Yol.  49.] 
CONGLOMERATES  IN  CAERNARVONSHIRE. 
465 
XI.  Age  of  the  overlying  Conglomerates  and  Grits. 
Assuming  that  these  have  now  been  proved  to  be  later  than  the 
Purple  Slates,  the  question  remains,  how  much  later  ?  At  one 
time  I  thought  they  might  be  Arenig,  partly  because  of  the  known 
overlap  of  Arenig  rocks  at  Caernarvon,  and  partly  because  they 
contain  masses  of  grey  and  greenish  slates  which  I  can  nowhere 
find  in  the  Cambrian  succession.  But,  if  this  were  their  age,  we 
ought  certainly  to  find  the  broken-off  ends  of  similar  rocks  cropping 
out  somewhere  on  the  flanks  of  Snowdon  between  the  summit  and 
Llanheris.  Last  year,  however,  when  I  sought  such  rocks  there, 
they  were  nowhere  to  he  found,  so  this  idea  must  he  given  up. 
The  difficulty  about  the  slate-fragments  may  be  got  over  if  the  con¬ 
glomerates  are  unconformable,  since  there  may  be  covered  beds 
above  the  Purple  Slates  from  which  these  may  be  derived,  and  it 
will  be  remembered  how  many  resemblances  there  are  between  the 
associated  grits,  etc.,  and  the  Bronllwyd  Grit  and  overlying  beds  ; 
indeed,  till  I  found  the  former  in  situ,  I  took  their  loose  blocks  for 
erratics  from  the  latter.  It  seems  to  me,  therefore,  most  probable 
that  they  are  extensions  of  the  immediately  overlying  rocks. 
XII.  Concluding  Speculations. 
If  this  conclusion  be  accepted,  it  follows  that  the  Bronllwyd 
Grits  and  associated  rocks  are  unconformable  to  the  Purple  Slates, 
etc.,  of  the  Cambrian  Series,  so  that  it  is  scarcely  desirable  to  class 
them  under  the  same  title.  Before,  however,  such  a  matter  is 
settled  it  is  desirable  to  know  whether  this  unconformity  is  any 
more  than  a  local  one.  This  is  a  question  which  I  cannot  at  present 
answer;  for,  though  I  have  spent  about  a  week  examining  the 
Merionethshire  anticlinal,  I  have  not  as  yet  succeeded  in  finding 
any  unconformity  there.  On  the  other  hand,  there  is  plenty  of 
room,  below  the  beds  containing  Paradoxides  in  North  Wales,  for 
Olenellus  to  occur  above  the  Bronllwyd  Grit  and  its  equivalents. 
Should  it  be  ever  found  there,  which  seems  to  me  far  more  likely 
than  its  occurrence  below  the  Pale  Slates  with  Conocoryphe ,  this — 
the  unconformity  which  I  have  here  attempted  to  prove — would 
force  on  us  the  question,  for  which  of  the  groups  of  rocks  thus 
separated  is  the  name'4  Cambrian’  to  be  retained? 
Discussion. 
The  President  said  he  had  no  doubt  that  the  paper  contained 
several  interesting  and  important  points,  but  only  those  who  were 
intimately  acquainted  with  the  district  could  follow  the  Author. 
The  sections  referred  to  by  the  Author  had  been  examined  by  many 
distinguished  geologists,  and  it  was  remarkable  that  in  spite  of  this 
there  was  still  great  difference  of  opinion.  The  Moel  Tryfaen  adit 
had  been  frequently  referred  to,  but  no  previous  observer  had  given 
a  detailed  description  of  it. 
