Yol.  49.]  AXXTVERSARY  ADDRESS  OE  THE  PRESIDENT.  9 1 
Chalky  Boulder-clay  as  even  roughly  equivalent  to  the  Upper  Boulder- 
clay  of  Yorkshire,  at  least  in  a  chronological  sense. 
We  may  naturally  suppose  that  the  Chalky  Boulder-clay  of  the 
South-east  of  England  in  its  march  towards  the  Thames  Yalley 
represents  the  most  intense  period  of  the  Great  Ice  Age — a  period 
when  the  vis-a-tergo  was  at  its  maximum.  Hence  there  does  not 
seem  to  be  much  chronological  value  in  the  tripartite  division  of 
the  Glacial  deposits  of  East  Yorkshire,  but  merely  the  physical 
history  of  a  great  glacier-movement.  We  learn,  however,  the  im¬ 
portant  lesson  that  the  origin  of  interglacial  gravels  may  be  explained 
on  other  and  perhaps  more  probable  grounds  than  those  of  subsidence 
and  interglacial  warm  periods. 
North-western  England  and  Scottish  Highlands. — Lastly  we  have 
to  consider  those  portions  of  our  island  where  glaciers  originated,  and 
in  this  case  we  naturally  turn  towards  the  Yorth-west  of  England 
and,  farther  still,  the  Highlands  of  Scotland,  regions  where  for  the 
most  part  the  land  is  mountainous  and  the  precipitation  excessive. 
The  glaciology  of  these  districts  had  perhaps  to  a  great  extent  been 
worked  out  in  previous  years  ;  at  least  there  have  been  no  more 
than  two  communications  to  the  Society  in  the  past  seven  years, 
and  these  relate  to  such  well-known  subjects  as  the  perched  blocks 
at  Yorber  and  the  Parallel  Boads  of  Glen  Boy. 
The  phenomenon  of  boulders  on  pedestals  is  one  that  lends  itself 
to  illustration.  The  subject  was  well  handled  by  Prof.  Hughes 
in  connexion  with  boulders,  chiefly  Silurian,  resting  on  pedestals  of 
Mountain  Limestone  in  the  Kendal  district  and  also  at  Yorber 
Brow  in  Craven.  He  assigned  their  origin,  not  to  icebergs  nor  to 
the  stony  residuum  of  a  washed-out  Boulder-clay,  but  to  certain 
conditions  which  arose  during  the  recession  of  the  great  ice-sheet. 
There  must  have  been,  as  he  remarks,  oscillations  during  the  general 
recession,  and  he  thought  that  the  glacier  in  its  last  advance  might 
have  picked  up  the  boulders  due  to  the  weathering  of  massive  beds, 
which  had  been  exposed  when  it  had  receded  somewhat.  Yor  was 
this  all,  for  the  ice  had  been  able  to  carry  these  boulders  up  and 
over  the  brow  of  a  hill.  On  Yorber  Brow,  he  says,  this  pushing 
uphill  of  the  boulders  is  well  marked,  for  here  the  blocking  of  the 
mouth  of  the  valley  by  a  ridge  of  grit  forced  the  ice  to  higher  levels. 
We  here  perceive  the  effects  of  an  obstruction  in  the  path  of  the  ice, 
though  on  a  small  scale  compared  with  those  gigantic  results  which 
have  been  claimed  for  the  ice  of  the  Irish  Sea. 
9 2 
