Tol.  49.]  CONGLOMERATES  IN  CAERNARVONSHIRE.  455 
series.  It  is  this  series  alone  which  occupies  all  the  ground  above  the. 
road  from  the  Glyn  Peris  Hotel  to  the  commencement  of  the  felsite, 
and  spreads  southward  in  the  hills  and  crags  above.  Nowhere  are 
the  felsite  and  Purple  Slate,  which  are  seen  at  the  level  of  the  rail¬ 
way  (11,  12),  to  be  found  above  ;  but  we  can  trace  the  conglomerate 
step  by  step  from  13  by  14,  etc.,  to  19,  thus  showing  a  distinct  overlap. 
The  associated  rocks  show  that  peculiar  crinkly  lamination  and 
mottled  colour  that  have  been  before  noted  at  Y  Bigl,  and  almost 
wherever  seen  these  laminae,  etc.,  are  horizontal — as  especially  at 
18,  16,  and  10 — a  circumstance  which  first  excited  my  suspicions 
that  they  were  not  what  they  had  been  taken  for. 
If  now  we  trace  the  boundary  between  felsite  and  conglomerate, 
starting  at  13,  we  find  them  in  contact  there,  and  all  along  as  far 
as  20,  and  farther  on  we  get  red  grit  (23)  and  conglomerate  (24) 
close  against  the  felsite  (25)  ;  but  at  21  a  knob  of  hard  Purple 
Slate  intervenes  between  the  felsite  at  22  and  the  grit  at  10  ; 
and  beyond  24  again  the  felsite  at  26,  27  is  followed  by  Purple 
Slate  at  28,  29,  30,  which  is  of  the  peculiar  mixed  character  it  often 
shows  as  it  approaches  the  felsite,  as  was  noted  in  the  inlet  at  11. 
After  this  we  can  trace  the  junction  between  conglomerate  and 
felsite  without  any  intervening  Purple  Slate  from  31,  32  to  33,  34. 
These  details  are  given  to  show  how  thoroughly  the  conglomerate 
behaves  as  an  un conformable  deposit  in  its  surface-distribution. 
The  surface-breadth  of  these  upper  rocks  is  here  considerable ;  con¬ 
glomerates  continue  as  far  as  35  and  are  then  succeeded  by  felspathic 
and  other  grits  at  36,  37. 
Farther  up  the  hill  we  get  into  some  difficulty.  An  amphitheatre 
of  crags  of  coarse  grit  extends  from  38  to  39,  and  at  40,  at  a 
lower  level,  is  a  felspathic  grit.  The  relation  of  these  to  the  slates 
of  the  adjacent  quarry  (42),  which  dip  S.E.  at  about  30°,'  is  seen 
in  a  tunnel-section  (41).  Here  a  conglomerate  certainly  underlies 
the  slate,  with  a  junction  making  an  angle  of  60°,  and  beyond 
the  conglomerate  comes  the  coarse  grit  of  38.  This,  no  doubt, 
is  an  observation  opposed  to  the  conclusions  derived  from  others, 
but  it  seems  to  be  easily  explained,  for  the  junction  is  slicken- 
sided  and  the  order  of  the  conglomerate  and  grit  is  reversed  from 
what  would  be  expected ;  so  that  probabty  the  slate  has  here  been 
slightly  pushed  over  the  grits.  That  some  such  explanation  is 
required  is  seen  from  the  fact  of  Purple  Slate  being  obtained  at 
43,  44,  and  felsite  at  45 ;  so  that  1000  feet  away  there  are  no  grits 
below  the  slate. 
Quite  at  the  summit,  however,  we  find  another  proof  to  counter¬ 
poise  this  last  difficulty.  Here  a  patch  of  coarse  grit  (46)  is  over- 
lain  by  a  green  ashy  grit,  on  three  sides  of  which  are  slate-holes, 
and  a  little  way  farther  on  the  conglomerate  is  seen  lying  upon 
the  felsite.  The  best  observation,  however,  is  to  be  made  at  the  slate 
quarry  (47)  and  adjoining  boss  of  conglomerate  (48),  fig.  10,  p.  456. 
On  the  surface  it  will  be  seen  that  the  order  of  the  rocks  is  felsite, 
conglomerate,  slate  ;  but  at  a  distance  of  only  60  feet  from  the 
conglomerate  we  find  in  the  quarry  70  feet  of  the  slate  actually 
