hills  {omitting  rocks  above  the  Corwen  Gnt).  • 
X.  s. ' 
and  low.  The  general  result,  as  may  be  seen  in  fig.  2,  or  in  part 
in  figs.  1  and  3,  is  a  series  of  synclinals  which  become  higher  and 
higher  as  we  proceed  towards  the  south,  i.  e.  towards  the  centre  of 
the  dome.  Omitting  beds  above  the  grit,  this  structure  is  shown 
diagrammatically  in  fig.  4. 
4.  Bast  of  the  Nant  Llechog  Fault. — At  the  eastern  end  of  the 
area,  in  Fant  Llechog,  two  nearly  parallel  faults  are  shown  running 
about  17°  W.  of  N. ;  and  since  it  is  here  that  we  found  some  of  the 
few  remnants  of  the  graptolite-snales,  it  will  be  necessary  to  describe 
the  section  up  this  stream  in  some  detail  (see  Map.  fig.  5,  p.  432). 
