The  height  reached  by  these  fossil  shells  on  Moel  Tryfaen  is
no  less  than  1,300  feet — a  most  important  fact  when  we  con-
sider how  very  few  instances  we  have  on  record  beyond  the
limits  of  Wales,  whether  in  Europe  or  North  America,  of
marine  shells  having  been  found  in  glacial  drift  at  half  the
height  above  indicated.  A  marine  molluscous  fauna,  however,
agreeing  in  character  with  that  of  Moel  Tryfaen  and  comprising
as  many  species,  has  been  found  in  drift  at  Macclesfield  and


158  ERRATICS  NEAR  CHICHESTER.  [CH.  xn.
other  places  in  central  England  sometimes  reaching  an  eleva-
tion of  1,200  feet.
Professor  Ramsay*  estimated  the  probable  amount  of  sub-
mergence during  some  part  of  the  glacial  period  at  about  2,300
feet  ;  for  he  was  unable  to  distinguish  the  superficial  sands  and
gravel  which  reached  that  high  elevation  from  the  drift  which,
at  Moel  Tryfaen  and  at  lower  points,  contains  shells  of  living
species.  The  evidence  of  the  marine  origin  of  the  highest
drift  is  no  doubt  inconclusive  in  the  absence  of  shells,  so  great
is  the  resemblance  of  the  gravel  and  sand  of  a  sea  beach  and  of
a  river's  bed,  when  organic  remains  are  wanting ;  but,  on  the
other  hand,  when  we  consider  the  general  rarity  of  shells  in
drift  which  we  know  to  be  of  marine  origin,  we  cannot  suppose
that,  in  the  shelly  sands  of  Moel  Tryfaen,  we  have  hit  upon  the
exact  uppermost  limit  of  marine  deposition,  or,  in  other  words,
a  precise  measure  of  the  submergence  of  the  land  beneath  the
sea  during  the  glacial  period.
