92 
PROCEEDINGS  OE  THE  GEOLOGICAL  SOCIETY.  [May  1 893. 
As  regards  Scotland,  Mr.  Jamieson  has  contributed  some 
Supplementary  Remarks  on  Glen  Roy,  and  this  is  the  only  paper 
on  Pleistocene  Geology  that  we  have  received  from  the  other  side 
of  the  Border.  The  history  of  this  controversy  is  familiar  to  all, 
and  most  geologists  are  acquainted  with  the  general  principles,  if 
not  with  the  details,  of  Mr.  Jamieson's  explanation  of  the  origin  of 
the  famous  Parallel  Roads. 
Since  there  had  been  objections  to  his  hypothesis  on  the  grounds 
that  it  seemed  strange  for  one  set  of  valleys  to  be  filled  with  ice  and 
another  set,  in  close  proximity,  with  water,  the  Author  points  out 
that,  as  the  rainfall  on  the  west  side  of  Scotland  is  quite  double  of 
that  on  the  east  side,  so  also  in  the  Glacial  Period  must  have  been 
the  snowfall.  He  indicates  on  a  map,  to  which  meteorologists  are  by 
no  means  strangers,  those  portions  of  the  country  which,  from  exces¬ 
sive  precipitation,  were  likely  to  have  been  the  most  strongly 
glaciated.  The  wettest  part  of  the  country  nowadays  lies  along  a 
line  extending  from  the  mouth  of  the  Clyde  to  the  island  of  Skye, 
passing  right  across  the  western  entrance  of  the  Great  Glen  of 
Scotland  through  which  runs  the  Caledonian  Canal.  The  two  great 
ice-fields  which  must  have  resulted  from  the  immense  snowfall  over 
this  district  would  coalesce  hereabouts,  and  there  must  have  been  a 
great  congestion,  especially  towards  the  head  of  Loch  Linnhe. 
He  concludes  that  the  quantity  of  ice  filling  the  Great  Glen  and 
the  mouth  of  Glen  Spean  was  such  that  it  eventually  overflowed  the 
passes  leading  eastwards  into  the  valleys  of  the  Nairn  and  the  Spey, 
notwithstanding  that  many  of  these  passes  are  higher  than  those  on 
the  west  which  lead  out  into  the  Atlantic.  Consequently,  before 
the  era  of  the  lakes  which  produced  the  Parallel  Roads  of  Glen  Roy,, 
the  western  ice  actually  discharged  itself  through  the  very  cols  over 
which  the  water  from  the  lakes  flowed  at  a  subsequent  period.  He 
further  points  out  that  during  the  maximum  glaciation  it  was  the 
cumulative  effect  of  such  storage  of  the  surplus  snow  and  ice,  con¬ 
tinuing  through  so  many  ages,  which  gave  rise  to  similar  remarkable 
results  not  only  in  Scotland,  but  in  Ireland,  Scandinavia,  and  North 
America. 
The  state  of  preservation  of  the  Parallel  Roads  is  such  that  it  is 
quite  clear  no  glaciers  can  have  gone  over  them  since  their  forma¬ 
tion  :  hence  their  origin  must  be  referred  to  a  comparatively  late 
stage  of  the  Glacial  Period.  Mr.  Jamieson  supposes  that  the  thinner 
ice  towards  the  north-east  was  the  first  to  disappear,  so  that  the 
ground  became  clear  a  long  time  before  the  ice  gave  way  in  the 
