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REV.  J.  E.  BLAKE  OK  FELSITES  AKD 
[Aug.  1893. 
north-western  side  this  is  skirted  by  conglomerate  (21,  22),  but  all 
along  the  margin  from  5  to  the  eastward  no  sign  of  such  a  rock, 
nor  of  the  rocks  of  Y  Bigl,  nor  of  the  Banded  Slates  can  be  seen. 
But  after  a  narrow  band  of  curious  breccias  derived  from  the  felsite 
(33,  34),  we  come  at  once  to  the  Purple  Slates,  and  farther  east  to 
the  St.  Ann’s  Grit,  whose  horizon  is  determined  by  the  fact  that  it 
overlies  purple  slate  in  Chwarel  Pawr.  I  can  account  for  these  facts 
in  no  other  way  than  that  this  felsite  is  a  later  eruption  than  that  of 
Clegyr  (from  which  it  differs  in  being  more  compact)  and  coeval 
with  that  of  the  Penrhyn  Tunnel,  that  its  natural  successor  is  the 
breccia  made  of  its  fragments,  and  therefore  that  the  conglomerate 
overlying  it  on  the  north-western  side  must  be  a  still  later  formation — 
later,  therefore,  at  least  than  the  Lower  Purple  Slates, — in  which  case 
it  must  be  uncouformable  on  the  Banded  Slates.  Thus  the  present 
interpretation  holds  together  everywhere,  which  is  what  no  other 
interpretation  does. 
Y.  The  Soeth-westerh  Side  of  Llyh  Padarh. 
In  this  district  also  we  have  a  continuous  section  exposed  along 
a  railway,  which  has  been  made  the  basis  of  most  of  the  conclusions 
hitherto  drawn,  but  of  which  a  new  interpretation,  not  originally 
suggested  by  the  section  itself,  will  now  be  given. 
Commencing  at  the  north-western  end  (see  fig.  6)  near  the 
tunnel,  on  the  far  side  of  the  inlet  crossed  by  the  railway,  we  • 
find  the  felsite  1  (?/).  Passing  this  we  come  to  the  massive  con¬ 
glomerate  (a)  in  crags  by  the  side  of  the  inlet,  rising  over  the  back 
of  the  next  crag  of  felsite.  This  felsite  comes  into  immediate  contact 
along  a  vertical  line  with  a  mass  of  Purple  Slate  ( b )  in  which 
another  thin  band  of  felsite  is  intercalated.2  The  slate  continues  in 
mass,  along  the  lower  levels  only,  and  forms  the  first  few  feet  of  the 
cutting.  It  is  there  succeeded  by  a  band  of  coarse  conglomerate  (c), 
dipping  E.S.E.  at  about  70°,  which  soon  becomes  laminated  parallel 
to  the  line  of  junction.  Conformable  with  this  is  a  massive  grey 
slate  ( cl )  with  a  band  of  fine  conglomerate,  and  into  this  has  been 
pushed  another  double  band  of  conglomerate  ( e ),  followed  by  some 
grey-green  grits  (/),  which  undulate,  become  horizontal,  and  end  by 
turning  up  the  other  way,  so  as  to  bring  in  the  conglomerate  again 
(,9),  which  mounts  over  the  back  of  a  dyke  of  greenstone  (x).  O11 
the  other  side  of  this  is  some  green  grit  ( h ),  interrupted  by  another 
dyke  followed  by  Purple  Slates  (i)  dipping,  to  judge  by  one  of  the 
bauds,  at  a  high  angle  to  the  E.S.E.  It  is  hereabouts  that  the 
upper  part  of  the  mass  shows  some  curious  zigzag  lines,  above  which, 
apparently,  are  some  curious  green  crinkly  grits  (&),  with  what 
1  Hereabouts  much  of  the  ‘  felsite  ’  is  really  felsitic  ash ;  but,  as  we  are 
dealing  now  with  the  stratigraphy  alone,  all  may  be  classed  under  one  title. 
“  I  have  not,  as  Dr.  Hicks  asserted  without  seeing  more  than  the  specimens 
I  exhibited,  ‘  mistaken  some  crushed  and  cleaved  pre-Cambrian  felsites  for 
Cambrian  Purple  Slates.’  It  is  lie  who  has  mistaken  these  Purple  Slates  for 
something  else. 
