82  PROCEEDIN' GS  OE  THE  GEOLOGICAL  SOCIETY.  [May  1893, 
the  belief  of  that  school  of  geologists  which  seeks  in  submergence 
and  the  direct  action  of  the  sea  for  a  true  explanation  of  these 
phenomena. 
But  whatever  theories  as  to  origin  we  may  adopt,  the  leading 
factor  in  the  Pleistocene  history  of  this  region  is  the  existence  of 
two  drifts,  viz.  the  Welsh  or  Arenig  Drift,  and  the  Northern  or 
Irish  Sea  Drift.  Prof.  Hughes  has  traced  the  Arenig  or  Great  Ice 
Drift,  as  he  calls  it,  from  the  Snowdon  and  Arenig  ranges  by  the 
strise  on  the  solid  rocks  and  by  the  included  fragments.  It  is 
described  as  consisting  of  Boulder-clay  and  striated  boulders,  all  of 
indigenous  origin,  and  contains  no  shells.  In  his  classification  of  the 
drifts  of  the  Yale  of  Clwyd,  this  drift  is  placed  at  the  base  of  the 
system,  but  Dr.  Hicks  was  of  opinion  that  the  Welsh  or  Arenig 
Drift  is  not  necessarily  the  oldest.  In  some  places  it  may  even  be 
the  newest,  as  it  is  known  from  well-sinkings  to  be  underlain  by 
sands  and  gravels  in  which  bones  of  animals  similar  to  those  found 
in  the  caverns  were  discovered.  The  explanation  of  this  divergence 
of  opinion  seems  to  be  that  the  indigenous  Drift  both  underlies  and 
overlies  the  Drift  of  the  Irish  Sea,  as  might  very  well  be  the  case 
where  the  two  inosculate,  just  as  in  Derbyshire  there  is  a  local 
Boulder-clay  both  older  and  newer  than  the  Middle  Pleistocene 
Chalky  Boulder-clay. 
The  following  is  an  abstract  of  the  views  expressed  by  the  late 
Prof.  Carvill  Lewis  when  the  paper  on  the  Drifts  of  the  Yale  of 
Clwyd  was  read.  He  maintained  that  there  had  been  “three 
main  areas  of  local  glacial  dispersion  in  Wales,  the  glaciers  from 
each  of  these  being  defined  by  terminal  moraines.  But  there  was 
also  satisfactory  evidence  that  an  ice-lobe  coming  from  Scotland 
[reinforced  by  Cumbrian  and  North  Irish  ice]  and  filling  the  Irish 
Sea  had  impinged  upon  the  extreme  northern  border  of  Wales, 
and  passing  over  Anglesey  and  along  the  west  of  the  Snowdonian 
mountains  on  the  one  side,  and  into  Cheshire  and  along  the  east  of 
the  mountains  on  the  other  side,  had  pushed  its  terminal  moraine 
against  the  highlands  and  in  the  teeth  of  the  opposing  local  glaciers. 
The  latter  were  both  earlier  and  later  than  the  northern  ice-lobe, 
and  the  two  Drifts  were  therefore  often  commingled.  The  line 
dividing  the  northern  ice-lobe  from  the  Snowdonian  glaciers  was 
close  to  the  Cae  Gwyn  cave,  and  the  massive  deposits  near  St.  Asaph 
were  probably  washed  out  of  the  common  terminal  moraine.7’  u  The 
undoubted  marine  deposits,”  he  continued,  “  full  of  shells,  which 
cover  the  lowlands  of  Lancashire  up  to  150  feet  above  the  sea,  also 
