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REV.  J.  E.  BLAKE  OK  EELSITES  AND 
[Aug.  1893, 
With  regard  to  the  conglomerates,  I  am  perfectly  at  one  with 
Dr.  Hicks  and  all  other  recent  writers  on  the  district  in  recognizing 
that  in  every  case  they  are  derived  in  part  from,  and  are  therefore 
posterior  in  date  to,  some  felsite;  but  this  will  only  prove  the 
pre-Cambrian  age  of  the  latter  (for  which  purpose  they  have  been 
principally  considered  of  importance),  if  they  lie  at  the  base  of  the 
Cambrian  Series.  That  none  of  those  which  are  found  on  the  eastern 
side  of  the  faulted  Silurian  strip  do  this  is  an  easy  matter  to  show ; 
indeed,  it  has  been  already  abundantly  shown,  though  further  proofs 
will  be  found  in  the  present  paper  ;  but  it  is  another  thing  to  demon¬ 
strate  that  any  of  them  are  of  later  age  than  the  workable  slates. 
It  must  at  once  be  admitted  that  this  is  not  immediately  evident ; 
the  proof  requires  a  careful  consideration  of  the  whole  ob¬ 
tainable  evidence,  and  this  is  doubtless  the  reason  why  the 
fact  has  not  been  recognized  before.  There  are  indeed  several 
sections  and  dispositions  of  the  rocks  that  are  in  themselves  highly 
unfavourable  to  this  view,  all  of  which  will  be  noted  further  on. 
There  is  not,  however,  a  single  one  which  cannot  be  explained, 
whereas  those  on  which  this  view  is  founded  admit  of  no  other 
explanation. 
It  will  easily  be  seen  that  if  my  contention  is  correct,  and  there  is 
really  an  unconformity  above  the  workable  slates  of  Llanberis  and 
Penrhyn,  this  has  far-reaching  consequences  of  greater  interest  than 
the  mere  controversy  as  to  the  expunction  of  the  supposed  pre- 
Cambrian  rocks  from  the  district ;  and  it  is  from  this  point  of  view 
that  I  am  chiefly  anxious  to  propagate  the  conviction  at  which  I 
have  arrived. 
In  the  descriptions  which  follow,  the  evidence  as  to  the  felsites 
and  the  conglomerates  is  so  interwoven  that  I  shall  take  the 
localities  in  geographical  order,  and  set  forth  the  whole  of  the  infor¬ 
mation  on  either  subject  obtainable  in  each. 
II.  The  Penrhyn  Quarry  Turner. 
In  his  description  of  the  Cambrian  rocks  of  Caernarvonshire 
Sir  Andrew  Hamsay  mentioned  that  felsite  was  met  with  in  a 
shaft  sunk  on  the  site  of  the  old  St.  Ann’s  Chapel,  near  Bethesda,1 
and  on  the  strength  of  this  occurrence,  though  the  rock  does 
not  reach  the  surface,  he  continued  the  felsitic  area  of  Clegyr 
and  Moel  Goronwy  to  this  point.  Within  the  last  few  years 
two  other  shafts  have  been  sunk  at  about  200  yards  to  the  east 
of  the  former  one,  and  from  the  bottom  of  one  of  these  there 
is  a  tunnel  running  for  about  200  yards  in  a  S.S.E.  direction  to 
the  lowest  level  at  which  the  slates  are  worked.  This  tunnel  I 
have  examined  under  the  guidance  of  Mr.  Morris,  one  of  the  super¬ 
intendents  of  the  mine,  and  a  series  of  specimens  has  been  collected 
for  me  by  Mr.  Pobert  Lloyd,  of  Cilgeraint  St.  Ann’s,  of  trilobite 
renown.  Pelsite  occupies  a  considerable  length  of  the  tunnel ;  it 
is  of  various  kinds,  some  being  nearly  white  and  of  a  waxy  lustre,  and 
1  Mem.  Geol.  Survey,  vol.  iii.  (1866)  p.  144. 
