322 
MR.  0.  A.  SHRUBSOLE  ON  THE 
[Aug.  1893, 
out  of  the  gravel  at  lower  levels  there  is  much  to  suggest  such 
agency.  Its  position  indicates  that  it  is  an  old  deposit,  and  its 
inclusion  of  so  small  a  proportion  of  the  rock-material  that  now 
constitutes  the  surface  of  the  Weald-country  points  to  its  having 
been  originally  formed  during  an  early  stage  of  the  Wealden 
denudation.  Possibly  we  have  here,  in  great  part,  old  fluviatile 
material  which  has  been  brought  within  the  reach  of  marine 
agencies.  The  precise  age  of  such  old  material  can  at  best  form  the 
subject  of  a  more  or  less  approximate  conjecture.  The  rude  imple¬ 
ments  (the  genuineness  of  which  must  he  to  some  extent  a  matter 
of  opinion)  evidently  belong  to  the  older  part  of  the  gravel,  and  as, 
hitherto,  none  but  specimens  of  a  simple  and  primitive  type  have 
been  found  at  high  levels  here,  such  an  indication,  so  far  as  it  goes, 
is  well  in  accord  with  the  evidence  of  age  in  the  gravel  itself. 
The  fragments  of  vein-quartz  and  the  pebbles  of  quartzite,  with 
a  proportion  of  the  flint-material,  might  be  accounted  for  by  a 
subsequent  submergence  up  to  a  height  of  400  feet  above  the  present 
sea- level.  Slight  irregularities  of  bedding  are  observable,  at  various 
levels  on  the  plateau  up  to  the  height  named,  which  to  some  extent 
suggest  the  agency  of  ice  ;  and  the  larger  quartz-fragments  do  not 
show  much  abrasion.  But  any  such  invasion  by  the  sea  could 
hardly  have  taken  place  at  the  time  of  the  general  dispersion  of  the 
Triassic  pebbles  and  other  material  of  northern  origin,  or  at  any 
later  date,  or  more  substantial  traces  of  it  would  have  been  found. 
The  quartzite-pebbles,  in  particular,  are  extremely  rare  here,  and 
none  have  been  observed  absolutely  in  situ.  It  is  therefore  de¬ 
sirable  to  await  further  evidence  and  the  complete  mapping  of  the 
gravels  of  the  district,  before  venturing  on  a  positive  conclusion  as 
to  the  significance  of  some  of  the  facts  adduced. 
Discussion  (on  the  two  preceding  papers). 
The  President  said  that  the  determination  of  the  position  of  the 
line  separating  the  gravels  of  northern  from  those  of  southern  origin 
in  the  Thames  basin  was  a  matter  of  great  importance  and  attended 
with  considerable  difficulty.  The  Authors  had  not  brought  forward 
any  evidence  tending  to  shake  our  faith  in  the  distinctness  of  the 
two  sets  of  gravels.  In  deciding  as  to  the  source  of  any  particular 
gravel,  he  thought  that  the  occurrence  of  rare  pebbles  should  not  be 
allowed  to  have  too  much  weight. 
Dr.  Hicks  said  that  the  sections  exhibited  clearly  showed  that 
the  valley,  running  more  or  less  in  a  line  from  W.  to  E.,  in  which 
the  Diver  Thames  now  flowed,  was  excavated  before  the  so-called 
Middle  Sands  and  Gravels  and  the  Chalky  Boulder  Clay  were 
deposited.  If  the  river  flowed  at  the  level  of  the  glacial  deposits, 
after  they  had  accumulated,  it  was  difficult  to  understand  how  the 
deposits  on  the  southern  side  are  so  different  from  those  on  the 
northern  side  of  the  valley. 
Mr.  I.  Allen  Brown  said  he  feared  his  remarks  would  tend  to 
still  further  complicate  the  subject,  when  he  stated,  as  the  result  of 
