Vol.  49.] 
CONGLOMERATES  IN  CAERNARVONSHIRE. 
459 
lated  to  give  the  coup  de  grace  to  the  idea  of  there  being  any  pre- 
Cambrian  rocks  in  the  district  at  all. 
In  1877 1  Prof.  Hughes  “  described  the  beds,”  “  and  thought  there 
was  much  reason  for  considering  them  pre-Cambrian,  but  they 
appeared  to  him  to  resemble  more  the  Dimetian  . . .  than  the  Pebidiauc 
beds.”  This  brought  Dr.  Hicks  into  the  county,  who,  by  the  aid  of 
“some  half-dozen  dip  candles,”  discovered  “at  the  entrance  and  for 
some  distance  inwards  ...  a  greenish,  sometimes  pinkish  or  flesh- 
coloured,  schistose  rock  containing  disseminated  quartz-grains ; 
farther  in,  a  more  porphyritie-looking  rock,  mostly  dark-coloured, 
with  spots  of  highly  vitreous  quartz  in  a  base  of  felsitic  matrix, 
undoubtedly  a  greatly  metamorphosed  rock  and  probably  of  ashy 
origin  ” ; 2  and  this  was  all,  before  the  Purple  Slates  were  reached. 
Prof.  Bonney  restricted  himself  to  the  examination  of  the  fragments 
outside.  There  he  found  four  varieties  of  rock  besides  the  Purple 
Slates :  “  (1)  a  rather  gritty  greenish  slate,  banded  with  rounded 
grains  of  a  pinkish  or  purplish  felsite  and  light-coloured  felspar  ; 
(2)  a  rock  of  mottled  and  streaky  aspect  containing  larger  fragments 
of  the  same  felsite  ;  (3)  a  conglomerate  of  the  same  ;  (4)  a  number 
of  greenish  slates  and  grits.”  3  He  also  states  that  the  felsite  here 
must  be  very  thick. 
Misled  by  the  poverty  of  these  results,  and  finding  felsite  at  the 
entrance,  I  unfortunately  did  not  think  it  necessary  to'  explore  this 
dirty  adit  before ;  but  on  taking  the  members  of  the  Geologists’ 
Association  there  I  found  that  we  had  in  it  an  exhibition  of  the 
ordinary  Cambrian  rocks  of  the  northern  part  of  the  district,  all  in 
their  proper  order.  This  was  a  result  so  different  from  what  I  had 
expected  that  I  have  since  made  a  careful  examination.  Accom¬ 
panied  by  Mr.  Robert  Lloyd,  and  provided  with  two  good  paraffin 
lamps  and  a  large  wax-candle,  I  made  a  measured  section  from  the 
purple  Cambrian  slates  to  the  entrance  by  stretching  a  piece  of  string 
450  yards  in  length  from  one  end  to  the  other,  tying  pieces  of  tape 
at  the  spots  where  the  strata  changed,  and  collecting  samples  of 
each,  with  the  following  result : — 
1  Quart.  Journ.  Geol.  Soc.  vol.  xxxiii.  p.  241. 
2  Ibid.  vol.  xxxiv.  (1878)  p.  147. 
3  Ibid.  vol.  xxxv.  (1879)  p.  310. 
2h  2 
